The Use of Contact Time and the Reactive Strength Index to Optimize Fast Stretch-Shortening Cycle Training

ArticleinStrength and conditioning journal 30(5):32-38 · October 2008with 9,069 Reads 
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Abstract
THIS ARTICLE REVIEWS RESEARCH RELATING TO THE STRETCH-SHORTENING CYCLE AND PLYOMETRICS. THE ARTICLE INSTRUCTS STRENGTH AND CONDITIONING PRACTITIONERS IN THE USE OF GROUND CONTACT TIMES AND THE REACTIVE STRENGTH INDEX IN PLYOMETRIC TRAINING. DOCUMENTATION ON HOW THESE MEASUREMENTS CAN BE USED TO OPTIMIZE PLYOMETRICS AND TO IMPROVE ATHLETES' FAST STRETCH SHORTENING CYCLE PERFORMANCE IS PROVIDED. RECOMMENDATIONS ARE MADE REGARDING THE USE OF GROUND CONTACT TIMES TO IMPROVE TRAINING SPECIFICITY AND THE USE OF THE REACTIVE STRENGTH INDEX TO OPTIMIZE PLYOMETRICS, TO MONITOR TRAINING PROGRESS, AND TO SERVE AS A MOTIVATIONAL TOOL. A 4-STEP PROGRESSION OF IMPLEMENTATION IS DETAILED.

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  • ... Reactive Strength Index (RSI) is generally described as an individual's muscles' ability to change quickly from eccentric to concentric contraction, which is considered as a measure of 'explosiveness' (5,6). RSI is one of a score of variables in evaluating jump performance in soccer players. ...
    Article
    Full-text available
    Objective: The purposes of this study were to investigate the comparison of some stretch-shortening cycle (SSC) parameters, and to correlate reactive strength index (RSI) scores from drop jumps (DJ) and sprint times (ST) among maturation groups according to peak height velocity (PHV). Methods: A total of 108 youth soccer players were included in this study (age: 13.0±1.5 years old; height: 162.7±12.1 cm; weight: 53.1±11.7 kg). Participants were divided into three groups (Pre-PHV, Mid-PHV and Post-PHV) according to calculation using the maturity offset equation. DJ tests from 20 and 40 cm drop heights (DH) and 30 m sprint tests were made by participants. RSI scores were taken during DJs. All tests were performed twice. One-way ANOVA and Welch ANOVA tests were performed to test differences between more than two independent groups for normally-distributed data. If a significant difference was found, Bonferroni and Games-Howell tests were performed for multiple comparisons, respectively. Pearson correlation coefficients were calculated for bivariate correlations between numeric variables, where appropriate. A value of p
  • ... This eccentric/concentric muscular contraction coupling produces a more powerful contraction compared with a purely concentric action (17). The DJ is commonly used by strength and conditioning (S&C) coaches as a training modality and to assess an athlete's SSC capabilities (12). It is also used as a readiness-to-train monitoring tool and for injury-risk screening purposes (6,23). ...
    Article
    Full-text available
    Comyns, TM, Brady, CJ, and Molloy, J. Effect of attentional focus strategies on the biomechanical performance of the drop jump. J Strength Cond Res 33(3): 626-632, 2019-Motor performance can be influenced by focusing an athlete's attention through the use of verbal instructions. There is limited research on the effect of internal, neutral, and external attentional focus strategies on drop jump (DJ) performance aimed at maximizing height jumped (HJ) and minimizing ground contact time (CT). The purpose of this study was to assess the effect of attentional focus strategies on biomechanical variables related to efficient DJ performance, namely HJ, CT, reactive strength index (RSI), leg-spring stiffness, and peak and relative peak ground reaction force (GRF). Seventeen male recreationally trained subjects performed 2 DJs after listening to instructions designed to evoke an internal, external, or neutral attentional focus. In total, 6 DJs were performed in the testing session, and the order of the instructions was randomly assigned. Significance was set at p ≤ 0.05. Results indicated that, compared with the neutral strategy, the external focus resulted in significantly higher RSI (p = 0.046), peak GRF (p = 0.025), relative GRF (p = 0.02), and leg-spring stiffness (p = 0.02). No significant difference was seen in DJ CT and HJ between all 3 conditions (p ≥ 0.05). These results indicate that the use of an external focus of attention may potentially result in a more effective and efficient fast stretch-shortening cycle performance because of the augmentation of RSI and leg stiffness. More research is warranted, however, because of the lack of significant results pertaining to CT and HJ.
  • ... Previous research suggests that determining an individual's optimal DJ height can be difficult, if the box is too low or too high the SSC stimulus will not be maximized (Byrne et al., 2010). RSI is one way to measure optimal DJ height, as optimal jump height has minimal purpose without paying attention to GCT (Beattie, Carson, Lyons, Kenny, 2017;Flanagan & Comyns, 2008;Young et al., 1995). While Peng (2011) does not recommend DHs over 60 cm due to increased injury risk, little is known about DHs above 60 cm. ...
  • ... Reactive strength index (RSI) was determined during drop jump as the ratio between jump height and time spent in contact with the ground as follows [19]: RSI = jump height (millimeters)/ground contact time (milliseconds). The ICC for RSI was 0.86 (95% CI: 0.75-0.92) ...
    Article
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    Background: This study examined the effects of 8 weeks of plyometric training on jumping, sprinting, and change of direction (COD) performance. Methods: Fifty female 7–9-year-old gymnasts were randomly assigned to a plyometric training group (PG; n = 33), that performed supplementary plyometric training twice per week, and a control group (CG; n = 17) that continued regular training. The following tests were performed before and after the intervention: 10 and 20 m sprints, 5 + 5 m and 10 + 10 m COD tests, one-leg and two-leg countermovement jump (CMJ), drop jump (DJ), squat jump (SJ), and standing long jump (SLJ). Results: Only a main effect for time was found for all jumping performance parameters (p = 0.001). However, the improvement of one- and two-leg CMJ in PG had a greater effect size than CG (0.72 and 0.67 vs. 0.34 and 0.18, respectively). Group × time interactions were found for 10 and 20 m sprint tests (p = 0.018 and p = 0.011, respectively) and for 10 + 10 m COD (p = 0.008) with the post hoc test showing improvement only for the PG (p = 0.001, 0.001, and 0.003 and d = 1.1, 1.14, and 0.6, respectively). Conclusions: Supplementary plyometric training increased sprint and COD performance more than regular gymnastics training, while jumping performance was equally improved in both groups.
  • ... Although related to RSI (since it is used in its calculation), RBJ CT was not related to any of the other variables. This contrasts to previous research (10,18) and may be due to the duration of the RBJ CT . Although reliability was high (average ICC 5 0.900 with no differences between trials; Table 1), 15 of the 21 subjects attained values that were greater than 250 ms. ...
  • ... 4 The reactive strength index (RSI) is frequently used to provide an indicator of fast-SSC capabilities. 5 However, despite being extensively used to evaluate drop jump performance, there is limited research that has used RSI during continuous maximal rebound jumps 6-12 , with only two studies to date examining the reliability of these measures. 13,14 Lloyd, et al. 14 examined the within and between session reliability of a maximal 5rebound jump (5max RJT) protocol in male youths and found that despite RSI having acceptable levels of test-retest reliability, the trial to trial variation (measurement error) in RSI scores was less reliable (coefficient of variation (CV): 11-21%) making it difficult to detect small but meaningful changes in RSI performance. ...
    Article
    Full-text available
    Purpose:: This investigation examined the inter-day reliability and usefulness of 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 sport athletes (24.5±3.0 y; 1.78±0.1 m; 84.9±5.2 kg) performed 2 maximal repetitions of the 5max RJT and the 10/5 RJT on two testing days following a specific warm up. A one week period separated each testing day and these sessions were proceeded by a familiarisation session. RSI was calculated by dividing jump height (m) by contact time (s). The 5max RJT and the 10/5 RJT trial with the highest RSI on each testing day was 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 ICCs ≥ 0.80 and the CV ≤ 10%. Only the 5max RJT was rated as 'good' at detecting the smallest worthwhile change (SWC) in performance for female athletes (SWC: 0.10 > TE:0.07). The 5max RJT for males and the 10/5 RJT for males and females were rated as '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 SWC is questionable.
  • ... Reactive Strength Index (RSI) was determined during a 5 maximum hop test which was performed on a mobile contact mat (FITRO Jumper, Fitronic, Slovakia). Participants were instructed to maximize jump height and minimize ground contact time (Dalleau et al., 2004) and the RSI variable was calculated using the equation of Flanagan and Comyns (2008). The first hop served as a CMJ (impetus) and was consequently excluded from analysis, with the 4 remaining hops averaged for analysis of RSI. ...
    Article
    Poor neuromuscular control and fatigue have been proposed as a risk factor for non-contact injuries especially around peak height velocity (PHV). This study explored the effects of competitive soccer match-play on neuromuscular performance and muscle damage in male youth soccer players. 24 youth players aged 13-16y were split into a PHV group (−0.5 to 0.5y) and post PHV group (1.0–2.5y) based on maturity off-set. Leg stiffness, reactive strength index (RSI), muscle activation, creatine kinase (CK), and muscle soreness were determined pre and post a competitive soccer match. Paired t-tests were used to explore differences pre and post competitive match play and independent sample t-tests for between groups differences for all outcome measures. There was no significant fatigue-related change in absolute and relative leg stiffness or muscle activation in both groups, except for the gastrocnemius in the post PHV group. RSI, CK and perceived muscle soreness were significantly different after soccer match-play in both groups with small to large effects observed (ES:0.41–2.82). There were no significant differences between the groups pre match-play except for absolute and relative leg stiffness (P < 0.001; ES = 1.16 and 0.63 respectively). No significant differences were observed in the fatigue related responses to competitive match play between groups except for perceived muscle soreness. The influence of competitive match-play on neuromuscular function and muscle damage is similar in male youth around the time of PHV and those post-PHV indicating that other factors must contribute to the heightened injury risk around PHV.
  • ... Subjects were instructed to maximize jump height and minimize ground contact time. The first jump was excluded with the 4 remaining trials being averaged for the calculation of RSI using the following formula: RSI 5 jump height (mm)/ground contact time (ms) (6). The best RSI score from 2 trials was recorded for further analysis. ...
    Article
    This study examined the effects of an 8-week plyometric training (PT) program on components of physical fitness in female young handball players. Twenty-one female adolescent handball players were assigned to an experimental group (EG, n=12; age=15.9±0.2 years) or an active control group (CG, n=9, age=15.9±0.3 years). While EG performed plyometric exercises in replacement of some handball specific drills, CG maintained the regular training schedule. Baseline and follow-up tests were carried out for the assessment of linear speed (i.e., 5-m, 10-m, and 20-m time), change-of-direction (CoD) speed (i.e., T-test time), muscle power (i.e., countermovement jump [CMJ] height, reactive strength index [RSI]), and repeated-sprint-ability (RSA) (RSA total-time [RSAtotal], RSA best-time [RSAbest], and RSA fatigue-index [RSAFI]). Data were analyzed using magnitude-based inferences. Within-group analyses for the EG revealed moderate-to-large improvements for the 5-m (effect size [ES]=0.81 [0.1 to 1.5]), 10-m sprint-time (ES=0.84 [0.1 to 1.5]), RSI (ES=0.75 [0.1 to 1.4]), RSAFI (ES=0.65 [0.0 to 1.3]), and T-test time (ES=1.46 [0.7 to 2.2]). Trivial-to-small ES were observed for RSAbest (ES=0.18 [-0.5 to 0.9]), RSAtotal (ES=0.45 [-0.2 to 1.1]), 20-m sprint-time (ES=0.56 [-0.1 to 1.2]), and CMJ height (ES=0.57 [-0.1 to 1.3]). For the CG, within-group analyses showed a moderate performance decline for T-test time (ES=-0.71 [-1.5 to 0.1]), small decreases for 5-m sprint-time (ES=-0.46 [-1.2 to 0.3]), and a trivial decline for 10-m (ES=-0.10 [-0.9 to 0.7]) and 20-m sprint-times (ES=-0.16 [-0.9 to 0.6)], RSAtotal (ES=0.0 [-0.8 to 0.8]) and RSAbest (ES=-0.20 [-0.9 to 0.6]). CG achieved trivial-to-small improvements for CMJ height (ES=0.10 [-0.68 to 0.87]) and RSI (ES=0.30 [-0.5 to 1.1]). In conclusion, a short-term in-season PT program, in replacement of handball specific drills, is effective in improving measures of physical fitness (i.e., linear/CoD speed, jumping, and RSA) in female young handball players.
  • ... For example, it has also been shown that power output and reactive strength performance may augment if drop height is increased from low to medium heights. However, if drop height is further increased from medium to high, overall muscle performance is inhibited (2,13). In this sense, the DJ drill is somewhat limited as a model to study the dose-response relationship between different PJT intensities and their effects. ...
    Article
    An 8-week single-blind randomized controlled trial was conducted to compare the effects of separate programs of equal volume, but different intensity, plyometric jump training (PJT), on physical fitness in healthy adults. Thirty-eight physically active males (mean age: 21.8 ± 2.5 years) participated. Subjects were randomly assigned to one of 3 PJT groups or a control (CON, n = 9) according to their jump performance. Plyometric jump training was conducted at maximal (PJT-100, n = 10), high (PJT-80, n = 9), or moderate (PJT-65, n = 10) intensity within each group. Baseline and follow-up tests were performed for the assessment of countermovement jump (CMJ) height, CMJ height with arm swing (CMJA), and drop jump height from a 20-cm drop box (DJ20), linear speed (30 m), and change-of-direction speed (CODS) (the Illinois CODS test). Results revealed significant group × time interactions for CMJ, CMJA, DJ20, 30-m sprint, and CODS (all p < 0.001; d = 0.39–0.76). Post hoc analyses showed significant improvements in all 5 fitness measures for PJT-100 (all p < 0.01, Δ3.7–13.5%, d = 0.26–1.4). For PJT-80, 3 of 5 fitness tests demonstrated significant change (CMJ: p < 0.001, Δ5.9%, d = 0.33; CMJA: p < 0.001, Δ7.0%, d = 0.43; CODS: p < 0.001, Δ3.9%, d = 0.9), and for PJT-65, only 1 test was significant (CMJ: p < 0.05, Δ2.8%, d = 0.15). No significant changes were observed in CON. Except for similar gains in DJ20 and 30-m sprint in PJT-100 and PJT-80, gains in physical fitness were, in general, greater (p < 0.05) after PJT-100 vs. PJT-80 vs. PJT-65 vs. CON. Therefore, maximal PJT intensity may induce larger physical fitness gains, although high and moderate intensities may also be useful, but to a lesser extent.
  • ... Reduced GCT during a DJ should be progressively developed alongside other strategies (such as integrative neuromuscular training) to help young players tolerate rapid impact forces. Importantly a CC should only be encouraged when a young athlete can produce short GCTs in the absence of a potentially injurious impact peak (3). An HC is likely to be the most appropriate introductory cue for injury free, young soccer players performing DJs as it can maximize jump height without increasing injury risk. ...
    Article
    Full-text available
    Abstract Oliver, JL, Barillas, SR, Lloyd, RS, Moore, I, and Pedley, J. External cueing influences drop jump performance in trained young soccer players. J Strength Cond Res XX(X): 000–000, 2019—Drop jump (DJ) characteristics provide insight on power production and injury risk. The purpose of this study was to investigate the effect of external cueing on DJ characteristics in young male soccer players. Fourteen academy soccer players performed DJs with 4 different conditions, control (CONT), contact cue (CC), height cue (HC), and quiet cue (QC). Performance measures were reactive strength index (RSI), jump height, ground contact time (GCT), and take-off impulse, with injury risk reflected by impact peak, impact timing, and landing impulse. Contact cue showed a very large significant reduction in GCT (effect size [ES] > 2.0, p < 0.05), and moderate to large increase in RSI, landing impulse, and push-off impulse (ES 0.70–1.55, p < 0.05) compared with all other conditions. Contact cue also moderately increased impact peak when compared with HC and QC (ES ≥ 0.78, p < 0.05). Height cue led to a significant increase in jump height that was moderately greater than other external cues (ES ≥ 0.87, p < 0.05), but with only a small nonsignificant increase compared (ES 0.54, p > 0.05) with CONT. The data showed that all cues provided a specific response; CC reduced GCT and increased RSI, HC increased jump height, and QC reduced outcomes associated with injury risk. Height cue may be advantageous for young soccer players with a low training age because it shows a small to moderate increase in jump height without increasing injury risk. Young players may need to be safely progressed to be able to use a CC to facilitate high reactive strength without being exposed to undue injury risk.
  • ... Jump height (cm) and contact time (sec) was recorded by Optojump -Microgate system (Microgate S.r.l -Bolzano, Italy). All participants performed three trials as indicated by Flanagan and Comyns (2008). ...
    Article
    Full-text available
    The aim of this study was the evaluation of a coordinative and plyometric training program on the functionality of foot in high school students. The use of modern technologies tools was used to made attractive the didactic approach. Sixty–three students were freely recruited and randomly divided into Training Group and Control Group. Training group consisted in plyometrics, balance and strength exercises while the control’s remained off-training. Subjects were tested for balance ability, reactive-strength and dynamic-ground-contact using high technology tool. The TG significative improved the balance ability performance by 68% while CG remained unchanged. The reactive-strength index revealed a 13% gain in training group although this increase resulted not significantly different from control. The dynamic-ground-contact performance revealed in TG only a tendency of decreasing. A specific training program affected the functionality of foot even if the application of stimulus was time restricted. Moreover, the use of technologies verified an interesting use of tools in school context that could involve students proactively.
  • ... The jump with the greatest height or distance for each variation was subsequently used for analysis. The DJ performance was evaluated by the highest reactive strength index (RSI) (Flanagan and Comyns, 2008;Prieske et al., 2018;Ramirez-Campillo et al., 2018), which was calculated by dividing the jump height by the corresponding ground contact time (Healy et al., 2018). ...
    Article
    Full-text available
    The aim of this study was to compare the effects of short-term strength training with and without superimposed whole-body electromyostimulation (WB-EMS) on straight sprinting speed (SSS), change of direction speed (CODS), vertical and horizontal jumping, as well as on strength and power in physically active females. Twenty-two active female participants (n = 22; mean ± SD: age: 20.5 ± 2.3 years; height: 171.9 ± 5.5 cm; body mass: 64.0 ± 8.2 kg; strength training experience 5.1 ± 3.6 years) were randomly assigned to two groups: strength training (S) or strength training with superimposed WB-EMS (S+E). Both groups trained twice a week over a period of 4 weeks and differed in the application of free weights or WB-EMS during four strength (e.g., split squats, glute-ham raises) and five sprinting and jumping exercises (e.g., side and box jumps, skippings). The WB-EMS impulse intensity was adjusted to 70% of individual maximal sustainable pain. SSS was tested via 30-m sprinting, CODS by a T-run, vertical and horizontal jumping using four different jump tests at pre-, post-, and retests. Maximal strength (Fmax) and power (Pmax) testing procedures were conducted on the Leg Press (LP), Leg Extension (LE), and Leg Curl (LC) machine. Significant time × group interaction effects revealed significant decreases of contact time of the Drop Jump and split time of CODS (p ≤ 0.043; η p 2 = 0.15-0.25) for S (≤ 11.6%) compared to S+E (≤ 5.7%). Significant time effects (p < 0.024; η p 2 = 0.17-0.57) were observed in both groups for SSS (S+E: ≤6.3%; S: ≤8.0%) and CODS (S+E: ≤1.8%; S: ≤2.0%) at retest, for jump test performances (S+E: ≤13.2%; S: ≤9.2%) as well as Fmax and Pmax for LE (S+E: ≤13.5%; S: ≤13.3%) and LC (S+E: ≤18.2%; S: ≤26.7%) at post- and retests. The findings of this study indicate comparable effects of short-term strength training with and without superimposed WB-EMS on physical fitness in physically active females. Therefore, WB-EMS training could serve as a reasonable but not superior alternative to classic training regimes in female exercisers.
  • ... Ø The similar isometric strength results indicate that both groups had minimal left:right imbalances, which is considered acceptable in current RTS testing 3 . Ø The observed differences in RSI and JH differences could be an indication that there could be inhibition of the stretch-shortening cycle 4 ...
    Poster
    Full-text available
    The poster was presented in the 11th International Conference of Strength Training 30.11.2018 -03.12..2018 at Perth, Western Australia
  • ... 5,6 In particular, the RSI (calculated as the ratio between jump time/height and ground contact time) has been considered an important marker for the identification of the "optimal drop-height" to generate the largest performance enhancements. 1,6,7 Of note, excessive drop-heights may induce performance decrements. 5,7,8 This decrease in performance has mainly been attributed to the activation of neuronal inhibitory mechanisms that prevent an overload of the muscle-tendon unit to avoid injuries. ...
    Article
    PURPOSE: The purpose of the present study was to examine the effects of drop-height on drop jump (DJ) performance and on associations between DJ and horizontal jump/sprint performances in ad-olescent athletes. METHODS: Male (n=119, 2.5±0.6 yrs post-peak height velocity [PHV]) and fe-male (n=120, 2.5±0.5 yrs post-PHV) adolescent handball players (national level) performed DJs in randomized order using 3 drop-heights (20, 35, and 50-cm). DJ performance (jump height, re-active strength index [RSI]) was analyzed using the Optojump Next system. Additionally, corre-lations were computed between DJ height and RSI with standing long jump (SLJ) and 20-m linear sprint performances. RESULTS: Statistical analyses revealed medium-sized main effects of drop-height for DJ height and RSI (p<.001, 0.63≤d≤0.71). Post-hoc tests indicated larger DJ heights from 20 to 35, and 35 to 50-cm (p≤.031, 0.33≤d≤0.71) and better RSI from 20 to 35-cm drop-height (p<.001, d=0.77). No significant difference was found for RSI between 35 and 50-cm drop-height. Irrespective of drop-height, associations of DJ height and RSI were small with 5-m split time (-.27≤r≤.05), medium with 10-m split time (-.44≤r≤.14), and medium-to-large with 20-m sprint time and SLJ distance (-.57≤r≤.22). CONCLUSIONS: The present findings indicate that, irre-spective of sex, 35-cm drop-heights are best suited to induce rapid and powerful DJ performance (i.e., RSI) during reactive strength training in elite adolescent handball players. Moreover, train-ing-related gains in DJ performance may at least partly translate to gains in horizontal jump and longer sprint distances (i.e., ≥20-m) and/or vice versa in male and female elite adolescent athletes, irrespective of drop-height.
  • ... 5,6 In particular, the RSI (calculated as the ratio between jump time/height and ground contact time) has been considered an important marker for the identification of the "optimal drop-height" to generate the largest performance enhancements. 1,6,7 Of note, excessive drop-heights may induce performance decrements. 5,7,8 This decrease in performance has mainly been attributed to the activation of neuronal inhibitory mechanisms that prevent an overload of the muscle-tendon unit to avoid injuries. ...
    Purpose: The purpose of the present study was to examine the effects of drop-height on drop jump (DJ) performance and on associations between DJ and horizontal jump/sprint performances in ad-olescent athletes. Methods: Male (n=119, 2.5±0.6 yrs post-peak height velocity [PHV]) and fe-male (n=120, 2.5±0.5 yrs post-PHV) adolescent handball players (national level) performed DJs in randomized order using 3 drop-heights (20, 35, and 50-cm). DJ performance (jump height, re-active strength index [RSI]) was analyzed using the Optojump Next system. Additionally, corre-lations were computed between DJ height and RSI with standing long jump (SLJ) and 20-m linear sprint performances. Results: Statistical analyses revealed medium-sized main effects of drop-height for DJ height and RSI (p<.001, 0.63≤d≤0.71). Post-hoc tests indicated larger DJ heights from 20 to 35, and 35 to 50-cm (p≤.031, 0.33≤d≤0.71) and better RSI from 20 to 35-cm drop-height (p<.001, d=0.77). No significant difference was found for RSI between 35 and 50-cm drop-height. Irrespective of drop-height, associations of DJ height and RSI were small with 5-m split time (-.27≤r≤.05), medium with 10-m split time (-.44≤r≤.14), and medium-to-large with 20-m sprint time and SLJ distance (-.57≤r≤.22). Conclusions: The present findings indicate that, irre-spective of sex, 35-cm drop-heights are best suited to induce rapid and powerful DJ performance (i.e., RSI) during reactive strength training in elite adolescent handball players. Moreover, train-ing-related gains in DJ performance may at least partly translate to gains in horizontal jump and longer sprint distances (i.e., ≥20-m) and/or vice versa in male and female elite adolescent athletes, irrespective of drop-height.
  • ... Traditionally, commonly used methods of enhancing these physical qualities include strength and power training exercises such as squats and deadlifts, as well as power cleans and other weightlifting variants [9,10]. Another popular means of improving speed and COD ability is through plyometric training, which refers to a wide range of jumping, hopping, and bounding exercises designed to utilize the elastic nature of the stretch-shortening cycle (SSC) in order to produce greater forces than would normally be produced by concentric-only muscle actions [9,11]. Previous studies have demonstrated that enhancements in speed and COD ability can be achieved through the use of plyometric training methods [9,[12][13][14][15], however, the majority of this research has focused on the development of concentric power of the lower limbs and resulting enhancements in performance during the propulsive phase of COD tasks. ...
    Article
    Full-text available
    This study investigated the effects of two plyometric training protocols on sprint and change of direction (COD) performance in elite hockey players. A parallel-group randomized controlled trial design was used and seventeen elite male and female field hockey players were randomly allocated into either low-to-high (L-H, n = 8) or high-to-low (H-L, n = 9) training groups. Each group performed separate variations of the drop jump exercise twice weekly for six weeks, with an emphasis on either jump height (L-H) or drop height (H-L). Performance variables assessed included sprint times over 10 m and 20 m, as well as 505 time. A two-way repeated measures analysis of variance was performed and Cohen’s d effect sizes (ESs) were calculated. The H-L group displayed a significant small ES improvement from baseline to post-training in the 10 m sprint (1.893 ± 0.08 s pre vs. 1.851 ± 0.06 s post) (ES = −0.44) (p < 0.05). Differences between groups for 10 m and 20 m sprint performance failed to reach statistical significance, and no significant differences were observed within or between groups for 505 time. These findings highlight the difficulty in substantially enhancing speed and COD ability in highly trained athletic populations through the addition of a low volume, short duration plyometric training protocol.
  • ... Participants were instructed to maximize jump height and minimize ground contact time. The first jump in each trial was discounted, whereas the remaining 4 hops were averaged for RSI analysis as follows: RSI = Jump height (m)/ground contact time (s) (Flanagan and Comyns, 2008). An electronic metronome provided required frequencies by means of an auditory signal. ...
    Article
    Full-text available
    Introduction: Studies that combined balance and resistance training induced larger performance improvements compared with single mode training. Agility exercises contain more dynamic and sport-specific movements compared with balance training. Thus, the purpose of this study was to contrast the effects of combined balance and plyometric training with combined agility and plyometric training and an active control on physical fitness in youth. Methods: Fifty-seven male soccer players aged 10–12 years participated in an 8-week training program (2 × week). They were randomly assigned to a balance-plyometric (BPT: n = 21), agility-plyometric (APT: n = 20) or control group (n = 16). Measures included proxies of muscle power [countermovement jump (CMJ), triple-hop-test (THT)], muscle strength [reactive strength index (RSI), maximum voluntary isometric contraction (MVIC) of handgrip, back extensors, knee extensors], agility [4-m × 9-m shuttle run, Illinois change of direction test (ICODT) with and without the ball], balance (Standing Stork, Y-Balance), and speed (10–30 m sprints). Results: Significant time × group interactions were found for CMJ, hand grip MVIC force, ICODT without a ball, agility (4 m × 9 m), standing stork balance, Y-balance, 10 and 30-m sprint. The APT pre- to post-test measures displayed large ES improvements for hand grip MVIC force, ICODT without a ball, agility test, CMJ, standing stork balance test, Y-balance test but only moderate ES improvements with the 10 and 30 m sprints. The BPT group showed small (30 m sprint), moderate (hand grip MVIC, ICODTwithout a ball) and large ES [agility (4 m × 9 m) test, CMJ, standing stork balance test, Y-balance] improvements, respectively. Conclusion: In conclusion, both training groups provided significant improvements in all measures. It is recommended that youth incorporate balance exercises into their training and progress to agility with their strength and power training.
  • ... Traditionally, commonly used methods of enhancing these physical qualities include strength and power training exercises such as squats and deadlifts, as well as power cleans and other weightlifting variants [9,10]. Another popular means of improving speed and COD ability is through plyometric training, which refers to a wide range of jumping, hopping, and bounding exercises designed to utilize the elastic nature of the stretch-shortening cycle (SSC) in order to produce greater forces than would normally be produced by concentric-only muscle actions [9,11]. Previous studies have demonstrated that enhancements in speed and COD ability can be achieved through the use of plyometric training methods [9,[12][13][14][15], however, the majority of this research has focused on the development of concentric power of the lower limbs and resulting enhancements in performance during the propulsive phase of COD tasks. ...
  • ... The reactive strength index (RSI), defined as the ratio between jump height and ground contact time, has been proposed as a means of assessing plyometric ability during jumping tasks [10]. The RSI was originally developed to assess plyometric ability during DJ [11] but has been modified for use in the assessment of plyometric ability in any vertical plyometric task. ...
    Article
    Full-text available
    The purpose of this study was to compare different methods for assessing plyometric ability during countermovement (CMJ) and drop jumps (DJ) in a group of adults and adolescents. Ten resistance-trained adult men (age: 22.6 ± 1.6 years) and ten adolescent male basketball players (age: 16.5 ± 0.7 years) performed a CMJ and a DJ from a height of 0.40 m. Jump height (JH), contact time, normalized work (WNORM), and power output (PONORM) during the absorption and propulsion phases were calculated from force platforms and 3-D motion analysis data. Plyometric ability was assessed using the modified reactive strength index (RSIMOD during CMJ) and the reactive strength index (RSI during DJ) as well as three indices using propulsion time, propulsion work (PWI), and propulsion power. Adults jumped significantly higher than adolescents (mean difference [MD]: 0.05 m) while JH (MD: 0.05 m) and ground contact time (MD: 0.29 s) decreased significantly from CMJ to DJ. WNORM (MD: 4.2 J/kg) and PONORM (MD: 24.2 W/kg) during the absorption phase of CMJ were significantly less than these variables during the propulsion phases of the jumps. The reactive strength index variants increased significantly from the CMJ to DJ (MD: 0.23) while all other plyometric indices decreased significantly. Neither RSIMOD nor RSI contributed significantly to the prediction of JH during CMJ and DJ, respectively, while PWI was able to explain ≥68% of the variance in JH. Variants of the reactive strength index do not reflect the changes in mechanical variables during the ground contact phase of CMJ and DJ and may not provide an accurate assessment of plyometric ability during different vertical jumps.
  • ... Trials where the gymnasts noticeably stepped down or jumped up from the box were discounted and repeated. Using previously established methods [35,36], the raw vertical force-time data were used to calculate the variables needed to determine reactive strength index (RSI). The Equation (A2) [35,36] for calculating RSI can be found in Appendix A. ...
    Article
    Full-text available
    This study examined individual responses in leg stiffness, reactive strength index (RSI), movement proficiency (deep overhead squat and in-line lunge), and trunk muscular endurance (flexor and extensor tests) in young female gymnasts following an 8-week neuromuscular training intervention. Thirty-four pre-peak height velocity (PHV) female gymnasts were divided into either an experimental group (EXP n = 17) or control group (CON n = 17). The EXP replaced their normal gymnastics physical preparation with a neuromuscular training program, while the CON continued with their habitual gymnastics program. Chi square analysis showed that the EXP resulted in significantly more positive responders compared to CON for measures of leg stiffness (41% versus 12% responded positively), extensor muscular endurance, (76% versus 29%), and competency in the deep overhead squat, (76% versus 29%) and in-line lunge (left lead leg) (65% versus 18%). Conversely, the number of positive responders for RSI (53% versus 61%), the flexor endurance test (88% versus 53%), and the right in-line lunge (47% versus 35%) were not significantly different between groups. These findings suggest that most young gymnasts responded positively to neuromuscular training from the perspective of improving movement proficiency and trunk endurance; however, changes in leg stiffness and RSI were more variable and may require higher intensities to realise further adaptations.
  • ... Vertical jump testing is commonly used by researchers and coaches alike as a means of monitoring physical capacities of athletes and assessing the effects of training interventions (Cronin and Hansen, 2005). Drop jumps and hopping tests can give coaches more information about the stretch shortening cycle capacity of their athletes (Flanagan and Comyns, 2008). Dynamic movements such as jumping and sprinting require the rapid coupling of eccentric and concentric muscle contractions, i.e. the stretch shortening cycle. ...
  • ... Previous research suggests that determining an individual's optimal DJ height can be difficult, if the box is too low or too high the SSC stimulus will not be maximized (Byrne et al., 2010). RSI is one way to measure optimal DJ height, as optimal jump height has minimal purpose without paying attention to GCT (Beattie, Carson, Lyons, Kenny, 2017;Flanagan & Comyns, 2008;Young et al., 1995). While Peng (2011) does not recommend DHs over 60 cm due to increased injury risk, little is known about DHs above 60 cm. ...
  • ... Reactive strength was formally introduced in 1995 by Warren Young [5] as a measure of ability for changing quickly from eccentric to concentric muscle-tendon action during countermovement and depth jumping. Intuitively, reactive strength is also suggested to reflect one's capacity for distributing external loads through the muscle-tendon complex [6]. Reactive strength is dependent on feedforward motor control processes and supported by time-sensitive spinal reflexivity [7]. ...
    Article
    Full-text available
    The reactive capacity of the muscle-tendon complex is commonly assessed using the reactive strength index (RSI). Conventionally, the RSI is a ratio of rebound jump height to ground contact time in depth jumping. Several assumptions regarding the linear mechanics acting through the whole-body center of gravity may threaten the internal validity of computation and interpretation of RSI scores. First, it is common for rebound jump height to be predicted from rebound jump flight time. This assumes that the angular positioning of body segments is equivalent at the time instances of rebound jump take-off and landing. Prior literature supports a mixed-methods approach for computing the RSI that is void of this assumption. The mixed-methods approach gives a more valid estimation of rebound jump height. In this approach, rebound jump height is estimated from rebound jump take-off velocity of the whole-body center of mass. This is accomplished by subtracting an estimate of impact velocity, acquired using videography, from change in whole-body center of mass velocity estimated from integrated vertical ground reaction force data. Second, it is often assumed that vertical displacement of the whole-body center of mass during the drop phase of the depth jump is predicted perfectly from the height of the platform used to perform the drop. This assumption may affect the internal validity of comparing RSI scores across individuals and within individuals performing depth jumps from varied heights. The purpose of the present study was to investigate the internal validity of RSI scores computed using the conventional approach and impact velocity variability, which may affect the interpretation of RSI scores. Seventy physically active young adults performed depth jumps from drop heights of 0.51, 0.66, and 0.81 m. RSI was computed using the conventional approach and a mixed-methods approach featuring the use of 2-dimensional videography, body segment parameters, and force platform dynamometry. The two computational methods were compared using linear regression performed on data from each drop height. In addition, a 2 (computational method) by 3 (drop height) Analysis of Variance (ANOVA) was performed to evaluate for main effects and interactions in RSI data. Multiple one sample t-tests were performed to compare estimated and theoretical impact velocities. The ANOVA revealed no main effect or interactions between computational approaches (p = 0.467–0.938). Linear regression revealed moderately strong associations between RSI scores computed using the conventional and mixed-methods approaches (R2 = 0.685–0.741). Moreover, linear regressions revealed that the conventional approach tends to overestimate the mixed methods approach for RSI scores below 1.0 and underestimate the mixed methods approach for RSI scores above 1.0. Lastly, estimated impact velocities were observed to be as much as 13% lower versus theoretical (p < 0.001). Researchers with access to motion capture and force platform technology may consider using a mixed-methods approach for computing the RSI, which likely maximizes the internal validity of scores. In addition, results suggest for practitioners to practice caution when comparing conventional RSI scores across individuals.
  • ... Reactive strength index is a measure of the ability of an athlete to change from concentric force to eccentric force in as little time as possible and gives an overall indication of lower limb power [13]. Apart from one study which examined RSI between the affected and unaffected limb among ACL rupture athletes [14], currently, there is very little research which includes measurement of RSI, especially those involving injured athletes. ...
    Article
    Purpose To measure the changes in athletic performance in athletes treated arthroscopically for femoroacetabular impingement and compare results to a matched controlled athletic cohort, over a 1-year period. Methods Male athletes scheduled for arthroscopic correction of symptomatic FAI were recruited and tested (pre-operatively and 1-year postsurgery) for measures of athletic performance which included acceleration (10-m sprint), change of direction speed (CODS), squatting depth, and reactive strength index (RSI). The FAI group was compared to a matched, healthy, control group who were tested at baseline and 1 year later with no disruption to their regular training or competition status; the prevalence of anterior groin pain during testing in either group was recorded. Hip range of motion (ROM) was also measured for both groups at baseline and at 1 year in the FAI group to look for change following intervention. Results Prior to surgery, the FAI group were slower than the control group (p < 0.001) for acceleration (3% slower) and CODS (10% slower). At 1 year, 91% of the FAI group returned to full competition at an average time of 17 weeks, while substantial reductions in pain were also noted during acceleration (51–6%, p = 0.004), CODS (62–8%, p = 0.001), and squat test (38–8%, p = 0.003). Significant improvements were seen in the FAI group for CODS (7%, p < 0.001) and squat depth measures (6%, p = 0.004) from baseline to 1 year (significant time × group interaction effects were noted for these also). The changes in performance in the control group over time were non-significant across all of the measures (n.s.). At 1-year postsurgery, there were no statistically significant differences between the groups for any of the athletic measures. There was a significant and clinically important improvement in range of hip motion in the FAI group at 1-year postsurgery (p < 0.05). Conclusion Symptomatic FAI causes substantial reductions in athletic performance compared to healthy competitors placing these athletes at a distinct performance disadvantage. The results from the current study demonstrate that arthroscopic correction (including labral repair) in athletes with symptomatic FAI, reduces pain and restores athletic performance to a level which is comparable to healthy athletes, at 1 year. Level of evidence II.
  • ... This popularity is a result of its adherence to the criteria dictating an effective SSC (Komi, 2003). A common measure of DJ performance is the reactive strength index [RSI: jump height / ground contact time (GCT)] (Flanagan and Comyns, 2008;Young, 1995), also named "FC ratio" (Marina and Jemni, 2014;Marina et al., 2012). Previous studies have reported the RSI to increase with drop height until reaching an individual threshold, beyond which, performance decreases with further increases in drop height. ...
    Article
    This study investigated how drop heights and their associated drop jump performance relate to stretch reflex modulations. Eleven male subjects performed ten drop jumps from each of three individually predetermined drop heights. These were the drop height resulting in maximal performance (OPT), as well as 10 cm below (LOW) and above (HIGH) maximal performance. To quantify drop jump performance the reactive strength index, derived from force plate measures, was used. High-density surface EMG provided both stretch reflex response timing and size, as well as novel insight into the associated motor unit recruitment via muscle fiber conduction velocity estimations. These measures were examined in the vastus lateralis (VL), soleus (SOL) and gastrocnemius medialis (GM). Drop jump performance improved by 9% (p < 0.001) from LOW to OPT and decreased by 5% (p = 0.008) from OPT to HIGH. Despite decreasing performance, stretch reflex responses were largest at HIGH. Stretch reflex responses timing did not change; staying within the short (SOL, <60 ms) and medium (VL, GM; 60–85 ms) latency response time-frames. Motor unit recruitment appeared to change across drop heights only for VL, whereas activation intensity only changed for SOL. These results indicate that during drop jumps above OPT neuromuscular modifications result in VL no longer being maximally recruited.
  • ... RSI and Kleg are the two most important tools for monitoring muscle performance, including stretch shortening cycle (SSC) movements such as jumping, sprinting, and throwing (McMahon et al., 2012;Lloyd et al., 2009;Flanagan et al., 2008). RSI is described as an individual's ability to change quickly from an eccentric to concentric contraction, and can be considered as a measure of "explosiveness" (Flanagan et al., 2008), while Kleg describes the relationship between a given force and the magnitude of deformation of an object or body (McMahon et al., 2012;Butler et al.,2003). ...
  • ... Any differences between these movements are likely a result of the performance-enhancing effect of the SSC (36). The SSC muscle action produces a more powerful muscle action than that which would result from a concentric action alone and has been viewed as essential for many sporting activities (13), as a result of the summation of elastic energy and neurological potentiation through stimulation of the muscle spindle (36). ...
    Article
    Full-text available
    Meechan, D, Suchomel, TJ, McMahon, JJ, and Comfort, P. A comparison of kinetic and kinematic variables during the midthigh pull and countermovement shrug, across loads. J Strength Cond Res XX(X): 000-000, 2020-This study compared kinetic and kinematic variables during the midthigh pull (MTP) and countermovement shrug (CMS). Eighteen men (age: 29.43 ± 3.95 years, height: 1.77 ± 0.08 m, body mass: 84.65 ± 18.79 kg, and 1 repetition maximum [1RM] power clean: 1.02 ± 0.18 kg·kg) performed the MTP and CMS at intensities of 40, 60, 80, 100, 120, and 140% 1RM, in a progressive manner. Peak force (PF), mean force (MF), peak velocity, peak barbell velocity (BV), peak power, (PP), mean power (MP), and net impulse were calculated from force-time data during the propulsion phase. During the CMS, PF and MF were maximized at 140% 1RM and was significantly greater than the MTP at all loads (p ≤ 0.001, Hedges g = 0.66-0.90); p < 0.001, g = 0.74-0.99, respectively). Peak velocity and BV were significantly and meaningfully greater during the CMS compared with the MTP across all loads (p < 0.001, g = 1.83-2.85; p < 0.001, g = 1.73-2.30, respectively). Similarly, there was a significantly and meaningfully greater PP and MP during the CMS, across all loads, compared with the MTP (p < 0.001, g = 1.45-2.22; p < 0.001, g = 1.52-1.92). Impulse during the CMS was also significantly greater across all loads (p < 0.001, g = 1.20-1.66) compared with the MTP. Results of this study demonstrate that the CMS may be a more advantageous exercise to perform to enhance force-time characteristics when compared with the MTP, due to the greater kinetics and kinematic values observed.
  • ... Initially, participants stepped off the platform, dropped down to the floor, landed on both feet and then immediately jumped up as quickly and as high as possible. The aim of the jumps was to minimise the contact time, while attempting to maximize flight time (Flanagan and Comyns, 2008). Between DJs, a rest period of 60 seconds was given to avoid any residual fatigue effects (Read and Cisar, 2001). ...
    Preprint
    The main and interactive effect of biological maturity and relative age upon physical performance in adolescent male soccer players was considered. Consistent with previous research, it was hypothesised that participants of greater maturity or born earlier in the selection year would perform better in terms of physical performance tests. This cross-sectional study consisted of 84 male participants aged between 11.3-16.2 years from a professional soccer academy in the English Premier League. Date of birth, height, weight and parental height were collected. Sprint, change of direction, counter-movement jump and reactive strength index was considered for physical performance. Relative age was based on birth quarter for the selection year. Maturity status was based upon percentage of predicted adult height attained. Linear regression models highlighted that maturation was associated with performance on all but one of the physical performance tests, reactive strength index. In contrast, relative age only served as a significant predictor of performance on the countermovement jump. This study showed that physical performance (in the tests studied) seems to be related to the biological maturity status of a player but not their relative age. This finding is important because the paper suggests early maturing players perform better in the majority of physical performance tests, and the commonly held belief that relative age effect influences performance may be overstated.
  • ... Briefly, the SSC is a naturally occurring muscle function whereby the muscle is immediately lengthened before shortening. This produces a more powerful muscle action than that which would result from a concentric action alone (12), via the storage and release of elastic energy and the neurological potentiation via the stimulation of the muscle spindle (38). ...
    Article
    Full-text available
    Meechan, D, McMahon, JJ, Suchomel, TJ, and Comfort, P. A comparison of kinetic and kinematic variables during the pull from the knee and hang pull, across loads. J Strength Cond Res XX(X): 000-000, 2020-Kinetic and kinematic variables during the pull from the knee (PFK) and hang pull (HP) were compared in this study. Eighteen men (age = 29.43 ± 3.95 years; height 1.77 ± 0.08 m; body mass 84.65 ± 18.79 kg) performed the PFK and HP with 40, 60, 80, 100, 120, and 140% of 1-repetition maximum (1RM) power clean, in a progressive manner. Peak force (PF), mean force (MF), peak system velocity (PSV), mean system velocity (MSV), peak power (PP), mean power (MP), and net impulse were calculated from force-time data during the propulsion phase. During the HP, small-to-moderate yet significantly greater MF was observed compared with the PFK, across all loads (p ≤ 0.001; Hedges g = 0.47-0.73). Hang pull PSV was moderately and significantly greater at 100-140% 1RM (p = 0.001; g = 0.64-0.94), whereas MSV was significantly greater and of a large-to-very large magnitude compared with PFK, across all loads (p < 0.001; g = 1.36-2.18). Hang pull exhibited small to moderate and significantly greater (p ≤ 0.011, g = 0.44-0.78) PP at 100-140%, with moderately and significantly greater (p ≤ 0.001, g = 0.64-0.98) MP across all loads, compared with the PFK. Hang pull resulted in a small to moderate and significantly greater net impulse between 100 and 140% 1RM (p = 0.001, g = 0.36-0.66), compared with PFK. The results of this study demonstrate that compared with the PFK, the HP may be a more beneficial exercise to enhance force-time characteristics, especially at loads of ≥1RM.
  • ... This has been similarly observed after the application of exercise protocols derived from the countermovement jump [Turner, Jeffreys 2010], applied over 6 [Lockie et al. 2012], 8 [Rimmer, Sleivert 2000], and 12 weeks [Chaouachi et al. 2014]. According to the above, and consistent with our results, training based on explosive jumps is recognized as a method to develop muscle function [Flanagan, Comyns 2008], speed and anaerobic power [Ramirez-Campillo et al. 2018]. In addition to other variables related to physical performance, such as agility [Davaran et al. 2014] and force [Ramirez-Campillo, Andrade, Izquierdo 2013]. ...
    Article
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    Background. e kumite section or karate kumite is characterized by high-intensity activity, including explosive actions. Problem and Aim. Determine the magnitude of the e ect on the physical performance of karate athletes of the application of two protocols: HIIT-SPRINT and HIIT-JUMP performed at the beginning of a training session (20 minutes) for six weeks. Methods. Both the HIIT-JUMP and HIIT-SPRINT group underwent a six-week HIIT program, while the CONTROL group con- tinued with their regular karate training. e athletes performed the following tests: squat jump, countermovement jump, 5m and 10m line speed, change of direction, aerobic capacity and body composition. Results. Fat mass (kg) decreased in the HIIT-JUMP group (ES = -0.63), while the HIIT-SPRINT group reduced the percent of body fat (ES = -0.85). Jump height for the squat and countermovement jumps increased in the HIIT-SPRINT group (ES = 0.82 and 0.94, respectively) and 10-m test (ES = -1.14) and change in direction (ES = -0.60) times were reduced. e HIIT-JUMP group decreased their times for the 5-m and 10-m tests (ES = -0.97 and -1.07, respectively). e HIIT SPRINT group improved in the 5-m test compared to the CONTROL group (ES = 0.62). Conclusions. ese results suggest that both HIIT modalities o er spe- ci c adaptations, and could be considered as complementary to the training of athletes.
  • ... This has been similarly observed after the application of exercise protocols derived from the countermovement jump [Turner, Jeffreys 2010], applied over 6 [Lockie et al. 2012], 8 [Rimmer, Sleivert 2000], and 12 weeks [Chaouachi et al. 2014]. According to the above, and consistent with our results, training based on explosive jumps is recognized as a method to develop muscle function [Flanagan, Comyns 2008], speed and anaerobic power [Ramirez-Campillo et al. 2018]. In addition to other variables related to physical performance, such as agility [Davaran et al. 2014] and force [Ramirez-Campillo, Andrade, Izquierdo 2013]. ...
    Article
    Background. The kumite section or karate kumite is characterized by high-intensity activity, including explosive actions. Problem and Aim. Determine the magnitude of the effect on the physical performance of karate athletes of the application of two protocols: HIIT-SPRINT and HIIT-JUMP performed at the beginning of a training session (20 minutes) for six weeks. Methods. Both the HIIT-JUMP and HIIT-SPRINT group underwent a six-week HIIT program, while the CONTROL group continued with their regular karate training. The athletes performed the following tests: squat jump, countermovement jump, 5m and 10m line speed, change of direction, aerobic capacity and body composition. Results. Fat mass (kg) decreased in the HIIT-JUMP group (ES =-0.63), while the HIIT-SPRINT group reduced the percent of body fat (ES =-0.85). Jump height for the squat and countermovement jumps increased in the HIIT-SPRINT group (ES = 0.82 and 0.94, respectively) and 10-m test (ES =-1.14) and change in direction (ES =-0.60) times were reduced. The HIIT-JUMP group decreased their times for the 5-m and 10-m tests (ES =-0.97 and-1.07, respectively). The HIIT SPRINT group improved in the 5-m test compared to the CONTROL group (ES = 0.62). Conclusions. These results suggest that both HIIT modalities offer specific adaptations, and could be considered as complementary to the training of athletes.
  • ... The mechanisms of the stretch-shortening cycle play a role in jump performance and, therefore, contribute to sporting activities [18]. The reactive strength index (RSI) is used to measure the explosiveness of an athlete and a way to quantify the performance of plyometric or stretch shortening activity [19]. In particular, the drop jump can be evaluated while using this index due to the identifiable ground contact time [18]. ...
    Article
    Full-text available
    This study examined the acute effects of self-myofascial release plus dynamic warm up versus dynamic warm up alone on ankle range of motion and drop jump performance. Twenty-five recreationally active participants (male: 16, female: 9) were randomly assigned into a foam rolling (FR) or a dynamic warm up group (CON) (age: 22.8 ± 3.9 years, body mass 75.9 ± 13.2 kg, stretch stature: 174.1 ± 10.1 cm). In a randomised crossover design, each participant completed two experimental sessions that were separated by seven days. Ankle range of movement was assessed while using a weight-bearing lunge test and drop jump performance was recorded via bilateral force plates. Following a 5 min cycle, the foam rolling group undertook self-myofascial release to the lower limb and thoracic/lumbar regions, followed by a dynamic warm up. The control group undertook the same initial warm up plus the dynamic exercises. The level of significance was set at p ≤ 0.05. There was a significant increase (p < 0.001) in ankle range of motion immediately after the warm up for both groups (pre CON: 37.5 ± 5.31, post CON: 39.8 ± 5.76; pre FR 38.7 ± 7, post FR: 40.3 ± 7.3 deg). No significant difference was found between the conditions (p > 0.05). There were no significant differences for any indices of jump performance (p > 0.05). Based on these results, foam rolling plus dynamic exercises does not appear to impair or enhance drop jump performance, despite the increases in ankle range of movement.
  • ... The countermovement jump (CMJ) and drop jump (DJ) are reliable and valid for the evaluation of jumping performance (Arteaga et al., 2000;de Villarreal et al., 2009). At this point it is worth noting that both tasks represent different muscle action patterns (Flanagan and Comyns, 2008). The CMJ is classified as slow SSC movements and DJ as fast due to shorter contraction time and a smaller range of motion when compared to CMJ. ...
    Article
    Full-text available
    Traditional, assisted and resisted plyometrics are considered to be effective training methods for improving vertical jump performance. The purpose of this systematic review and meta-analysis was to compare effectiveness of traditional, assisted and resisted plyometric methods on vertical jumping ability in adults. Available literature was searched using MEDLINE (via EBSCO), SPORTDiscus (via EBSCO), Scopus and Web of Science databases. The methodological quality of studies was assessed using the PEDro scale. Peer-reviewed studies were accepted only if they met all eligibility criteria: (a) healthy adults mean age > 18 years (b) training program based on plyometric exercises (c) the study reported on vertical jump height for the countermovement jump or drop jump performance. Of the 5092 articles identified, 17 studies were included in the qualitative and quantitative analyses. Both funnel plot analysis and Egger's test (p = 0.04) indicated publication bias for the comparison of resisted plyometrics and control condition. No publication bias was found for the other meta-analyses (p > 0.05). The effects of the traditional and assisted plyometric methods, when compared with the control condition (a non-plyometric condition), on jump height were moderate (SMD = 0.68, 95% CI 0.37 to 0.99, p < 0.0001; SMD = 0.70, 95% CI 0.20 to 1.20, p = 0.006, respectively). The effects of the resisted plyometric methods, when compared with the control condition, on a jump height was small (SMD = 0.48, 95% CI 0.17 to 0.79, p = 0.002). There were no significant differences between the training effects of the assisted and traditional plyometric interventions on jump height (SMD = 0.62, 95% CI-1.66 to 2.91, p = 0.59), nor between the resisted and traditional plyometric training programs (SMD = 0.2, 95% CI-0.19 to 0.23, p = 0.86). Traditional, assisted and resisted plyometric methods are effective training modalities for augmenting vertical jump performance in healthy adults. Resisted and assisted plyometric methods are equally effective as the traditional plyometric method in improving vertical jumping ability in healthy adults.
  • ... 125 However, these assertions are not without opposition. [128][129][130][131][132][133] Considering this, although training intensity is a key factor to acknowledge in exercise prescription, 134 consensus on optimal markers of intensity or a clear definition. Different researchers have provided different conceptual definitions, [135][136][137] and when operational (quantitative-objective) attempts have been made to define PJT intensity, again, contrast findings have emerged. ...
    Article
    The aim of this scoping review was i) to update a previous review on the main methodological characteristics and shortcomings in the plyometric jump training (PJT) literature, and ii) to recommend, in light of the identified methodological gaps, future research perspectives. We searched four electronic databases. From 6,128 potentially relevant articles, 420 were considered eligible for inclusion. As an update of a previous review, this represents an increase of ~200 articles, illustrating that this field of research is growing fast. However, the relative “quality” or shortcomings were similar when compared to the preceding scoping review. In the current article, the main identified shortcomings were an insufficient number of studies conducted with females, individual sports, and high-level athletes (~22%, ~7%, and ~14% of overall studies, respectively); insufficient description of training prescription (~54% of studies); and studies missing an active/passive control group and a randomised group allocation process (~37% and ~24% of overall studies, respectively). Furthermore, PJT was often combined with other training methods and added to the participants’ regular training routines (~50% and ~35% of overall studies, respectively). The main outcomes of this scoping review urge researchers to conduct PJT studies of high methodological quality (e.g., randomised controlled trials) to get trustworthy evidence-based knowledge. In addition, owing to the limited research conducted with females, individual sports, and high-level athletes, more studies are needed to substantiate the available findings. Finally, the identification of cohort-specific PJT dose-response relations which elicit optimal training effects still need to be identified, particularly in the long term. Key words: power; exercise therapy; resistance training; exercise; stretch-shortening cycle; muscle strength.
  • ... All data are reported as exercise volume load (load per set 3 number of repetitions), mean exercise load (mean load per exercise), and mean repetitions completed per training set. Plyometric exercises were differentiated as either: slow or fast stretch-shortening-cycle, based on the ground contact/movement time of above/below 250 ms (Slow 5 Vertical box jumps, broad jumps, squat jumps; Fast 5 pogo jumps, depth rebound jumps) (11). All plyometric training data are reported as total contacts per type of exercise. ...
    Article
    Jones, TW, Shillabeer, BC, Ryu, JH, and Cardinale, M. Development in adolescent middle-distance athletes: a study of training loadings, physical qualities, and competition performance. J Strength Cond Res XX(X): 000-000, 2019-The purpose of this study was to examine changes in running performance and physical qualities related to middle-distance performance over a training season. The study also examined relationships between training loading and changes in physical qualities as assessed by laboratory and field measures. Relationships between laboratory and field measures were also analyzed. This was a 9-month observational study of 10 highly trained adolescent middle-distance athletes. Training intensity distribution was similar over the observational period, whereas accumulated and mean distance and training time and accumulated load varied monthly. Statistically significant (p < 0.05) and large effect sizes (Cohen's d) (>0.80) were observed for improvements in: body mass (5.6%), 600-m (4.6%), 1,200-m (8.7%), and 1,800-m (6.1%) time trial performance, critical speed (7.1%), V[Combining Dot Above]O2max (5.5%), running economy (10.1%), vertical stiffness (2.6%), reactive index (3.8%), and countermovement jump power output relative to body mass (7.9%). Improvements in 1,800 m TT performance were correlated with increases in V[Combining Dot Above]O2max (r = 0.810, p = 0.015) and critical speed (r = 0.918, p = 0.001). Increases in V[Combining Dot Above]O2max and critical speed were also correlated (r = 0.895, p = 0.003). Data presented here indicate that improvements in critical speed may be reflective of changes in aerobic capacity in adolescent middle-distance athletes.
  • ... Previous research suggests that determining an individual's optimal DJ height can be difficult, if the box is too low or too high the SSC stimulus will not be maximized (Byrne et al., 2010). RSI is one way to measure optimal DJ height, as optimal jump height has minimal purpose without paying attention to GCT (Beattie, Carson, Lyons, Kenny, 2017;Flanagan & Comyns, 2008;Young et al., 1995). While Peng (2011) does not recommend DHs over 60 cm due to increased injury risk, little is known about DHs above 60 cm. ...
    Article
    Full-text available
    Background: Drop jumps (DJ) are commonly implemented in plyometric training programs in an attempt to enhance jump performance. However, it is unknown how different drop heights (DH) affect reactive strength index (RSI), jump height (JH) and ground contact time (GCT). Objectives: The purpose of this study was to assess the effect of various DHs on RSI, JH, and GCT. Methods: Twenty volunteers with a history of plyometric training (Males = 13, Females = 7; age: 22.80 ± 2.69 yr, height: 175.65 ± 11.81 cm, mass: 78.32 ± 13.50 kg) performed DJs from 30 cm (DJ30), 45 cm (DJ45), 60 cm (DJ60), 76 cm (DJ76), and 91 cm (DJ91) and a countermovement jump (0 cm). A 16-camera Vicon system was used to track reflective markers to calculate JH; a Kistler force plate was used to record GCT. RSI was calculated by dividing JH by GCT. RSI and GCT were compared using a 2x5 (sex x DH) mixed factor repeated measures ANOVA, while JH was compared using a 2x6 (sex x DH) repeated measures ANOVA. Results: There were no interactions, but there was a main effect for sex for both JH (M>F) and GCT (F>M). JH demonstrated no main effect for DH: DJ30 (0.49 ± 0.11 m), DJ45 (0.50 ± 0.11 m), DJ60 (0.49 ± 0.12 m), DJ76 (0.50 ± 0.11 m), and DJ91 (0.48 ± 0.12 m). However, GCT showed a main effect where DJ30 (0.36 ± 0.10 s), DJ45 (0.36 ± 0.12 s), and DJ60 (0.37 ± 0.10 s) were not significantly different but were less than DJ76 (0.40 ± 0.12 s) and DJ91 (0.42 ± 0.12 s). Conclusions: Increasing DH beyond 60 cm increased GCT but did not affect JH, resulting in decreased RSI. Therefore, practitioners designing plyometric training programs that implement DJs may utilize DHs up to 60 cm, thereby minimizing GCT without compromising JH.
  • ... Pocas investigaciones han analizado el impacto del entrenamiento mediante la pliometría en la capacidad de repetir sprints, mostrando que 8 semanas de entrenamiento pliométrico (hurdle y drop) son efectivas para la mejora del RSA con cambios de dirección, pero no en esfuerzos en línea recta (Hammami, Negra, Aouadi, Shephard, & Chelly, 2016). Flanagan & Comyns, 2008), sugirieron una progresión a través de las siguientes fases para la realización de entrenamientos pliométricos: Carga excéntrica y correctos mecanismos de aterrizaje (caídas drop); bajas intensidades pliometría rápida, donde el tiempo de contacto es mejorado; saltos de vallas y en profundidad con énfasis en el corto tiempo de contacto y optimizando la altura de salto (saltos drop). ...
    Article
    Full-text available
    : Los deportes de equipo se caracterizan por demandar a los jugadores la realización de esfuerzos máximos o submáximos, entre los cuales se producen periodos de recuperación. La capacidad de repetir estos esfuerzos, se denomina “repeat sprint ability” o RSA y es considerada determinante en el rendimiento en estos deportes. Por lo tanto, definir las estrategias de entrenamiento del RSA es importante para entrenadores y preparadores físicos. Diferentes estudios han analizado los efectos de entrenamientos basados en distintas estrategias, concluyendo que no existe una única estrategia para optimizar el rendimiento en esta capacidad. Es necesaria la periodización del entrenamiento para la mejora del RSA durante el ciclo competitivo incluyendo estrategias de entrenamiento de fuerza, resistencia, velocidad y el propio RSA, tanto mediante tareas g
  • ... Participants were instructed to maximize jump height and minimize ground contact time (Dalleau, Belli, Vialoe, Lacour, & Bourdin, 2004). The RSI variable was calculated using the equation of Flanagan and Comyns (2008) as RSI = jump height (mm) / contact time (ms). The first hop served as counter-movement jump (impetus) and was consequently excluded from analysis with the 4 remaining hops averaged for analysis of RSI. ...
    Article
    Full-text available
    Background: Basketball players are among the players with a great risk of anterior cruciate ligament injury due to the high-intensity manoeuvres which have been identified as very common factors preceding this injury. Objective: This study aimed to assess differences in leg stiffness and reactive strength throughout a competitive season in youth basketball players and to assess the effect of age and performance level on these variables. Methods: The research study involved a total of 48 male basketball players from the age group U14 and U16 played the first and second highest league in Czech Republic. Reactive strength index (RSI) and leg stiffness were measured at the beginning of the season, mid-season, and at the end of the season. Analysis of Variance for repeated measures was used to identify the influence of age, season phases, and levels of performance to monitored variables. Results: The results showed significant changes among season phases in RSI (F = 4.48, p = .014) and relative leg stiffness (F = 7.17, p = .002) in observed players, however significantly higher values at the end of the season than at its beginning were found in RSI only (p = .014). Differences between subgroups with different levels of performance were not significant in both categories as well as age differences. Conclusions: The current study did not point-out to significant changes among season phases in reactive strength and leg stiffness in adolescent basketball players. The study did not confirm that reactive strength and leg stiffness is gradually improving during adolescence and suggestion that level of performance positively influences reactive strength and leg stiffness was confirmed only in the case of reactive strength.
  • ... Subjects were instructed to maximize jump height and minimize ground contact time. The first jump was excluded with the four remaining trials being averaged for the calculation of reactive strength index using the following formula: reactive strength index = jump height (mm)/ground contact time (ms) [15]. ...
    Article
    Full-text available
    Objective This study examined the effects of 8-week stretch-shortening cycle-based (SSC-based) versus non-SSC-based jump exercises on physical fitness in prepubertal male soccer players. Methods Twenty-six participants were randomly assigned to either a SSC-based using countermovement jump (CMJG; n = 13) or a non-SSC-based jump group using squat jump (SJG; n = 13). Pre- and post-training, tests were conducted to assess measures of muscle power (countermovement jump, reactive strength index), speed (5 m, 20 m), change of direction (CoD), and sport-specific performance (maximal kicking distance). To establish the effect of the interventions on the dependent variables, a 2 (group: CMJG and SJG) × 2 (time: pre, post) ANOVA with repeated measures was determined for each parameter. Results Findings demonstrated a main effect of time for countermovement jump, reactive strength index, and maximal kicking distance (p < 0.05, effect size [ES] = 0.56–0.71). Group × time interactions were identified for (5 m, 20 m, and reactive strength index (p < 0.05, ES = 0.59–0.64) in favor of CMJG. Particularly, pre–post-performance improvements have been observed for 5 m (∆1.6%; p = 0.04; ES = 0.54) and 20 m (∆5.3%; p < 0.01; ES = 1.00) in the CMJG. For SJG, 5 m (∆− 5.5%; p = 0.01; ES = − 1.12) and 20 m (∆− 3.7%; p = 0.01; ES = − 0.82) pre–post-performance declines were observed. Regarding reactive strength index, pre–post-improvement was noted for CMJG only (∆− 40.1%; p < 0.01; ES = 3.7). In addition, a tendency towards a group × time interaction was found for CoD (p = 0.06, ES = 0.54) with a performance decrement for SJG (∆− 6.0%; p < 0.01; ES = − 1.8) and no pre–post changes for CMJG (∆0.15%; p > 0.05; ES = 0.05). Conclusion Overall, jump exercises which utilize the SSC seem to be more effective in improving measures of speed and muscle power performance in young athletes. However, jump exercises that do not involve the SSC appear to negatively affect CoD performance in young athletes.
  • ... Requisite reactive strength may therefore be necessary to rapidly absorb and return large vertical ground reaction forces during maximum velocity sprinting. Furthermore, eccentric strength may directly aid lower limb stiffness and reactive strength by preventing excessive lengthening of muscle under high stretch loads, and indirectly by increasing force production during a subsequent quasi-isometric action via residual force enhancement (Fukutani, Misaki, & Isaka, 2017) and reflex potentiation (Flanagan & Comyns, 2008), thereby maximising the utilisation of elastic structures within the stretch-shortening cycle (SSC) (Beaumatin et al., 2018). As it stands, it remains unclear how reactive strength or eccentric strength qualities influence leg spring stiffness regulation during maximum velocity sprinting in highly trained athletes. ...
    Article
    Full-text available
    This study investigated the role of reactive and eccentric strength in stiffness regulation during maximum velocity sprinting (Vmax) in team sport athletes compared with highly trained sprinters. Thirteen team sport athletes and eleven highly trained sprinters were recruited. Vmax was measured using radar, and stiffness regulation was inferred from modelled vertical and leg spring stiffness. Reactive strength (RSI) was determined from a 0.50 m drop jump, and an eccentric back squat was used to assess maximum isoinertial eccentric force. Trained sprinters attained a higher Vmax than team sport athletes, partly due to a briefer contact time and higher vertical stiffness. Trained sprinters exhibited a moderately higher RSI via the attainment of a briefer and more forceful ground contact phase, while RSI also demonstrated large to very large associations with vertical stiffness and Vmax, respectively. Isoinertial eccentric force was largely correlated with Vmax, but only moderately correlated with vertical stiffness. Reactive and eccentric strength contribute to the ability to regulate leg spring stiffness at Vmax, and subsequently, the attainment of faster sprinting speeds in highly trained sprinters versus team sport athletes. However, stiffness regulation appears to be a task-specific neuromuscular skill, reinforcing the importance of specificity in the development of sprint performance.
  • ... 24 We also examined the reliability and sensitivity of RSImod, which has been suggested as a superior measure to jump height and other force and power variables in assessing the stretchshortening cycle of athletes and therefore their explosiveness when jumping. 33,34 Research in professional rugby league reported players with a greater RSImod demonstrated superior force, power, and impulse during both the concentric and eccentric phases of a CMJ in comparison with their lower RSImod counterparts. 34 We found RSImod to have relatively low TE (CV%: 7.0%) and high sensitivity (SNR: 1.9), indicating it to be a useful global measure of CMJ performance in professional AF players. ...
    Article
    Full-text available
    Purpose: To examine the measurement reliability and sensitivity of common athlete monitoring tools in professional Australian Football players. Methods: Test-retest reliability (noise) and weekly variation (signal) data were collected from 42 professional Australian footballers from 1 club during a competition season. Perceptual wellness was measured via questionnaires completed before main training sessions (48, 72, and 96 h postmatch), with players providing a rating (1-5 Likert scale) regarding their muscle soreness, sleep quality, fatigue level, stress, and motivation. Eccentric hamstring force and countermovement jumps were assessed via proprietary systems once per week. Heart rate recovery was assessed via a standard submaximal run test on a grass-covered field with players wearing a heart rate monitor. The heart rate recovery was calculated by subtracting average heart rate during final 10 seconds of rest from average heart rate during final 30 seconds of exercise. Typical test error was reported as coefficient of variation percentage (CV%) and intraclass coefficients. Sensitivity was calculated by dividing weekly CV% by test CV% to produce a signal to noise ratio. Results: All measures displayed acceptable sensitivity. Signal to noise ratio ranged from 1.3 to 11.1. Intraclass coefficients ranged from .30 to .97 for all measures. Conclusions: The heart rate recovery test, countermovement jump test, eccentric hamstring force test, and perceptual wellness all possess acceptable measurement sensitivity. Signal to noise ratio analysis is a novel method of assessing measurement characteristics of monitoring tools. These data can be used by coaches and scientists to identify meaningful changes in common measures of fitness and fatigue in professional Australian football.
  • ... Three maximal efforts were performed for all jumps with the best score used for analysis. The VDJ was performed from a 30 cm box to assess reactive strength index (RSI) which was calculated for each jump (flight time/contact time) permitting ground contact time was <0.25 ms (Flanagan & Comyns, 2008). Assessment of HCMJ performance required players to stand with feet shoulder width and their toes behind a marked line on the floor. ...
    Thesis
    Full-text available
    The physical demands of soccer match play have significantly increased in recent years. As such, training methods must evolve to ensure players are able to cope with these demands over the course of a season. Speed endurance training is recommended to improve physical performance in elite soccer players, however scientific investigations into different protocols and modalities are sparse. The aim of Study 1 was to determine the exposure to speed endurance training over a season relative to all other conditioning drills. Secondary data was quantified over a 42-week season in an elite youth soccer team using five different conditioning drill categorisations. Speed endurance maintenance and extensive endurance where the most prominent conditioning drills whilst speed endurance production was the least frequent. Nonetheless, the relative distribution of running drills and small-sided games were almost equal for both speed endurance protocols. An investigation into different speed endurance modes and protocols in Study 2 revealed running drills elicit greater heart rate, blood lactate concentration and subjective ratings of perceived exertion than respective small- sided games. Players covered less total distance and high-intensity running distance in the small-sided games, but greater high-intensity acceleration/deceleration distance than in the respective running drills. Additionally, the speed endurance production drills produced greater blood lactate concentrations and high speed running demands than the respective maintenance protocols. These findings suggest speed endurance small-sided games could be used to train the anaerobic energy system, however a greater physiological response may be possible with soccer drills that expose players to greater high speed running demands. The aim of study 3 was to quantify movement patterns, technical skills and tactical actions associated with high speed running efforts during elite match play to provide information for position-specific speed endurance drills. Twenty individual English Premier League players high-intensity running profiles were observed multiple times using a computerised tracking system. Data was coded using a novel ‘High-intensity Movement Programme’ and revealed position-specific trends in and out of possession. This investigation was the first study to contextualise why playing positions perform high- intensity running efforts rather than simply reporting distances covered. In possession, wide midfielders executed more tricks post effort than centre backs and central midfielders whilst fullbacks and wide midfielders performed more crosses post effort than other positions. Out of possession, forwards completed more efforts closing down the opposition but less efforts tracking opposition runners than other positions. Distinct movement patterns were also evident out of possession with forwards performing more arc runs before efforts compared to centre backs, fullbacks and wide midfielders, however centre backs completed more 0-90° turns compared to fullbacks, central and wide midfielders. The data from Study 3 was used to design five individual position-specific speed endurance drills with the aim of exposing players to high speed running and the associated technical and tactical actions performed during a match. An investigation into the position- specific speed endurance drills in Study 4 revealed players covered greater distances across all speed thresholds attaining greater peak and average running speeds during the speed endurance production protocol compared to the maintenance drill. Mean and peak heart rate responses were greater in the maintenance protocol whilst blood lactate concentrations were higher following the production protocol. Minimal differences in neuromuscular function and ratings of perceived recovery were evident following either protocol up to 24 h post drill. The findings suggest position-specific speed endurance production drills should be prescribed to achieve a greater anaerobic stimulus and expose players to high running speeds whilst the maintenance protocol should be administered when a greater cardiovascular load is desirable with a concomitant reduction in high speed running. This research programme provides novel information comparing the physiological response and physical demands of various speed endurance drills in soccer. These studies were the first to report seasonal speed endurance practice and detail generic and position-specific speed endurance soccer drills based on contextualised match data. It is hoped the data from this research project can help applied staff understand the most appropriate speed endurance practices for elite youth players.
  • ... To our knowledge, studies to date have only investigated the effect of CR on the CMJ, which is an important test using the SSC, while the DJ and related parameters such as ODH, RSI [2], and GCT are becoming more important indicators of the SSC [17][18][19]. The RSI [2] is especially useful to determine the ODH [17,20]. ...
    Article
    Full-text available
    Abstract BACKGROUND: The circadian rhythm (CR) is a 24-hour cyclic period that influences a wide array of physiological systems and performance sports. However, its specific effect on drop jump (DJ) scores have not been studied. OBJECTIVE: To investigate the effect of circadian rhythm on DJ performances. METHODS: Thirty-three healthy university students (men, n = 16, age: 23.47±2.9 years; fewomen, n = 17, age: 22.25 ±2.27 years) participated in this study. Subjects were tested twice, over two separate days, once in the morning and once in the evening. Subjects started from a drop height of 20 cm and continued until the height where the reactive strength index (RSI) started to decrease. This height was recorded as the optimal drop height (ODH). Ground contact time (GCT) and jump height were also recorded. RESULTS: The ODH values were similar between testing sessions for both genders (p > 0.05). A significant increase in jump height during the evening session was observed in men (p = 0.005, d = 0.80). The RSI values increased significantly in men (p = 0.006, _2 = 0.77) while GCT was similar in both genders (p > 0.05). CONCLUSION: In men, the optimal time of day for DJ explosive training is the evening. Women may benefit from this type of training both during morning and evening sessions. Keywords: Circadian rhythm, drop jump, reactive strength index, optimal drop height, jump height, ground contact time
  • ... These improvements can occur where there are high eccentric stretch loads, such as landing and change of direction mechanics, and fast stretchshortening cycle (SSC) demands, because an athlete's reactive strength ability is underpinned by relative maximal eccentric strength [145]; this again reinforces the need of substantial high levels of strength values before developing SSC capabilities [59]. The reactive strength index (RSI) has been widely employed to quantify plyometric or SSC performance, that is the ability to change quickly from an eccentric to concentric muscle action [146]. The factors that underpin an efficient SSC are related to the storage and the reutilization of elastic energy. ...
    Article
    Injuries have a detrimental impact on team and individual athletic performance. Deficits in maximal strength, rate of force development (RFD), and reactive strength are commonly reported following several musculoskeletal injuries. This article first examines the available literature to identify common deficits in fundamental physical qualities following injury, specifically strength, rate of force development and reactive strength. Secondly, evidence-based strategies to target a resolution of these residual deficits will be discussed to reduce the risk of future injury. Examples to enhance practical application and training programmes have also been provided to show how these can be addressed.
  • ... The ability to produce powerful 41 concentric muscle actions in order to maximize propulsive force is believed to be a key determinant weightlifting variants [9-10]. Another popular means of improving speed and COD ability is through 48 plyometric training, which refers to a wide range of jumping, hopping, and bounding exercises 49 designed to utilize the elastic nature of the stretch-shortening cycle (SSC) in order to produce greater 50 forces than would normally be produced by concentric-only muscle actions [9,11]. Previous studies 51 have demonstrated enhancements in speed and COD ability can be achieved through the use of 52 plyometric training methods [9,[12][13][14][15], however the majority of this research has focused on the 53 development of concentric power of the lower limbs, and resulting enhancements in performance 54 during the propulsive phase of COD tasks. ...
    Preprint
    This study investigated the effects of two plyometric training protocols on sprint and change of direction (COD) performance in elite hockey players. A parallel-group randomized controlled trial design was used and seventeen elite male and female field hockey players were randomly allocated into either low-to-high (L-H, n = 8) or high-to-low (H-L, n = 9) training groups. Each group performed separate variations of the drop jump exercise twice weekly for six weeks, with an emphasis on either jump height (L-H) or drop height (H-L). Performance variables assessed included sprint times over 10 m and 20 m, as well as 505 time. A two-way repeated measures analysis of variance was performed and Cohen’s d effect sizes were calculated. The H-L group displayed significant small ES improvement from baseline to post-training in the 10 m sprint (1.893 ± 0.08 s pre vs 1.851 ± 0.06 s post) (ES = −0.44) (P = <0.05). Small but not statistically significant differences between groups were observed for 10 m and 20 m sprint performance, and no significant differences were observed within or between groups for 505 time. These findings highlight the difficulty in substantially enhancing speed and COD ability in highly trained athletic populations through the addition of a low volume, short duration plyometric training protocol.
  • Article
    The proper application of the principle of specificity is essential to any strength and conditioning program. However, the transfer of resistance training to sport is highly complex, difficult to predict, and challenging to assess. This brief review examines the principle of dynamic correspondence as an aid towards better understanding and predicting an exercise or training method’s potential transfer to sport. Practical training recommendations are given based on the research reviewed.
  • Article
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    Background: It has been reported that boys’ and girls’ physical activity (PA) levels decline throughout adolescence. Boys are at risk of physical inactivity during adolescence however, in intervention research they are an under-represented group relative to girls. It is suggested that the school environment may be central to developing interventions that support adolescents in meeting the current PA guidelines. The aim of this systematic review and meta-analysis was to investigate the efficacy of school-based physical activity interventions for improving muscular fitness (MF) in adolescent males. Methods: This systematic review and meta-analysis followed the preferred reporting systems for meta-analyses guidelines and was registered on PROSPERO (Registration number: CRD42018091023). Eligible studies were published in English within peer-reviewed articles. Searches were conducted in three databases, with an additional grey literature search in Google Scholar. Studies investigating MF outcomes were included. Results: There were 43 data sets identified across 11 studies, from seven countries. Overall methodological quality of the studies was moderate to strong. Interventions targeting MF evidenced a small to medium effect (g = 0.32, CI 0.17, 0.48, P = <.001). Sub-group analyses of MF delivery method resulted in small to medium effects: Upper limb MF measures (g = 0.28, 95% CI -0.02, 0.58, p = 0.07), lower limb MF measures (g = 0.28, 95% CI 0.09, 0.68, p 0.03), combined MF activities (g = 0.24, 95% CI -0.04 – 0.49, p = 0.05), plyometric activities (g = 0.39, 95% CI 0.09, 0.68, p = 0.01), body weight (g = 0.27, 95% CI -0.10, 0.65, p = 0.15), and traditional MF methods (g = 0.43, 95% CI 0.09, 0.78, p = 0.01). Conclusions: School-based interventions which aimed to increase MF outcomes in adolescent boys demonstrated small to moderate effects. Traditional and plyometric methods of resistance training appear to be the most effective form of PA delivery in adolescent males. More quality research is required to assess the impact of MF delivered in the school environment in order to inform future intervention design.
  • Article
    Stastny, P, Lehnert, M, De Ste Croix, M, Petr, M, Svoboda, Z, Maixnerova, E, Varekova, R, Botek, M, Petrek, M, Lenka, K, and Cięszczyk, P. Effect of COL5A1, GDF5, and PPARA genes on a movement screen and neuromuscular performance in adolescent team sport athletes. J Strength Cond Res 33(8): 2057-2065, 2019-The risk of injury increases with adolescents' chronological age and may be related to limited muscle function neuromuscular, genetic, and biomechanical factors. The purpose of this study was to determine whether COL5A1, PPARA, and GDF5 genes are associated with muscle functions and stretch-shortening cycle performance in adolescent athletes. One hundred forty-six youth players (14.4 ± 0.2 years) from various team sports (basketball n = 54, soccer n = 50, handball n = 32) underwent a manual test for muscle function, maturity estimation, functional bend test (FBT), passive straight leg raise (SLR) test, leg stiffness test, test of reactive strength index (RSI), and gene sampling for COL5A1, PPARA, and GDF5. The χ test did not show any differences in allele or genotype frequency between participants before and after peak height velocity. Multivariate analysis of variance showed that COL5A1 rs12722 CT heterozygotes had worse score in FBT (p < 0.001), worse score in SLR (p = 0.003), and lower maturity offset (p = 0.029, only in females) than TT homozygotes. Male GDF5 rs143383 GG homozygotes showed better score in SLR than AA and AG genotypes (p = 0.003), and AA and AG genotypes in both sex had greater RSI than GG homozygotes (p = 0.016). The PPARA rs4253778 CC homozygotes had greater RSI than GG and GC genotypes (p = 0.004). The CT genotype in COL5A1 rs12722 is possible predictor of functional movement disruption in the posterior hip muscle chain, causing shortening in FBT and SLR, which includes hamstrings function. CT genotype in COL5A1 rs12722 should be involved in programs targeting hamstring and posterior hip muscle chain.
  • Article
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    Previously it has been reported that eccentric muscle actions result in higher force production (20-60%) compared to concentric muscle actions (1, 2). This may be the result of both mechanical (2, 3) and neural differences (4-6) between the two actions. As a consequence of athletes being stronger eccentrically, traditional strength testing may not adequately assess eccentric strength (7). Therefore, it may be necessary to assess eccentric muscle actions independently.
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  • Conference Paper
    Full-text available
    Performance in fast and slow stretch shortening cycle (SSC) activity was examined. 13 NCAA Div. I cross country skiers and runners performed a countermovement jump (CMJ) and a drop jump (DJ) on a force platform. These jumping actions were classified as slow and fast SSC activities respectively based on ground contact times. In the slow SSC subjects achieved significantly greater jump heights while in the fast SSC subjects produced greater peak ground reaction force and measured higher on the reactive strength index. A weak correlation was found between slow SSC and fast SSC ability suggesting that training in slow SSC tasks might not accrue benefit in fast SSC ability and vice versa. Consideration to ground contact duration and the principle of specificity should be given when using the CMJ or the DJ as a testing tool or as a training exercise.
  • Article
    Examines some critical definitional and experimental-design problems that underlie the principles of knowledge of results (KR) and learning, the KR literature, and how newer principles of KR lead to notions of how KR works in human motor-learning situations. KR is defined as augmented feedback, where the KR is additional to those sources of feedback that are naturally received when a response is made. Transfer tests, usually under no-KR conditions, are essential for unraveling the temporary effects of KR manipulations from their relatively permanent learning effects. When this is considered, the literature reveals findings that produce reasonable agreement, although there are a number of inconsistencies in studies examining the same variables. When learning vs performance effects of KR are separated, a number of contradictions occur; new principles that emerge include the notion that KR acts as guidance, that it is motivating or energizing, and that it has a role in the formation of associations. It is suggested that KR may guide an S to the proper target behavior, with other processes (e.g., simple repetition) being the critical determinants of learning. (4 p ref) (PsycINFO Database Record (c) 2006 APA, all rights reserved).
  • Article
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    The purpose of the study was to determine if six weeks of plyometric training can improve an athlete's agility. Subjects were divided into two groups, a plyometric training and a control group. The plyometric training group performed in a six week plyometric training program and the control group did not perform any plyometric training techniques. All subjects participated in two agility tests: T-test and Illinois Agility Test, and a force plate test for ground reaction times both pre and post testing. Univariate ANCOVAs were conducted to analyze the change scores (post - pre) in the independent variables by group (training or control) with pre scores as covariates. The Univariate ANCOVA revealed a significant group effect F2,26 = 25.42, p=0.0000 for the T-test agility measure. For the Illinois Agility test, a significant group effect F2,26 = 27.24, p = 0.000 was also found. The plyometric training group had quicker posttest times compared to the control group for the agility tests. A significant group effect F2,26 = 7.81, p = 0.002 was found for the Force Plate test. The plyometric training group reduced time on the ground on the posttest compared to the control group. The results of this study show that plyometric training can be an effective training technique to improve an athlete's agility. Key PointsPlyometric training can enhance agility of athletes.6 weeks of plyometric training is sufficient to see agility results.Ground reaction times are decreased with plyometric training.
  • Article
    Knowledge of muscle actions is essential for understanding biomechanics in running. In this study, 17 young runners were investigated at 13 different running speeds. Telemetric surface electromyograms from lower leg muscles were recorded continuously, and they were synchronized with the recordings of 3-dimensional ground reaction forces from a 10-m-long force platform. As expected, the rate of force production and the peak forces increased with increasing running speed. In the lateral forces, there was a short-duration inward force at the beginning of the contact followed by a longer-lasting outward force. The results revealed further the importance of preactivity and eccentric activity of the leg extensor muscles and the role of the hamstring muscles. The preactivity appears to be a preparatory requirement both for the enhancement of electromyographic activity during the braking phase and for timing of muscular action with respect to the ground contact. The increased force production with increased running speed is, furthermore, partly due to high and long-lasting activity of the hip extensor muscles during the contact phase. (C) 1999 National Strength and Conditioning Association
  • Article
    This target article addresses the role of storage and reutilization of elastic energy in stretch-shortening cycles. It is argued that for discrete movements such as the vertical jump, elastic energy does not explain the work enhancement due to the prestretch. This enhancement seems to occur because the prestretch allows muscles to develop a high level of active state and force before starting to shorten. For cyclic movements in which stretch- shortening cycles occur repetitively, some authors have claimed that elastic energy enhances mechanical efficiency. In the current article it is demonstrated that this claim is often based on disputable concepts such as the efficiency of positive work or absolute work, and it is argued that elastic energy cannot affect mechanical efficiency simply because this energy is not related to the conversion of metabolic energy into mechanical energy. A comparison of work and efficiency measures obtained at different levels of organization reveals that there is in fact no decisive evidence to either support or reject the claim that the stretch- shortening cycle enhances muscle efficiency. These explorations lead to the conclusion that the body of knowledge about the mechanisms and energetics of the stretch-shortening cycle is in fact quite lean. A major challenge is to bridge the gap between knowledge obtained at different levels of organization, with the ultimate purpose of understanding how the intrinsic properties of muscles manifest themselves under in-vivo-like conditions and how they are exploited in whole-body activities such as running. To achieve this purpose, a close cooperation is required between muscle physiologists and human movement scientists performing inverse and forward dynamic simulation studies of whole-body exercises.
  • Article
    An alternating cycle of eccentric-concentric contractions in locomotion represents a sequence when storage and utilization of elastic energy takes place. It is possible that this storage capacity and its utilization depends on the imposed stretch loads in activated muscles, and that sex differences may be present in these phenomena. To investigate these assumed differences, subjects from both sexes and of good physical condition performed vertical jumps on the force-platform from the following experimental conditions: squatting jump (SJ) from a static starting position; counter-movement jump (CMJ) from a free standing position and with a preparatory counter-movement; drop jumps (DJ) from the various heights (20 to 100 cm) on to the platform followed immediately by a vertical jump. In all subjects the SJ, in which condition no appreciable storage of elastic energy takes place, produced the lowest height of rise of the whole body center of gravity (C.G.). The stretch load (drop height) influenced the performance so that height of rise of C. of G. increased when the drop height increased from 26 up to 62 cm (males) and from 20 to 50 cm (females). In all jumping conditions the men jumped higher than the women. However, examination of the utilization of elastic energy indicated that in CMJ the female subjects were able to utilize most (congruent to 90%) of the energy produced in the prestretching phase. Similarly, in DJ the overall change in positive energy over SJ condition was higher in women as compared to men. Thus the results suggest that although the leg extensor muscles of the men subjects could sustain much higher stretch loads, the females may be able to utilize a greater portion of the stored elastic energy in jumping activities.
  • Article
    Full-text available
    Twelve experienced male weight lifters performed a rebound bench press and a purely concentric bench press lift. Data were obtained pertaining to 1) the benefits to concentric motion derived from a prior stretch and 2) the movement frequency adopted during performance of the stretch-shorten cycle (SSC) portion of the rebound bench press lift. The subjects also performed a series of quasi-static muscular actions in a position specific to the bench press movement. A brief perturbation was applied to the bar while these isometric efforts were maintained, and the resulting damped oscillations provided data pertaining to each subject's series elastic component (SEC) stiffness and natural frequency of oscillation. A significant correlation (r = -0.718, P less than 0.01) between maximal SEC stiffness and augmentation to concentric motion derived from prior stretch was observed. Subjects were also observed to perform the SSC portion of the rebound bench press movement to coincide with the natural frequency of oscillation of their SEC. These results are interpreted as demonstrating that the optimal stiffness in a rebound bench press lift was a resonant-compliant SEC.
  • Article
    In the literature, athletes preparing for explosive activities are recommended to include drop jumping in their training programs. For the execution of drop jumps, different techniques and different dropping heights can be used. This study was designed to investigate for the performance of bounce drop jumps the influence of dropping height on the biomechanics of the jumps. Six subjects executed bounce drop jumps from heights of 20 cm (designated here as DJ20), 40 cm (designated here as DJ40), and 60 cm (designated here as DJ60). During jumping, they were filmed, and ground reaction forces were recorded. The results of a biomechanical analysis show no difference between DJ20 and DJ40 in mechanical output about the joints during the push-off phase. Peak values of moment and power output about the ankles during the push-off phase were found to be smaller in DJ60 than in DJ40 (DJ20 = DJ60). The amplitude of joint reaction forces increased with dropping height. During DJ60, the net joint reaction forces showed a sharp peak on the instant that the heels came down on the ground. Based on the results, researchers are advised to limit dropping height to 20 or 40 cm when investigating training effects of the execution of bounce drop jumps.
  • Article
    In the literature, drop jumping is advocated as an effective exercise for athletes who prepare themselves for explosive activities. When executing drop jumps, different jumping techniques can be used. In this study, the influence of jumping technique on the biomechanics of jumping is investigated. Ten subjects executed drop jumps from a height of 20 cm and counter-movement jumps. For the execution of the drop jumps, two different techniques were adopted. The first technique, referred to as bounce drop jump, required the subjects to reverse the downward velocity into an upward one as soon as possible after landing. The second technique, referred to as counter-movement drop jump, required them to do this more gradually by making a larger downward movement. During jumping, the subjects were filmed, ground reaction forces were registered, and electromyograms were recorded. The results of a biomechanical analysis show that moments and power output about knee and ankle joints reach larger values during the drop jumps than during counter-movement jumps. The largest values were attained during bounce drop jumps. Based on this finding, it was hypothesized that bounce drop jump is better suited than counter-movement drop jump for athletes who seek to improve the mechanical output of knee extensors and plantar flexors. Researchers are, therefore, advised to control jumping technique when investigating training effects of executing drop jumps.
  • Article
    Examines some critical definitional and experimental-design problems that underlie the principles of knowledge of results (KR) and learning, the KR literature, and how newer principles of KR lead to notions of how KR works in human motor-learning situations. KR is defined as augmented feedback, where the KR is additional to those sources of feedback that are naturally received when a response is made. Transfer tests, usually under no-KR conditions, are essential for unraveling the temporary effects of KR manipulations from their relatively permanent learning effects. When this is considered, the literature reveals findings that produce reasonable agreement, although there are a number of inconsistencies in studies examining the same variables. When learning vs performance effects of KR are separated, a number of contradictions occur; new principles that emerge include the notion that KR acts as guidance, that it is motivating or energizing, and that it has a role in the formation of associations. It is suggested that KR may guide an S to the proper target behavior, with other processes (e.g., simple repetition) being the critical determinants of learning. (4 p ref) (PsycINFO Database Record (c) 2012 APA, all rights reserved)
  • Article
    In the literature, it is well established that subjects are able to jump higher in a countermovement jump (CMJ) than in a squat jump (SJ). The purpose of this study was to estimate the relative contribution of the time available for force development and the storage and reutilization of elastic energy to the enhancement of performance in CMJ compared with SJ. Six male volleyball players performed CMJ and SJ. Kinematics, kinetics, and muscle electrical activity (EMG) from six muscles of the lower extremity were monitored. It was found that even when the body position at the start of push-off was the same in SJ as in CMJ, jump height was on average 3.4 cm greater in CMJ. The possibility that nonoptimal coordination in SJ explained the difference in jump height was ruled out: there were no signs of movement disintegration in SJ, and toe-off position was the same in SJ as in CMJ. The greater jump height in CMJ was attributed to the fact that the countermovement allowed the subjects to attain greater joint moments at the start of push-off. As a consequence, joint moments were greater over the first part of the range of joint extension in CMJ, so that more work could be produced than in SJ. To explain this finding, measured and manipulated kinematics and electromyographic activity were used as input for a model of the musculoskeletal system. According to simulation results, storage and reutilization of elastic energy could be ruled out as explanation for the enhancement of performance in CMJ over that in SJ. The crucial contribution of the countermovement seemed to be that it allowed the muscles to build up a high level of active state (fraction of attached cross-bridges) and force before the start of shortening, so that they were able to produce more work over the first part of their shortening distance.
  • Article
    Rehabilitation continues to evolve with the increased emphasis on patient management and proprioceptive training. Proprioception can be defined as a specialized variation of the sensory modality of touch that encompasses the sensation of joint movement (kinesthesia) and joint position (joint position sense). Numerous investigators have observed that afferent feedback to the brain and spinal pathways is mediated by skin, articular, and muscle mechanoreceptors. Examining the effects of ligamentous injury, surgical intervention, and proprioceptively mediated activities in the rehabilitation program provides an understanding of the complexity of this system responsible for motor control. It appears that this neuromuscular feedback mechanism becomes interrupted with injury and abnormalities, and approaches restoration after surgical intervention and rehabilitation. Rehabilitation programs should be designed to include a proprioceptive component that addresses the following three levels of motor control: spinal reflexes, cognitive programming, and brainstem activity. Such a program is highly recommended to promote dynamic joint and functional stability. Thus far, current knowledge regarding the basic science and clinical application of proprioception has led the profession of sports medicine one step closer to its ultimate goal of restoring function.
  • Article
    To isolate any difference muscular contraction history may have on concentric work output, 40 trained male subjects performed three separate isokinetic concentric squats that involved differing contraction histories, 1) a concentric-only (CO) squat, 2) a concentric squat preceded by an isometric preload (IS), and 3) a stretch-shorten cycle (SSC) squat. Over the first 300 ms of the concentric movement, work output for both the SSC and IS conditions was significantly greater (154.8 +/- 39.8 and 147.9 +/- 34.7 J, respectively; P < 0.001) compared with the CO squat (129.7 +/- 34.4 J). In addition, work output after the SSC test over the first 300 ms was also significantly larger than that for the corresponding period after the IS protocol (P < 0.05). There was no difference in normalized, integrated electromyogram among any of the conditions. It was concluded that concentric performance enhancement derived from a preceding stretch of the muscle-tendon complex was largely due to the attainment of a higher active muscle state before the start of the concentric movement. However, it was also hypothesized that contractile element potentiation was a significant contributor to stretch-induced muscular performance under these conditions.
  • Article
    Stretch-shortening cycle (SSC) in human skeletal muscle gives unique possibilities to study normal and fatigued muscle function. The in vivo force measurement systems, buckle transducer technique and optic fiber technique, have revealed that, as compared to a pure concentric action, a non-fatiguing SSC exercise demonstrates considerable performance enhancement with increased force at a given shortening velocity. Characteristic to this phenomenon is very low EMG-activity in the concentric phase of the cycle, but a very pronounced contribution of the short-latency stretch-reflex component. This reflex contributes significantly to force generation during the transition (stretch-shortening) phase in SSC action such as hopping and running. The amplitude of the stretch reflex component - and the subsequent force enhancement - may vary according to the increased stretch-load but also to the level of fatigue. While moderate SSC fatigue may result in slight potentiation, the exhaustive SSC fatigue can dramatically reduce the same reflex contribution. SSC fatigue is a useful model to study the processes of reversible muscle damage and how they interact with muscle mechanics, joint and muscle stiffness. All these parameters and their reduction during SSC fatigue changes stiffness regulation through direct influences on muscle spindle (disfacilitation), and by activating III and IV afferent nerve endings (proprioseptic inhibition). The resulting reduced stretch reflex sensitivity and muscle stiffness deteriorate the force potentiation mechanisms. Recovery of these processes is long lasting and follows the bimodal trend of recovery. Direct mechanical disturbances in the sarcomere structural proteins, such as titin, may also occur as a result of an exhaustive SSC exercise bout.
  • Article
    The purposes of this study are: a) to examine the possibility of influencing the leg stiffness through instructions given to the subjects and b) to determine the effect of the leg stiffness on the mechanical power and take-off velocity during the drop jumps. A total of 15 athletes performed a series of drop jumps from heights of 20, 40 and 60 cm. The instructions given to the subjects were a) "jump as high as you can" and b) "jump high a little faster than your previous jump". The jumps were performed at each height until the athlete could not achieve a shorter ground contact time. The ground reaction forces were measured using a "Kistler" force plate (1000 Hz). The athletes body positions were recorded using a high speed (250 Hz) video camera. EMG was used to measure muscle activity in five leg muscles. The data was divided into 5 groups where group 1 was made up of the longest ground contact times of each athlete and group 5 the shortest. The leg and ankle stiffness values were higher when the contact times were shorter. This means that by influencing contact time through verbal instructions it is possible to control leg stiffness. Maximum center of mass take-off velocity the can be achieved with different levels of leg stiffness. The mechanical power acting on the human body during the positive phase of the drop jumps had the highest values in group 3. This means that there is an optimum stiffness value for the lower extremities to maximize mechanical power.
  • Article
    The relationships between football playing ability (FPA) and selected anthropometric and performance measures were determined among NCAA Division I-A football players (N = 40). Football playing ability (determined by the average of coaches' rankings) was significantly correlated with vertical jump (VJ) in all groups (offense, defense, and position groups of wide receiver-defensive back, offensive linemen-defensive linemen, and running back-tight end-linebacker). Eleven of 50 correlations (groups by variables), or 22%, were important for FPA. Five of the 11 relationships were related to VJ. Forward stepwise regression equations for each group explained over half of the criterion variable, FPA, as indicated by the R(2) values for each model. Vertical jump was the prime predictor variable in the equations for all groups. The findings of this study are discussed in relation to the specificity hypothesis. Strength and conditioning programs that facilitate the capacity for football players to develop forceful and rapid concentric action through plantar flexion of the ankle, as well as extension of the knee and hip, may be highly profitable.
  • Article
    Full-text available
    This study examined whether the elasticity of the tendinous tissues plays an important role in human locomotion by improving the power output and efficiency of skeletal muscle. Ten subjects performed one-leg drop jumps (DJ) from different dropping heights with a constant rebound height. The fascicle length of the vastus lateralis muscle was measured by using real-time ultrasonography during DJ. In the braking phase of the DJ, fascicle lengthening decreased and the tendinous tissue lengthening increased with increased dropping intensity. In the subsequent push-off phase, the shortening of tendinous tissues increased with higher dropping intensity. The averaged electromyographic activities of the preactivation and braking phases increased and those of the push-off phase decreased as the drop height was increased. With higher dropping height but constant submaximal rebound jump, the stretched tendinous tissue length increased with less stretched fascicle during the braking phase. In the subsequent push-off phase, the recoil of tendinous tissues became greater. These results suggest that the increased prestretch intensity has considerable influence on the process of storage and subsequent recoil of the elastic energy during the stretch-shortening cycle action.
  • Article
    Full-text available
    We examined the effects of 2 plyometric training programs, equalized for training volume, followed by a 4-week recovery period of no plyometric training on anaerobic power and vertical jump performance. Physically active, college-aged men were randomly assigned to either a 4-week (n = 19, weight = 73.4 +/- 7.5 kg) or a 7-week (n = 19, weight = 80.1 +/- 12.5 kg) program. Vertical jump height, vertical jump power, and anaerobic power via the Margaria staircase test were measured pretraining (PRE), immediately posttraining (POST), and 4 weeks posttraining (POST-4). Vertical jump height decreased in the 4-week group PRE (67.8 +/- 7.9 cm) to POST (65.4 +/- 7.8 cm). Vertical jump height increased from PRE to POST-4 in 4-week (67.8 +/- 7.9 to 69.7 +/- 7.6 cm) and 7-week (64.6 +/- 6.2 to 67.2 +/- 7.6 cm) training programs. Vertical jump power decreased in the 4-week group from PRE (8,660.0 +/- 546.5 W) to POST (8,541.6 +/- 557.4 W) with no change in the 7-week group. Vertical jump power increased PRE to POST-4 in 4-week (8,660.0 +/- 546.5 W to 8,793.6 +/- 541.4 W) and 7-week (8,702.8 +/- 527.4 W to 8,931.5 +/- 537.6 W) training programs. Anaerobic power improved in the 7-week group from PRE (1,121.9 +/- 174.7 W) to POST (1,192.2 +/- 189.1 W) but not the 4-week group. Anaerobic power significantly improved PRE to POST-4 in both groups. There were no significant differences between the 2 training groups. Four-week and 7-week plyometric programs are equally effective for improving vertical jump height, vertical jump power, and anaerobic power when followed by a 4-week recovery period. However, a 4-week program may not be as effective as a 7-week program if the recovery period is not employed.
  • Article
    Full-text available
    The purpose of this study was to assess the usefulness of the vertical jump and estimated vertical-jump power as a field test for weightlifting. Estimated PP output from the vertical jump was correlated with lifting ability among 64 USA national-level weightlifters (junior and senior men and women). Vertical jump was measured using the Kinematic Measurement System, consisting of a switch mat interfaced with a laptop computer. Vertical jumps were measured using a hands-on-hips method. A counter-movement vertical jump (CMJ) and a static vertical jump (SJ, 90 degrees knee angle) were measured. Two trials were given for each condition. Test-retest reliability for jump height was intra-class correlation (ICC) = 0.98 (CMJ) and ICC = 0.96 (SJ). Athletes warmed up on their own for 2-3 minutes, followed by 2 practice jumps at each condition. Peak power (PP) was estimated using the equations developed by Sayers et al. (24). The athletes' current lifting capabilities were assessed by a questionnaire, and USA national coaches checked the listed values. Differences between groups (i.e., men versus women, juniors versus resident lifters) were determined using t-tests (p < or = 0.05). Correlations were determined using Pearson's r. Results indicate that vertical jumping PP is strongly associated with weightlifting ability. Thus, these results indicate that PP derived from the vertical jump (CMJ or SJ) can be a valuable tool in assessing weightlifting performance.
  • Article
    The purposes of this study are (a) to examine the effects of contact time manipulation on jump parameters and (b) to examine the interaction between starting height changes and contact time changes on important jump parameters. Fifteen male athletes performed a series of drop jumps from heights of 20, 40, and 60 cm. The instructions given to the subjects were (a) "jump as high as you can" and (b) "jump high a little faster than your previous jump." Jumps were performed at each height until the athlete could not achieve a shorter ground contact time. The data were divided into 5 groups where group 1 was made up of the longest ground contact times of each athlete and groups 2-4 were composed of progressively shorter contact times, with group 5 having the shortest contact times. The jumps of group 3 produced the highest maximum and mean mechanical power (p <0.05) during the positive phase of the drop jumps regardless of starting jump height. The vertical takeoff velocities for the first 3 groups did not show significant (p < 0.05) differences. These results indicate that the manipulation of jump technique plays larger role than jump height in the manipulation of important jump parameters.
  • Article
    For many sporting activities, initial speed rather than maximal speed would be considered of greater importance to successful performance. The purpose of this study was to identify the relationship between strength and power and measures of first-step quickness (5-m time), acceleration (10-m time), and maximal speed (30-m time). The maximal strength (3 repetition maximum [3RM]), power (30-kg jump squat, countermovement, and drop jumps), isokinetic strength measures (hamstring and quadriceps peak torques and ratios at 60 degrees .s(-1) and 300 degrees .s(-1)) and 5-m, 10-m, and 30-m sprint times of 26 part-time and full-time professional rugby league players (age 23.2 +/- 3.3 years) were measured. To examine the importance of the strength and power measures on sprint performance, a correlational approach and a comparison between means of the fastest and slowest players was used. The correlations between the 3RM, drop jump, isokinetic strength measures, and the 3 measures of sport speed were nonsignificant. Correlations between the jump squat (height and relative power output) and countermovement jump height and the 3 speed measures were significant (r = -0.43 to -0.66, p < 0.05). The squat and countermovement jump heights as well as squat jump relative power output were the only variables found to be significantly greater in the fast players. It was suggested that improving the power to weight ratio as well as plyometric training involving countermovement and loaded jump-squat training may be more effective for enhancing sport speed in elite players.
  • Article
    Full-text available
    Objective: To define the nomenclature and physiologic mechanisms responsible for functional joint stability. Data sources: Information was drawn from an extensive MEDLINE search of the scientific literature conducted in the areas of proprioception, neuromuscular control, and mechanisms of functional joint stability for the years 1970 through 1999. An emphasis was placed on defining pertinent nomenclature based on the original references. Data synthesis: Afferent proprioceptive input is conveyed to all levels of the central nervous system. They serve fundamental roles in optimal motor control and sensorimotor control over functional joint stability. Conclusions/applications: Sensorimotor control over the dynamic restraints is a complex process that involves components traditionally associated with motor control. Recognizing and understanding the complexities involved will facilitate the continued development and institution of management strategies based on scientific rationales.
  • Article
    Fifteen highly trained distance runners VO(2)max 71.1 +/- 6.0 ml.min(-1).kg(-1), mean +/- SD) were randomly assigned to a plyometric training (PLY; n = 7) or control (CON; n = 8) group. In addition to their normal training, the PLY group undertook 3 x 30 minutes PLY sessions per week for 9 weeks. Running economy (RE) was assessed during 3 x 4 minute treadmill runs (14, 16, and 18 km.h(-1)), followed by an incremental test to measure VO(2)max. Muscle power characteristics were assessed on a portable, unidirectional ground reaction force plate. Compared with CON, PLY improved RE at 18 km.h(-1) (4.1%, p = 0.02), but not at 14 or 16 km.h(-1). This was accompanied by trends for increased average power during a 5-jump plyometric test (15%, p = 0.11), a shorter time to reach maximal dynamic strength during a strength quality assessment test (14%, p = 0.09), and a lower VO(2)-speed slope (14%, p = 0.12) after 9 weeks of PLY. There were no significant differences in cardiorespiratory measures or VO(2)max as a result of PLY. In a group of highly-trained distance runners, 9 weeks of PLY improved RE, with likely mechanisms residing in the muscle, or alternatively by improving running mechanics.
  • Article
    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.
  • Article
    Full-text available
    Alternating a resistance exercise with a plyometric exercise is referred to as "complex training". In this study, we examined the effect of various resistive loads on the biomechanics of performance of a fast stretch-shortening cycle activity to determine if an optimal resistive load exists for complex training. Twelve elite rugby players performed three drop jumps before and after three back squat resistive loads of 65%, 80%, and 93% of a single repetition maximum (1-RM) load. All drop jumps were performed on a specially constructed sledge and force platform apparatus. Flight time, ground contact time, peak ground reaction force, reactive strength index, and leg stiffness were the dependent variables. Repeated-measures analysis of variance found that all resistive loads reduced (P < 0.01) flight time, and that lifting at the 93% load resulted in an improvement (P < 0.05) in ground contact time and leg stiffness. From a training perspective, the results indicate that the heavy lifting will encourage the fast stretch-shortening cycle activity to be performed with a stiffer leg spring action, which in turn may benefit performance. However, it is unknown if these acute changes will produce any long-term adaptations to muscle function.