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The aim of this systematic review and meta-analysis was to evaluate the effects of high-repetition strength training (HRST) on performance in competitive endurance athletes. The methodology followed the Preferred Reporting Items for Systematic Review and Meta-Analysis protocol. A search of databases was performed until December 2020. Inclusion criteria were (a) competitive endurance athletes, (b) ≥4 weeks HRST intervention, (c) control or comparison group, (d) outcome measures of performance (either physiological or time trial performance), and (e) all experimental designs. Quality assessment was performed using the Physiotherapy Evidence Database (PEDro) scale. Of the 615 studies retrieved, 11 studies were included (216 subjects) and 9 studies provided sufficient data for the meta-analysis (137 subjects). The PEDro scale score had a mean of 5 of 10 points (range: 3-6). There was no significant difference between the HRST and control groups (g = 0.35; 95% confidence interval [CI] = -0.38 to 1.07; p = 0.35) or HRST and low-repetition strength training (LRST) groups (g = 0.24; 95% CI = -0.24 to 0.72; p = 0.33). The findings of this review and meta-analysis indicate that HRST does not result in improved performance over a 4-to 12-week period, and the results seem to be similar to LRST. The majority of studies involved recreational endurance athletes and had a mean duration of 8 weeks, which is a limitation of the findings. Future intervention studies should be > 12 weeks in duration and involve well-trained endurance athletes (maximal oxygen uptake [V̇o2max] of >65 ml·kg-1·min-2). [ABSTRACT FROM AUTHOR]

Purpose: To examine the relationships between the isometric midthigh pull (IMTP), isometric squat (ISqT), and sprint acceleration performance in track-and-field sprinters and to determine whether there are differences between men and women. Methods: Fifteen male and 10 female sprinters performed 3 maximal-effort IMTPs, ISqTs, and 3x30-m sprints from blocks. Results: Among the men, the results showed significant negative correlations between IMTP and ISqT peak force; relative peak force; force at 100, 150, and 200 ms; rate of force development (0-150 and 0-200 ms); and impulse (0-200 ms) and 0- to 5-m time (r = -.517 to -.714; P < .05). IMTP impulse (B = -0.582, P - .023) and ISqT relative peak force (B = -0.606, P = .017) significantly predicted 0- to 5-m time. Among the women, no IMTP or ISqT variables significantly correlated with any sprint times. Men measured significantly higher than women for all IMTP measures except relative peak force. Men were significantly faster than women at all splits. When comparing measures of the ISqT, there were no significant differences between men and women. Conclusions: Variables measured during the IMTP and ISqT significantly correlated with 0- to 5-m sprint performance in male athletes. Isometric strength can have a sizable influence on 0- to 5-m time, but in some cases, the maximum effect could be very small. [ABSTRACT FROM AUTHOR]

Purpose: To examine the interday reliability and usefulness of a reactive strength index (RSI) derived from a maximal 5-rebound jump test (5max RJT) and a maximal 10-rebound jump test (10/5 RJT). Methods: Twenty male field-spoil athletes (24.5 [3.0] y, 1.78 [0.1] m, 84.9 [5.2] kg) and 15 female participants (21.1 [0.9] y, 1.65 [0.73] m, 62.0 [5.1] kg) performed 2 maximal repetitions of the 5max RJT and the 10/5 RJT on 2 testing days after a specific warm-up. A 1-wk period separated testing days, and these sessions were preceded by a familiarization session. RSI was calculated by dividing jump height (in meters) by contact time (in seconds). The 5max RJT and the 10/5 RJT trial with the highest RSI on each testing day were used for reliability and usefulness analysis. Results: Both tests were deemed reliable for determining RSI for male, female, and pooled male and female cohorts, as the intraclass correlation coefficients were ≥80 and the coefficient of variation was <10%. Only the 5max RJT was rated as "good" at detecting the smallest worthwhile change in performance for female athletes (smallest worthwhile change: 0.10 > typical error: 0.07). The 5max RJT for men and the 10/5 RJT for men and women were rated "good" in detecting a moderate change in performance only. Conclusions: Both tests are reliable for the determination of RSI, but the usefulness of the tests in detecting the smallest worthwhile change is questionable. [ABSTRACT FROM AUTHOR]

Purpose: To examine the reliability and usefulness of the isometric midthigh pull (IMTP) and isometric squat (ISqT) performed at the same knee and hip angles. The scores produced in each test were compared to determine the magnitude of differences between tests. Methods: Twenty-six male and female athletes (age, 23.6 [4.3] y; height, 1.75 [0.07] m; and body mass, 68.8 [9.7] kg) performed 2 maximal repetitions of the IMTP and ISqT following a specific warm-up. Results: Maximum force, absolute peak force (PF), relative PF, allometrically scaled PF, rate of force development (0–200 and 0–250 ms), and impulse (0–300 ms) were deemed reliable (intraclass correlation coefficient [ICC] ≥.86 and coefficient of variation [CV] ≤9.4%) in the IMTP and ISqT based on predetermined criteria (ICC ≥.8 and CV ≤10%). Impulse (0–200 and 0–250 ms) was reliable in the ISqT (ICC ≥.92 and CV ≤9.9%). Participants produced significantly (P <.05) greater PF and impulse (0–300 ms) during the ISqT compared with the IMTP. When split by sex, female participants produced significantly greater PF (P =.042) during the ISqT, with no significant differences among male participants (P =.245). Both tests are capable of detecting changes in performance in maximum force and absolute PF. Conclusions: Both tests are reliable for non-time-dependent maximal strength measures when measured at the same knee and hip angles. The ISqT may be preferred when coaches want to test an athlete’s true maximum lower-limb strength, especially female athletes. [ABSTRACT FROM AUTHOR]

The study assessed the effect of current activation potentiation by evaluating jaw clenching and its effect on the rate of force development (RFD), time to peak force (TTPF). and peak force (PF) during the countermovement jump. Fourteen subjects performed the countermovement jump on a force platform while maximally clenching their jaw on a dental vinyl mouthguard (JAW) as well as without clenching their jaw by jumping with an open mouth (NON-JAW). Results reveal that the RFD was 19.5% greater in the JAW compared with the NON-JAW condition (p < 0.05). The TTPF was 20.15% less in the JAW compared with the NON-JAW condition (p < 0.05). There were no significant differences (p = 0.60) in PF between the JAW and NON-JAW conditions. These findings indicate that concurrent activation potentiation is manifested through jaw clenching during the countermovement jump. As a result, athletes may employ this strategy of maximally clenching their jaws to gain an ergogenic advantage during the countermovement jump. KEY WORDS Jendrassik maneuver, remote voluntary contractions, motor control, plyometrics

The purpose of this article is to provide strength and conditioning practitioners with an understanding of the role of elastic energy in activities with high force and power requirements. Specifically, the article covers 1) the nature of elasticity and its application to human participants, 2) the role of elastic energy in activities requiring a stretch-shorten cycle such as the vertical jump, 3) the role of muscular stiffness in athletic performance, 4) the control of muscular stiffness through feedforward and feedback mechanisms, and 5) factors affecting muscular stiffness. Finally, practical applications are provided. In this section, it is suggested that the storage and reuse of elastic energy is optimized at relatively higher levels of stiffness. Because stiffness decreases as fatigue ensues as well as with stretching before an event, the article emphasizes the need for proper preparation phases in a periodized cycle and the avoidance of long static stretches before high-force activities. The importance of teaching athletes to transition from eccentric to concentric movements with minimal time delays is also proposed due to the finding that time delays appear to decrease the reuse of elastic energy. In addition to teaching within the criterion tasks, evidence is provided that minimizing transitions in plyometric training, a technique demonstrated to increase musculotendinous stiffness, can optimize power output in explosive movements. Finally, evidence is provided that training and teaching programs designed to optimize muscular stiffness may protect athletes against sports-related injuries. KEY WORDS stiffness, stretch-shorten cycle, counter-movement jump, stretch reflex, stretching, strength

The reliability of the reactive strength index (RSI) and time to stabilization (TTS) during maximal-effort plyometric depth jumps was examined. Twenty-two subjects performed three depth jumps from a height of 30 cm. Measures such as height of jump (JH), ground-contact time (CT), RSI, and TTS were obtained and analyzed for reliability using Cronbach alpha reliability coefficient and intraclass correlations. The JH, CT, and RSI were shown to be highly reliable from trial to trial (evidenced by high Cronbach reliability coefficients ([alpha] > 0.95) and high single- and average-measures intraclass correlations (>0.9). Time to stabilization was not reliable from trial to trial, as evidenced by a low Cronbach reliability coefficient ([alpha] < 0.7) and poor single( KEY WORDS plyometrics, balance, stretch shortening cycle

Differences in muscle dynamics between the preferred and nonpreferred jumping legs of subjects in maximal, explosive exercise were examined. Eight subjects performed nonfatiguing bouts of single-legged drop jumps and rebound jumps on a force sledge apparatus. Measures of flight time, reactive strength index, peak vertical force, and vertical leg-spring stiffness were obtained for 3 drop jumps and 3 rebound jumps on both legs. Subjects utilized a stiffer leg spring and a more explosive jumping action in the nonpreferred leg when performing a cyclical rebound jumping task in comparison to a single drop jump task (observed through differences in vertical leg-spring stiffness, peak vertical force, and reactive strength index, p < 0.05). The preferred leg performed equally well in both tasks. Between-leg analysis showed no differences in dependent variables between the preferred and the nonpreferred leg in the rebound jumping protocol. However, the drop jump protocol showed significant performance differences, with flight time and reactive strength index greater in the preferred leg than the nonpreferred leg (p < 0.05). We hypothesize that, throughout the lifespan, both legs are equally trained in cyclical rebound jumping tasks through running. However, because a preferred leg must be selected when performing any one-off, single-legged jump, imbalances in this specific task develop over time with consistent selection of a preferred jumping leg. The data demonstrate that the rebound jump protocol is representative of the symmetrical mechanics of forward running and that leg-spring stiffness is modulated depending on the demands of the specific task involved. Strength and conditioning practitioners should give careful consideration to appropriate jump protocol selection and should exercise caution when comparing laboratory results to data gathered in field testing. KEY WORDS. leg-spring stiffness, reactive strength index, drop jump, rebound jump, ground reaction force

The purpose of this investigation was to determine the concurrent validity of two devices used in velocity-based monitoring of resistance training. The TendoTM Fitrodyne is a linear position transducer (LPT) which attaches to the barbell to measure velocity of movement. PUSHTM is a wearable inertia sensor (WIS) that is worn on the athlete's forearm and utilizes an integrated gyroscope and accelerometer to provide a value for movement velocity. Both devices were compared with 3D motion capture data. The validation of such devices is paramount as they are being more frequently used in a strength and conditioning and biomechanics setting. Ten subjects completed 2 sets of 6 repetitions on the barbell bench press at loads of 40% and 80% of 1RM. All subjects had a minimum of one year's resistance training experience. Results for the LPT and the WIS were both strongly correlated with the criterion measure (ICC > 0.9). However the wearable inertia sensor (WIS) consistently displayed lower mean concentric velocity (0.06 - 0.50 m.s-1 lower) values than the criterion measure (%error - 29.17%) suggesting it is not a valid measure of mean concentric velocity in the bench press exercise. Conversely the LPT was deemed a valid velocity-based monitoring device for the chosen exercise. [ABSTRACT FROM AUTHOR]

Due to intense training or competition periods, athletes can experience acute neuromuscular fatigue. The drop-jump reactive-strength index (DJ-RSI) is a test used by coaches and sport scientists to monitor reactive-strength, and potentially neuromuscular readiness, in athletes. The aim of this paper was to establish the trial-to-trial and interday reliability of the DJ-RSI measured via a 40cm drop-jump in a practical setting and to demonstrate how this data can be utilised to examine the 'meaningfulness' of monitoring data. Elite junior international rugby players (n = 15), who were competing in an 8 week international tournament, participated in this study. Trial-to-trial analyses showed that the DJRSI demonstrated adequate reliability with a coefficient of variance (CV) of 5% and an observed intraclass correlation (ICCα) of 0.90. Interday analyses also demonstrated that DJ-RSI had acceptable reliability with a CV of 8% and ICCα of 0.93. However, both trial-to-trial and inter-day CV (5.27 & 8.47 %) were greater than the smallest worthwhile change (2.79 & 3.31 %), and between-athlete CV for the reactive strength index ranged from 1 - 15%. It is advised that in this scenario, when a monitoring tool is reliable but the SWC < CV, each individual athlete's CV should be used as the threshold for 'meaningful change' in individual monitoring analyses. This paper also highlights, that where possible, practitioners should calculate individual athlete's own reliability data to optimise the interpretation of acute monitoring data. [ABSTRACT FROM AUTHOR]

The article discusses the benefits of monitoring movement velocity during strength training exercises. The speed of lifting can reliably measured in different strength training exercises using commercial linear position transducers (LPT). The relationship between velocity and load can be described using linear regression that yields slope and intercept of the line.

Gender differences have not been evaluated with respect to an athletes' ability to develop force during the countermovement jump. This study assessed the acute time course of take off as well as the rate of force development (RFD) during the countermovement jump. This study also assessed gender differences in these variables and whether or not these variables were correlated to jump height. Forty-four NCAA division-I track and field athletes, including 24 men and 21 women, performed the countermovement jump with kinetic data obtained via an AMTI force plate with time to takeoff (TTT) and RFD calculated for the concentric phase. No statistically significant differences were found between men and women for the TTT (p = 0.08) or RFD (p = 0.11). Mean TTT values were 413.91 ± 84.71 and 468.14 ± 114.59 ms, for men and women, respectively. Mean RFD values were 5038.39 ± 1592.13 and 4118.89 ± 2184.03 N·sec, for men and women, respectively. Rate of force development was not correlated to the countermovement jump (r = 0.19, p= 0.22), though TTT was (r = -0.33, p = 0.03). Results indicate that women jump as quickly and develop force at a rate that is similar to men. [ABSTRACT FROM AUTHOR]