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The training of horizontal propulsive force generation is one aspect of many sports that is not easily simulated with traditional gym-based resistance training methods, which principally work the leg musculature in a vertical direction. Given that most motion involves an integration of both vertical and horizontal force production, transference of gym-based strength gains may be improved if exercises were used that involved both vertical and horizontal force production. [ABSTRACT FROM AUTHOR]

Training at a load maximizing power output (Pmax) is an intuitively appealing strategy for enhancement of performance that has received little research attention. In this study we identified each subject's Pmax for an isoinertial resistance training exercise used for testing and training, and then we related the changes in strength to changes in sprint performance. The subjects were 18 well-trained rugby league players randomized to two equal-volume training groups for a 7-week period of squat jump training with heavy loads (80% 1RM) or with individually determined Pmax loads (20.0-43.5% 1RM). Performance measures were 1RM strength, maximal power at 55% of pretraining 1RM, and sprint times for 10 and 30 m. Percent changes were standardized to make magnitude-based inferences. Relationships between changes in these variables were expressed as correlations. Sprint times for 10 m showed improvements in the 80% 1RM group (-2.9 +/- 3.2%) and Pmax group (-1.3 +/- 2.2%), and there were similar improvements in 30-m sprint time (-1.9 +/- 2.8 and -1.2 +/- 2.0%, respectively). Differences in the improvements in sprint time between groups were unclear, but improvement in 1RM strength in the 80% 1RM group (15 +/- 9%) was possibly substantially greater than in the Pmax group (11 +/- 8%). Small-moderate negative correlations between change in 1RM and change in sprint time (r approximately -0.30) in the combined groups provided the only evidence of adaptive associations between strength and power outputs, and sprint performance. In conclusion, it seems that training at the load that maximizes individual peak power output for this exercise with a sample of professional team sport athletes was no more effective for improving sprint ability than training at heavy loads, and the changes in power output were not usefully related to changes in sprint ability. [ABSTRACT FROM AUTHOR]

The purpose of this investigation was to examine the potential strength, power, and anthropometric contributors to vertical jump performances that are considered specific to volleyball success: the spike jump (SPJ) and counter-movement vertical jump (CMVJ). To assess the relationship among strength, power, and anthropometric variables with CMVJ and SPJ, a correlation and regression analysis was performed. In addition, a comparison of strength, power, and anthropometric differences between the seven best subjects and the seven worst athletes on the CMVJ test and SPJ test was performed. When expressed as body mass relative measures, moderate correlations (0.53-0.65; p < or = 0.01) were observed between the 1RM measures and both relative CMVJ and relative SPJ. Very strong correlations were observed between relative (absolute height-standing reach height) depth jump performance and relative SPJ (0.85; p < or = 0.01) and relative CMVJ (0.93; p

Strength testing is often used with team-sport athletes, but some measures of strength may have limited prognostic/diagnostic value in terms of the physical demands of the sport. The purpose of this study was to investigate relationships between sprint ability and the kinetic and kinematic outputs of a machine squat jump. Thirty elite level rugby union and league athletes with an extensive resistance-training background performed bilateral concentric-only machine squat jumps across loads of 20% to 90% 1 repetition maximum (1RM), and sprints over 10 meters and 30 or 40 meters. The magnitudes of the relationships were interpreted using Pearson correlation coefficients, which had uncertainty (90% confidence limits) of approximately +/-0.3. Correlations of 10-meter sprint time with kinetic and kinematic variables (force, velocity, power, and impulse) were generally positive and of moderate to strong magnitude (r = 0.32-0.53). The only negative correlations observed were for work, although the magnitude was small (r = -0.18 to -0.26). The correlations for 30- or 40-meter sprint times were similar to those for 10-meter times, although the correlation with work was positive and moderate (r = 0.35-0.40). Correlations of 10-meter time with kinetic variables expressed relative to body mass were generally positive and of trivial to small magnitude (r = 0.01-0.29), with the exceptions of work (r = -0.31 to -0.34), and impulse (r = -0.34 to -0.39). Similar correlations were observed for 30- and 40-meter times with kinetic measures expressed relative to body mass. Although correlations do not imply cause and effect, the preoccupation with maximizing power output in this particular resistance exercise to improve sprint ability appears problematic. Work and impulse are potentially important strength qualities to develop in the pursuit of improved sprinting performance. [ABSTRACT FROM AUTHOR]

Timing light systems are commonly used to measure sprint times of athletes. In this study, the reliability and effect of timing light height on sprint times was investigated. Two sets of timing lights set at hip and shoulder height, simultaneously timed subjects over 10 and 20 meters. The within-trial variation of both timing light heights were equally consistent; all coefficients of variation (CV) less than 1.2% with less variability associated with the longer (20 m) distances (CV < 0.85%). The typical error between the two timing light heights for both distances was small (< or = 1.3%). The mean difference between the two heights was significantly different (0.7 second, 95% CL = 0.05-0.10 second) at both the 10 and 20 m distances. Faster times were recorded at hip height as opposed to shoulder due to the legs breaking the beam before the upper body. It is suggested that standardized procedures are necessary for speed assessment using timing lights in order for comparisons to be made between athletic populations. [ABSTRACT FROM AUTHOR]

Context: Advancements in portable load-cell technology have enabled high-quality assessment of shoulder internal (IR) and external rotation (ER) peak force (Fmax) and rate of force development (RFD). This study's purpose was to explore the reliability and differences between IR and ER Fmax and RFD in different testing positions using a novel load-cell device., Design: A within-subjects repeated-measures design was employed to compare the intersession values and reliability of Fmax and RFD for both shoulder IR and ER across 3 positions: seated-0°, supine-0° and supine-90°., Methods: National-level swimmers (n = 19; age = 16.8 [1.0] y) completed 3 testing occasions of each condition (combination of arm, rotation, and test position) separated by 7 to 14 days., Results: IR superseded ER in all testing positions. The association between these positions across IR and ER was typically strong for both Fmax and RFD (r > .85, P < .001) except for IR RFD (r = .56-.73, P < .05). For sessions 2 to 3, Fmax intraclass correlation coefficient and CV (intraclass correlation coefficient = .89-.96, CV = 5.2%-8.8%) were typically within acceptable ranges, whereas RFD (intraclass correlation coefficient = .74-.90, CV = 11.5%-18.1%) often exhibited inflated error., Conclusion: The supine (90°) position was the most consistent position across both measures. Load-cell technology can be confidently used to assess shoulder rotation Fmax in 3 different positions, whereas RFD should be used with caution without protocol refinement.

The purpose of this research was to characterize the difference between high school (HS) and collegiate pitcher's throwing velocity, shoulder internal (IR) and external rotator (ER) maximum strength (Fmax) and rate of force development (RFD) and explore relationships between these measures. Competitive HS and collegiate pitchers (n = 26) participated in a single session assessment in which shoulder rotator isometric Fmax and RFD were quantified via a portable strain gauge device and throwing velocity via radar. Paired t-tests, stepwise linear regression models and correlational analyses were used to answer the questions of interest. No significant differences (p > 0.05) in pitching velocity were observed between HS and collegiate pitchers, and all pitchers were pooled into one sample for subsequent analyses. For both IR and ER models, the explained variance of Fmax with throwing velocity was small (R 2  = 0.12-0.13). RFD and arm length did not contribute to the models. Large correlations (r ≥ 0.50; p < 0.001) were observed between IR and ER for Fmax and RFD measures, as well as between Fmax and RFD for IR and ER. In terms of throwing velocity, having strong IR and ER Fmax capabilities would seem more important than the ability to express force quickly in this cohort., Competing Interests: Declaration of competing interest The authors declare the following financial interests/personal relationships which may be considered as potential competing interests: John Cronin is an inventor and shareholder in the strain gauge technology used in this study. The results of the present study do not constitute endorsement of the product by authors., (Copyright © 2024 The Authors. Published by Elsevier Ltd.. All rights reserved.)

Context: Horizontal hops can provide insight into how athletes can tolerate high-intensity single-leg stretch loads and are commonly used in athlete monitoring and injury management. Variables like flight, contact, and total time provide valuable diagnostic information to sports science professionals. However, gold-standard assessment tools (eg, 3-dimensional motion capture, force plates) require monetary and technological resources. Therefore, we used a tablet and free software to determine the between-rater, within-rater, and test-retest variability of the temporal events of multiple horizontal hop tests., Design: Reliability study., Methods: Nine healthy males (20.8 [1.3] y, 71.4 [9.8] kg, 171.7 [4.5] cm) across various university sports teams and clubs volunteered and performed several triple (3-Hop) and quintuple (5-Hop) horizontal hops over 3 testing sessions. Six raters detected temporal events from video to determine between-rater variability, while a single rater quantified within-session and test-retest variability. The temporal variables of flight time, ground contact time for each individual hop, and the total time of each hoping series were determined. The consistency of measures was interpreted using the coefficient of variation and interclass correlation coefficients (ICC)., Results: Good to excellent between-rater consistency was observed for all hops (ICC = .85-1.00). Absolute (coefficient of variation ≤ 2.0%) and relative consistency (ICC = .98-1.00) was excellent. Test-retest variability showed acceptable levels of absolute consistency (coefficient of variation ≤ 8.7%) and good to excellent consistency in 10/16 variables (ICC = .81-.93), especially those later in the hopping cycle., Conclusions: A tablet and free digitizing software are reliable in detecting temporal events during multiple horizontal hops, which could have exciting implications for power diagnostics and return-to-play decisions. Therefore, rehabilitation and performance professionals can confidently utilize the highly accessible equipment from this study to track multiple hop performances.

Eccentric quasi-isometric (EQI) contractions (maintaining a yielding contraction for as long as possible, beyond task failure) have gained interest in research and applied settings. However, little is known regarding the biomechanical profile of EQIs. Fourteen well-trained males performed four maximal effort knee-extensor EQIs, separated by 180 seconds. Angular impulse, velocity, and time-under-tension through the 30-100º range of motion (ROM), and in eight ROM brackets were quantified. Statistical parametric mapping, analyses of variance, and standardised effects (Hedges' g (ES), %Δ) detected between-contraction joint-angle-specific differences in time-normalised and absolute variables. Mean velocity was 1.34º·s -1 with most (62.5 ± 4.9%) of the angular impulse imparted between 40-70º. Most between-contraction changes occurred between 30-50º ( p ≤ 0.067, ES = 0.53 ± 0.31, 60 ± 52%), while measures remained constant between 50-100º (= 0.069-0.83, ES = 0.10 ± 0.26, 14.3 ± 24.6%). EQIs are a time-efficient means to impart high cumulative mechanical tension, especially at short to medium muscle lengths. However, angular impulse distribution shifts towards medium to long muscle lengths with repeat contractions. Practitioners may utilise EQIs to emphasize the initial portion of the ROM, and limit ROM, or apply EQIs in a fatigued state to emphasize longer muscle lengths.

Background: The inclusion of skateboarding in the Olympics suggests that athletes and coaches are seeking ways to enhance their chances of succeeding on the world stage. Understanding what constitutes performance, and what physical, neuromuscular, and biomechanical capacities underlie it, is likely critical to success., Objective: The aim was to overview the current literature and identify knowledge gaps related to competitive skateboarding performance and associated physical, technical, and tactical demands of Olympic skateboarding disciplines., Methods: A systematic scoping review was performed considering the Preferred Reporting Items for Systematic Reviews and Meta-Analysis (Extension for Scoping Reviews) guidelines. Data sources were MEDLINE (Ovid), Scopus, SPORTDiscus, and PubMed. We included all peer-reviewed literature after 1970 describing the physiological, neuromuscular, biomechanical, and/or tactical aspects of skateboarding., Results: Nineteen original articles explored the physiological (n = 9), biomechanical (n = 8), and technical (n = 10) demands of skateboarding. No research explored the tactical demands of competition. Moreover, although competitive males (n = 2 studies) and females (n = 1 study) were recruited as participants, no research directly related skateboarding demands to performance success in competitive environments., Conclusions: Ultimately, what constitutes and distinguishes competitive skateboarding is unexplored. There is some evidence indicating aspects of the sport require flexibility and elevated and fast force output of the lower limbs, which may be valuable when attempting to maximise ollie height. Nonetheless, a lack of ecological validity, such as using static ollie tests as opposed to rolling, restricted our ability to provide practical recommendations, and inconsistency of terminology complicated delineating discipline-specific outcomes. Future researchers should first look to objectively identify what skaters do in competition before assessing what qualities enable their performance., (© 2024. The Author(s).)

The importance of hip adductor strength for injury prevention and performance benefits is well documented. The purpose of this study was to establish the intra- and inter-day variability of peak force (PF) of a groin squeeze protocol using a custom-designed compression strain gauge device. Sixteen semi-professional soccer players completed three trials over three separate testing occasions with at least 24-h rest between each session. The main findings were that the compression strain gauge was a reliable device for measuring PF within and between days. All intraclass correlations were higher than 0.80 and coefficients of variations were below 10% across the different sessions and trials. Due to the information gained through the compression strain gauge, the higher sampling frequency utilized, portability, and the relatively affordable price, this device offers an effective alternative for measuring maximal strength for hip adduction., Competing Interests: John B. Cronin owns stock in Kiwi Texas LLC, a funder of this research. Dana Ye‐Lee is an employee for associated projects, funded by Kiwi Texas LLC. The remaining authors have no conflicts of interest to declare., (© 2024 The Authors. Healthcare Technology Letters published by John Wiley & Sons Ltd on behalf of The Institution of Engineering and Technology.)

Abstract: Pichardo, AW, Neville, J, Tinwala, F, Cronin, JB, and Brown, SR. Validity and reliability of force-time characteristics using a portable load cell for the isometric midthigh pull. J Strength Cond Res 38(1): 185-191, 2024-Many practitioners use the isometric midthigh pull (IMTP) to assess maximal strength in a safe, time-effective manner. However, expensive, stationary force plates are not always practical in a large team setting. Therefore, the purpose of this study was to establish the validity and between-session reliability of peak force, rate of force development (RFD), and impulse during an IMTP using 2 experimental protocols: a traditional fixed bar with a force plate (BarFP) and a flexible chain measured with a force plate (ChainFP) and a load cell (ChainLC). After a familiarization session, 13 resistance-trained men performed 3 trials of the BarFP condition and 3 trials of the chain-based conditions. The identical procedures were replicated twice more, with a week between each testing session. The main findings were (a) no RFD or impulse measures were found to achieve acceptable reliability across all methodological approaches and testing occasions; (b) peak force was reliable across all methods, with coefficient of variation ranging from 4.6 to 8.3%, intraclass correlation coefficient ranging from 0.94 to 0.98, and the least variability associated with the ChainLC condition; and (c) the ChainFP method was found to significantly underrepresent peak force by 4.8% (p < 0.05), with no significant differences between the ChainLC and BarFP methods. Therefore, the ChainLC would seem a valid, reliable, portable, and cost-effective alternative to force plates when assessing maximal isometric strength in the IMTP., (Copyright © 2023 National Strength and Conditioning Association.)

Evaluating anatomical contributions to performance can increase understanding of muscle mechanics and guide physical preparation. While the impact of anatomy on muscular performance is well studied, the effects of regional quadriceps architecture on rapid torque or force expression are less clear. Regional (proximal, middle, and distal) quadriceps (vastus lateralis, rectus femoris, and vastus intermedius) thickness (MT), pennation angle (PA), and fascicle length (FL) of 24 males (48 limbs) were assessed via ultrasonography. Participants performed maximal isometric knee extensions at 40°, 70°, and 100° of knee flexion to evaluate rate of force development from 0 to 200 ms (RFD 0-200 ). Measurements were repeated on three occasions with the greatest RFD 0-200 and mean muscle architecture measures used for analysis. Linear regression models predicting angle-specific RFD 0-200 from regional anatomy provided adjusted correlations (√adj R 2 ) with bootstrapped compatibility limits. Mid-rectus femoris MT (√adj R 2  = 0.41-0.51) and proximal vastus lateralis FL (√adj R 2  = 0.42-0.48) were the best single predictors of RFD 0-200 , and the only measures to reach precision with 99% compatibility limits. Small simple correlations were found across all regions and joint angles between RFD 0-200 and vastus lateralis MT (√adj R 2  = 0.28 ± 0.13; mean ± SD), vastus lateralis FL (√adj R 2  = 0.33 ± 0.10), rectus femoris MT (√adj R 2  = 0.38 ± 0.10), and lateral vastus intermedius MT (√adj R 2  = 0.24 ± 0.10). Between-correlation comparisons are reported within the article. Researchers should measure mid-region rectus femoris MT and vastus lateralis FL to efficiently and robustly evaluate potential anatomical contributions to rapid knee extension force changes, with distal and proximal measurements providing little additional value. However, correlations were generally small to moderate, suggesting that neurological factors may be critical in rapid force expression.

Lower-limb wearable resistance (WR) facilitates targeted resistance-based training during sports-specific movement tasks. The purpose of this study was to determine the effect of two different WR placements (thigh and shank) on joint kinematics during the acceleration phase of sprint running. Eighteen participants completed maximal effort sprints while unloaded and with 2% body mass thigh- or shank-placed WR. The main findings were as follows: 1) the increase to 10 m sprint time was small with thigh WR (effect size [ES] = 0.24), and with shank WR, the increase was also small but significant (ES = 0.33); 2) significant differences in peak joint angles between the unloaded and WR conditions were small (ES = 0.23-0.38), limited to the hip and knee joints, and <2° on average; 3) aside from peak hip flexion angles, no clear trends were observed in individual difference scores; and, 4) thigh and shank WR produced similar reductions in average hip flexion and extension angular velocities. The significant overload to hip flexion and extension velocity with both thigh- and shank-placed WR may be beneficial to target the flexion and extension actions associated with fast sprint running.

Effective directional change in sport is imperative to success in key game situations. Change of direction (COD) ability is underpinned by various athletic qualities which can be developed through specific and non-specific training methods. This review examined the effect of specific and non-specific training methods on pro-agility performance, by analysing the intervention type and resulting magnitude of training effects on pro-agility shuttle performance. A total of 20 studies were included for review. Data from 638 subjects and 29 intervention groups involving seven different training methods were extracted and analysed in relation to training method classification and primary outcome measures. Interventions involving sprint training, plyometric training, resistance training, and combined resistance, plyometric, and sprint training were found to produce statistically significant positive change on pro-agility performance per session (p < 0.05). Sprint training (0.108 ES), plyometric training (0.092 ES), resistance training (0.087 ES), and combined resistance, plyometric, and sprint training (0.078 ES) methods were found to have the highest per session training effect. While total time is the typical unit of measure for this test, different types of training may lead to preferential improvements in either acceleration, deceleration, or COD phases of the pro-agility shuttle. Specifically, resisted or inclined sprinting may develop the linear acceleration phases, unilateral resistance training may promote increased strength to overcome the imposed forces during the deceleration and COD phases, multiplanar plyometrics can help enhance stretch-shortening cycle capabilities across different force vectors, and a combination of two or more of these methods may enable simultaneous development of each of these qualities., (© 2022 James W. D. Forster, Aaron M. Uthoff, Michael C. Rumpf, John B. Cronin, published by Sciendo.)

Context: Intrasession reliabilities of isometric knee extension kinetics via portable strain gauge have been reported across several knee joint angles and constraints. However, intersession variabilities, which are more valuable, have yet to be determined. Therefore, we aimed to quantify the intersession variability of knee extension kinetics over 3 testing sessions using an affordable and portable strain gauge., Design: Participants performed maximum voluntary isometric contractions of the knee extensors over 3 sessions., Methods: Eleven (6 men and 5 women; 31 [6.4] y) volunteers performed maximum voluntary isometric contractions in constrained (isokinetic setup with thigh and chest straps) and unconstrained (treatment plinth) conditions. Peak force (PF), peak rate of force development, rate of force development (RFD), and impulse (IMP) from 20% to 80% of PF were assessed. Means, SDs, percentage changes, minimal detectable changes, coefficients of variation (CV), and intraclass correlation coefficients (ICC) were calculated and reported., Results: PF had the lowest intersession variability regardless of condition (CV = 5.5%-13.8%, ICC = .67-.93). However, variability of peak rate of force development (CV [range] = 12.2%-24.7%, ICC = .50-.78), RFD (CV = 10.0%-26.8%, ICC = .48-.84), and IMP (CV = 15.2%-35.4%, ICC = .44-.88) was moderate at best. The constrained condition (CV [SD] = 14.1% [4.8%], ICC = .74 [.08]) had lower variability compared with the plinth (CV = 19.8% [7.9%], ICC = .68 [.15]). Variability improved from sessions 1 to 2 (CV = 20.4% [7.7%], ICC = .64 [.14]) and to sessions 2 to 3 (CV = 15.3% [6.4%], ICC = .76 [.10])., Conclusions: PF can be assessed regardless of setup. However, RFD and IMP changes across sessions should be approached with caution. Backrests and thigh straps improve RFD and IMP variability, and at least 1 familiarization session should be provided before relying on knee-extensor kinetics while utilizing a portable strain gauge.

This study determined the acute changes in rotational work with thigh attached wearable resistance (WR) of 2% body mass during 50-m sprint-running. Fourteen athletes completed sprints with, and without, WR in a randomised order. Sprint times were measured via timing gates at 10-m and 50-m. Rotational kinematics were obtained over three phases (steps 1-2, 3-6 and 7-10) via inertial measurement unit attached to the left thigh. Quantification of thigh angular displacement and peak thigh angular velocity was subsequently derived to measure rotational work. The WR condition was found to increase sprint times at 10-m (1.4%, effect size [ES] 0.38, p 0.06) and 50-m (1.9%, ES 0.55, p 0.04). The WR condition resulted in trivial to small increases in angular displacement of the thigh during all phases (0.6-3.4%, ES 0.04-0.26, p 0.09-0.91). A significant decrease in angular velocity of the thigh was found in all step phases (-2.5% to -8.0%, ES 0.17-0.51, p < 0.001-0.04), except extension in step phase 1 with the WR. Rotational work was increased (9.8-18.8%, ES 0.35-0.53, p < 0.001) with WR in all phases of the sprint. Thigh attached WR provides a means to significantly increase rotational work specific to sprinting.

Light wearable resistance is used in sprint training but the scientific evidence to guide its implementation is limited. This study investigated thigh and shank loading protocols which were matched based on the average increase in moment of inertia about the hip over a stride cycle. Seven university-level sprinters completed three counterbalanced conditions (unloaded, shank-loaded, thigh-loaded), and kinematic variables were measured between 30 and 40 m. Both thigh and shank loading led to small reductions in step velocity (mean change = -1.4% and -1.2%, respectively). This was due to small reductions in step frequency (-1.8%; -1.7%) because of small increases in contact time (+2.7%; +1.5%) in both conditions and a small increase in flight time (+2.0%) in the shank-loaded condition. Both conditions led to moderate increases in hip extension at toe-off (+2.7°; +1.4°), whilst thigh loading led to a small reduction in peak hip flexion angle during swing (-2.5°) and shank loading led to a small increase in peak biceps femoris muscle-tendon unit length (+0.4%). Thigh and shank loading can both be used to provide small reductions in sprint velocity, and each has specific overload effects which must be considered in the rationale for their implementation.

The aim of this acute cross-sectional study was to quantify the kinematic and kinetic changes that occur during sprint acceleration when lower body WR is worn. Fifteen male rugby athletes (19 years; 181 cm; 91 kg) were assessed during maximal effort over-ground and treadmill sprinting over 20 m under three different loading conditions: 0%, 3% and 5% body mass (BM) added weight attached to the lower body. Treadmill data provided a convenient estimate of kinetic changes in the absence of in-ground force plates. The loaded conditions resulted in significantly increased ground contact time (5 to 6%) and decreased step frequency (-2 to -3%) during sprint accelerations (effect size = 0.32-0.72). Moderate WR loading (3% BM) resulted in increased (9%; effect size = 0.66) theoretical maximum horizontal force (relative to BM) and unchanged 20 m sprint times (p > 0.05). Heavier WR loading (5% BM) resulted in a significant decrease (-4%) in vertical ground reaction forces (relative to total system mass) and slower (1 to 2%) 20 m sprint times (effect size = 0.38-0.70). Lower body WR loading up to 5% BM can provide specific sprint training overload, while affecting sprint acceleration biomechanics by ≤ 6%.

This systematic review aimed to quantify the acute and longitudinal effects that occur with weighted vests during sprint-running. PubMed, SPORTDiscus, and Web of Science were searched using the Boolean phrases (vest OR trunk) AND (sprint*) AND (resist* OR weight OR load*). From 170 articles retrieved, 11 studies (6 acute, 5 longitudinal) met the inclusion criteria. Vest loads (5-40% body mass) were found to significantly increase acute over-ground times (10-50 m 4.1-16.9%, effect sizes [ES] = 0.93-3.11) through significantly decreased velocity (-2.2% to -17.3%, ES = -0.41 to -3.19), horizontal force (-5.9% to -22.1%, ES = -0.85 to -3.30), maximal power (-4.3% to -35.6%, ES = -0.32 to -3.44), and flight times (-8.3% to -14.6%, ES = -0.88 to -1.03), while increasing contact times (14.7-19.6%, ES = 1.80-3.17). Treadmill sprints were less effected until loads >11% body mass were used. Improvements in velocity (1.2-1.3%, ES = 0.24-0.37) and times (10-50 m 1.2-9.4%, ES = 0.25-3.30) were found in longitudinal studies (5.6-18.9% body mass, 3-7 weeks). Future studies should focus on determining the optimum load and volume to clearly establish the training benefits of this form of resisted sprinting.

Context: Light lower-limb wearable resistance has little effect on running biomechanics. However, asymmetrical wearable resistance may potentially alter the kinetics and kinematics of high speed, enabling greater loading or unloading of an injured or rehabilitative lower limb., Design: A cross-sectional study design was used to quantify the influence of asymmetric calf loading on the kinematics and kinetics during 90% maximum sprinting velocity., Methods: Following a familiarization session, 12 (male = 7 and female = 5) physically active volunteers ran at 90% of maximal velocity. In random order, participants ran with zero (0) wearable resistance and with loads of 300 g (L300) and 600 g (L600) fixed to one shank. A nonmotorized treadmill quantified vertical and horizontal kinetics and step kinematics. The kinetics and kinematics of the loaded (L0, L300, and L600) and unloaded (UL; UL0, UL300, and UL600) limbs were compared., Results: Vertical step ground reaction force of the loaded limb tended to increase between unloaded and 300 and 600 conditions (effect size [ES] = 0.48 to 0.76, all P ≤ .12), while the horizontal step force of the UL tended to decrease (ES = 0.54 to 1.32, all P ≤ .09) with greater external loading. Step length increased in the UL in 0 versus 300 and 600 conditions (ES = 0.60 to 0.70, all P ≤ .06). Step frequency decreased in the ULs in unloaded versus 300 and 600 conditions (ES = 0.73 to 1.10, all P ≤ .03). Mean step velocity tended to be greater in the ULs than the 300 and 600 conditions (ES = 0.52 to 1.01, all P ≤ .10). Only 4 of 16 variables were significantly different between the 300 and 600 conditions., Conclusions: Asymmetrical shank resistance could be used during high-speed running to reduce or increase the kinetic loading of an injured/rehabilitative limb during return to play protocols. Asymmetrical wearable resistance could also be used to alter step kinematics in runners with known asymmetries. Finally, meaningful alterations in high-speed running biomechanics can be achieved with only 300 g of shank loading.

The biomechanics of the rotational shot put is used to direct coaching to enhance throwing performance. Maximising shot put distance and velocity at the point of release through increasing momentum is of interest to coaches. This narrative review aimed to examine and summarise the critical kinematic variables within each of the six phases of rotational shot put associated with performance and release velocity. Databases were searched using 'shot put', 'biomechanics' and 'track and field throwing', from which 20 articles based on the inclusion criteria were reviewed. The results indicate that the magnitude of transverse thrower-shot angular momentum and thrower-shots path of translation are crucial to performance. In achieving high angular momentum, sweep leg and arm actions need to be well-timed, and their timings and movement likely determine key biomechanical events such as hip to shoulder separations. Generating high release velocities stems from the development and transference of momentum through each phase. Kinematics and kinetics within each phase are co-dependent within and across each phase; therefore, coaches should consider the biomechanics of an athlete through preceding phases when seeking biomechanical change within a given phase. Further research and consideration of kinetics and energy transfer would add value to kinematic observations.

Abstract: Oranchuk, DJ, Storey, AG, Nelson, AR, Neville, JG, and Cronin, JB. Variability of multiangle isometric force-time characteristics in trained men. J Strength Cond Res 36(1): 284-288, 2022-Measurements of isometric force, rate of force development (RFD), and impulse are widely reported. However, little is known about the variability and reliability of these measurements at multiple angles, over repeated testing occasions in a homogenous, resistance-trained population. Thus, understanding the intersession variability of multiangle isometric force-time characteristics provides the purpose of this article. Three sessions of isometric knee extensions at 40°, 70°, and 100° of flexion were performed by 26 subjects across 51 limbs. All assessments were repeated on 3 occasions separated by 5-8 days. Variability was qualified by doubling the typical error of measurement (TEM), with thresholds of 0.2-0.6 (small), 0.6-1.2 (moderate), 1.2-2.0 (large), 2.0-4.0 (very large), and >4.0 (extremely large). In addition, variability was deemed large when the intraclass correlation coefficient (ICC) was <0.67 and coefficient of variation (CV) >10%; moderate when ICC >0.67 or CV <10% (but not both); and small when both ICC >0.67 and CV <10%. Small to moderate between-session variability (ICC = 0.68-0.95, CV = 5.2-18.7%, TEM = 0.24-0.49) was associated with isometric peak force, regardless of angle. Moderate to large variability was seen in early-stage (0-50 ms) RFD and impulse (ICC = 0.60-0.80, CV = 22.4-63.1%, TEM = 0.62-0.74). Impulse and RFD at 0-100 ms, 0-200 ms, and 100-200 ms were moderately variable (ICC = 0.71-0.89, CV = 11.8-42.1%, TEM = 0.38-0.60) at all joint angles. Isometric peak force and late-stage isometric RFD and impulse measurements were found to have low intersession variability regardless of joint angle. However, practitioners need to exercise caution when making inferences about early-stage RFD and impulse measures due to moderate-large variability., (Copyright © 2019 National Strength and Conditioning Association.)

Fusiform weighted garments enable specific loading strategies during sport-specific movements. Loading the arms over during accelerated sprinting from a 2-point start position is pertinent to a variety of sporting performances. Fourteen sprint-trained individuals (age = 20.61 ± 1.16 years; height = 1.73 m ± 3.85 cm; body mass 65.33 ± 4.86 kg; personal best 100-m race time 11.40 ± 0.39 s) performed unloaded/loaded wearable resistance (WR) sprints. Between-condition step kinematics and kinetics were compared over four acceleration phases: steps 1-4, 5-8, 9-12 and 13-16. Sprint performance did not differ between unloaded and loaded WR at 10-m (-1.41%; ES = -0.32), or 30-m (-0.76%; ES = -0.24). Sprinting with forearm WR significantly decreased step frequency during phase two (p < 0.05, -3.42%; ES = -0.81) and three (-3.60%; ES = -0.86) and step velocity during phase four of the 30 m sprinting task (p < 0.05, -3.61%; ES: 0.91) only. There were no significant differences (p ≤ 0.05) between step kinetics amongst the two conditions. Findings indicate that arm-loaded WR may provide specific sprinting overload for 2-point starting positions. This may be relevant to a wider sporting context such as field and team sport performances.

Abstract: Cahill, MJ, Oliver, JL, Cronin, JB, Clark, KP, Cross, MR, and Lloyd, RS. Sled-push load-velocity profiling and implications for sprint training prescription in young athletes. J Strength Cond Res 35(11): 3084-3089, 2021-Resisted sled pushing is a popular method of sprint-specific training; however, little evidence exists to support the prescription of resistive loads in young athletes. The purpose of this study was to determine the reliability and linearity of the force-velocity relationship during sled pushing, as well as the amount of between-athlete variation in the load required to cause a decrement in maximal velocity (Vdec) of 25, 50, and 75%. Ninety (n = 90) high school, male athletes (age 16.9 ± 0.9 years) were recruited for the study. All subjects performed 1 unresisted and 3 sled-push sprints with increasing resistance. Maximal velocity was measured with a radar gun during each sprint and the load-velocity (LV) relationship established for each subject. A subset of 16 subjects examined the reliability of sled pushing on 3 separate occasions. For all individual subjects, the LV relationship was highly linear (r > 0.96). The slope of the LV relationship was found to be reliable (coefficient of variation [CV] = 3.1%), with the loads that cause a decrement in velocity of 25, 50, and 75% also found to be reliable (CVs = <5%). However, there was large between-subject variation (95% confidence interval) in the load that caused a given Vdec, with loads of 23-42% body mass (%BM) causing a Vdec of 25%, 45-85 %BM causing a Vdec of 50%, and 69-131 %BM causing a Vdec of 75%. The Vdec method can be reliably used to prescribe sled-push loads in young athletes, but practitioners should be aware that the load required to cause a given Vdec is highly individualized., (Copyright © 2020 National Strength and Conditioning Association.)

Lower-limb wearable resistance (WR) provides a specific and targeted overload to the musculature involved in sprint running, however, it is unknown if greater impact forces occur with the additional limb mass. This study compared the contact times and ground reaction force waveforms between sprint running with no load and 2% body mass (BM) shank-positioned WR over 30 m. Fifteen male university-level sprint specialists completed two maximum effort sprints with each condition in a randomized order. Sprint running with shank WR resulted in trivial changes to contact times at 5 m, 10 m, and 20 m (effect size [ES] = <0.20, p > 0.05) and a small, significant increase to contact time at 30 m by 1.94% (ES = 0.25, p = 0.03). Significant differences in ground reaction force between unloaded and shank loaded sprint running were limited to the anterior-posterior direction and occurred between 20% and 30% of ground contact at 10 m, 20 m, and 30 m. Shank WR did not result in greater magnitudes of horizontal or vertical forces during the initial impact portion of ground contact. Practitioners can prescribe shank WR training with loads ≤2% BM without concern for increased risk of injurious impact forces.

This study determined the effects of two wearable resistance (WR) placements (i.e. thigh and shank) on horizontal force-velocity and impulse measures during sprint running acceleration. Eleven male athletes performed 50 m sprints either unloaded or with WR of 2% body mass attached to the thigh or shank. In-ground force platforms were used to measure ground reaction forces and determine dependent variables of interest. The main findings were: 1) increases in sprint times and reductions in maximum velocity were trivial to small when using thigh WR (0.00-1.93%) and small to moderate with shank WR (1.56-3.33%); 2) athletes maintained or significantly increased horizontal force-velocity mechanical variables with WR (effect size = 0.32-1.23), except for theoretical maximal velocity with thigh WR, and peak power, theoretical maximal velocity and maximal ratio of force with shank WR; 3) greater increases to braking and vertical impulses were observed with shank WR (2.72-26.3% compared to unloaded) than with thigh WR (2.17-12.1% compared to unloaded) when considering the entire acceleration phase; and, 4) no clear trends were observed in many of the individual responses. These findings highlight the velocity-specific nature of this resistance training method and provide insight into what mechanical components are overloaded by lower-limb WR.

This study determined the effects of a six-week lower-limb wearable resistance training (WRT) intervention on sprint running time, velocity, and horizontal force-velocity mechanical variables. Twenty-two collegiate/semi-professional rugby athletes completed pre- and post-intervention testing of three maximal effort 30 m sprints. A radar device was used to measure sprint running velocity from which horizontal force-velocity mechanical profiling variables were calculated. All athletes completed two dedicated sprint training sessions a week for six-weeks during pre-season. The intervention (wearable resistance, WR) group completed the sessions with 1% body mass load attached to the left and right shanks (i.e. 0.50% body mass load on each limb), whilst the control group completed the same sessions unloaded. For the control group, all variables were found to detrain significantly ( p  ≤ 0.05) over the training period with large detraining effects (ES > 0.80) for theoretical maximal horizontal force, slope of the force-velocity profile, maximal ratio of force, index of force application, 5 and 10 m times. For the WR group, there were no significant changes to any recorded variables (all p  >  0.05) and all effects of training were trivial or small (ES < 0.50). After adjustment for baseline differences, significant between group differences were found for all variables (large effects, ES > 0.80) except theoretical maximal velocity, 30 m time, and maximal velocity. The addition of light wearable resistance to sprint training during a six-week pre-season block enables the maintenance of sprint performance and mechanical output qualities that otherwise would detrain due to inadequate training frequencies.

Nutritional intake can influence exercise metabolism and performance, but there is a lack of research comparing protein-rich pre-exercise meals with endurance exercise performed both in the fasted state and following a carbohydrate-rich breakfast. The purpose of this study was to determine the effects of three pre-exercise nutrition strategies on metabolism and exercise capacity during cycling. On three occasions, seventeen trained male cyclists (VO 2peak 62.2 ± 5.8 mL·kg -1 ·min -1 , 31.2 ± 12.4 years, 74.8 ± 9.6 kg) performed twenty minutes of submaximal cycling (4 × 5 min stages at 60%, 80%, and 100% of ventilatory threshold (VT), and 20% of the difference between power at the VT and peak power), followed by 3 × 3 min intervals at 80% peak aerobic power and 3 × 3 min intervals at maximal effort, 30 min after consuming a carbohydrate-rich meal (CARB; 1 g/kg CHO), a protein-rich meal (PROTEIN; 0.45 g/kg protein + 0.24 g/kg fat), or water (FASTED), in a randomized and counter-balanced order. Fat oxidation was lower for CARB compared with FASTED at and below the VT, and compared with PROTEIN at 60% VT. There were no differences between trials for average power during high-intensity intervals (367 ± 51 W, p = 0.516). Oxidative stress (F 2 -Isoprostanes), perceived exertion, and hunger were not different between trials. Overall, exercising in the overnight-fasted state increased fat oxidation during submaximal exercise compared with exercise following a CHO-rich breakfast, and pre-exercise protein ingestion allowed similarly high levels of fat oxidation. There were no differences in perceived exertion, hunger, or performance, and we provide novel data showing no influence of pre-exercise nutrition ingestion on exercise-induced oxidative stress.

The aim of this study was to investigate the load effects of thigh attached wearable resistance (WR) on linear and angular kinematics and linear kinetics during sprint-running. Fourteen recreational active subjects performed a series of maximal sprints with and without WR of 1%, 2%, and 3% body mass (BM) in a randomised order. Sprints were performed on a non-motorised treadmill that collected velocity, and linear step kinematics and kinetics. Angular kinematics of the thigh were collected from an inertial measurement unit attached to the left thigh. Trivial decreases were found in peak velocity with all WR loads (-0.9 to -.2.4%, effect size [ES] 0.09-0.17, p  > .05). The WR conditions resulted in significantly decreased average step frequency (-2.0% to -3.0%, ES = 0.35-0.44, p  < .05) with loads of ≥2% BM, whereas average step length was statistically unchanged (1.9-2.8%, ES = 0.20-0.33). Average angular displacement was significantly decreased (-7.0% to -10.3%, ES = 0.88-1.10, p  = 0.00-0.03) with loads of ≥2% BM. Average angular flexion velocity (-10.2%, ES = 1.07, p  = .02) and extension velocity (-12.0%, ES = 0.85, p  = .01) were significantly decreased with 3% BM. Trivial to small ES changes ( p  > .05) were found in the linear kinetic measures of interest. Thigh WR provides a sprint-specific rotational form of resistance resulting in greater changes to angular kinematics than linear properties of sprint-running. For practitioners who wish to target thigh angular kinematics and step frequency without decreasing step length, thigh WR of ≥2% BM offers a sprint-specific resistance training tool.

The length-tension relationship affects knee extension performance; however, whether anatomical variations in different quadriceps regions affect this relationship is unknown. Regional (proximal, middle, distal) quadriceps thickness (MT), pennation angle, and fascicle length of 24 males (48 limbs) were assessed via ultrasonography. Participants also performed maximal voluntary isometric torque (MVIT) assessments at 40°, 70°, and 100° of knee flexion. Measures were recorded on 3 separate occasions. Linear regression models predicting angle-specific torque from regional anatomy provided adjusted simple and multiple correlations (√adj R 2 ) with bootstrapped compatibility limits to assess magnitude. Middle vastus lateralis MT and MVIT at 100° (√adj R 2 = 0.64) was the largest single correlation, with distal vastus lateralis MT having the greatest mean correlations regardless of angle (√adj R 2 = 0.61 ± 0.05, mean ± SD). Lateral distal MT and architecture had larger (Δ√adj R 2 = 0.01 to 0.43) single and multiple correlations with MVIT than the lateral proximal (√adj R 2 = 0.15 to 0.69 vs -0.08 to 0.65). Conversely, middle anterior MT had greater (Δ√adj R 2 = 0.08 to 0.38) single and multiple correlations than proximal MT (√adj R 2 = 0.09 to 0.49 vs -0.21 to 0.14). The length-tension relationship was trivially affected by regional quadriceps architecture. The middle and distal quadriceps were the strongest predictors of MVIT at all joint angles. Therefore, researchers may wish to focus on middle and distal lateral quadriceps anatomy when performing ultrasonographic evaluations. Novelty: The length-tension relationship is minimally affected by regional quadriceps anatomical parameters. Middle and distal vastus lateralis and lateral vastus intermedius anatomy were consistently the best predictors of torque. Practitioners may focus their assessments on the middle and distal regions of the lateral quadriceps' musculature.

The cable-pulley downswing is a movement similar to the golf downswing, and therefore may offer a valuable golf specific rotational diagnostic and training tool. However, to be of value, measurements need to be stable across testing occasions. Therefore, the aim of this study was to quantify the test-retest reliability of the cable downswing across a spectrum of load-velocities. Ten male participants (21.7 ± 3.0 years, 84.6 ± 9.8 kg, 1.80 ± 0.05 m) volunteered to participate over 3 testing sessions' separated by a minimum of 3 days. Participants performed maximal velocity cable downswings across eight loads (1.25-18.75 kg), which were incrementally increased by 2.5 kg. Vertical cable stack velocity was collected at 50 Hz via a GymAware linear position transducer. Downswing velocity across all eight loads was observed to be extremely reliable (change in mean = -5.1% to 2.9%, coefficient of variation = 1.5-6.4% and intra-class correlation = 0.70-0.98), with reliability increasing with increasing trials. In conclusion, the cable downswing is a reliable method of tracking rotational ability similar to the golf downswing. Practitioners should establish an upper load relative to the apparatus and participant. Future research should determine the utility and sensitivity of this measure.

Purpose: Eccentric quasi-isometric (EQI) contractions have been proposed as a novel training method for safely exposing the musculotendinous system to a large mechanical load/impulse, with few repetitions. However, understanding of this contraction type is rudimentary. We aimed to compare the acute effects of a single session of isotonic EQIs with isokinetic eccentric (ECC) contractions., Methods: Fifteen well-trained men performed a session of impulse-equated EQI and ECC knee extensions, with each limb randomly allocated to one contraction type. Immediately PRE, POST, 24/48/72 h, and 7 days post-exercise, regional soreness, quadriceps swelling, architecture, and echo intensity were evaluated. Peak concentric and isometric torque, rate of torque development (RTD), and angle-specific impulse were evaluated at each time point., Results: There were substantial differences in the number of contractions (ECC: 100.8 ± 54; EQI: 3.85 ± 1.1) and peak torque (mean: ECC: 215 ± 54 Nm; EQI: 179 ± 28.5 Nm). Both conditions elicited similar responses in 21/53 evaluated variables. EQIs resulted in greater vastus intermedius swelling (7.1-8.8%, ES = 0.20-0.29), whereas ECC resulted in greater soreness at the distal and middle vastus lateralis and distal rectus femoris (16.5-30.4%, ES = 0.32-0.54) and larger echogenicity increases at the distal rectus femoris and lateral vastus intermedius (11.9-15.1%, ES = 0.26--0.54). Furthermore, ECC led to larger reductions in concentric (8.3-19.7%, ES = 0.45-0.62) and isometric (6.3-32.3%, ES = 0.18-0.70) torque and RTD at medium-long muscle lengths., Conclusion: A single session of EQIs resulted in less soreness and smaller reductions in peak torque and RTD versus impulse-equated ECC contractions, yet morphological shifts were largely similar. Long-term morphological, architectural, and neuromuscular adaptations to EQI training requires investigation.

Arm action is critical for optimising sprinting performance. This study aimed to examine overground sprinting performance and step characteristics during unloaded and 2% body mass (BM) forearm wearable resistance loaded sprinting. Fourteen collegiate male track sprinters performed unloaded and forearm loaded sprints over thirty metres of in-ground force plates. Step kinematics and relative kinetics were compared between the unloaded and forearm loaded conditions over four acceleration phases (i.e. steps 1-4, 5-8, 9-12 and 13-16). Affixing 2% BM loads to the forearms did not significantly alter 0-30-m sprint times ( p  > 0.05; -1.38 to -1.75%; ES = -0.38 to -0.54). Sprinting with forearm loads resulted in significant ( p  ≤ 0.05) increases in relative propulsive impulse (5.48%; ES = 1.09) and step length (4.01%; ES = 1.04) over the 1st acceleration phase. Relative vertical impulse was the only variable to change over the middle two acceleration phases (3.94-4.18%; ES = 0.77-1.00). Over the last acceleration phase stride frequency was lower (-4.86%, ES = -0.92), yet both flight time (7.70%; ES = 0.79) and vertical impulse (4.12%; ES = 0.89) increased. These findings provide interesting programming implications for coaches who wish to improve the determinants of sprinting via dedicated and specific arm loaded training. Sprinting with forearm loads may be used to develop longer stride lengths by generating greater horizontal propulsion during early acceleration and promote alterations to step frequency and flight time imposed through greater vertical loading demands over the later phases of accelerated sprinting.

Wearable resistance training involves added load attached directly to the body during sporting movements. The effects of load position during running are not yet fully established. Therefore, the purpose of this research was to determine spatio-temporal and kinetic characteristics during submaximal running using upper, lower and whole-body wearable resistance (1-10% body mass (BM)). Twelve trained male runners completed eight 2-min treadmill running bouts at 3.9 m/s with and without wearable resistance. The first and last bouts were unloaded, while the middle 6 were randomised wearable resistance conditions: upper body (UB) 5% BM, lower body (LB) 1%, 3%, 5% BM and whole body (WB) 5%, 10% BM. Wearable resistance of 1-10% BM resulted in a significant increase in heart rate (5.40-8.84%), but minimal impact on spatio-temporal variables. Loads of 5% BM and greater caused changes in vertical stiffness, vertical and horizontal force, and impulse. Functional and effective propulsive force (2.95%, 2.88%) and impulse (3.40%, 3.38%) were significantly (p  < 0.05) greater with LB5% than UB5%. Wearable resistance may be used to increase muscular kinetics during running without negatively impacting spatio-temporal variables. The application of these findings will vary depending on athlete goals. Future longitudinal studies are required to validate training contentions.

Cahill, MJ, Oliver, JL, Cronin, JB, Clark, K, Cross, MR, Lloyd, RS, and Lee, JE. Influence of resisted sled-pull training on the sprint force-velocity profile of male high-school athletes. J Strength Cond Res 34(10): 2751-2759, 2020-Although resisted sled towing is a commonly used method of sprint-specific training, little uniformity exists around training guidelines for practitioners. The aim of this study was to assess the effectiveness of unresisted and resisted sled-pull training across multiple loads. Fifty-three male high-school athletes were assigned to an unresisted (n = 12) or 1 of 3 resisted groups: light (n = 15), moderate (n = 14), and heavy (n = 12) corresponding to loads of 44 ± 4 %BM, 89 ± 8 %BM, and 133 ± 12 %BM that caused a 25, 50, and 75% velocity decrement in maximum sprint speed, respectively. All subjects performed 2 sled-pull training sessions twice weekly for 8 weeks. Split times of 5, 10, and 20 m improved across all resisted groups (d = 0.40-1.04, p < 0.01) but did not improve with unresisted sprinting. However, the magnitude of the gains increased most within the heavy group, with the greatest improvement observed over the first 10 m (d ≥ 1.04). Changes in preintervention to postintervention force-velocity profiles were specific to the loading prescribed during training. Specifically, F0 increased most in moderate to heavy groups (d = 1.08-1.19); Vmax significantly decreased in the heavy group but increased in the unresisted group (d = 012-0.44); whereas, Pmax increased across all resisted groups (d = 0.39-1.03). The results of this study suggest that the greatest gains in short distance sprint performance, especially initial acceleration, are achieved using much heavier sled loads than previously studied in young athletes.

Individualisation can improve resistance training prescription. This is accomplished via monitoring or autoregulating training. Autoregulation adjusts variables at an individualised pace per performance, readiness, or recovery. Many autoregulation and monitoring methods exist; therefore, this review's objective was to examine approaches intended to optimise adaptation. Up to July 2019, PubMed, Medline, SPORTDiscus, Scopus and CINAHL were searched. Only studies on methods of athlete monitoring useful for resistance-training regulation, or autoregulated training methods were included. Eleven monitoring and regulation themes emerged across 90 studies. Some physiological, performance, and perceptual measures correlated strongly (r ≥ 0.68) with resistance training performance. Testosterone, cortisol, catecholamines, cell-free DNA, jump height, throwing distance, barbell velocity, isometric and dynamic peak force, maximal voluntary isometric contractions, and sessional, repetitions in reserve-(RIR) based, and post-set Borg-scale ratings of perceived exertion (RPE) were strongly associated with training performance, respectively. Despite strong correlations, many physiological and performance methods are logistically restrictive or limited to lab-settings, such as blood markers, electromyography or kinetic measurements. Some practical performance tests such as jump height or throw distance may be useful, low-risk stand-ins for maximal strength tests. Performance-based individualisation of load progression, flexible training configurations, and intensity and volume modifications based on velocity and RIR-based RPE scores are practical, reliable and show preliminary utility for enhancing performance., (© 2020 Eric R. Helms, Kedric Kwan, Colby A. Sousa, John B. Cronin, Adam G. Storey, Michael C. Zourdos, published by Sciendo.)

Abstract Horizontal force-velocity (F-V) profiling is a strategy to assess athletes' individual performance capabilities during sprinting. This study investigated the acute changes in F-V profiles during sprinting of fourteen collegiate male sprinters with a mean 100-m sprint time of 11.40 ± 0.39 s, from a split-stance starting position. The subjects sprinted 30-m with, and without, wearable resistance (WR) equivalent to 2% body mass, attached to their forearms. Sprinting time at 5, 10, 20, and 30-m was assessed using laser technology. External horizontal F-V relationships were calculated via velocity-time signals. Maximal theoretical velocity ( V 0 ), theoretical relative and absolute horizontal force ( F 0 ), and horizontal power ( P max ) were determined from the F-V relationship. Paired t-tests were used to determine statistical differences ( p  ≤ 0.05) in variables across conditions with Cohen's d as effect sizes (ES) calculated to assess practical changes. Sprint times at 10-m and beyond were significantly increased (1.9-3.3%, p 0.01-0.03, ES 0.46-0.60) with WR compared to unloaded sprinting. The only significant change in F-V with the WR condition was found in relative P max system (-6.1%, p 0.01, ES 0.66). A small decrease was reported in V 0 (-1.0%, p 0.11, ES 0.27), with small to medium ES decreases reported in F 0 (-4.8% to -6.1%, p 0.07-0.21, ES 0.25-0.51) and P max (-4.3% to -4.6%, p 0.06-0.08, ES 0.32-0.45). The greater changes to F 0 and P max suggest that forearm WR may be a possible training tool for athletes who wish to focus on force and power adaptation during sprint acceleration from a standing start.

Moeskops, S, Oliver, JL, Read, PJ, Cronin, JB, Myer, GD, Haff, GG, and Lloyd, RS. The influence of biological maturity and competitive level on isometric force-time curve variables and vaulting performance in young female gymnasts. J Strength Cond Res 34(8): 2136-2145, 2020-This cross-sectional study investigated isometric force-time curve variables and vaulting performance in young female gymnasts of varying maturity and competitive levels. One hundred twenty gymnasts aged 5-14 years were subdivided into maturity groupings and also according to their competitive level. Subjects performed isometric midthigh pulls (IMTP) before completing straight jump vaults that were recorded using two-dimensional video. All significance values were accepted at p < 0.05. Absolute peak force (PF abs) and force at various time epochs were significantly greater in more mature gymnasts, although no significant differences were observed in relative peak force (PF rel). When grouped by competitive level, elite gymnasts produced a significantly greater absolute rate of force development (RFD abs) at 0-150, 0-200, and 0-250 ms as well as relative RFD (RFD rel) at 0-200 and 0-250 ms than recreational gymnasts. Based upon regression analyses, force at 50 ms during the IMTP test explained 15% of vertical takeoff velocity during vaulting. Biological maturation seems to impact isometric force-time curve characteristics in young female gymnasts, and higher-level gymnasts produce greater RFD than those competing at a lower level. Vaulting vertical takeoff velocity seems to be largely independent of isometric force-time characteristics with only a small amount of variance explained by force at 50 ms.

Quantifying echo intensity (EI), a proposed measure of muscle quality, is becoming increasingly popular. Additionally, much attention has been paid to regional differences in other ultrasonically evaluated measures of muscle morphology and architecture. However, the variability of regional (proximal, middle, distal) EI of the vastus lateralis, rectus femoris, and lateral and anterior vastus intermedius has yet to be determined. Twenty participants (40 limbs), were evaluated on 3 occasions, separated by 7 days. Intersession variability of EI with and without subcutaneous fat correction was quantified. Furthermore, the interchangeability of corrected EI across regions was evaluated. Variability of regional quadriceps EI was substantially lower with subcutaneous fat correction (intraclass correlation coefficient (ICC) = 0.81-0.98, coefficient of variation (CV) = 4.5%-16.8%, typical error of measure (TEM) = 0.13-0.49) versus raw values (ICC = 0.69-0.98, CV = 7.7%-42.7%, TEM = 0.14-0.68), especially when examining the vastus intermedius (ICC = 0.81-0.95, CV = 7.1%-16.8%, TEM = 0.23-0.49 vs. ICC = 0.69-0.92, CV = 22.9%-42.7%, TEM = 0.31-0.68). With the exception of the rectus femoris and vastus intermedius ( p ≥ 0.143, effect size (ES) ≤ 0.18), corrected EI was greater for proximal and distal regions when compared with the midpoint ( p ≤ 0.038, ES = 0.38-0.82). Researchers and practitioners should utilize subcutaneous fat thickness correction to confidently evaluate EI at all regions of the quadriceps. Regional EI cannot be used interchangeably for the vastus muscles, likely because of an increase in fibrous content towards the myotendinous junctions. Novelty Regional quadriceps echo intensity was reliable with and without correction for subcutaneous fat thickness. Intersession variability of regional quadriceps echo intensity was substantially improved following subcutaneous fat correction. Quadriceps echo intensity increased towards myotendinous junctions in the vastus muscles.

This study determined the acute changes in spatio-temporal and impulse variables when wearable resistance (WR) of 2% body mass was attached distally to the thighs during 50 m maximal sprint-running. Fifteen sub-elite male sprinters performed sprints with and without WR over 50 m of in-ground force platforms in a randomised order. A paired t-test was used to determine statistical differences ( p  < .05), with effect sizes (ES) calculated between conditions over steps: 1-4, 5-14, and 15-23. WR resulted in small increased 10 and 50 m sprint times (1.0%, ES = 0.31, 0.9%, ES = 0.44, respectively, p  > .05) compared to the unloaded sprint condition. For spatio-temporal variables, the WR condition resulted in moderate ES changes in step frequency (-2.8%, ES = -0.53, steps 5-14, p  > .05), and contact time (2.5%, ES = 0.57, steps 5-14, and 3.2%, ES = 0.51, average of 23 steps, p  > .05), while step length was unaffected during all step phases of the sprint (ES = 0.02-0.07, p  > .05). Regarding kinetics, during steps 5-14, WR resulted in a moderate decrease (-4.8%, ES = -0.73, p  < .05) in net anterior-posterior impulses and a moderate decrease in vertical stiffness (-5.7%, ES = -0.57, p  > .05). For athletes seeking to overload step frequency and develop anterior-posterior impulse during mid to late accelerated sprinting, WR enables the application of a sprint-specific form of resistance training to be completed without decreasing step length.

The aim of this review was to examine the literature that has used lower limb wearable resistance (WR) during sprint running. A systematic search was completed to identify acute and longitudinal studies assessing the effects of lower limb WR on sprint running performance from international peer-reviewed journals. The Boolean phrases (limb OR leg OR lower extremity) AND (sprint*) AND (resist* OR weight OR load*) were used to search PubMed, SPORTDiscus, and Web of Science electronic databases. Ten studies met the inclusion criteria and were retained for analysis that reported the acute kinematic and kinetic effects ( n  = 8), acute performance effects ( n  = 3), and longitudinal effects ( n  = 1). Results showed that the WR micro-loading (0.6-5% body mass) significantly increased contact time (2.9-8.9%), decreased step frequency (-1.4 to -3.7%), and slowed total sprint times (0.6-7.4%). Unloaded sprinting immediately following sprints with lower limb WR resulted in no significant  change to total sprinting times. One longitudinal training study did not find a significant effect on maximal sprinting speed for non-trained participants. It can be concluded that not all step kinematic variables are affected during sprinting with an added load up to 5% body mass. Therefore, coaches can use lower limb WR to selectively overload certain aspects of sprint running, in particular stride frequency. It also appears that lower limb WR overloads sprint movement velocity and may provide a stimulus to increase horizontal force output, therefore, it may be inferred that lower limb WR has the potential to elicit improved sprinting performance.

Background: Currently jump-landing ground reaction forces have only been quantified in the vertical direction as a stimulus for bone development. This study quantified the full-spectrum of jump-landing force magnitudes (body weight's) and rates of strain (body weights per second) of bilateral multidirectional jumps (star jump and stride jump) with reactive jump-landings (i.e. jumping immediately after initial jump-landing) among premenopausal women. It was also of interest to quantify the influence of instruction on the magnitude and rate of the jump-landing ground reaction forces., Methods: Twenty-one women [Mean (SD): 43.3(5.9)yr; 69.4(9.6)kg; 167(5.5)cm; 27.5(8.7)% body fat] performed a jump testing session 'with instruction' followed by a jump testing session performed one week later with 'instruction withdrawn'., Findings: The resultant magnitudes (3.90 to 5.38, body weights) and rates of strain (192 to 329, body weights per second) for the jump-landings, performed on a force plate, exceeded previously determined osteogenic thresholds (>3body weight's and >43body weights per second, respectively). An instruction effect was observed for resultant (↑8% and ↑12%; P ≤ .01) and vertical (↑8% and ↑7%; P ≤ .01) ground reaction force's (Newtons and body weight, respectively) indicating learning/practice effects for these exercises. A jump-landing effect was observed, with larger peak rates of strain (↑29%; P < .0001, body weight per second) and peak forces (↑12% to ↑48%; P ≤ .01, body weights) for the second jump-landing (post-reactive jump)., Interpretation: These multidirectional bilateral jumps represent a unique training stimulus for premenopausal women and achieve osteogenic thresholds thought pre-requisite for bone growth and could be utilized in the development of osteogenic exercise programs., Competing Interests: Declaration of competing interest The authors have no conflicts of interest to disclose., (Copyright © 2019 Elsevier Ltd. All rights reserved.)

When new protocols are developed, there is a requirement to investigate test-retest reliability of measures for valid use and interpretation of data in research and practice. Therefore, the aim of this investigation was to determine the inter-day reliability of the cable put and seated rotation assessment protocols. On three occasions, nine resistance-trained men performed cable puts and cable rotations at different loads between 6 and 42 kg on a commercially available cable cross over machine. Load stack movement was recorded using a PT5A linear position transducer from which all kinematic and kinetic variables were calculated. Reliability was excellent for peak velocity and displacement based on intraclass correlation coefficient (ICC) and coefficient of variation (CV) across the majority of loads and movements (cable put: ICC = 0.92 to 0.99, CV = 3.1% to 8.6%; cable seated rotation: ICC = 0.76 to 0.99, CV = -1.7% to 16.1%). However, kinetic variables demonstrated inadequate reliability across the majority of days, loads and movements (ICC = 0.70, CV >10%). It was concluded that peak velocity is a reliable kinematic measure to assess muscular capability from cable put and seated rotation protocols; however, kinetic measures are too variable to provide reliable outputs across testing occasions.

Purpose: Regional muscle-architecture measures are reported widely; however, little is known about the variability of these measurements in the rectus femoris, vastus lateralis, and anterior and lateral vastus intermedius. The aim of this study was to quantify this variability., Methods: Regional muscle thickness, pennation angle (PA), and calculated and extended-field-of-view-derived fascicle length (FL) were quantified in 26 participants using ultrasonography across 51 limbs on 3 occasions. To quantify variability, the typical error of measurement (TEM) was multiplied by 2, and thresholds of 0.2-0.6 (small), 0.6-1.2 (moderate), 1.2-2.0 (large), 2.0-4.0 (very large), and >4.0 (extremely large) were applied. In addition, variability was deemed large when the intraclass correlation coefficient (ICC) was <.67 and coefficient of variation (CV) >10%, moderate when ICC > .67 or CV < 10% (but not both), and small when both ICC > .67 and CV < 10%., Results: Muscle thickness of all muscles and regions had low to moderate variability (ICC = .88-.98, CV = 2.4-9.3%, TEM = 0.15-0.47). PA of the proximal and distal vastus lateralis had low variability (ICC = .85-.96, CV = 3.8-8%) and moderate to large TEM (TEM = 0.42-0.83). PA of the rectus femoris was found to have moderate to very large variability (ICC = .38-.74, CV = 11.4-18.5%, TEM = 0.61-1.29) regardless of region. Extended-field-of-view-derived FL (ICC = .57-.94, CV = 4.1-11.5%, TEM = 0.26-0.88) was superior to calculated FL (ICC = .37-.84, CV = 7.4-17.9%, TEM = 0.44-1.33)., Conclusions: Variability of muscle thickness was low in all quadriceps muscles and regions. Only rectus femoris PA and FL measurements were highly variable. The extended-field-of-view technique should be used to assess FL where possible. Inferences based on rectus femoris architecture should be interpreted with caution.

Objective: Length-tension relationships are widely reported in research, rehabilitation and performance settings; however, several isometric contractions at numerous angles are needed to understand these muscular outputs. Perhaps a more efficient way to determine torque-angle characteristics is via isokinetic dynamometry; however, little is known about the variability of isokinetic measurements besides peak torque and optimal angle. This paper examines the variability of angle-specific isokinetic torque and impulse measures., Approach: Three sessions of concentric (60°·s -1 ) knee extensions were performed by both limbs of 32 participants. Assessments were repeated on three occasions, separated by 5-8 d. To quantify variability, the standardized typical error of measurement (TEM) was doubled and thresholds of 0.2-0.6 (small), 0.6-1.2 (moderate), 1.2-2.0 (large), 2.0-4.0 (very large) and  >4.0 (extremely large) were applied. Additionally, variability was deemed large when the intraclass correlation coefficient (ICC) was  <0.67 and coefficient of variation (CV)  >  10%; moderate when ICC  >  0.67 or CV  <  10% (but not both); and small when both ICC  >  0.67 and CV  <  10%., Main Results: Isokinetic torque and angular impulse show small to medium variability (ICC  =  0.75-0.96, CV  =  6.4%-15.3%, TEM  =  0.25-0.53) across all but the longest (100°) and shortest (10°) muscle lengths evaluated. However, moderate to large variability was found for the optimal angle (ICC  =  0.58-0.64, CV  =  7.3%-8%, TEM  =  0.76-0.86), and torque and impulse at the beginning and end of the range of motion (ICC  =  0.57-0.85, CV  =  11-42.9%, TEM  =  0.40-0.89). Intersession variability of isokinetic torque and impulse were small to moderate at medium (90-20°) joint angles., Significance: Researchers and practitioners can examine the muscle torque-angle relationship and activity-specific torque outputs within these ranges, without resorting to more strenuous and time-consuming isometric evaluations.