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The application of force is a key aspect of performance during athletic activities. In jumping, the timing and magnitude of force application are important performance factors. The relative timing of forces has only been investigated in the countermovement jump. This study aimed to explore if the synchronization of peak concentric force with the instance of zero velocity during a drop jump impacted performance and examine the relationship of force–time curve shape to performance. Sixty‐six state‐level athletes (24 males and 42 females) completed drop jumps from a 30 cm box onto dual force plates. The jump with the highest reactive strength index (RSI) score was taken for analysis and classified as synchronous or asynchronous based on the relative timing of peak concentric force and zero velocity. RSI and other force–time variables were compared between groups, and functional principal component analysis (fPCA) was performed on the force–time curves, which were used to perform functional principal component regression (fPCR). Synchronous jumpers exhibited greater RSI scores and shorter contact times compared to asynchronous jumpers. Performance differences were largely driven by improved concentric kinetics, which the fPCR model revealed to have the greatest influence on RSI. Sex was also found to be a significant factor for RSI in the fPCR model. fPCA revealed that greater force application preceding and throughout the amortization phase was positively associated with RSI. The timing of peak concentric force and the shape of the force–time curve are key factors for drop jump performance, and these concepts should be investigated further in other athletic activities. [ABSTRACT FROM AUTHOR]

The aim of this scoping review was a) to update a previous review on the main methodological characteristics and shortcomings in the plyometric jump training (PJT) literature, and b) to recommend, in light of the identified methodological gaps, future research perspectives. We searched four electronic databases. From 6128 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 randomized 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 (eg, randomized 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 needs to be identified, particularly in the long term. [ABSTRACT FROM AUTHOR]

Objective: To determine the effect of lower body plyometric training (PLY) on jumping, sprint performance, and lower body muscle strength in healthy adults. Methods: A systematic literature search (PubMed, Embase) was performed. Studies were included if they (a) described a lower body PLY intervention lasting ≥4 weeks; (b) included measures of jumping, sprint, and/or lower body muscle strength; (c) included healthy individuals ≥18 years; (d) included a training or non‐training control group; and (e) were written in English. Meta‐analyses identifying the effects of PLY on jumping, sprint, and lower body muscle strength were conducted providing the standardized mean difference (SMD). Results: A total of 826 records were identified of which 25 fulfilled the inclusion criteria, yielding 19, 11, and seven data points for the meta‐analyses of jumping, sprint performance, and lower body muscle strength, respectively. The data showed improvements for all three performance variables after 4‐12 weeks of PLY. The SMD (CI95%) across studies for jump height, sprint time, and muscle strength were 0.45 (0.16: 0.75), −0.59 (−1.01: −0.17), and 0.33 (0.03: 0.63), respectively, where the latter two showed within‐sample heterogeneity. Conclusion: The systematic review and meta‐analyses showed that PLY elicits a small‐to‐moderate positive effect on jumping, sprint performance, and lower body muscle strength in healthy adults being recreationally active or athletes. [ABSTRACT FROM AUTHOR]

The aims of this study were to compare both eccentric‐ and concentric‐phase adaptations in highly trained handball players to 4 weeks of twice‐weekly rebound bench press throw training with varying loads (30%, 50% and 70% of one‐repetition maximum [1‐RM]) using either known (KL) or unknown (UL) loads and to examine the relationship between changes in eccentric‐ and concentric‐phase performance. Twenty‐eight junior team handball players were divided into two experimental groups (KL or UL) and a control group. KL subjects were told the load prior each repetition, while UL were blinded. For each repetition, the load was dropped and then a rebound bench press at maximum velocity was immediately performed. Both concentric and eccentric velocity as well as eccentric kinetic energy and musculo‐articular stiffness prior to the eccentric‐concentric transition were measured. Results showed similar increases in both eccentric velocity and kinetic energy under the 30% 1‐RM but greater improvements under 50% and 70% 1‐RM loads for UL than KL. UL increased stiffness under all loads (with greater magnitude of changes). KL improved concentric velocity only under the 30% 1‐RM load while UL also improved under 50% and 70% 1‐RM loads. Improvements in concentric movement velocity were moderately explained by changes in eccentric velocity (R2=.23‐.62). Thus, UL led to greater improvements in concentric velocity, and the improvement is potentially explained by increases in the speed (as well as stiffness and kinetic energy) of the eccentric phase. Unknown load training appears to have significant practical use for the improvement of multijoint stretch‐shortening cycle movements. [ABSTRACT FROM AUTHOR]

Stretching can decrease a muscle's maximal force, whereas short but intense muscle contractions can increase it. We hypothesized that when combined, postactivation potentiation induced by reactive jumps would counteract stretch-induced decrements in drop jump ( DJ) performance. Moreover, we measured changes in muscle twitch forces and ankle joint stiffness ( KAnkle) to examine underlying mechanisms. Twenty subjects completed three DJs and 10 electrically evoked muscle twitches of the triceps surae subsequent to four different conditioning activities and control. The conditioning activities were 10 hops, 20s of static stretching of the triceps surae muscle, 20s of stretching followed by 10 hops, and vice versa. After 10 hops, twitch peak torque ( TPT) was 20% and jump height 5% higher compared with control with no differences in KAnkle. After stretching, TPT and jump height were both 9% and KAnkle 6% lower. When hops and stretching were combined as conditioning activities, jump height was not different compared with control but significantly higher (11% and 8%) compared with stretching. TPTs were 16% higher compared with control when the hops were performed after stretching and 9% higher compared with the reverse order. KAnkle was significantly lower when stretching was performed after the hops (6%) compared with control, but no significant difference was observed when hops were performed after stretching. These results demonstrate that conditioning hops can counteract stretch-related declines in DJ performance. Furthermore, the differences in TPTs and KAnkle between combined conditioning protocols indicate that the order of conditioning tasks might play an important role at the muscle-tendon level. [ABSTRACT FROM AUTHOR]

The purpose of this study was to examine whether drop height-induced changes in leg muscle activity during drop jumps ( DJ) are additionally modulated by surface condition. Twenty-four healthy participants (23.7 ± 1.8 years) performed DJs on a force plate on stable, unstable, and highly unstable surfaces using different drop heights (i.e., 20 cm, 40 cm, 60 cm). Electromyographic ( EMG) activity of soleus ( SOL), gastrocnemius ( GM), tibialis anterior ( TA) muscles and coactivation of TA/ SOL and TA/ GM were analyzed for time intervals 100 ms prior to ground contact (preactivation) and 30-60 ms after ground contact [short latency response ( SLR)]. Increasing drop heights resulted in progressively increased SOL and GM activity during preactivation and SLR ( P < 0.01; 1.01 ≤ d ≤ 5.34) while TA/ SOL coactivation decreased ( P < 0.05; 0.51 ≤ d ≤ 3.01). Increasing surface instability produced decreased activities during preactivation ( GM) and SLR ( GM, SOL) ( P < 0.05; 1.36 ≤ d ≤ 4.30). Coactivation increased during SLR ( P < 0.05; 1.50 ≤ d ≤ 2.58). A significant drop height × surface interaction was observed for SOL during SLR. Lower SOL activity was found on unstable compared to stable surfaces for drop heights ≥40 cm ( P < 0.05; 1.25 ≤ d ≤ 2.12). Findings revealed that instability-related changes in activity of selected leg muscles are minimally affected by drop height. [ABSTRACT FROM AUTHOR]

It has previously been shown that fatigue and unstable surfaces affect jump performance. However, the combination thereof is unresolved. Thus, the purpose of this study was to examine the effects of fatigue and surface instability on jump performance and leg muscle activity. Twenty elite volleyball players (18 ± 2 years) performed repetitive vertical double-leg box jumps until failure. Before and after a fatigue protocol, jump performance (i.e., jump height) and electromyographic activity of selected lower limb muscles were recorded during drop jumps ( DJs) and countermovement jumps ( CMJs) on a force plate on stable and unstable surfaces (i.e., balance pad on top of force plate). Jump performance (3-7%; P < 0.05; 1.14 ≤ d ≤ 2.82), and muscle activity (2-27%; P < 0.05; 0.59 ≤ d ≤ 3.13) were lower following fatigue during DJs and CMJs, and on unstable compared with stable surfaces during DJs only (jump performance: 8%; P < 0.01; d = 1.90; muscle activity: 9-25%; P < 0.05; 1.08 ≤ d ≤ 2.54). No statistically significant interactions of fatigue by surface condition were observed. Our findings revealed that fatigue impairs neuromuscular performance during DJs and CMJs in elite volleyball players, whereas surface instability affects neuromuscular DJ performance only. Absent fatigue × surface interactions indicate that fatigue-induced changes in jump performance are similar on stable and unstable surfaces in jump-trained athletes. [ABSTRACT FROM AUTHOR]

The Achilles tendon moment arm ( MA_ AT) and foot lever ratio ( FLR) can play important roles for force production and movement economy during locomotion. This notion has become more relevant, and suggestion has been given that the Kenyan runners belonging to the world elite would have specific anatomical, mechanical, and functional properties in their lower limbs and that this feature could be responsible for their high running economy. The present study aimed to characterize the AT of elite Kenyan distance runners as compared with Japanese ones, and to examine the potential relationship with their running performance. Ultrasonography was used to measure AT cross-sectional area and AT soleus and gastrocnemius lengths. MA_ AT and FLR were calculated from the position of anatomical landmarks using sagittal plane photographs. MA_ AT was significantly longer and the FLR lower in Kenyans than in Japanese. Independently of the group, the running performance was positively related to the MA_ AT ( r = 0.55, P < 0.001) and negatively to the FLR ( r = −0.45, P = 0.002). These results suggest that longer MA_ AT and lower FLR could be advantageous in elite Kenyan runners, by contributing to effective endurance running performance in a protective and economical way. [ABSTRACT FROM AUTHOR]

This study explored the age-related deterioration in stretch-shortening cycle ( SSC) muscle power and concurrent force-velocity properties in women and men across the adult life span. A total of 315 participants (women: n = 188; men: n = 127) aged 18-81 years performed maximal countermovement jumps on an instrumented force plate. Maximal SSC leg extension power expressed per kg body mass ( Ppeak) was greater in men than in women across the adult age span ( P < 0.001); however, this gender difference was progressively reduced with increasing age, because men showed an ∼50% faster rate of decline in SSC power than women ( P < 0.001). Velocity at peak power ( VPpeak) was greater in men than in women ( P < 0.001) but declined at a greater rate in men than in women ( P = 0.002). Vertical ground reaction force at peak power ( FPpeak) was higher in men than in women in younger adults only ( P < 0.001) and the age-related decline was steeper in men than in women ( P < 0.001). Men demonstrated a steeper rate of decline in Ppeak than women with progressive aging. This novel finding emerged as a result of greater age-related losses in men for both force and velocity. Consequently, maximal SSC power production was observed to converge between genders when approaching old age. [ABSTRACT FROM AUTHOR]

The effect of whole body vibration ( WBV) on reflex responses is controversially discussed in the literature. In this study, three different modalities of reflex activation with increased motor complexity have been selected to clarify the effects of acute WBV on reflex activation: (1) the electrically evoked H-reflex, (2) the mechanically elicited stretch reflex, and (3) the short-latency response ( SLR) during hopping. WBV-induced changes of the H-reflex, the stretch reflex, and the SLR during hopping were recorded in the soleus and gastrocnemius muscles and were analyzed before, during (only the H-reflex), immediately after, 5 min and 10 min after WBV. The main findings were that (1) the H-reflexes were significantly reduced during and at least up to 5 min after WBV, (2) the stretch reflex amplitudes were also significantly reduced immediately after WBV but recovered to their initial amplitudes within 5 min, and (3) the SLR during hopping showed no vibration-induced modulation. With regard to the modalities with low motor complexities, the decreased H- and stretch reflex responses are assumed to point toward a reduced Ia afferent transmission during and after WBV. However, it is assumed that during hopping, the suppression of reflex sensitivity is compensated by facilitatory mechanisms in this complex motor task. [ABSTRACT FROM AUTHOR]

The present study investigated the regulation of leg and joint stiffness in hopping at different intensity levels. Eight male subjects performed bilateral hopping at various intensity levels that were determined by peak vertical ground reaction force (GRF). In addition to the GRF, the measurements included hopping kinematics and electromyography (EMG) of selected leg muscles. While the leg and ankle joint stiffness remained invariant, the knee joint stiffness increased significantly ( P<0.01) with the hopping intensity. EMG analysis revealed a significant increase in averaged EMG for all the measured muscles before and during the early phase of ground contact ( P<0.05-0.001) with increasing hopping intensity. However, only the vastus lateralis muscle showed significant increase in stretch reflex EMG with increasing hopping intensity ( P<0.01). The present study indicates that in hopping with short contact time the leg stiffness modulation is sensitive to changes in ankle joint stiffness and the role of knee joint stiffness is to regulate the jumping performance (height). Furthermore, our results suggest that leg and joint stiffness in hopping is mainly adjusted by centrally programmed motor commands and the contribution of stretch reflexes to muscle force output is muscle-dependent. [ABSTRACT FROM AUTHOR]

Exercise-induced muscle damage (EIMD) is known to decrease muscle strength and power but its effect on endurance performance is unclear. Thirty moderately trained adult runners (24 men and six women) were randomly assigned to EIMD or control. The EIMD group jumped 100 times from a 35 cm bench, while controls did not perform any muscle-damaging exercise. Before and 48 h after treatment, subjects were tested on markers of EIMD, steady-state cardiorespiratory, metabolic and perceptual responses during a constant speed submaximal run; distance ran in 30 min on a treadmill. There were significant changes in muscle soreness, creatine kinase, and knee extensors strength ( P<0.01). This EIMD significantly reduced self-paced time trial performance by 4% ( P<0.01) because subjects reduced running speed ( P=0.02), with no change in perceived exertion ( P=0.31). No significant alterations in running economy and other physiological responses to submaximal running were found. However, there was a trend ( P=0.08) for increased perceived exertion, which was correlated with decreased time trial performance ( P<0.01). In conclusion, EIMD has a significant impact on endurance running performance in humans, and this effect seems to be mediated by alterations in the sense of effort. [ABSTRACT FROM AUTHOR]