Is vertical jump height a body size-independent measure of muscle power?

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.     

Influence of football match time–motion parameters on recovery time course of muscle damage and jump ability

ABSTRACT

We analysed the time course of recovery of creatine kinase (CK) and countermovement jump (CMJ) parameters after a football match, and correlations between changes in these variables and match time–motion parameters (GPS-accelerometry) in 15 U-19 elite male players. Plasma CK and CMJ height (CMJ_H), average concentric force (CMJ_CON) and average eccentric force (CMJ_ECC) were assessed 2 h before and 30 min, 24 h and 48 h post-match. There were substantially higher CK levels 30 min, 24 h and 48 h (ES: 0.43, 0.62, 0.40, respectively), post-match. CMJ_ECC (ES: ?0.38), CMJ_H (ES: ?0.35) decreased 30 min post, CMJ_CON (ES: ?0.35), CMJ_ECC (ES: ?0.35) and CMJ_H (ES: ?1.35) decreased 24 h post, and CMJ_CON (ES: ?0.41) and CMJ_H (ES: ?0.53) decreased 48 h post. We found correlations between distance covered at velocities ≤21 km · h^?1 and changes in CK at 24 h (r = 0.56) and at 48 h (r = 0.54) and correlations between CK and distance covered >14 km · h^?1 (r = 0.50), accelerations (r = 0.48), and decelerations (r = 0.58) at 48 h. Changes in CMJ_CON 30 min and 24 h post (both r = ?0.68) correlated with impacts >7.1·G. Decelerations >2 m · s^?2 correlated with changes CMJ_CON (r = ?0.49) at 48 h and CMJ_ECC (r = ?0.47) at 30 min. Our results suggest that match GPS-accelerometry parameters may predict muscle damage and changes in components of neuromuscular performance immediately and 24–48 h post-match.     

Changes in joint range of motion and muscle–tendon unit stiffness after varying amounts of dynamic stretching

The purpose of this study was to examine the effects of varying amounts of dynamic stretching (DS) on joint range of motion (ROM) and stiffness of the muscle–tendon unit (MTU). Fifteen healthy participants participated in four randomly ordered experimental trials, which involved one (DS1), four (DS4) and seven (DS7) sets of DS, or control conditions/seated at rest (CON). Each DS set consisted of 15 repetitions of an ankle dorsiflexion–plantarflexion movement. The displacement of the muscle–tendon junction (MTJ) was measured using ultrasonography while the ankle was passively dorsiflexed at 0.0174 rad · s^?1 to its maximal dorsiflexion angle. Passive torque was also measured using an isokinetic dynamometer. Ankle ROM was significantly increased after DS4 and DS7 compared with the pre-intervention values (P < 0.05), but there were no significant differences in ankle ROM between DS4 and DS7. No differences were observed in ankle ROM after DS1 and CON. In addition, the stiffness of the MTU, passive torque and displacement of the MTJ at submaximal dorsiflexion angles did not change in any of the experimental conditions. These results indicate that DS4 increased ankle ROM without changing the mechanical properties of the MTU, and that this increase in ankle ROM plateaued after DS4.     

Alternative assessment of knee joint muscle balance of soccer players through total work-based hamstring: quadriceps ratios

Isokinetic hamstring-to-quadriceps (H:Q) ratios are frequently used to assess knee muscle strength imbalances and risk of injuries/re-injuries. The use of peak torque (PT) or total work (TW) to estimate joint stability may lead to different results because of the differences between these two neuromuscular variables. Thus, the current study aimed to compare the conventional and functional H:Q ratios calculated by PT and TW. Ninety-three male professional soccer players from Brazilian first division teams performed isokinetic concentric and eccentric contractions of the quadriceps and the hamstrings at 60°/s. Muscle strength balance was calculated using the conventional torque ratio (CTR) and conventional work ratio (CWR), functional torque ratio (FTR) and functional work ratio (FWR) were highly and moderately correlated between them (r?=?0.83 and r?=?0.73, respectively). The Wilcoxon statistical test revealed significant differences between CTR and CWR, as well as FTR and FWR (p?T-test demonstrated significant differences in mean CTR–CWR and FTR–FWR, whereas Bland–Altman plots showed non-consistent bias. In addition, the chi-square test demonstrated significant differences between players below the conventional reference values and functional reference values (p?相似文献   

Maximal isometric force and muscle cross‐sectional area of the forearm in fencers

The maximal isometric force (MIF) of a muscle is directly related to its cross‐sectional area (CSA). Strength training produces an increase in muscular force while muscular hypertrophy becomes appreciable at a later time; in asymmetric sports, training causes significant increases in force and muscular mass of the dominant limb of the athlete. The aim of this study was to analyse the differences in muscular force and trophism between the dominant and non‐dominant forearms in fencers and in controls.

The data of 17 male distance runners (age 21.4±2.4 years, body mass 74.0±5.0 kg, height 180 ± 6 cm) were compared with those of 58 male fencers (age 23.0 ± 6.7 years, body mass 71.9±9.3 kg, height 178 ± 7 cm) drawn from the ranking lists of the National Fencing Committee. They trained for a mean of 11.4±6.0 (range 2–36) years, commencing at 10.7 ± 4.5 years of age.

Cross‐sectional area (muscle plus bone) was estimated in the dominant and non‐dominant forearm using a simplified anthropometric method. Maximal isometric force was determined using a mechanical handgrip dynamometer. The differences in CSA and isometric force between the two limbs and between fencers and controls were tested using paired and unpaired Student's i‐tests, respectively. Significant differences in CSA and maximal force were observed between the dominant and non‐dominant forearm in fencers (both P<0.001) and in controls (P<0.005 and P<0.001, respectively). The fencers showed a greater CSA (P<0.001) and force (P< 0.001) in the dominant forearm compared with the control group. Furthermore, the differences between the dominant and non‐dominant limb of the fencers were significantly greater than the differences between the dominant and non‐dominant limb of the controls (P<0.001 for CSA and P<0.05 for force). No significant differences in stress ratio (force/CSA) were obtained in either group.

The results of this study suggest that asymmetric sports training at submaximal intensities produces significant asymmetries in force and CSA which are independent of technical level and years of training. Despite this, the force/CSA ratio is constant and independent of training.     

Do kinaesthetic tapes affect plantarflexor muscle performance?

Abstract

This study aimed to examine the effects of application of kinaesthetic tapes on plantarflexor muscle performance. We hypothesised that taping of the triceps surae muscle would improve plantarflexor muscle strength and endurance with no significant effect on drop jump performance. Using a repeated-measures design, all performance measures were obtained in 24 volunteers on two separate occasions: without tapes and after application of kinaesthetic tapes. Performance tests included measurements of isometric plantarflexor muscle strength and the associated electromyographic activity of the gastrocnemius muscle, an isokinetic fatigue resistance test (30 contractions at 180° · s^?1) and assessments of drop jump performance. The taping-intervention was associated with an increase in gastrocnemius electromyographic activity. However, significant increases in isometric strength were only found at fully dorsiflexed ankle positions (+12% at ?20°). Strength gains were negatively correlated to baseline strength (r = ?.58). The intervention did not affect the results of the isokinetic fatigue and drop jump tests. The application of kinaesthetic tapes over the triceps surae muscle promotes an increase in isometric strength and gastrocnemius muscle activity. Our data suggest that these effects are joint-angle dependent and more prominent in weaker individuals. By contrast, the taping-intervention improves neither drop jump performance nor muscular endurance.     

Agonist–antagonist muscle activation during drop jumps

Abstract

Pre-programmed and stretch-induced muscle activities of agonist muscles can play important roles during stretch-shortening cycle exercises. It is still not clear how the antagonist muscles function when the drop and rebound intensities are varied during drop jump (DJ) exercises. The purpose of the present study was to examine the regulation of agonist–antagonist muscle activation during DJ with different drop and rebound heights. The subjects performed DJs with two drop heights (0.2 and 0.4 m) and three different efforts (maximal rebound height, 50% effort of maximal rebound height and landing without rebound). Ankle and knee joint angles, and vertical ground reaction force together with an electromyogram of the lower leg muscles (medial gastrocnemius [MG], soleus [SOL] and tibialis anterior [TA]) were measured simultaneously during DJ. Our results clearly showed that the pre-activation of the antagonist TA was increased with increasing rebound height. Our results further showed that the coactivations of agonist and antagonist muscles during the post-impact 30-ms phase were increased with increasing rebound height. These results suggested that not only the pre-programmed agonist MG muscle activation, but also the pre-programmed antagonist TA activation and the coactivation of the post-impact 30-ms phase may play important roles in the control of rebound height.     

Influence of single‐leg training on muscle metabolism and endurance during exercise with the trained limb and the untrained limb

We have previously shown that single‐leg training results in improved endurance for exercise with the untrained leg (UTL) as well as for exercise with the trained leg (TL). The purpose of this study was to see whether the improved endurance of the untrained leg could be explained on the basis of changes in muscle metabolism. Exercise time to exhaustion at 80% of maximum oxygen uptake (VO₂ max) was determined for each leg separately, pre‐ and post‐training. Muscle metabolite concentrations were measured pre‐ and post‐training in biopsy samples obtained immediately before this endurance test and at the pre‐training point of exhaustion (END1). After six weeks of single‐leg training endurance time was increased for both the UTL and the TL (UTL 34.0+16.4 min vs 97.9±26.3 min, P<0.01; TL 28.3 + 10.1 min vs 169.0 + 32.6 min, P < 0.01). No changes in muscle metabolite concentrations were found in resting muscle. Training increased muscle ATP (P <0.05) and glycogen (P <0.01) concentrations and decreased muscle lactate concentration (P<0.05) in the TL at END1. No significant changes in muscle metabolite concentrations were found for the UTL. The improved endurance of the contralateral limb after single‐leg training could not be explained on the basis of changes in muscle metabolism.     

Sexual dimorphism in bone–muscle relationship in young adults

The purpose of this study was to analyse associations between lean soft tissue (LST), a surrogate of skeletal muscle mass and key fracture-related geometric characteristics of the proximal femur. Moreover, we examined the role that muscle played on the proximal femur geometry in response to physical activity (PA). Participants were 83 young adults. Leg LST (exposure) was assessed by dual energy X-ray absorptiometry (DXA). Proximal femur geometry was derived from a left hip DXA scan. Geometric variables (outcomes) included the femoral neck axis length (FNAL), the femoral neck width (FNW), the neck–shaft angle and FNW|FNAL (an index of robustness). PA was evaluated by accelerometry. Linear regression was used to analyse relationships. Additional exposure variables included body height and mass. In males, leg LST explained 17.4% of variation in FNAL (P < 0.001) and 15% in FNW (P = 0.015). In females, it explained 8.8% of the variance in FNAL (P = 0.020). Associations remained significant in males, but not in females, when vigorous PA was added to the models. These results suggest that public health approaches to promote PA may be particularly important in females since vigorous PA seems to convey advantages in femur geometry and consequently in bone strength.     

Esports players,got muscle? Competitive video game players’ physical activity,body fat,bone mineral content,and muscle mass in comparison to matched controls

BackgroundEsports players, like traditional athletes, practice for long hours and, thus, are vulnerable to the negative health effects of prolonged sitting. There is a lack of research on the physical activity and the health ramifications of prolonged sitting by competitive players. The purpose of this study was to investigate activity levels, body mass index (BMI), and body composition in collegiate esports players as compared to age-matched controls.MethodsTwenty-four male collegiate esports players and non-esports players between 18 and 25 years of age signed a written consent to participate. Physical activity was examined using daily activity (step count) with a wrist-worn activity tracker. A questionnaire assessing physical activity was also administered. Secondary outcomes included body-fat percentage, lean-body mass, BMI, and bone mineral content measured using dual X-ray absorptiometry.ResultsThe step count in the esports players was significantly lower than the age-matched controls (6040.2 ± 3028.6 vs. 12843.8 ± 5661.1; p = 0.004). Esports players exhibited greater body-fat percentage (p = 0.05), less lean body mass (p = 0.003), and less bone mineral content (p = 0.03), despite no difference in BMI between the esports and non-esports players.ConclusionAs compared to non-esports players, collegiate esports players were significantly less active and had a higher body-fat percentage, with lower lean body mass and bone mineral content. The BMIs showed no difference between the 2 groups. Esports athletes displayed significantly less activity and poor body composition, which are all correlated with potential health issues and risk of injury. BMI did not capture this difference and should not be considered as an accurate measure of health in competitive esports players.     

Exercise‐induced muscle cramp: A prospective biochemical study in marathon runners

Exercise‐induced muscle cramp has been considered to result from disturbances of fluid and electrolyte balance resulting from excessive sweat loss. Serum biochemical and haematological measurements were made on 82 male marathon runners before and after a 42.2‐km race. Fifteen (18%) of the runners reported an attack of muscle cramp which occurred after 35 ± 6 km (mean±s.d.) had been covered. These subjects were not different from the others in terms of racing performance or training status. Serum electrolyte concentrations, including sodium and potassium, were not different between those suffering from cramp and those not so affected either before or after the race, although a significant (P< 0.001) increase in serum sodium concentration occurred in both groups. Serum bicarbonate concentrations fell to the same extent (from 28 to 24 mmol 1^‐1) in both groups. Significant decreases in plasma volume, calculated from the changes in circulating haemoglobin and haemotocrit, occurred in both groups of subjects, but there was no difference in the extent of the haemoconcentration. The results suggest that exercise‐induced muscle cramp may not be associated with gross disturbances of fluid and electrolyte balance.     

Are muscle activation patterns altered during shod and barefoot running with a forefoot footfall pattern?

This study aimed to investigate the activation of lower limb muscles during barefoot and shod running with forefoot or rearfoot footfall patterns. Nine habitually shod runners were asked to run straight for 20 m at self-selected speed. Ground reaction forces and thigh and shank muscle surface electromyographic (EMG) were recorded. EMG outcomes (EMG intensity [iEMG], latency between muscle activation and ground reaction force, latency between muscle pairs and co-activation index between muscle pairs) were compared across condition (shod and barefoot), running cycle epochs (pre-strike, strike, propulsion) and footfall (rearfoot and forefoot) by ANOVA. Condition affected iEMG at pre-strike epoch. Forefoot and rearfoot strike patterns induced different EMG activation time patterns affecting co-activation index for pairs of thigh and shank muscles. All these timing changes suggest that wearing shoes or not is less important for muscle activation than the way runners strike the foot on the ground. In conclusion, the guidance for changing external forces applied on lower limbs should be pointed to the question of rearfoot or forefoot footfall patterns.     

A randomised trial comparing the efficacy and safety of topical ketoprofen in Transfersome® gel (IDEA-033) with oral ketoprofen and drug-free ultra-deformable Sequessome™ vesicles (TDT 064) for the treatment of muscle soreness following exercise

We compared the effectiveness of topical ketoprofen in Transfersome^® gel (IDEA-033) with oral ketoprofen and drug-free Sequessome? vesicles (FLEXISEQ^® Sport; TDT 064) in reducing calf muscle soreness. One hundred and sixty eight healthy individuals with a pain score ≥3 (10-point scale) 12–16 h post-exercise (walking down stairs with an altitude of 300–400 m) were randomised to receive IDEA-033 plus oral placebo (two dose groups), oral ketoprofen plus TDT 064, or TDT 064 plus oral placebo. The primary endpoint was muscle soreness reduction from pre-dosing to Day 7. Higher pain scores were recorded with oral ketoprofen plus TDT 064 (mean ± s 462.4 ± 160.4) versus IDEA-033 plus oral placebo (434.7 ± 190.8; P = 0.2931) or TDT 064 plus oral placebo (376.2 ± 159.1; P = 0.0240) in the 7 days post-exercise. Recovery from muscle soreness was longer with oral ketoprofen plus TDT 064 (mean 91.0 ± 19.5 h) versus IDEA-033 plus placebo (mean 81.4 ± 22.9 h; P = 0.5964) or TDT 064 plus placebo (mean 78.9 ± 22.8 h; P = 0.0262). In conclusion, ultradeformable phospholipid vesicles ± ketoprofen did not retard recovery from muscle soreness. TDT 064 improves osteoarthritis-related pain and could be of interest as a treatment for joint pain during and post-exercise.     

Does maturation influence neuromuscular performance and muscle damage after competitive match-play in youth male soccer players?

Abstract

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.     

Vitamin D in relation to bone health and muscle function in young female soccer players

The present work investigated serum vitamin D (25(OH)D) status in relation to bone and muscle qualities and functions in 19 female soccer players (13–16 years) resident at northern latitude with very low sun exposure (～32–36?h/month) during winter season (late January to early March). Serum 25(OH)D, parathyroid hormone and bone turnover markers osteocalcin (OC) and beta carboxy-terminal collagen cross-links (β-Ctx), as well as body composition and muscle performance were examined. Hormones were tested using routine laboratory methods. Fat mass, lean mass, and bone mineral density in whole body, as well as femur and lumbar spine were evaluated with dual-energy X-ray absorptiometry. Muscle performance was assessed through isokinetic knee extension and flexion, countermovement jump, and sprint running. 25(OH)D was low (50.5?±?12.8?nmol?l^?1), whereas the values of bone turnover markers were markedly high (OC: 59.4?±?18.6?µg?l^?1; β-Ctx: 1075?±?408?ng?l^?1). All bone and muscle measurements were normal or above normal. 25(OH)D was not significantly correlated with most of the parameters of bone and muscle quality or function, except the knee extension time to peak torque (r ?=??0.50, p?=?.03). In conclusion, the level of vitamin D is markedly low in adolescent female soccer players during the winter in Sweden. However, vitamin D levels did not significantly correlate with measures of bone and muscle except a moderate correlation in time to peak torque in the knee extensors. The practical implication of low vitamin D levels in young growing female athletes remains unclear.     

Greater basal skeletal muscle AMPKα phosphorylation in men than in women: Associations with anaerobic performance

Objectives: This study was designed to investigate the association of gender, fibre type composition, and anaerobic performance with the basal skeletal muscle signalling cascades regulating muscle phenotype. Design: Muscle biopsies were obtained from 25 men and 10 women all young and healthy. Methods. Protein phosphorylation of Thr¹⁷²AMPKα, Ser²²¹ACCβ, Thr²⁸⁶CaMKII as well as total protein abundance of PGC-1α, SIRT1, and CnA were measured by Western blot and anaerobic performance by the Wingate test. Results: Percent type I myosin heavy chain (MHC I) was lower in men (37.1?±?10.4 vs. 58.5?±?12.5, P?P?P?221ACCβ and Thr²⁸⁶CaMKII fractional phosphorylation tended to be higher in men (P?=?.1). PGC1-α and SIRT1 total protein expression was similar in men and women, whereas CnA tended to be higher in men (P?=?.1). Basal AMPKα phosphorylation was linearly related to the percentage of MHC I in men (r?=?0.56; P?Conclusion: In summary, skeletal muscle basal AMPKα phosphorylation is higher in men compared to women, with no apparent effect on anaerobic performance.