Stretch-shortening Cycle Research Articles

Characteristics of the stretch-shortening cycle movement ability of male field hockey players

Characteristics of the stretch-shortening cycle movement ability of male field hockey players

Medial Gastrocnemius Muscle Architecture Is Altered After Exhaustive Stretch-Shortening Cycle Exercise.

Muscle architecture is an important component of muscle function, and recent studies have shown changes in muscle architecture with fatigue. The stretch-shortening cycle is a natural way to study human locomotion, but little is known about how muscle architecture is affected by this type of exercise. This study investigated potential changes in medial gastrocnemius (MG) muscle architecture after exhaustive stretch-shortening cycle exercise. Male athletes (n = 10) performed maximal voluntary contractions (MVC) and maximal drop jump (DJ) tests before and after an exercise task consisting of 100 maximal DJs followed by successive rebound jumping to 70% of the initial maximal height. The exercise task ceased upon failure to jump to 50% of maximal height or volitional fatigue. Muscle architecture of MG was measured using ultrasonography at rest and during MVC, and performance variables were calculated via a force plate and motion analysis. After SSC exercise, MVC (−13.1%; p = 0.005; dz = 1.30), rebound jump height (−14.8%, p = 0.004; dz = 1.32), and ankle joint stiffness (−26.3%; p = 0.008; dz = 1.30) decreased. Ankle joint range of motion (+20.2%; p = 0.011; dz = 1.09) and MG muscle-tendon unit length (+12.0%; p = 0.037; dz = 0.91) during the braking phase of DJ, the immediate drop-off in impact force (termed peak force reduction) (Δ27.3%; p = 0.033; dz = 0.86), and lactate (+9.5 mmol/L; p < 0.001; dz = 3.58) increased. Fascicle length increased at rest (+4.9%; p = 0.013; dz = 1.16) and during MVC (+6.8%; p = 0.048; dz = 0.85). Pennation angle decreased at rest (−6.5%; p = 0.034, dz = 0.93) and during MVC (−9.8%; p = 0.012; dz = 1.35). No changes in muscle thickness were found at rest (−2.6%; p = 0.066; dz = 0.77) or during MVC (−1.6%; p = 0.204; dz = 0.49). The greater MG muscle-tendon stretch during the DJ braking phase after exercise indicates that muscle damage likely occurred. The lower peak force reduction and ankle joint stiffness, indicative of decreased active stiffness, suggests activation was likely reduced, causing fascicles to shorten less during MVC.

Pre-activation affects the effect of stretch-shortening cycle by modulating fascicle behavior.

ABSTRACTThe torque attained during active shortening is enhanced after an active stretch (stretch-shortening cycle, SSC). This study examined the influence of pre-activation on fascicle behavior and the SSC effect. Subjects exhibited the following three conditions by electrically induced plantar flexions. In the isometric-concentric (ISO-CON) condition, subjects exhibited active shortening from dorsiflexion of 15° to 0° after isometric pre-activation. In the eccentric-concentric (ECC-CON) condition, subjects exhibited the above active shortening immediately after the eccentric pre-activation. In the isometric-eccentric-concentric (ISO-ECC-CON) condition, isometric pre-activation was conducted before exhibiting the ECC-CON maneuver. Joint torque and fascicle length of the medial gastrocnemius were compared. The joint torque at the onset and end of shortening was larger in the ISO-ECC-CON than in the ISO-CON or ECC-CON conditions, while no differences were found between ISO-CON and ECC-CON conditions. The magnitude of fascicle elongation attained during the active stretch was larger in the ISO-ECC-CON than in the ECC-CON condition. This could be caused by the shorter fascicle length at the onset of active stretch due to isometric pre-activation. This shorter fascicle length could lead to larger fascicle elongation during the subsequent active stretch, which should emphasize the effect of active stretch-induced force enhancement mechanism.

Do Stretch-Shortening Cycles Really Occur in the Medial Gastrocnemius? A Detailed Bilateral Analysis of the Muscle-Tendon Interaction During Jumping.

The effect of stretch-shortening cycles (SSCs) is often studied in laboratory settings, yet it remains unclear whether highly active muscle SSCs actually occur during in vivo movement. Nine highly trained jumping athletes performed single-leg pre-hop forward jumps at maximal effort. We hypothesized that these jumps would induce a SSC at the level of the muscle in the medial gastrocnemius. Kinematic and kinetic data were collected together with electromyography signals (EMG) and muscle fascicle length and pennation angle changes of the medial gastrocnemius of both legs and combined with a musculoskeletal model to calculate the stretch-shortening behavior of the muscle (fascicles) and tendon (series-elastic element). The length changes of the fascicles, longitudinal muscle displacement, series-elastic element, and whole muscle-tendon unit further allowed for a detailed analysis of the architectural gearing ratio between different phases of the SSC within a single movement. We found a SSC at the level of the joint, muscle-tendon unit and tendon but not at the muscle. We further found that the average architectural gearing ratio was higher during the stretching of the series-elastic element as compared to when the series-elastic element was shortening, yet this was not statistically tested because of low sample size for this parameter. However, we found no correlation when plotting the architectural gearing ratio as a function of the fascicle velocities at each instance in time. Despite the athletes having a clear preferred leg for jumping, we found no differences in any kinematic or kinetic parameter between the preferred and non-preferred leg or any parameter from the muscle-tendon interaction analysis other than a reduced longitudinal muscle shortening in the non-preferred leg (p = 0.008). We conclude that, although common at the level of the joints, MTUs, and tendon (series-elastic element), highly active SSCs very rarely occur in the medial gastrocnemius, even in movements that induce high loading. This has important implications for the translation of ex vivo findings on SSC effects, such as residual force enhancement, in this muscle. We further conclude that there is no precise tuning of the architectural gearing ratio in the medial gastrocnemius throughout the whole movement.

Limits in reliability of leg-spring and joint stiffness measures during single-leg hopping within a sled-based system.

Research examining the reliability of stiffness measures during hopping has shown strong consistency in leg-spring stiffness (kleg), but high variability in joint stiffness (kjoint) measures. Sled-based systems (SBS) reduce movement degrees-of-freedom and are used to examine stretch-shortening cycle (SSC) function under controlled conditions. The aim of this study was to examine the reliability of kleg and kjoint during single-leg hopping within an SBSKinematic and kinetic data were collected on four occasions (Day_1, Day_2, Day_3 and Day_3Offset). Participants completed two trials of single-leg hopping at different frequencies (1.5, 2.2 and 3.0 Hz) while attached to an inclined-SBS. Stiffness was determined using models of leg-spring (kleg) and torsional (kjoint) stiffness. Statistical analysis identified absolute and relative measures of reliability. Results showed moderate reliability for kleg at 1.5 Hz between inter-day testing bouts, and weak consistency at 2.2 and 3.0 Hz. Examination of intra-day comparisons showed weak agreement for repeated measures of kleg at 1.5 and 2.2 Hz, but moderate agreement at 3.0 Hz. Limits in kleg reliability were accompanied by weak-to-moderate agreement in kjoint measures across inter- and intra-day testing bouts. Results showed limits in the reliability of stiffness measures relative to previous reports on overground hopping. Lack of consistency in kleg and kjoint may be due to the novelty of hopping within the current inclined-SBS. Constraints imposed on the hopping task resulting from SBS design (e.g. additional chair mass, restricting upper body movement) may have also influenced limits in kleg and kjoint reliability. Researchers should consider these findings when employing inclined-SBS of a similar design to examine SSC function.

Influence of muscle length on the stretch-shortening cycle in skinned rabbit soleus

Muscle force generated during shortening is instantaneously increased after active stretch. This phenomenon is called as stretch-shortening cycle (SSC) effect. It has been suggested that residual force enhancement contributes to the SSC effect. If so, the magnitude of SSC effect should be larger in the longer muscle length condition, because the residual force enhancement is prominent in the long muscle length condition. This hypothesis was examined by performing the SSC in the short and long muscle length conditions. Skinned fibers obtained from rabbit soleus (N = 20) were used in this study. To calculate the magnitude of SSC effect, the SSC trial (isometric-eccentric-concentric-isometric) and the control trial (isometric-concentric-isometric) were conducted in the short (within the range of 2.4 to 2.7 μm) and long muscle (within the range of 3.0 to 3.3 μm). The magnitude of SSC effect was calculated as the relative increase in the mechanical work attained during the shortening phase between control and SSC trials. As a result, the magnitude of SSC effect was significantly larger in the long (176.8 ± 18.1%) than in the short muscle length condition (157.4 ± 8.5%) (p < 0.001). This result supports our hypothesis that the magnitude of SSC effect is larger in the longer muscle length condition, possibly due to the larger magnitude of residual force enhancement.

Combined Aerobic and Resistance Training Increases Stretch- Shortening Cycle Potentiation and Walking Economy in Postmenopausal Women.

PurposeSecondary analyses were performed to test whether combined aerobic and resistance training altered walking economy (i.e., net oxygen uptake) and/or stretch-shortening cycle potentiation (SSCP). A further objective was to determine if walking economy and SSCP were related before or after training.MethodsNinety-two postmenopausal women were enrolled wherein 76 completed 16 weeks of supervised aerobic and resistance training. Participants were randomized to one of three training groups based on frequencies: (a) 1 d⋅wk–1 (n = 23); (b) 2 d⋅wk–1 (n = 30) or; (c) 3 d⋅wk–1 (n = 23). Following assessments were performed at baseline and post-training. Indirect calorimetry was used to measure maximal oxygen uptake () and walking economy (submaximal – resting = net ) during a graded exercise test and steady-state treadmill task, respectively. SSCP was determined by measuring the difference between a concentric (CO) and counter-movement (CM) leg press throw.Results, walking economy, CO and CM velocity were significantly improved (p < 0.05) for all training groups, however; no time by group interactions were observed. Paired t-tests revealed participants exercise training 2 d⋅wk–1 exhibited a significant time effect for SSCP (+0.04 ± 0.09 ms–1; p = 0.03). At baseline, multiple linear regression showed a negative relationship between walking net and SSCP (r = −0.22; p < 0.04) adjusted for relative proportion of . No such relationship was found post-training.ConclusionAmong older postmenopausal women, our results indicate that irrespective of frequency of training, 16 weeks of combined aerobic and resistance exercise training increased ease of walking and economy. Additionally, only participants exercising 2 d⋅wk–1 exhibited significant improvement in SSCP.

Effects of jump exercises with and without stretch-shortening cycle actions on components of physical fitness in prepubertal male soccer players

This study examined the effects of 8-week stretch-shortening cycle-based (SSC-based) versus non-SSC-based jump exercises on physical fitness in prepubertal male soccer players. Twenty-six participants were randomly assigned to either a SSC-based using countermovement jump (CMJG; n = 13) or a non-SSC-based jump group using squat jump (SJG; n = 13). Pre- and post-training, tests were conducted to assess measures of muscle power (countermovement jump, reactive strength index), speed (5 m, 20 m), change of direction (CoD), and sport-specific performance (maximal kicking distance). To establish the effect of the interventions on the dependent variables, a 2 (group: CMJG and SJG) × 2 (time: pre, post) ANOVA with repeated measures was determined for each parameter. Findings demonstrated a main effect of time for countermovement jump, reactive strength index, and maximal kicking distance (p < 0.05, effect size [ES] = 0.56–0.71). Group × time interactions were identified for (5 m, 20 m, and reactive strength index (p < 0.05, ES = 0.59–0.64) in favor of CMJG. Particularly, pre–post-performance improvements have been observed for 5 m (∆1.6%; p = 0.04; ES = 0.54) and 20 m (∆5.3%; p < 0.01; ES = 1.00) in the CMJG. For SJG, 5 m (∆− 5.5%; p = 0.01; ES = − 1.12) and 20 m (∆− 3.7%; p = 0.01; ES = − 0.82) pre–post-performance declines were observed. Regarding reactive strength index, pre–post-improvement was noted for CMJG only (∆− 40.1%; p < 0.01; ES = 3.7). In addition, a tendency towards a group × time interaction was found for CoD (p = 0.06, ES = 0.54) with a performance decrement for SJG (∆− 6.0%; p < 0.01; ES = − 1.8) and no pre–post changes for CMJG (∆0.15%; p > 0.05; ES = 0.05). Overall, jump exercises which utilize the SSC seem to be more effective in improving measures of speed and muscle power performance in young athletes. However, jump exercises that do not involve the SSC appear to negatively affect CoD performance in young athletes.

Effects of Eccentric Preloading on Concentric Vertical Jump Performance in Youth Athletes.

This study measured peak force (PF), peak rate of force development (PRFD), peak power (PP), concentric impulse, and eccentric impulse during static jump (SJ), countermovement jump (CMJ), and drop jump (DJ) in youth athletes to examine changes in vertical jump power with progressively greater eccentric preloading in relation to age, maturity, and muscle mass. Twenty-one males ranging from 6 to 16 years old performed the following vertical jumps in a random order: SJ, CMJ, and DJ from drop heights of 20, 30, and 40cm (DJ20, DJ30, and DJ40, respectively). Measurements included PF, PRFD, PP, eccentric impulse, and concentric impulse for each vertical jump condition. Maturity offset was calculated, while ultrasound images quantified thigh muscle cross-sectional area (CSA). PF and PRFD increased from CMJ to DJ20. PP increased from SJ to CMJ. Concentric impulse remained unchanged, but eccentric impulse increased systematically from across jumps. The change in PP from SJ to CMJ was correlated with age, height, weight, maturity offset, and CSA. The CMJ resulted in the greatest concentric PP with the least amount of eccentric preloading. The inability of young athletes to translate the energy absorbed during the eccentric phase of the stretch-shortening cycle of DJs may be influenced by growth and development.

Changes in joint, muscle, and tendon stiffness following repeated hopping exercise.

The purpose of this study was to elucidate the mechanisms of decline in joint stiffness after repeated stretch‐shortening cycle exercises according to changes in both muscle‐tendon properties and neuromuscular activities. Eleven males performed fatigue task (5 sets of 50 hopping). Ankle joint stiffness and electromyographic activities (mEMG) of plantar flexor and tibial anterior muscles during drop jump were measured before and after fatigue task. Active muscle stiffness with (100 deg·sec−1) and without (250 deg·sec−1) stretch reflex were calculated according to changes in estimated muscle force and fascicle length during fast stretching after submaximal isometric contractions. Tendon stiffness was measured during ramp and ballistic contractions. After fatigue task, joint stiffness significantly decreased by 20.7 %, whereas mEMG of measured muscles during drop jump did not. After fatigue task, active muscle stiffness with and without stretch reflex significantly decreased by 15.7 % and 21.5 %, and tendon stiffness measured during ramp and ballistic contractions did not change. In addition, the relative change in joint stiffness was significantly correlated with that in active muscle stiffness with stretch reflex (r = 0.737, P = 0.009), but not with those in the other measured variables. These results suggested that the decline in joint stiffness after repeated hopping exercises would be caused by changes in active muscle stiffness, but not those in tendon properties or neuromuscular activities.

Pelvic floor muscle displacement during jumps in continent and incontinent women: An exploratory study.

The prevalence of stress urinary incontinence during high-impact activities is high. Enhanced comprehension of pelvic floor muscle (PFM) displacement and activity is clinically relevant for the development of specific approaches in rehabilitation. The aim of the study is to investigate and to compare PFM displacement between the continent and incontinent women during jumps. A cross-sectional, exploratory design was applied to investigate PFM displacement during drop jumps (DJ) and countermovement jumps (CMJ). PFM displacement was assessed in craniocaudal translation and forward-backward rotation with an electromagnetic tracking system. Twenty-eight continent and 22 incontinent women were included. During the first landing of DJ, a primary caudal, during the second landing of DJ/CMJ a primary cranial translation and during all jump a primary backward rotation was observed. No significant difference between the groups was found. PFM displacement during running demonstrated caudal translation/forward rotation before and cranial translation/backward rotation after heel strike. During the second landing of DJ/CMJ a cranial translation/backward rotation and during the first landing of DJ a caudal translation/backward rotation has been observed after ground contact. This may be due to the longer lasting bodyweight force in the first landing of DJ. No eccentric-concentric stretch-shortening cycle could be seen. This study indicates that during jumps two opposite reactions of involuntary PFM displacement happen, but no stretch-shortening cycle with an eccentric-concentric contraction could be found. Jumping stimuli inducing involuntary PFM displacement should be used for future investigations to consider a beneficial effect concerning continence.

Sex-related differences in plantarflexor function during repeated stretch-shortening cycle loading

Introduction: Differences between male and female muscle-tendon units have been previously observed. It is unknown if a sex-related difference exists in the plantarflexor response to repeated stretch-shortening cycles, as occurs during activities of daily living such as walking and running. Methods: An adapted force sledge was used with three dimensional motion analysis to investigate the response of the plantarflexors of 34 age and training-matched males and females during stretchshortening cycle impacts. Results: Contact times and flight times were found to be similar between groups. Statistically significant differences in absolute peak force and rates of force development were observed during loading. With normalisation to plantarflexor muscle volume, small and moderate effect sizes were observed for all force and rate of force development variables but only peak force remained statistically significant. Differences in absolute stiffness, peak negative and positive power and work were statistically significant with moderate effect size, but with normalisation only differences in peak negative power and work remained statistically significant with a moderate effect size. Conclusion: These results show females have lower force, rate of force production and force absorption capabilities, which are of relevance in injury prevention and rehabilitation, and informing personalised engineering design. Level of evidence: III b (individual case-control study).

Force depression following a stretch-shortening cycle depends on the amount of residual force enhancement established in the initial stretch phase.

Studies on residual force enhancement (rFE) and residual force depression (rFD) of the muscle‐tendon unit (MTU) have typically been conducted independent of each other, with little information available on how stretch‐induced rFE affects the shortening phase and the steady‐state MTU isometric force at the end of stretch‐shortening cycles (SSCs). We showed previously that when rFE is kept constant, but the force at the end of the stretch is varied by changing the stretch speed, the steady‐state forces at the end of SSCs were the same. These results led to the hypothesis that the amount of rFE of the MTU established in the initial stretch phase of SSCs determines the steady‐state force following the shortening phase of SSCs. This study was aimed at testing this hypothesis. Steady‐state MTU isometric thumb adduction forces were measured for pure isometric contractions, following pure shortening contractions, following pure stretch contractions, and following SSCs with constant shortening speed and magnitude. However, two stretch magnitudes (30° and 10° thumb abduction) and stretch speeds (15°/sec and ~ 60°/sec, respectively) were chosen such that forces at the end of the stretch phase of the SSCs were the same, while rFE differed substantially. As hypothesized, the steady‐state isometric MTU forces following SSCs were positively related to the stretch‐magnitude dependent amount of rFE established in the stretch phase and were independent of the force reached at the end of the stretch phase in SSCs. Among many competing theories, these results can potentially be explained with the idea that there is a length‐specific engagement of a passive structural element at the initial length of muscle activation.

Effect of COL5A1, GDF5, and PPARA Genes on a Movement Screen and Neuromuscular Performance in Adolescent Team Sport Athletes.

Stastny, P, Lehnert, M, De Ste Croix, M, Petr, M, Svoboda, Z, Maixnerova, E, Varekova, R, Botek, M, Petrek, M, Lenka, K, and Cięszczyk, P. Effect of COL5A1, GDF5, and PPARA genes on a movement screen and neuromuscular performance in adolescent team sport athletes. J Strength Cond Res 33(8): 2057-2065, 2019-The risk of injury increases with adolescents' chronological age and may be related to limited muscle function neuromuscular, genetic, and biomechanical factors. The purpose of this study was to determine whether COL5A1, PPARA, and GDF5 genes are associated with muscle functions and stretch-shortening cycle performance in adolescent athletes. One hundred forty-six youth players (14.4 ± 0.2 years) from various team sports (basketball n = 54, soccer n = 50, handball n = 32) underwent a manual test for muscle function, maturity estimation, functional bend test (FBT), passive straight leg raise (SLR) test, leg stiffness test, test of reactive strength index (RSI), and gene sampling for COL5A1, PPARA, and GDF5. The χ test did not show any differences in allele or genotype frequency between participants before and after peak height velocity. Multivariate analysis of variance showed that COL5A1 rs12722 CT heterozygotes had worse score in FBT (p < 0.001), worse score in SLR (p = 0.003), and lower maturity offset (p = 0.029, only in females) than TT homozygotes. Male GDF5 rs143383 GG homozygotes showed better score in SLR than AA and AG genotypes (p = 0.003), and AA and AG genotypes in both sex had greater RSI than GG homozygotes (p = 0.016). The PPARA rs4253778 CC homozygotes had greater RSI than GG and GC genotypes (p = 0.004). The CT genotype in COL5A1 rs12722 is possible predictor of functional movement disruption in the posterior hip muscle chain, causing shortening in FBT and SLR, which includes hamstrings function. CT genotype in COL5A1 rs12722 should be involved in programs targeting hamstring and posterior hip muscle chain.

Strength differences between trained and untrained pre-pubertal children: stretch shortening cycle of muscle contractions

This study investigated jumping performance in pre-pubertal children with respect to age, gender and trained level and their ability to use the stretch-shortening cycle (SSC). One hundred and twenty-seven (n=127) children participated in this study that included 66 from a basketball academy (age: 9.88±1.38 years) and 61 sedentary schoolchildren (age: 9.93±1.55 years). Neuromuscular variables, such as the Squat Jump (SJ), the Counter Movement Jump (CMJ), the Drop Jump (DJ) and the Standing Long Jump (SLJ) were measured. There were no significant differences between boys and girls in all the jumps for the basketball group. In the sedentary group, boys exhibit higher scores in DJ-40cm than the girls. The trained group achieves better scores in several jumps than the sedentary group. Significant differences between the sedentary and trained groups in relation to different age groups are found in all the jumps. High scores on the DJ-40cm and SLJ are a risk factor for trained status. Pre-pubertal children exhibit considerable trainability in relation to explosive leg strength; however, there is an inability to use the stretch-shortening cycle to vertical jumping performance.Keywords: Strength; Children; Trainability; Jump performance

The relationship between leg stiffness, forces and neural control of the leg musculature during the stretch-shortening cycle is dependent on the anticipation of drop height.

This study aimed at investigating how prior knowledge of drop heights affects proactive and reactive motor control in drop jumps (DJ). In 22 subjects, the effect of knowledge of three different drop heights (20, 30, 40cm) during DJs was evaluated in seven conditions: three different drop heights were either known, unknown or cheated (announced 40cm, but actual drop height was 20cm). Peak ground reaction force (Fmax) to body weight (BW) ratio (Fmax/BW) and electromyographic (EMG) activities of three shank and five thigh muscles were assessed 150ms before and during ground contact (GC). Ankle, knee and hip joint kinematics were recorded in the sagittal plane. Leg stiffness, proactive and reactive EMG activity of the leg muscles diminished in unknown and cheat conditions for all drop heights (7-33% and 2-26%, respectively). Antagonistic co-activation increased in unknown (3-37%). At touchdown, increased flexion in knee (~ 5.3° ± 1.9°) and hip extension (~ 2° ± 0.6°) were observed in unknown, followed by an increased angular excursion in hip (~ 2.3° ± 0.2°) and knee joints (~ 5.6° ± 0.2°) during GC (p < 0.05). Correlations between changes in activation intensities, joint kinematics, leg stiffness and Fmax/BW (p < 0.05) indicate that anticipation changes the neuromechanical coupling of DJs. No dropouts were recorded. These findings underline that anticipation influences timing and adjustment of motor responses. It is argued that proactive and reactive modulations associated with diminished activation intensities in leg extensors are functionally relevant in explaining changes in leg stiffness and subsequent decline in performance.

Acute Effects of "Composite" Training on Neuromuscular and Fast Stretch-Shortening Cycle Drop Jump Performance in Hurling Players.

Byrne, PJ, Moody, JA, Cooper, SM, and Kinsella, S. Acute effects of "composite" training on neuromuscular and fast stretch-shortening cycle drop jump performance in hurling players. J Strength Cond Res 35(12): 3474-3481, 2021-"Composite" training is a term developed by the authors and defined as the combination of a plyometric exercise with an explosive activity such as a sprint run, performed as a "combined repetition"/session. The purposes of this study were to investigate the acute effect of a "composite" training session on neuromuscular and fast stretch-shortening cycle bounce drop jumps (BDJs) in hurling players' immediately, after session, and after 7 days of recovery. Eight hurling players first completed a drop jump test to identify individual BDJ drop height, followed 72 hours later with a single "composite" training session. Three repetition maximum (3RM) back squat strength, BDJ, countermovement jump (CMJ), and sprint performance testing were performed 10 minutes before and immediately after session and 7 days after session. An analysis of variance reported a significant decrease in CMJ measures (height, velocity, and eccentric rate of force development) and sprint performance from presession to postsession (p ≤ 0.05). Moreover, a significant increase was evident for CMJ performance (height and power), sprint performance (5 and 20 m), 3RM back squat strength, and BDJ performance (reactive strength index and height) from postsession to post-7-day recovery (p ≤ 0.05). Pairwise comparisons indicated that absolute and relative 3RM strength significantly increased from presession to post-7 days (absolute 3RM: p = 0.0001; relative 3RM: p = 0.01). The findings indicate that "composite" training results in an immediate decline in CMJ measures after session possibly due to acute muscle fatigue, and supercompensation augments maximum lower-limb strength after 7 days of recovery.

Photobiomodulation Therapy Does Not Attenuate Fatigue and Muscle Damage in Judo Athletes: A Randomized, Triple-Blind, Placebo-Controlled Trial.

Fatigue and muscle damage negatively affect performance in lower limb exercises involving the stretch-shortening cycle in judo athletes during competition and training sessions. Photobiomodulation therapy has emerged as an effective non-invasive strategy to attenuate fatigue and muscle damage when applied before different types of exercises. Our objective was to investigate the effects of photobiomodulation therapy on fatigue and muscle damage in judo athletes. Sixteen judo athletes participated in the study (23.1 ± 3.8 years, 77.9 ± 14.9 kg, 173.1 ± 8.9 cm, 17.5 ± 7.3 body fat%, 12.9 ± 5.0 years of practice). Each participant received, in a randomized manner, photobiomodulation in one limb and placebo in the contralateral limb on the same day. Thereafter, subjects performed a stretch-shortening cycle protocol to induce muscle fatigue and damage. Countermovement jump (impulse, peak power, peak velocity, and peak force), echo intensity (rectus femoris and vastus lateralis), and muscle soreness were assessed at different time points before, during, immediately post, and 24 and 48 h after the protocol. Muscle fatigue was detected due to reductions in countermovement jump impulse (14.7 ± 9.8 and 15.9 ± 15.5%), peak power (12.9 ± 8.5 and 11.9 ± 6.9%), peak velocity (8.6 ± 8.1 and 6.5 ± 6.0%), and peak force (7.0 ± 5.3 and 8.0 ± 6.1%) after the protocol (p < 0.001), for placebo and photobiomodulation therapy, respectively. Muscle damage was detected due to reductions in countermovement jump impulse (−6.1 ± 19.2% and −4.5 ± 9.2%, p < 0.05), increases in echo intensity (rectus femoris, 21.0 ± 11.9 and 20.8 ± 9.0%; and vastus lateralis, 22.4 ± 23.2%; and 16.7 ± 23.8%; p < 0.001), and quadriceps muscle soreness (3.6 ± 1.6 and 3.5 ± 1.7 a.u; p < 0.011), 48 h after the protocol, for placebo and photobiomodulation therapy, respectively. No differences were observed between photobiomodulation therapy and placebo at any time points for any variables (p > 0.05), indicating no positive effect favoring photobiomodulation therapy. In conclusion, our findings suggest no effect of photobiomodulation therapy applied before exercise to reduce lower limb muscle fatigue and damage during and following a stretch-shortening cycle protocol in judo athletes.

Comparison of Pre-stretch and Reactive Strength Between Men and Women During Bench Press

Pre-stretch augmentation (PAI) and reactive strength (RSI) indices have been used to assess the stretch-shortening cycle (SSC) contribution to vertical jumping. SSC activation is also a part of many upper extremity (UE) activities, however quantification of SCC contribution to UE function largely remains unknown. Furthermore, based on differences in UE muscle-tendon properties, the SSC effect is likely different between men and women PURPOSE: To compare UE PAI and RSI indices between men and women. METHODS: 20 men (26±2.4 yrs) and 17 women (21.4±2.6 yrs) with >6 months of UE resistance training completed 3 bench press trials using 2 styles, pure concentric (PC) and rebound (RB) (no pause between eccentric the concentric phases), using 75% of their one repetition maximum. Participants were instructed to complete the concentric phase as quickly as possible. Concentric phase vertical average force (AF) and power (AP) were computed from barbell kinematic data and used to calculate PAI [(RB-PC)/PC*100] and RSI (RB-PC). Independent t tests, adjusted for unequal variances, were conducted to compare indexes between sexes RESULTS: Except for one man and one woman, participants demonstrated greater AF and AP during the RB bench press compared to PC bench press. Men (.49±.38) had significantly higher (P=.004, d=.75) AF PAI than the women (.27±.17). There was no significant (P=.068, d=.64) sex difference for AP PAI. Men (AF:3.9±2.9, AP:129.0±56.7) demonstrated significantly higher RSI for both AF (P<.001, d=1.5) and AP (P<.001, d=2.3) than women (AF:.76±.54, AP: 29.6±18.1). CONCLUSIONS: Except for two participants, as expected, preceding the concentric phase with SSC resulted in greater average force and power production. With the exception of AP PAI, SSC augmentation was greater for the men. Consistent with the RSI reflecting the AP/AF difference between RB and PC bench press styles, the sex comparison effects sizes were larger for the RSI than the PAI, which expresses the difference relative to the PC. Further research is needed to determine the extent to which UE muscle-tendon properties explain the sex differences identified.

TheEffects of Eccentric Duration on Squat and Bench Press Concentric Performance

Many resistance training exercises incorporate both eccentric and concentric phases of muscle contraction. Through the stretch shortening cycle, the velocity and magnitude in which the eccentric phase is completed directly affects performance during the concentric phase. PURPOSE: Therefore, the purpose of this research was to investigate the effects of eccentric phase duration on concentric outcomes at 60% and 80% of one-repetition maximum (1RM) in the back squat and bench press. METHODS: Sixteen resistance-trained males (Age: 23.25±2.57yrs, Height: 171.82±7.48cm, Body Mass: 81.96±12.16 kg) completed four laboratory visits as follows: Day 1- 1RM testing; Day 2- establishment of normative eccentric durations; Days 3 and 4- randomized fast (0.75 times) or slow (2.0 times) eccentric duration conditions, which were controlled by visual and auditory metronomes. Outcome measures assessed during the concentric phase were: average concentric velocity (ACV), peak concentric velocity (PCV), rating of perceived exertion (RPE), range of motion (ROM), and barbell path. A one-way ANOVA and Pearson’s Product Moment correlations were used for analysis with significance set at p≤0.05. RESULTS: Eccentric duration was significantly and inversely correlated with average concentric velocity (ACV) at 60% (r = -0.408) and 80% (r = -0.477) of 1RM squat and at 100% (r = -0.604) of 1RMM bench press. At 60% of 1RM squat, both fast and slow eccentric conditions produced greater (p<0.001) peak concentric velocity (PCV) than normative duration with fast also producing greater PCV than slow (p=0.044). Eccentric duration had no impact on RPE, ROM, or barbell path. CONCLUSIONS: Therefore, our results show that well-trained athletes performing a deliberately faster eccentric phase may enhance squat and bench press performance. However, caution should be used when interpreting these results as athletes who already perform a fast eccentric duration may not benefit from deliberately increasing eccentric velocity.