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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occasions of each condition (combination of arm, rotation, and test position) separated by 7 to 14 days., Results: IR superseded ER in all testing positions.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.

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.

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.

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.

Context: Frequency and magnitude of ground reaction forces (GRF) have been implicated in causing injuries such as "jumpers knee.", Objective: To investigate whether a single session of augmented feedback concerning landing technique would decrease GRF., Design: Pretest posttest experimental design., Setting: University biomechanics laboratory., Participants: Fifteen female Division 1 intercollegiate volleyball players., Intervention: Participants were required to land on a force platform after spiking a volleyball from a four-step approach before and after an intervention involving visual and aural augmented feedback on correct jumping and landing technique., Main Outcome Measures: Mediolateral (ML), anterioposterior (AP), and vertical (V) GRF normalized to body weight (BW)., Results: Augmented feedback was found to significantly (P = 0.01) decrease VGRF by 23.6% but not ML (25%, P = 0.16) and AP (4.9%, P = 0.40) peak GRF., Conclusions: A single session of augmented feedback may be effective in reducing VGRF in collegiate athletes.