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General and local muscular fatigue is postulated to negatively alter lower limb biomechanics; however, few prospective studies have been done to examine the effect of fatigue on tuck-jump performance. The tuck-jump assessment (TJA) is a criteria-based visual screening tool designed to identify neuromuscular deficits associated with anterior cruciate ligament (ACL) injury. Use of kinetics during the TJA after an intense sport-specific fatigue protocol may identify fatigue-induced neuromuscular deficits associated with ACL injury risk. To examine the effects of a sport-specific fatigue protocol on visually evidenced (2-dimensional) technical performance of repeated tuck jumps and lower limb kinetic stabilization. Cross-sectional study. Laboratory. Twelve female netball athletes (age = 20.8 ± 2.6 years, height = 170.0 ± 0.04 cm, mass = 67.5 ± 7.4 kg). Participants performed 1 set of a TJA before and after a sport-specific fatigue protocol. Paired t tests and effect sizes were used to evaluate differences and the magnitude of differences in TJA scoring criterion, kinetics, and kinetic stabilization prefatigue to postfatigue. A small increase was observed for vertical relative lower extremity stiffness postfatigue (P =.005; Hedges g = 0.45). Peak center-of-mass displacement, time of jump cycle, ground contact time, flight time, jump height, and vertical net impulse decreased with small to moderate effect sizes (P <.01; Hedges g range, 0.41–0.74). No differences were observed for TJA composite scores, peak vertical ground reaction force, and stabilization indices of kinetic variables after the fatigue protocol (P >.05). Kinetic analysis of repeated tuck jumps after a fatigue protocol identified an altered jumping strategy, which was not identifiable via visual 2-dimensional assessment. However, based on kinetic measures, fatigue induces a stiffer jumping strategy, and practitioners should consider assessing load attenuation strategies that may not be visually evident when evaluating ACL-injury risk factors in athletes who are fatigued. [ABSTRACT FROM AUTHOR]

Purpose: To compare the effects of variable-resistance complex training (VRCT) versus traditional complex training (TCT) on strength, power, speed, and leg stiffness (Kleg) in rugby league players during a 6-week mesocycle. Methods: Twenty-four rugby league players competing in the British University and Colleges Sport Premier North Division were randomized to VRCT (n = 8), TCT (n = 8), or control (CON; n = 8). Experimental groups completed a 6-week lower-body complex training intervention (2×/wk) that involved alternating high-load resistance exercise with plyometric exercise within the same session. The VRCT group performed resistance exercises at 70% of 1-repetition maximum (1RM) + 0% to 23% of 1RM from band resistance with a 90-second intracontrast rest interval, whereas the TCT group performed resistance exercise at 93% of 1RM with a 4-minute intracontrast rest interval. Back-squat 1RM, countermovement jump peak power, reactive strength index, sprint times, and Kleg were assessed pretraining and posttraining. Results: VRCT and TCT significantly improved 1RM back squat, countermovement jump peak power, and 5-m sprint time (all P <.05). VRCT also improved Kleg, whereas TCT improved 10- and 20-m sprint times (all P <.05). Between groups, both VRCT and TCT improved 1RM back squat compared with CON (both P <.001). Additionally, VRCT improved Kleg compared with CON (right leg: P =.016) and TCT improved 20-m sprint time compared with CON (P =.042). Conclusions: VRCT and TCT can be implemented during the competitive season to improve strength, power, and 5-m sprint time. VRCT may lead to greater improvements in reactive strength index and Kleg, whereas TCT may enhance 10- and 20-m sprint times. [ABSTRACT FROM AUTHOR]

Purpose: To evaluate the test–retest reliability of isokinetic leg-press power–force–velocity profile (P–F–v) parameters in male and female elite athletes. In addition, we determined the concurrent validity of leg-press against squat-jump (SJ) P–F–v parameters in task-experienced athletes. Methods: For test–retest reliability, 22 female and 23 male elite athletes (22.3 [4.1] y) with different sporting backgrounds conducted 3 isokinetic leg-press test sessions over 3 consecutive weeks. The testing consisted of bilateral leg extensions at isokinetic velocities of 0.1, 0.3, 0.7, and 1.2 m·s−1. For concurrent validity, 13 ski jumpers (20.3 [3.3] y) were recruited to perform the isokinetic leg-press and SJ P–F–v profile tests using 5 predefined loading conditions of 0%, +20%, +40%, +60%, and +80% of body mass. Results: Relative and absolute reliability were acceptable for female (intraclass correlation coefficient ≥.87 and coefficient of variation ≤6.5%) and male (intraclass correlation coefficient ≥.89 and coefficient of variation ≤5.7%) elite athletes. In contrast, concurrent validity was insufficient, with correlations ranging from −.26 to.69 between isokinetic and SJ P–F–v parameters. Conclusion: Irrespective of sex, isokinetic leg-press P–F–v profiles provide reliable parameters. However, leg-press P–F–v profiles do not serve as a valid substitute for SJ P–F–v profiles. P–F–v parameter magnitudes are likely dependent on the constraints of the tested movement and testing device. [ABSTRACT FROM AUTHOR]

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Time of flight (ToF) is an objective scoring component of elite trampolining, assessed in training by maximal jump tests. The aim of this study was to assess the relationship between physical floor based performance meaures and 20-maximum ToF. Thirty-two elite level gymnasts (13 senior; 19 junior) performed a battery of floor based tests and a 20-maximum jump test. Floor based tests included cycling peak power output, reactive strength index (RSI), unloaded countermovement jumps (CMJ), and loaded CMJ's to construct a load-velocity profile for prediction of theoretical maximum force (CMJ F0). Very large and large, positive bivariate relationships were observed between CMJ F0 and ToF for the seniors (r = 0.85) and juniors (r = 0.56), respectively. Very large, positive bivariate relationships were observed between CMJ height and total ToF for both seniors (r = 0.74) and juniors (r = 0.77). Step-wise multiple regression analyses revealed CMJ F0 predicted 72% of ToF variability between seniors, and CMJ height (59%), 10 to 5 RSI (13%), and CMJ F0 (10%) predicting 82% of ToF variability between juniors. This suggests CMJ F0, lower limb maximal isometric capabilities, and CMJ height are important floor based predictors of maximal ToF in elite gymnasts. [ABSTRACT FROM AUTHOR]

This randomized control study aimed to assess 12 weeks of a novel neuromuscular training program (KneeRugbyWomen) on jump-related biomechanical variables in amateur female rugby players. Twenty-four participants were randomly allocated to either an experimental group (EG; n = 12, age: 20.05 ± 4.43 yrs., height: 166.54 ± 4.46 cm, weight: 64.65 ± 6.44 kg) or a control group (CG; n = 12, age: 20.04 ± 4.88 yrs., height: 166.83 ± 7.30 cm, weight: 69.83 ± 12.84 kg). Participants were tested before and after a 12-week intervention for jump-related biomechanical variables (leg stiffness, Reactive Strength Index (RSI), and landing mechanics using the Landing Error Scoring System (LESS)). A significant increase in RSI was found in EG (p = 0.012, r = 0.70, large effect). At post-testing, players in EG had significantly greater RSI scores compared to CG at post-intervention (p = 0.007, r = 0.55, large effect). LESS scores of CG were significantly greater compared to EG at pre-intervention (p = 0.008, r = 0.55, large effect) and post-intervention (p = 0.003, r = 0.60, large effect). Results of this study demonstrate a positive effect of the KneeRugbyWomen training program on RSI, which has been previously associated with increased ACL injury risk in female players. [ABSTRACT FROM AUTHOR]

Harry, JR, Krzyszkowski, J, Harris, K, Chowning, L, Mackey, E, Bishop, C, and Barker, LA. Momentum-based load prescriptions: Applications to jump squat training. J Strength Cond Res 36(9): 2657–2662, 2022—Velocity-based training is often applied to ballistic exercises, like the barbell jump squat, to improve vertical jump performance. However, determining the ideal training load based on velocity data remains difficult because load prescriptions tend to be limited to subjective velocity loss thresholds, velocity ranges, or both. Using data from jump squats performed with 0, 15, 30, 45, and 60% of the 1-repetition maximum squat, we explored subjective and objective methods to determine the ideal training load. Specifically, we explored takeoff velocity and a related metric only recently discussed in the literature, system momentum (i.e., takeoff velocity multiplied by the mass of the athlete-load system). At the group level, an ideal training load could not be revealed objectively using takeoff velocity. With individual subjects, the process remained challenging using takeoff velocity. Conversely, an ideal training load could be revealed easily and objectively using system momentum at the group average and individual subject levels. System momentum at takeoff is well-suited to assist practitioners seeking to identify appropriate training loads for jump squat training and potentially other ballistic exercises. We suggest a pivot from velocity to system momentum when seeking to objectively establish training loads for the jump squat and related exercises. [ABSTRACT FROM AUTHOR]

The purpose of this study was to investigate associations between, and within, drop jump (DJ) neuromuscular performance (NMP) qualities and maximal horizontal deceleration ability. We also compared DJ NMP qualities in "high" versus "low" horizontal deceleration ability athletes. Twenty-nine university athletes performed: (1) DJs on force plates from 20 (DJ20) and 40 cm (DJ40) heights and (2) maximal horizontal deceleration, measured using radar, following a 20 m acceleration. Maximal horizontal deceleration was evaluated using deceleration (HDEC; m·s−2), across the entire deceleration phase and during early and late deceleration sub-phases. Of the DJ variables assessed, DJ20 and DJ40 reactive strength index (RSI) and concentric mean force had the largest correlations with HDEC (r = −0.54 to −0.61) and the largest differences between high and low HDEC groups (d = 1.20 to 1.40). These correlations were stronger with the early than late HDEC sub-phase (r = −0.54 to −0.66 vs. r = −0.24 to −0.40). Notably, eccentric mean force in DJ40 had large correlations with both DJ20 and DJ40 concentric mean force (r = 0.67 to 0.77), whereas at DJ20 these correlations were small (r = 0.22 to 0.40). Similarly, DJ40 eccentric mean force had a much larger difference between the high and low HDEC groups than DJ20 (d = 1.11 vs. 0.51). These findings suggest DJ RSI from either height may be used as a proxy for HDEC ability, while DJ kinetic analyses should use a higher height to distinguish those with a better capacity to generate eccentric braking forces under increased eccentric loading demands. Players with greater drop jump reactive strength index (RSI) demonstrated superior horizontal deceleration ability. Drop jump RSI had a greater association with the early compared to the late horizontal deceleration sub-phase. Of the drop jump kinetic variables examined, concentric mean force had the largest associations with horizontal deceleration ability. [ABSTRACT FROM AUTHOR]

Purpose: To analyze the reliability and validity of a simple computation method to evaluate force (F), velocity (v), and power (P) output during a countermovement jump (CMJ) suitable for use in field conditions and to verify the validity of this computation method to compute the CMJ force-velocity (F-v) profile (including unloaded and loaded jumps) in trained athletes. Methods: Sixteen high-level male sprinters and jumpers performed maximal CMJs under 6 different load conditions (0-87 kg). A force plate sampling at 1000 Hz was used to record vertical ground-reaction force and derive vertical-displacement data during CMJ trials. For each condition, mean F, v, and P of the push-off phase were determined from both force-plate data (reference method) and simple computation measures based on body mass, jump height (from flight time), and push-off distance and used to establish the linear F-v relationship for each individual. Results: Mean absolute bias values were 0.9% (± 1.6%), 4.7% (± 6.2%), 3.7% (± 4.8%), and 5% (± 6.8%) for F, v, P, and slope of the F-v relationship (SFv), respectively. Both methods showed high correlations for F-v-profile-related variables (r = .985-.991). Finally, all variables computed from the simple method showed high reliability, with ICC >.980 and CV <1.0%. Conclusions: These results suggest that the simple method presented here is valid and reliable for computing CMJ force, velocity, power, and F-v profiles in athletes and could be used in practice under field conditions when body mass, push-off distance, and jump height are known. [ABSTRACT FROM AUTHOR]

Aim: (i) to compare the effects of two different low-volume resistance priming sessions, where the external load is modified on neuromuscular performance after 6 h of rest; and (ii) to identify the effects on psychological readiness in participants with resistance training experience. Methods: Eleven participants (Body mass: 77.0 ± 8.9 kg; Body height: 1.76 ± 0.08 m; Half squat repetition maximum: 139.8 ± 22.4 kg) performed the priming session under three experimental conditions in a randomized and cross-over design during the morning. The control (CON) condition: no resistance training, "optimal load" (OL) condition: two half-squat sets with a velocity loss of around 20% were performed with the "optimal load", and 80% of repetition maximum (80% RM) condition: 2 half-squat sets with a velocity loss of around 20% were performed with the 80% RM. Countermovement jump (CMJ), mean power with OL (MPOL) and 80% RM (MP80RM), and mean velocity with OL (MVOL) and 80% RM (MV80RM) were assessed six hours after the intervention. Subjective readiness was also recorded prior to resistance training and evaluation. Significance was set at p < 0.05. Results: CMJ was higher after the 80% RM intervention than CON (p < 0.001; Δ = 6.5% [3.4–9.5]). MPOL and MVOL seemed to be unaffected by both morning sessions. Higher MP80RM (p = 0.044; Δ = 9.7% [4.0–15.6]; d = 0.24[0.10–0.37]) and MV80RM (p = 0.004; Δ = 8.1% [3.2–13.3]; d = 0.32[0.13–0.52]) after 80% RM than after CON were observed. No effect was observed on psychological readiness. Conclusions: 80% RM priming session increased CMJ height and the capacity to generate power and velocity under a high-load condition without any effect on psychological readiness. [ABSTRACT FROM AUTHOR]

Explosive actions are integral to soccer performance and highly influenced by the ability to generate maximal power. The purpose of this study was to investigate the relationship between force-velocity profile, jump performance, acceleration and maximal sprint speed in elite female soccer players. Thirty-nine international female soccer players (24.3±4.7 years) performed 40-m sprints, maximal countermovement jumps and five loaded squat jumps at increasing loads to determine individual force-velocity profiles. Theoretical maximal velocity, theoretical maximal force, maximal power output, one repetition maximal back squat and one repetition maximal back squat relative to body mass were determined using the force-velocity profile. Counter movement jump, squat jump and maximal power output demonstrated moderate to large correlation with acceleration and maximal sprint speed (r=− 0.32 to −0.44 and −0.32 to −0.67 respectively, p<0.05). Theoretical maximal velocity and force, one repetition maximal and relative back squat demonstrated a trivial to small relationship to acceleration and maximal sprint speed (p>0.05). Vertical force-velocity profiling and maximal strength can provide valuable insight into the neuromuscular qualities of an athlete to individualize training, but the ability to produce force, maximal power, and further transference into sprint performance, must be central to program design. [ABSTRACT FROM AUTHOR]

Resisted sprinting (RS) is a popular training method used to enhance sprinting performance in youth. However, research has only explored the effects of forward RS (FRS) training. We examined the effects of FRS and backward RS (BRS) and compared these with a traditional physical education curriculum (CON). One hundred fifteen boys (age 13-15 years) were matched for maturity and allocated to either an FRS (n = 34), BRS (n = 46), or CON (n = 35) group. Training groups towed progressively overloaded sleds (20-55% body mass) 2 d⋅wk-1 for 8 weeks. Pre-training and post-training data were collected for sprinting times over 10 and 20 m, countermovement jump (CMJ) height, and leg stiffness (KN). Performance remained unchanged for the CON group (all p > 0.05), whereas all variables significantly improved (p < 0.05) after BRS, and all but 10-m performance improved after FRS. Compared with the CON, BRS and FRS significantly (p > 0.05) improved CMJ (Effect size [ES] = 0.67 and 0.38) and KN (ES = 0.94 and 0.69), respectively. No differences were found between training groups. The probabilities of improving sprinting performance after BRS (~70%) were on average ~10 and ~8% better than the FRS and CON groups, respectively. The BRS and FRS showed similar probabilities of improving CMJ (75 and 79%) and KN (80 and 81%), respectively, over the CON group. It seems that BRS may be a means to improve sprint performance, and regardless of direction, RS seems to be a beneficial method for improving jumping height and leg stiffness in youth male athletes. [ABSTRACT FROM AUTHOR]

Specific force capacities might be a limiting factor for alpine skiing performance, yet there is little consensus on the capabilities in question, and whether they differ between disciplines. We aimed to test discipline (speed and technical) and performance (event‐specific world standing) effects on lower limb force‐production qualities. National‐level skiers (N = 31) performed loaded squat jumps and isometric mid‐thigh pulls to detect dynamic force output at extremely low and high velocities and maximum isometric force and rate of force development, respectively. Discipline differences were assessed via a general linear model including performance and allowing for interaction effects, with performance associations further characterized via distinct Pearson's correlations. Jump height did not differentiate disciplines, with absolute power slightly higher in speed athletes (F(1,27) = 4.42, P =.045, ω2 = 0.10), and neither variables were related to performance. Speed athletes possessed greater dynamic force at low velocities (F0; F(1,27) = 13.8, P <.001, ω2 = 0.17), and greater relative and absolute maximum isometric force (F(1,25) = 11.19‐20.70, ω2 = 0.16‐0.22, P <.003). Overall, higher ranked athletes possessed more force‐dominant profiles (F(1,27) = 16.28, ω2 = 0.34; r = 0.60 to 0.67, P <.001) and increased rate of force development characteristics (average and maximum, r = −0.50 to −0.82, P <.048). Very robust associations existed between maximum isometric force and speed performance (r = −0.88, P <.001), but only a trend for higher absolute isometric force in technical athletes (r = −0.49, P =.052). Alpine skiers display a preponderance for dynamic force output at low velocities, and isometric force for speed athletes, which highlights the interest in specific assessment and conditioning practices for ski athletes. [ABSTRACT FROM AUTHOR]

Stiffness describes the resistance of a body to deformation. In regard to athletic performance, a stiffer leg-spring would be expected to augment performance by increasing utilisation of elastic energy. Two-dimensional spring-mass and torsional spring models can be applied to model whole-body (vertical and/or leg stiffness) and joint stiffness. Various tasks have been used to characterise stiffness, including hopping, gait, jumping, sledge ergometry and change of direction tasks. Appropriate levels of reliability have been reported in most tasks, although they vary between investigations. Vertical stiffness has demonstrated the strongest reliability across tasks and may be more sensitive to changes in high-velocity running performance than leg stiffness. Joint stiffness demonstrates the weakest reliability, with ankle stiffness more reliable than knee stiffness. Determination of stiffness has typically necessitated force plate analyses; however, validated field-based equations permit determination of whole-body stiffness without force plates. Vertical, leg and joint stiffness measures have all demonstrated relationships with performance measures. Greater stiffness is typically demonstrated with increasing intensity (i.e., running velocity or hopping frequency). Greater stiffness is observed in athletes regularly subjecting the limb to high ground reaction forces (i.e., sprinters). Careful consideration should be given to the most appropriate assessment of stiffness on a team/individual basis. [ABSTRACT FROM AUTHOR]

This study compared the effects of 2 sprint-specific training programs against the natural development of speed, power, and stiffness in a group of adolescent male athletes. Forty-three male adolescents (aged 13-15 years) were randomly assigned to 1 of 2 training groups; backward running training (BRT = 26), or forward running training (FRT = 17). A physical education class (n = 24) of similar age constituted a control (CON) group. Both training groups performed running sessions matched for distance and intensity biweekly for 8 weeks. Parametric and magnitude-based inferences were used to analyze within group (pre-post measures) and between group (gain scores) for 10-m, 10- to 20-m, and 20-m sprint times, vertical countermovement jump (CMJ) height, and vertical leg stiffness. Both running groups significantly improved (p ≤ 0.05) in all performance tests from pre-training to post-training, with effect sizes ranging from -1.25 to 0.63. When the groups were compared, the BRT and FRT groups improved significantly (p ≤ 0.01) on all sprint performances and stiffness relative to the CON group. The BRT group demonstrated favorable effects for 10-m and 20-m sprint performances (effect size [ES] = -0.47 and -0.26, respectively) and CMJ height (ES = 0.51) compared with the FRT group. These results demonstrate that forward and backward sprint-specific training programs enhance speed and power measures more than natural development in adolescent male athletes. Furthermore, the greater training responses in sprint performance and CMJ ability indicate that BRT is a useful tool for improving concentric strength and power and may be classified as a sprint-specific training method. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

This study investigated split-step timing when returning serves and whether this timing is related to neuromechanical capabilities in world-class tennis players. In Experiment 1, the split-step timing of four groups of world-class players (male and female ATP/WTA seniors, and ITF juniors) was measured on court when returning serves of the same level players. The four groups initiated the split-step at a similar time, starting around the time ball-racket contact in the serve stroke and landed when early ball-flight information was available. In Experiment 2, the neuromechanical capabilities (leg stiffness and vertical jump performance) of a group of world-class players and three groups of less-skilled tennis players were examined. The results showed an increase in leg stiffness with an increase in the level of expertise. A cross-experiment analysis in world-class male players (ATP/ITF, n = 10) revealed that the timing of initial foot movement was significantly correlated with the leg stiffness (r2 = 0.54), with later lateral step after the serve in the players who had higher stiffness. The findings support the hypothesis that world-class tennis players adapt perceptual-motor control on the basis of their neuromechanical capabilities and maximise the time before initiating their interceptive action to rely on more reliable information. [ABSTRACT FROM AUTHOR]

BACKGROUND: Cluster set plyometrics (CSP) promise greater muscular performance than traditional set plyometrics (TSP). OBJECTIVE: The purpose of this study was to compare the influence of TSP and CSP warm-ups via bounce drop jump (BDJ) on reactive strength index (RSI), leg stiffness (K leg), ground contact time (CT), and jump height (JH). METHODS: Thirteen male rugby players (age, 20.92 ± 2.25 years; body mass, 82.88 ± 9.22 kg; rugby experience, 3.61 ± 3.04 years; training volume, 10.69 ± 3.75 h/week) were recruited for this study from two rugby clubs competing in the Second League in Turkey. The players completed 3 different set configurations of equal jump volume 72 h apart in a randomized, balanced order. The sets configurations were TSP (2 × 10 jump with 90 s interval), CSP-1 (4 × 5 jump with 30 s interval), and CSP-2 (10 × 2 jump with 10 s interval). Pre and post values of RSI, K leg , CT, and JH on each session were determined via the Myotest Pro system. RESULTS: Statistically significant changes were not found between pre- and post-values of RSI, K leg , CT, and JH in each session, either positive or negative (p > 0.05), as well as among the three different set configurations in any of the outcome variables according to post-results (p > 0.05). These findings indicated that low-volume TSP and CSP bounce drop jump had no effect on RSI, K leg , CT, and JH in male rugby players. CONCLUSIONS: Set configurations, jump volume, and intensity applied in this study may be too low to change muscle-tendon complex (MTC) stiffness and produce a post-activation potentiation (PAP) effect. Further research, with larger samples, is needed to determine which set configurations, jump volume (> 20 jumps/session), and intensity (box height > 30 cm) are the best option for enhancement of RSI, K leg , CT, and JH. [ABSTRACT FROM AUTHOR]

The purpose of this study was to determine the braking and propulsive phase kinetic variables underpinning reactive strength in highly trained sprint athletes in comparison with a nonsprint-trained control group. Twelve highly trained sprint athletes and 12 nonsprint-trained participants performed drop jumps (DJs) from 0.25, 0.50, and 0.75 m onto a force plate. One familiarization session was followed by an experimental testing session within the same week. Reactive strength index (RSI), contact time, flight time, and leg stiffness were determined. Kinetic variables including force, power, and impulse were assessed within the braking and propulsive phases. Sprint-trained athletes demonstrated higher RSI vs. nonsprint-trained participants across all drop heights {3.02 vs. 2.02; ES (±90% confidence limit [CL]): 3.11 ± 0.86}. This difference was primarily attained by briefer contact times (0.16 vs. 0.22 seconds; effect size [ES]: -1.49 ± 0.53) with smaller differences observed for flight time (0.50 vs. 0.46 seconds; ES: 0.53 ± 0.58). Leg stiffness, braking and propulsive phase force, and power were higher in sprint-trained athletes. Very large differences were observed in mean braking force (51 vs. 38 N·kg; ES: 2.57 ± 0.73) which was closely associated with contact time (r ±90% CL: -0.93 ± 0.05). Sprint-trained athletes exhibited superior reactive strength than nonsprint-trained participants. This was due to the ability to strike the ground with a stiffer leg spring, an enhanced expression of braking force, and possibly an increased utilization of elastic structures. The DJ kinetic analysis provides additional insight into the determinants of reactive strength which may inform subsequent testing and training. [ABSTRACT FROM AUTHOR]

Stretching has long been used in many physical activities to increase range of motion (ROM) around a joint. Stretching also has other acute effects on the neuromuscular system. For instance, significant reductions in maximal voluntary strength, muscle power or evoked contractile properties have been recorded immediately after a single bout of static stretching, raising interest in other stretching modalities. Thus, the effects of dynamic stretching on subsequent muscular performance have been questioned. This review aimed to investigate performance and physiological alterations following dynamic stretching. There is a substantial amount of evidence pointing out the positive effects on ROM and subsequent performance (force, power, sprint and jump). The larger ROM would be mainly attributable to reduced stiffness of the muscle-tendon unit, while the improved muscular performance to temperature and potentiation-related mechanisms caused by the voluntary contraction associated with dynamic stretching. Therefore, if the goal of a warm-up is to increase joint ROM and to enhance muscle force and/or power, dynamic stretching seems to be a suitable alternative to static stretching. Nevertheless, numerous studies reporting no alteration or even performance impairment have highlighted possible mitigating factors (such as stretch duration, amplitude or velocity). Accordingly, ballistic stretching, a form of dynamic stretching with greater velocities, would be less beneficial than controlled dynamic stretching. Notwithstanding, the literature shows that inconsistent description of stretch procedures has been an important deterrent to reaching a clear consensus. In this review, we highlight the need for future studies reporting homogeneous, clearly described stretching protocols, and propose a clarified stretching terminology and methodology. [ABSTRACT FROM AUTHOR]

The purpose of this study was: (a) to develop a new sport-specific, repeated-sprint ability test involving 4 changes of direction, namely, the multiple repeated sprint ability (MRSAB) test for badminton players; (b) to determine its validity by comparing the results of 5 different skill levels; and (c) to assess the link between the new test and neuromuscular lower limb and physiological variables. For this purpose, 42 participants were separated into 5 groups to perform the MRSAB test at the same time of day, on 2 occasions, separated by at least 48 hours. The MRSAB test consisted of 2 repetitions of 4 movements (4 x 3 m) separated by 30 seconds of passive recovery. This pattern was repeated 10 times. The best time (BT), mean time (MT), and fatigue index (FI) were measured. Heart rate and blood lactate concentration were also recorded to determine the participants' physiological responses to the test. The results show that the MRSAB test is valid, because it differentiates between the 5 skill levels for BT, MT and FI and offers a reliable method (intraclass correlation coefficient = 0.95 for BT and MT) for testing badminton players, with no differences between the sessions (p > 0.05). Moreover, the link between MT and neuromuscular variables, such as jump height in squats and countermovements (r = -0.55 and -0.60, respectively) and with ...O2max (r = -0.92) reveals that this test uses a combination of the anaerobic and aerobic systems; thus, it can be used by trainers either to improve movement ability or increase these physical qualities. [ABSTRACT FROM AUTHOR]

Rowing races require developing high level of force and power output at high contraction velocity. This study determined the force-velocity and power-velocity (F-P-V) profiles of lower and upper limbs of adolescent rowers and their relationships with a 1,500-m rowing ergometer performance. The power developed during the 1,500-m (P1500) was evaluated in fourteen national-level male rowers (age: 15.3 ± 0.6 yrs). F-P-V profiles were assessed during bench pull (BP) and squat jump (SJ) exercises. The theoretical maximal values of force (F0), velocity (V0), power output (Pmax) and the F-V relationship slope (SFV) were determined. The body mass (BM) influence on these relationships was considered using an allometric approach. F0 was 720 ± 144 and 2146 ± 405 N, V0 was 1.8 ± 0.1 and 1.8 ± 0.3 m ⋅ s-1, Pmax was 333 ± 83 and 968 ± 204 W and SFV was - 391 ± 54 and - 1,200 ± 260 N ⋅ s ⋅ m-1 for BP and SJ, respectively. Upper and lower limb F0 and Pmax were significantly related. P1500 was significantly (P < 0.05) correlated to V0-BP, F0-BP, SFV-BP, Pmax-BP, F0-SJ and Pmax-SJ (r² = 0.29 to 0.79). BM accounted for more than 90 % of these relationships. Rowers' F-P-V profiles reflect adaptations to chronic rowing practice. F-P-V profiles and rowing performance correlations suggest that BP and SJ exercises are relevant to evaluate young rowers' explosive abilities. [ABSTRACT FROM AUTHOR]

The aim was to determine the position of the one-repetition maximum (1RM) squat point on the force-velocity (F-V) relationship obtained during squat jump (SJ). Ten healthy athletes performed a 1RM squat during which ground reaction force and lower-limb extension velocity were measured, and six loaded SJs to determine individual F-V relationship. The goodness of fit of the linear F-V relationship with or without the 1RM point was tested. The vertical and horizontal coordinates were determined relative to the theoretical maximal force (F0) and the highest loaded SJ (load of 44.5 ± 4.6 % 1RM). The goodness of fit of the individual F-V relationship did not differ with or without the 1RM condition, even if the 1RM point was slightly below the curve (- 5 ± 5 %, P = 0.018). The 1RM point can be considered as a point of the F-V relationship. The velocity (0.22 ± 0.05 m.s-1) of the 1RM point corresponded to ~30 % of the velocity reached during the highest loaded SJ. The force developed in the 1RM condition was ~16 % higher than during the highest loaded SJ and ~11 % lower than F0. This finding underlines the difference between F0 and the 1RM condition. [ABSTRACT FROM AUTHOR]

This study aimed to determine mountain ultra-marathon (MUM) performance factors in a large group of endurance mountain runners. Maximal aerobic speed (MAS) was assessed one week prior to the MUM. The level and graded (10 %) energy cost of running, stiffness, knee extensors force (KEf<), and jump height on a counter movement jump (CMJ) were measured in 24 male ultra runners before (pre) and immediately after (post) the Interlacs Trail (75 km and 3 930/3 700 m d + /d -). Performance time was correlated with MAS (r = - 0.74, p < 0.001), fraction of MAS (FMAS) sustained (r = - 0.89, p < 0.001), KEf (r = - 0.51, p < 0.05), and KEf loss (r = - 0.51, p < 0.05). A multiple regression analysis was performed using performance time in minutes (T) and the calculated individual characteristics, resulting in T = - 11.852 x FMAS - 37.195 x MAS - 0.118 x KEf + 2090.581 (R² = 0.98, with 95 % confidence interval). Contrary to expectations, performance was neither correlated to the level or uphill energy cost of running nor to the changes of these costs post-MUM. To perform in a MUM, training should take into account muscle strength of the KE, MAS and FMAS. [ABSTRACT FROM AUTHOR]

The aim of this study was to examine individual responses to different forms of resistance training on measures of jumping and sprinting performance in school-aged boys. Eighty boys were categorized into 2 maturity groups (pre- or post-peak height velocity [PHV]) and randomly assigned to a plyometric training, resistance training, combined training, or control group. Intervention groups participated in training twice weekly for 6 weeks, with measures of acceleration, maximal running velocity, squat jump height, and reactive strength index (RSI) collected preintervention and postintervention. In the pre-PHV cohort, plyometric training and combined training resulted in significantly more positive responders than the other 2 groups in both sprint variables (standardized residual values >1.96). In the post-PHV cohort, significantly more positive responders for acceleration and squat jump height resulted from traditional strength training and combined training groups, compared with other groups. Conversely, plyometric training and combined training resulted in a significantly greater number of positive responders than the other 2 groups for maximal velocity and RSI. Control participants rarely demonstrated meaningful changes in performance over the 6-week period. Irrespective of maturation, it would seem that combined training provides the greatest opportunity for most individuals to make short-term improvements in jump and sprint performance. Taking maturation into account, our data show that a plyometric training stimulus is important for individuals in the pre-PHV stage of development, whether as a standalone method or in combination with traditional strength training, when attempting to improve jumping and sprinting ability. However, individuals in the post-PHV stage require a more specific training stimulus depending on the performance variable that is being targeted for improvement. [ABSTRACT FROM AUTHOR]

The purpose of the present study was to investigate the explosive strength and endurance adaptations in young elite soccer players who underwent a supervised training program for a period of two years. Nineteen players, with seven years of training experience (age: 13.3 ± 0.1 years; body weight: 57.9 ± 4.9 kg; height: 168.9 ± 4.7 cm; BMI: 20.1 ± 1.1 kg/m2), voluntarily participated in the present study. The testing sessions were performed at the beginning of the preparation period in the first (T1), second (T2), and third year (T3). The following performance variables were measured: explosive strength [squat-jump (SJ) and counter-movement-jump (CMJ)], pre-stretch augmentation (CMJ-SJ), leg stiffness [hopping test (HT)], short sprint performance [15 m (SSP15) and 30 m (SSP30)], aerobic endurance [test of Leger (VO2max)], maximal heart rate [at the last step of Leger (HR)], and speed-strength endurance [continuous counter-movement-jumps (CCMJ)]. A significant main effect on the VO2Max (+5.72%; F(2.49) = 3.822; p = 0.029; ES = 1.00), HR (-1.70%; F(2.54) = 3.472; p = 0.038; ES = 0.97), CCMJ (+7.64%; F(2.54) = 5.438; p = 0.007; ES = 1.15), SJ (+10.26%; F(2.54) = 15.254; p = 0.0001; ES = 1.53), CMJ (+7.36; F(2.54) = 8.270; p = 0.001; ES = 1.33), HT (+8.34%; F(2.48) = 3.297; p = 0.046; ES = 1.01), SSP15 (-3.50%; F(2.44) = 12.760; p = 0.0001; ES = 1.53), and SSP30 (-4.44%; F(2.44) = 5.797; p = 0.006; ES = 1.16) was observed in the two soccer seasons. These results highlight that, in long-term training, the monitoring of the adaptive responses in relation to the training load may provide a guideline to optimize the trainability of some performance variables in young elite soccer players (13–15 years). In the present study, we cannot exclude the influence of growth and maturation on some performance variables; therefore, the monitored adaptive responses should be considered as the possible results of an interaction between the applied training load and maturation. [ABSTRACT FROM AUTHOR]

Balance training may have a preconditioning effect on subsequent power training with youth. There are no studies examining whether the sequencing of balance and plyometric training has additional training benefits. The objective was to examine the effect of sequencing balance and plyometric training on the performance of 1 2- to 13-year-old athletes. Twenty-four young elite soccer players trained twice per week for 8 weeks either with an initial 4 weeks of balance training followed by 4 weeks of plyometric training (BPT) or 4 weeks of plyometric training proceeded by 4 weeks of balance training (PBT). Testing was conducted pre- and posttraining and included medicine ball throw; horizontal and vertical jumps; reactive strength; leg stiffness; agility; 10-, 20-, and 30-m sprints; Standing Stork balance test; and Y-Balance test. Results indicated that BPT provided significantly greater improvements with reactive strength index, absolute and relative leg stiffness, triple hop test, and a trend for the Y-Balance test (p = 0.054) compared with PBT. Although all other measures had similar changes for both groups, the average relative improvement for the BPT was 22.4% (d = 1.5) vs. 15.0% (d = 1.1) for the PBT. BPT effect sizes were greater with 8 of 13 measures. In conclusion, although either sequence of BPT or PBT improved jumping, hopping, sprint acceleration, and Standing Stork and Y-Balance, BPT initiated greater training improvements in reactive strength index, absolute and relative leg stiffness, triple hop test, and the Y-Balance test. BPT may provide either similar or superior performance enhancements compared with PBT. [ABSTRACT FROM AUTHOR]

The present study explored the method of testing muscle mechanical properties through the linear force–velocity (F–V) relationships obtained from loaded vertical jumps. Specifically, we hypothesised that theF–Vrelationship parameters depicting the force, power, and velocity of the tested muscles will differ among individuals of different physical fitness. Strength trained, physically active, and sedentary male participants (N = 10 + 10 + 10; age 20–29 years) were tested on maximum countermovement and squat jumps where manipulation of external loads provided a range ofFandVdata. The observedF–Vrelationships of the tested leg muscles were approximately linear and mainly strong (median correlation coefficients ranged from 0.77 to 0.92; allp < 0.05), independently of either the tested group or the jump type. The maximum power revealed higher values in the strength trained than in the physically active and sedentary participants. This difference originated from the differences inF-intercepts, rather than from theV-intercepts. We conclude that the observed parameters could be sensitive enough to detect the differences among both the individuals of different physical fitness and various jump types. The present findings support using loaded vertical jumps and, possibly, other maximum performance multi-joint movements for the assessment of mechanical properties of active muscles. [ABSTRACT FROM AUTHOR]

The purpose of this study was to examine both short- and long-term neuromuscular and perceptual fatigue in youth rugby players during a seven-week in-season mesocycle. Eleven male youth rugby players (age 16.9 ± 0.8 years) were assessed for countermovement jump (CMJ), reactive strength index (RSI) and leg stiffness to monitor neuromuscular performance, together with a well-being questionnaire to monitor perceptual fatigue. Players trained and competed throughout a seven-week block with test variables measured at baseline and 24 h pre- and post-matches played in weeks 1, 4 and 7. Players trained on average 9.7 ± 1.1 h per week and competed in 10.5 ± 1.9 games over the seven-week block. Pre- to post-match reductions were significant across all games for CMJ, RSI and well-being (allP < 0.05), ranging from likely to almost certain negative reductions. Well-being and RSI demonstrated non-significant (P < 0.05) unclear or inconsistent changes when comparing pre-match scores to baseline. Significant reductions to baseline were observed pre-match for CMJ (weeks 4 and 7) and stiffness (week 7), representing very likely to almost certain negative long-term decrements. CMJ, RSI and well-being were all sensitive to detecting post-match fatigue. Importantly, CMJ and stiffness were sensitive to detecting accumulated fatigue over a seven-week period, whereas RSI and well-being were not. Consequently, either a CMJ or leg stiffness should be monitored to detect long-term, accumulated fatigue in academy rugby players. [ABSTRACT FROM PUBLISHER]

The purpose of this study was to quantify the inter-session reliability of force–velocity–power profiling and estimated maximal strength in youth. Thirty-six males (11–15 years old) performed a ballistic supine leg press test at five randomized loads (80%, 100%, 120%, 140%, and 160% body mass) on three separate occasions. Peak and mean force, power, velocity, and peak displacement were collected with a linear position transducer attached to the weight stack. Mean values at each load were used to calculate different regression lines and estimate maximal strength, force, velocity, and power. All variables were found reliable (change in the mean [CIM] = − 1 to 14%; coefficient of variation [CV] = 3–18%; intraclass correlation coefficient [ICC] = 0.74–0.99), but were likely to benefit from a familiarization, apart from the unreliable maximal force/velocity ratio (CIM = 0–3%; CV = 23–25%; ICC = 0.35–0.54) and load at maximal power (CIM = − 1 to 2%; CV = 10–13%; ICC = 0.26–0.61). Isoinertial force–velocity–power profiling and maximal strength in youth can be assessed after a familiarization session. Such profiling may provide valuable insight into neuromuscular capabilities during growth and maturation and may be used to monitor specific training adaptations. [ABSTRACT FROM PUBLISHER]

The article discusses research which investigated correlation between vertical and horizontal jump variables and muscular architecture in athletes. Topics explored include the use of jumping movements such as countermovement jump, squat jump, and drop jump in the evaluation of lower-limb strength, the recruitment and compliance of study participants to muscle power testing sessions, and the observed link between sprint performance and muscular strength.

This study determined the concurrent validity and reliability of force, velocity and power measurements provided by accelerometry, linear position transducer and Samozino’s methods, during loaded squat jumps. 17 subjects performed squat jumps on 2 separate occasions in 7 loading conditions (0–60% of the maximal concentric load). Force, velocity and power patterns were averaged over the push-off phase using accelerometry, linear position transducer and a method based on key positions measurements during squat jump, and compared to force plate measurements. Concurrent validity analyses indicated very good agreement with the reference method (CV=6.4– 14.5%). Force, velocity and power patterns comparison confirmed the agreement with slight differences for high-velocity movements. The validity of measurements was equivalent for all tested methods (r=0.87–0.98). Bland-Altman plots showed a lower agreement for velocity and power compared to force. Mean force, velocity and power were reliable for all methods (ICC=0.84–0.99), especially for Samozino’s method (CV=2.7–8.6%). Our findings showed that present methods are valid and reliable in different loading conditions and permit between-session comparisons and characterization of training-induced effects. While linear position transducer and accelerometer allow for examining the whole time-course of kinetic patterns, Samozino’s method benefits from a better reliability and ease of processing. [ABSTRACT FROM AUTHOR]

Double-leg repeated jumping tasks are commonly used as measures of lower limb stiffness in exercise science research. Within similar stiffness calculations, variation in data-reduction criteria exists. The impact of these varied data-reduction methods on stiffness measures is unknown. Sixteen adolescent female participants from varied physical activity backgrounds performed 15 self-paced, bent-knee continuous jumps (CJb) on two force plates. Leg stiffness was calculated as the ratio of the peak force and the centre of mass displacement for each contact. Using combinations of criteria based on previous literature, 83 data-reduction methods were applied to the raw data. Data reduction suitability was assessed based on intra-trial reliability, the number of participants excluded and the average contacts excluded. Four data-reduction methods were deemed suitable for use with adolescent female populations, with three consecutive contacts within 1 SD of the average jump frequency considered optimal. The average individual stiffness values were not greatly influenced by the data-reduction method; however, for a single participant, a stiffness change of up to 6 kN · m−1(30%) was observed. The role and potential impact of data-reduction methods used to evaluate measures of lower limb stiffness during repeated jumping tasks warrants consideration. [ABSTRACT FROM AUTHOR]

Purpose: To study the effect of a countermovement on the lower limb force-velocity ( F- v) mechanical profile and to experimentally test the influence of F- v mechanical profile on countermovement jump (CMJ) performance, independently from the effect of maximal power output ( P). Methods: Fifty-four high-level sprinters and jumpers performed vertical maximal CMJ and squat jump (SJ) against five to eight additional loads ranging from 17 to 87 kg. Vertical ground reaction force data were recorded (1,000 Hz) and used to compute center of mass vertical displacement. For each condition, mean force, velocity, and power output were determined over the entire push-off phase of the best trial, and used to determine individual linear F- v relationships and P. From a previously validated biomechanical model, the optimal F- v profile maximizing jumping performance was determined for each subject and used to compute the individual mechanical F- v imbalance ( Fv) as the difference between actual and optimal F- v profiles. Results: A multiple regression analysis clearly showed ( r = 0.952, P < 0.001, SEE 0.011 m) that P, Fv and lower limb extension range ( h) explained a significant part of the interindividual differences in CMJ performance ( P < 0.001) with positive regression coefficients for P and h and a negative one for Fv. Conclusion: Compared to SJ, F- v relationships were shifted to the right in CMJ, with higher P, maximal theoretical force and velocity (+35.8, 20.6 and 13.3 %, respectively). As in SJ, CMJ performance depends on Fv, independently from the effect of P, with the existence of an individual optimal F- v profile ( Fv having an even larger influence in CMJ). [ABSTRACT FROM AUTHOR]

This study sought to lend experimental support to the theoretical influence of force-velocity (F-v) mechanical profile on jumping performance independently from the effect of maximal power output (Pmax). 48 high-level athletes (soccer players, sprinters, rugby players) performed maximal squat jumps with additional loads from 0 to 100 % of body mass. During each jump, mean force, velocity and power output were obtained using a simple computation method based on flight time, and then used to determine individual linear F-v relationships and Pmax values. Actual and optimal F-v profiles were computed for each subject to quantify mechanical F-v imbalance. A multiple regression analysis showed, with a high-adjustment quality (r² = 0.931, P < 0.001, SEE = 0.015 m), significant contributions of P max , F-v imbalance and lower limb extension range (hpo) to explain interindividual differences in jumping performance (P < 0.001) with positive regression coefficients for Pmax and hpo and a negative one for F-v imbalance. This experimentally supports that ballistic performance depends, in addition to Pmax, on the F–v profile of lower limbs. This adds support to the actual existence of an individual optimal F-v profile that maximizes jumping performance, a F-v imbalance being associated to a lower performance. These results have potential strong applications in the field of strength and conditioning. [ABSTRACT FROM AUTHOR]

An athletic profile should encompass the physiological, biomechanical, anthropometric and performance measures pertinent to the athlete's sport and discipline. The measurement systems and procedures used to create these profiles are constantly evolving and becoming more precise and practical. This is a review of strength and ballistic assessment methodologies used in sport, a critique of current maximum strength [one-repetition maximum (1RM) and isometric strength] and ballistic performance (bench throw and jump capabilities) assessments for the purpose of informing practitioners and evolving current assessment methodologies. The reliability of the various maximum strength and ballistic assessment methodologies were reported in the form of intra-class correlation coefficients (ICC) and coefficient of variation (%CV). Mean percent differences $$ \left( {M_{\text{diff}} = \left[ {\frac{{{\mid }X_{{{\text{method}}1}} - X_{{{\text{method}}2}} {\mid }}}{{(X_{{{\text{method}}1}} + X_{{{\text{method}}2}} )}}} \right] \times 100} \right) $$ and effect size (ES = [ X − X] ÷ SD) calculations were used to assess the magnitude and spread of methodological differences for a given performance measure of the included studies. Studies were grouped and compared according to their respective performance measure and movement pattern. The various measurement systems (e.g. force plates, position transducers, accelerometers, jump mats, optical motion sensors and jump-and-reach apparatuses) and assessment procedures (i.e. warm-up strategies, loading schemes and rest periods) currently used to assess maximum isometric squat and mid-thigh pull strength (ICC > 0.95; CV < 2.0 %), 1RM bench press, back squat and clean strength (ICC > 0.91; CV < 4.3 %), and ballistic (vertical jump and bench throw) capabilities (ICC > 0.82; CV < 6.5 %) were deemed highly reliable. The measurement systems and assessment procedures employed to assess maximum isometric strength [ M = 2-71 %; effect size (ES) = 0.13-4.37], 1RM strength ( M = 1-58 %; ES = 0.01-5.43), vertical jump capabilities ( M = 2-57 %; ES = 0.02-4.67) and bench throw capabilities ( M = 7-27 %; ES = 0.49-2.77) varied greatly, producing trivial to very large effects on these respective measures. Recreational to highly trained athletes produced maximum isometric squat and mid-thigh pull forces of 1,000-4,000 N; and 1RM bench press, back squat and power clean values of 80-180 kg, 100-260 kg and 70-140 kg, respectively. Mean and peak power production across the various loads (body mass to 60 % 1RM) were between 300 and 1,500 W during the bench throw and between 1,500 and 9,000 W during the vertical jump. The large variations in maximum strength and power can be attributed to the wide range in physical characteristics between different sports and athletic disciplines, training and chronological age as well as the different measurement systems of the included studies. The reliability and validity outcomes suggest that a number of measurement systems and testing procedures can be implemented to accurately assess maximum strength and ballistic performance in recreational and elite athletes, alike. However, the reader needs to be cognisant of the inherent differences between measurement systems, as selection will inevitably affect the outcome measure. The strength and conditioning practitioner should also carefully consider the benefits and limitations of the different measurement systems, testing apparatuses, attachment sites, movement patterns (e.g. direction of movement, contraction type, depth), loading parameters (e.g. no load, single load, absolute load, relative load, incremental loading), warm-up strategies, inter-trial rest periods, dependent variables of interest (i.e. mean, peak and rate dependent variables) and data collection and processing techniques (i.e. sampling frequency, filtering and smoothing options). [ABSTRACT FROM AUTHOR]

The purpose of this study was to determine the influence of lumbar spine extension and erector spinae muscle activation on vertical jump height during maximal squat jumping. Eight male athletes performed maximal squat jumps. Electromyograms of the erector spinae were recorded during these jumps. A simulation model of the musculoskeletal system was used to simulate maximal squat jumping with and without spine extension. The effect on vertical jump height of changing erector spinae strength was also tested through the simulated jumps. Concerning the participant jumps, the kinematics indicated a spine extension and erector spinae activation. Concerning the simulated jumps, vertical jump height was about 5.4 cm lower during squat jump without trunk extension compared to squat jump.These results were explained by greater total muscle work during squat jump, more especially by the erector spinae work (+119.5 J). The erector spinae may contribute to spine extension during maximal squat jumping. The simulated jumps confirmed this hypothesis showing that vertical jumping was decreased if this muscle was not taken into consideration in the model. Therefore it is concluded that the erector spinae should be considered as a trunk extensor, which enables to enhance total muscle work and consequently vertical jump height. [ABSTRACT FROM PUBLISHER]

Research is presented which compared the effectiveness of plyometric only (PLYO) training with balance and plyometric (COMBINED) training on balance and power measures in children, noting the variables include static and dynamic balance, sprint running speed, shuttle run ability, and leg stiffness. The study found that COMBINED training can be a consideration in reducing high velocity impacts and stretch-shortening cycle stress on the neuromuscular system.

The aim of this study was to determine the potential of lower extremity muscle and has been made a comparison between the two types of vertical jumps with students of the first year of high school. The sample of examinees in this study were high school students and students of "9. May" in Nis. 37 students, aged 15 ± 6 months were divided into two groups according to gender. All subjects were divided into two subgroups: boys N = 14 and N = 23 girls. The variables of the jump to a halfsquat (CMJ) andjump from a squatting (SJ) are: the flying time (TF) sec, jump height (H) cm. On the basis of the realized research, it can be concluded the following: There was a statistically significant difference between the half squat vertical jump and a jump from a squat for the first grade girls. There »-as a statistically significant difference between the half squat vertical jump and a jump from a squat for the first grade boys. [ABSTRACT FROM AUTHOR]

With respect to cyclic movements such as human gait, running or hopping, leg stiffness is a little variable parameter. The aim of this study was to investigate changes in leg stiffness during the phase of countermovement and take-off when performing a single maximum counter-movement jump. Kistler force plates and a BTS SMART system for comprehensive motion analysis were employed in the study. The study covered a group of 12 athletes from university basketball teams. Leg stiffness was calculated in those parts of countermovement and take-off phases where its level is relatively constant and the relationship F(δl) is similar to linear one. Mean total stiffness (±SD) in both legs in the countermovement phase amounted to 6.5 ± 1.5 kN/m, whereas during the take-off phase this value was 6.9 ± 1 kN/m. No statistically significant differences were found between leg stiffness during the countermovement phase and takeoff phase in the study group at the level of significance set at ɑ = 0.05. This suggests that the leg stiffness in phase of countermovement and phase of take-off are much similar to each other, despite different function of both phases. Similar to cyclic movements, leg stiffness turned out relatively constant when performing a single vertical jump. There are also reported statistically significant correlations between body mass, body height, length of lower limbs and leg stiffness. The stiffness analysed by the authors should be understood as quasi-stiffness because the measurements of δF(δl) were made during transient states where inertia and dumping forces are likely to affect the final result. [ABSTRACT FROM AUTHOR]

The interest in whole-body vibration (WBV) for the enhancement of neuromuscular performance has received considerable attention. However, scientific evidence supporting the optimal prescription of WBV settings is lacking. This study investigated the acute eff ect of WBV combining high frequency/high peak-to-peak displacement (HH) or low frequency/low peakto- peak displacement (LL) vs. sham intervention (SHAM) on lower limb muscle power and stiffness. A total of 223 volunteers were randomly assigned to either the HH, LL or SHAM group. Countermovement jump (CMJ) height, maximal and average power, maximal and average lower limbs stiff ness obtained during a hopping test were recorded before and after the respective intervention. After the intervention, the HH group showed an increase of 4.64 % in CMJ height (p < 0.001) whereas the values of both the LL and SHAM groups did not change. In addition, maximal and average power of the lower limbs were signifi cantly increased in all groups (p < 0.001; 10.89 % and 12.82 %, respectively) while no eff ect on lower limbs stiff ness was observed. Our data show that high frequency combined with high peak-to-peak displacement is the most optimal WBV setting for CMJ height enhancement. Further investigation should be undertaken to ascertain the eff ectiveness of WBV on lower limbs stiff ness. [ABSTRACT FROM AUTHOR]

An adequate level of leg stiffness is necessary for an optimal tennis performance and leg stiffness should be adapted to frequently changing surfaces as tennis players usually play on different courts. The aim of this study was to evaluate leg stiffness in competitive tennis players on different court surfaces. Ten healthy competitive tennis players (nine men and one woman; mean age = 17.6 ± 3.2 years) underwent leg stiffness testing by modeling the vertical ground reaction force using an optical system. Flight time and contact time were determined during hopping on two different tennis court surfaces (clay and acrylic). No significant difference was found in the flight time, contact time, and jump height between the surfaces. No significant difference in leg stiffness was found between the surfaces (18.25 ± 5.8 and 19.27 ± 4.9 kN/m for clay and acrylic, respectively;p = 0.28). This study demonstrated that contact time and flight time as well as leg stiffness of tennis players remained unchanged when hopping on two different tennis surfaces. Results of this research provide objective data regarding the tennis-specific loading of the locomotor system and proper mechanical adaptation of the player on different surfaces, which may be useful for testing protocols and planning training programs. [ABSTRACT FROM PUBLISHER]

Previous authors have reported that chronic eccentric cycling facilitates greater changes in multi-joint leg function (hopping frequency, maximum jumping height) compared with concentric cycling. Our purpose was to evaluate changes in leg spring stiffness and maximum power following eccentric and concentric cycling training. Twelve individuals performed either eccentric ( n=6) or concentric ( n=6) cycling for 7 weeks (3 sessions/week) while training duration progressively increased. Participants performed trials of submaximal hopping, maximal counter movement jumps, and maximal concentric cycling to evaluate leg spring stiffness, maximum jumping power, and maximum concentric cycling power respectively, before and 1 week following training. Total work during training did not differ between eccentric and concentric cycling (126 ± 15-728 ± 91 kJ vs 125 ± 10-787 ± 76 kJ). Following training, eccentric cycling exhibited greater changes in kleg and jumping Pmax compared with CONcyc (10 ± 3% vs −2 ± 4% and 7 ± 2% vs −2 ± 3%, respectively, P=0.05). Alterations in CONcyc Pmax did not differ between ECCcyc (1035 ± 142 vs 1030 ± 133 W) and CONcyc (1072 ± 98 vs 1081 ± 85 W). These data demonstrate that eccentric cycling is an effective method for improving leg spring stiffness and maximum power during multi-joint tasks that include stretch-shortening cycles. Improvements in leg spring stiffness and maximum power would be beneficial for both aging and athletic populations. [ABSTRACT FROM AUTHOR]

The article discusses research on the influence of chronological age on stretch-shortening cycle (SSC) performance in pre- and post-pubescent boys. The study suggests that windows of accelerated adaptation exist for squat jumping and countermovement jump height in male youths. The reactive strength index and developmental trend for leg stiffness are noted.

Many activities necessitate a high degree of static joint range of motion (ROM) for an extended duration. The objective of this study was to examine whether ROM could be improved with a short duration and volume of static stretching within a warm-up, without negatively impacting performance. Ten male recreationally active participants completed 2 separate protocols to examine changes in ROM and performance, respectively, with different warm-ups. The warm-up conditions for the ROM protocol were static stretching (SS), consisting of 6 repetitions of 6 s stretches; 10 min of running prior to the SS (AS); and 5 min of running before and after the SS (ASA). The performance protocol included a control condition of 10 min of running. Measures for the ROM protocol included hip flexion ROM, passive leg extensor tension, and hamstring electromyographic (EMG) activity at pre-warm-up, and at 1, 10, 20, and 30 min post-warm-up. Performance measures included countermovement jump (CMJ) height, reaction time (RT), movement time (MT), and balance at pre-warm-up and at 1 and 10 min post-warm-up. The ASA produced greater ROM overall than the SS and AS conditions (p < 0.0001), persisting for 30 min. There were no significant alterations in passive muscle tension or EMG. For the performance protocol, there were no main effects for condition, but there was a main effect for time, with CMJ height being greater at 1 and 10 min post-warm-up (p = 0.0004). Balance ratios and MT improved at 10 min post-warm-up (p < 0.0001). Results indicate that the ASA method can provide ROM improvements for 30 min with either facilitation or no impairment in performance. This may be especially important for athletes who substitute later into a game with minimal time for a full warm-up. De nombreuses activités requièrent un haut niveau d'amplitude articulaire statique (ROM) d'une durée prolongée. Cette étude se propose de vérifier si on peut améliorer la ROM par l'inclusion de quelques exercices d'étirement statique de courte durée au cours de la séance d'échauffement, et ce, sans nuire à la performance. Dix participants masculins physiquement actifs dans leur loisir participent à 2 séances expérimentales constituées respectivement d'exercices d'échauffement différents afin d'en évaluer l'impact sur la ROM et la performance. Les exercices d'échauffement de la séance expérimentale portant sur la ROM consistent en des étirements statiques (SS), soit 2 efforts d'une durée de 6 s; ou une course d'une durée de 10 min avant les SS (AS); ou une course d'une durée de 5 min avant et après les SS (ASA). La séance expérimentale portant sur la performance comporte une course de contrôle d'une durée de 10 min. Les mesures prises avant l'échauffement puis 1 min, 10 min, 20 min et 30 min après l'échauffement pour l'évaluation de la ROM sont l'amplitude de flexion de la hanche, la tension passive des extenseurs de la jambe et l'activité myoélectrique (EMG) des muscles ischiojambiers. Les mesures de performance incluent la hauteur de saut précédé d'un contre-mouvement (CMJ), le temps de réaction (TR), le temps de mouvement (MT) et l'équilibre, et ce, avant l'échauffement puis 1 min et 10 min après l'échauffement. La condition ASA améliore plus la ROM que les conditions SS et AS (p < 0,0001); cet effet dure 30 min. On n'observe aucune différence significative de tension musculaire passive et d'activité myoélectrique. En ce qui concerne la séance expérimentale portant sur la performance, on n'observe pas d'effets principaux reliés à la condition en tant que telle, mais un effet dans le temps : la hauteur du CMJ est plus grande 1 min et 10 min après l'échauffement (p = 0,0004). Les ratios d'équilibre et le MT sont meilleurs 10 min après l'échauffement (p < 0,0001). D'après ces observations, la condition ASA peut susciter des améliorations de la ROM durant 30 min tout en améliorant la performance ou en ne lui nuisant pas. Ces observations sont pertinentes pour tout athlète s'intégrant plus tard dans le match et disposant de peu de temps pour un échauffement complet. [ABSTRACT FROM AUTHOR]

The aim of the study was to assess the reliability of a mobile contact mat in measuring a range of stretch-shortening cycle parameters in young adolescents. Additionally, vertical leg stiffness using contact mat data was validated against a criterion method using force-time data. The reliability study involved 18 youths completing a habituation and three separate test sessions, while 20 youths completed a single test session for the validity study. Participants completed three trials of a squat jump, countermovement jump, and maximal hopping test and a single trial of repeated sub-maximal hopping at 2.0 Hz and 2.5 Hz. All tests were performed on the contact mat. Reliability statistics included repeated-measures analysis of variance, intraclass correlation coefficient, and coefficient of variation (CV), while the correlation coefficient (r) and typical error of estimate (TEE) were reported for the validity study. Squat jump height was the most reliable measure (CV = 8.64%), while leg stiffness during sub-maximal hopping, and reactive strength index produced moderate reliability (CV = 10.17-13.93% and 13.98% respectively). Measures of leg stiffness obtained from contact mat data during sub-maximal hopping were in agreement with the criterion measure (r = 0.92-0.95; TEE = 6.5-7.5%), but not during maximal hopping (r = 0.59; TEE = 41.9%). The contact mat was deemed a valid tool for measuring stretch-shortening cycle ability in sub-maximal but not maximal hopping. Although reliability of performance was generally moderate, the tests offer a replicable assessment method for use with paediatric populations. [ABSTRACT FROM AUTHOR]

Mechanical stiffness (vertical, leg and joint stiffness) can be calculated during normal human movements, such as running and hopping. Mechanical stiffness is thought to influence several athletic variables, including rate of force development, elastic energy storage and utilization and sprint kinematics. Consequently, the relationship between mechanical stiffness and athletic performance is of great interest to the sport and research communities. Unfortunately, these relationships are relatively unexplored by researchers. For example, there are no longitudinal studies that have investigated the effects of strength or power training on mechanical stiffness levels (calculated during human running). In addition to reviewing the available literature on the relationships between mechanical stiffness (calculated during human running) and functional performance, this review focuses its discussion on the various equipment and methods used to calculate leg-spring stiffness during human running. Furthermore, future implications are presented for practitioners and researchers based on both the limitations and the gaps in the literature reviewed. It is our hope that a better understanding of mechanical stiffness will aid in improving the methodological quality of research in this area and its subsequent effect on athletic performance. [ABSTRACT FROM AUTHOR]

We tested the hypothesis that the performance of rapid movements represents body size-independent indices of muscle power. Physical education students (n = 159) were tested on various vertical jump (jump height and average power calculated from the ground reaction force) and muscle strength tests. When non-normalized data were used, a principal components analysis revealed a complex and inconsistent structure where jump height and muscle power loaded different components, while muscle strength and power partially overlapped. When the indices of muscle strength and power were properly normalized for body size, a simple and consistent structure of principal components supported the hypothesis. Specifically, the recorded height and muscle power calculated from the same jumps loaded the same components, separately for the jumps predominantly based on concentric actions and jumps based on a rapid stretch - shortening cycle of the leg extensors. The finding that the performance of rapid movements assesses the same physical ability as properly normalized tests of muscle power could be important for designing and interpreting the results of batteries of physical performance tests, as well as for understanding some basic principles of human movement performance. [ABSTRACT FROM AUTHOR]