The relationship between mechanical stiffness and athletic performance markers in sub-elite footballers

This study investigated the relationship between several measures of lower-body stiffness and physical performance variables in 22 sub-elite male football players (mean ± SD; 21.9 ± 1.5 yr; 1.79 ± 0.06 m; 72.2 ± 7.2 kg). The participants were assessed for individual muscle stiffness of the Rectus Femoris (RF), Biceps Femoris (BF) and Medial Gastrocnemius (MG) muscles and vertical stiffness (Kvert) was also assessed assessed running acceleration, maximal sprint speed, agility, vertical jumping and muscular strength. Pearson’s correlations quantified the relationships and participants were also separated into relatively stiff (SG) and compliant groups (CG) for each variable. When ranked by Kvert the SG exhibited superior performance during sprinting, agility, jumping and strength (p ≤ 0.05) and when ranked by RF stiffness, SG exhibited superior sprint, agility and drop jump performance (p ≤ 0.05), while MG and BF stiffness were not related to performance. Higher stiffness appears to be beneficial to athletic performance for football players and therefore it may be beneficial for practitioners working with athletes that are required to perform dynamic activities to consider the contribution of stiffness to athletic performance.     

Magnesium status and the physical performance of volleyball players: effects of magnesium supplementation

Abstract

The aim of this study was to test the hypothesis that magnesium supplementation influences the physical performance of volleyball players, as the efficacy of this approach remains questionable. Twenty-five professional male volleyball players were assigned randomly to experimental (350 mg Mg · d^–1, 4 weeks) and control groups (500 mg maltodextrin · d^–1, 4 weeks) maintaining inter-group homogeneity of urinary magnesium. Erythrocyte, plasma and urinary magnesium levels, plasma creatine kinase activity, lactate production, maximal oxygen uptake (VO₂ max) and plyometric (squat jump, countermovement jump, countermovement jump with arm swing) and isokinetic (peak torque, potency and total work) performances were evaluated before (T₀) and after (T₁) supplementation. Levels of erythrocyte and urinary magnesium and creatine kinase activity and VO₂ max remained within normal ranges in both groups. Plasma magnesium decreased significantly only within the experimental group. Significant decreases in lactate production and significant increases (of up to 3 cm) in countermovement jump and countermovement jump with arm swing values were detected in the experimental group following magnesium supplementation, but not in the control group at T₁. It is concluded that magnesium supplementation improved alactic anaerobic metabolism, even though the players were not magnesium-deficient.     

The relationship between muscle cross-sectional area and strength in various isokinetic movements among soccer players

Abstract

The aim of the present study was to examine the relationships between muscle cross-sectional area (CSA) and muscular strength in terms of knee extension and flexion, hip extension and flexion, and hip abduction and adduction among well-trained soccer players. Fourteen university soccer players participated in the study, who had previously been divided into two groups based on ability (Group A: above-average ability; Group B: average ability). Maximal isokinetic and concentric muscular strength was measured in knee extension/flexion, hip extension/flexion and hip abduction/adduction using an isokinetic dynamometer at 1.57 and 4.19 rad·s^?1 (3.14 rad·s^?1) in both the dominant and non-dominant leg. The CSAs of the thigh, gluteus muscles and iliopsoas muscles were calculated based on magnetic resonance imaging. There was no significant difference between the two groups in muscle CSA and isokinetic strength. Although there were some statistically significant differences between the dominant and non-dominant leg in terms of CSA and strength (P<0.05–0.01), these were small and negligible. Apart from a non-significant relationship between the CSAs of the adductor muscles and hip adductor strength (r<0.26, n.s.), the CSA of the other muscle groups correlated with maximal isokinetic strength (r=0.38–0.64, P<0.05). These results suggest that no difference in muscle characteristics (in terms of muscle CSA and strength) was apparent among well-trained soccer players, even between the dominant and non-dominant leg. There is also a case that the anatomical function of a single (or group of) muscle(s) may not be reflected by the strength—CSA relationship depending on the movements (such as hip adduction-adductor muscle CSA). Thus, further studies are required to develop methods to assess neuromuscular function in relation to muscle morphology among soccer players.     

The influence of ankle dorsiflexion on jumping capacity and the modified agility t-test performance

Abstract

Dorsiflexion sport shoes aim to increase jumping capacity and speed by means of a lower position of the heel in comparison with the forefoot, favouring additional stretching of the ankle plantar flexors. In previous studies, contradictory results have been found on the benefits of using this type of shoe. With the aim of comparing a dorsiflexion sport shoe model (DF) with a conventional sport shoe (CS), 41 participants performed a countermovement jump (CMJ) test and an agility test (MAT) with both models of shoe. There were no significant differences in the jump test [CS=35.3 cm (6.4) and DF=35.6 cm (6.4), P>0.05]. In the agility test, the conventional shoe obtained better results than the model with dorsiflexion with regard to time taken to complete the circuit [CS=6236 ms (540) and DF=6377 ms (507), P<0.05)]. In spite of producing pre-stretching of the plantar muscles, the DF sport shoes were not effective for improving either jump power or agility in a specific test.     

Biomechanical mechanisms of jumping performance in youth elite female soccer players

ABSTRACT

We aimed to determine key biomechanical parameters explaining age-related jumping performance differences in youth elite female soccer players. Multiple biomechanical parameters from countermovement (CMJ) squat (SJ) and drop (DJ) jump testing of elite female soccer players (n = 60) within the same national training centre were analysed across ages 9-11y, 12-14y and 15-19y. Effects of age group and jump type on jump height were found, with the older jumping higher than the younger groups in all jumps (P < 0.05). For DJ, higher reactive strength index was found for older, compared to each younger group (P < 0.001). For CMJ and SJ, peak power was the most decisive characteristic, with significant differences between each group for absolute peak power (P < 0.0001) and body-weight-normalised peak power in CMJ (57 ± 7W/kg, 50 ± 7W/kg, 44.7 ± 5.5W/kg; P < 0.05) and between the older and each younger group in SJ (56.7 ± 7.1W/kg, 48.9 ± 7.1W/kg, 44.6 ± 6W/kg; P < 0.01). Age-related differences in jumping performance in youth elite female soccer players appear to be due to power production during standing jumps and by the ability to jump with shorter ground contact times during reactive jumps.     

Tensiomyography parameters and jumping and sprinting performance in Brazilian elite soccer players

Tensiomyography has been suggested as an indirect marker of muscle stiffness, which is associated with strength/power performance. Therefore, it is reasonable to suggest that tensiomyography parameters could be associated with power-related motor tasks. The purpose of this study was to investigate the association between tensiomyography parameters (from rectus and biceps femoris) and jumping and sprinting abilities in elite soccer players. In addition, we used tensiomyography parameters to compare the lateral symmetry between dominant and non-dominant legs. Twenty elite soccer players (age: 23.3 ± 4.8 years; height: 183.5 ± 6.6 cm; weight: 77.8 ± 7.5 kg) volunteered to participate in the study. Significant moderate negative correlations between biceps femoris displacement and contact time (r = –0.5, p = 0.03), rectus femoris displacement and contact time (r = –0.51, p = 0.02), and a significant moderate correlation between biceps femoris displacement and reactive strength index (r = 0.5, p = 0.03) were found. There were no correlations between tensiomyography parameters and power-related motor tasks. In addition, no differences in tensiomyography parameters between dominant and non-dominant legs were found. Our data suggest that tensiomyography parameters are not associated with power-related motor tasks performance in elite soccer players.     

The asymmetry of pectoralis muscles is greater in male prepubertal than in professional tennis players

It is generally accepted that preadolescents have a limited capacity to develop muscle hypertrophy in response to exercise compared with older populations; however, studies are scarce and conflicting. The main aim of the present study was to assess if playing tennis is associated with the hypertrophy of dominant pectoralis muscles (PM) in professional (PRO) and in prepubescent tennis players (PRE). A secondary aim was to assess if the degree of asymmetry of PM is greater in PRO than PRE. The volume of PM of both sides was determined using magnetic resonance imaging in 8 male PRO (21.9 years), 6 male PRE (11 years, Tanner 1–2) and 12 male non-active controls (6 adults: 23.5 years; and 6 prepubescents: 10.7 years, Tanner 1–2). PRO and PRE had 15 and 30% greater volume, respectively, in the dominant than in the contralateral PM (P?P?=?.34 in adults and 5%, P?=?.17 in children). The degree of side-to-side asymmetry in PM volume was greater in PRE than in PRO (P?相似文献   

男排运动员专项力量发展水平的检查与评定

运用献资料研究、问卷调查、数理统计等方法，从分析我国优秀排球运动员的专项力量特征入手，对优秀男排运动员专项力量发展水平进行检查与判定的手段和方法，进行了探讨和研究，以期为排球选材和训练工作提供参考。     

The effects of postseason break on stabilometric performance in female volleyball players

Ankle sprain is a common injury in volleyball. Poor stabilometric performance (SP) is associated with high risks of sustaining ankle sprain. Balance training can improve SP and reduce ankle sprain, but no research has studied the effects of detraining on SP in highly trained athletes. The purpose of this study was to determine the effects of one-month postseason break on SP in female volleyball players. Eleven NCAA female volleyball players participated in two eye-closed single-leg stance tests before and after a one-month postseason break. Stance time, center of pressure (COP) area, COP standard deviation, and COP mean velocity were assessed during the tests. During the postseason break, subjects conducted self-selected exercise and the average training duration was 87% lower compared to the competition season. Subjects demonstrated significant increases in anterioposterior (A/P) COP standard deviation (1.6 ± 0.4 vs. 1.8 ± 0.4 cm, p = 0.05), mediolateral (M/L) COP velocity (6.5 ± 1.5 vs. 7.1 ± 1.3 cm/s, p = 0.05), and overall COP velocity (10.1 ± 2.0 vs. 11.6 ± 1.9 cm/s, p = 0.02) after postseason break. SP decreased in highly trained female volleyball players after one-month postseason break. The decrease in SP indicated a possible increased risk for ankle sprain injury.     

Imitation jumps in ski jumping: Technical execution and relationship to performance level

ABSTRACT

Imitation jumps are frequently used in training for ski jumping. Yet, the dynamics of these jumps differ considerably. Thus, the relevance of imitation jumps for ski jumping performance is not elucidated. The aim of this study was to investigate the relationship between the technical execution of imitation jumps and ski jumping performance level. We compared the imitation jumps of 11 ski jumpers of different performance levels using a Spearman correlation transform of time traces of the kinetics (measured using force cells and motion capture) of imitation jumps. The kinetic aspects that were related to performance centred on the moment arm of ground reaction force to the centre of mass before the onset of the push-off, angular momentum early in push-off, thigh angle during the main period of push-off and vertical velocity towards the end of push-off. We propose that the thigh angle may be a key element allowing high development of linear momentum while preparing for appropriate aerodynamic position. Furthermore, the findings suggest that the kinetic development prior to (and during) push-off is more important than the kinematic end state at take-off.     

Optimised force-velocity training during pre-season enhances physical performance in professional rugby league players

ABSTRACT

The effectiveness of 8-week force-velocity optimised training was assessed in highly trained professional rugby league athletes. Players (age 24 ± 3 years; body mass 94.9 ± 21.6 kg; height 181.3 ± 6.0 cm) were strength-matched and assigned to a force-velocity optimised group (OP; n = 15) or a general strength-power group (GP; n = 14). Tests included 10-m, 20-m sprints, 3 repetition-maximum squat and squat jumps over five load conditions to ascertain vertical force-velocity relationship. ANCOVA revealed there was a group effect for force-velocity deficit (P < 0.001), with the OP two-fold greater than the GP group (OP pre: 51.13 ± 31.42%, post: 62.26 ± 31.45%, GP pre: 33.00 ± 19.60%, post: 31.14 ± 31.45%, P < 0.001). There were further group effects for 3RM squat (OP pre: 151.17 ± 22.95 kg, post: 162.17 ± 24.16 kg, GP pre: 156.43 ± 25.07 kg, post: 163.39 ± 25.39 kg, P < 0.001), peak power (OP pre: 3195 ± 949 W, post: 3552 ± 1033 W, GP pre: 3468 ± 911 W, post: 3591 ± 936 W, P < 0.001), and SJ (OP pre: 39.79 ± 7.80 cm, post: 42.69 ± 7.83 cm, GP pre: 40.44 ± 6.23 cm, post: 41.14 ± 5.66 cm, P < 0.001). Prescribing F-V deficit training is superior for improving physical performance within highly trained RL players.     

Relationships between functional movement screen scores,maturation and physical performance in young soccer players

The purpose of this study was to examine relationships between functional movement screen scores, maturation and physical performance in young soccer players. Thirty males (11–16 years) were assessed for maturation, functional movement screen scores and a range of physical performance tests (squat jump, reactive strength index protocol and reactive agility cut). Older players significantly outperformed younger participants in all tests (P < 0.05; effect sizes = 1.25–3.40). Deep overhead squat, in-line lunge, active straight leg raise and rotary stability test were significantly correlated to all performance tests. In-line lunge performance explained the greatest variance in reactive strength index (adjusted R² = 47%) and reactive agility cut (adjusted R² = 38%) performance, whilst maturation was the strongest predictor of squat jump performance (adjusted R² = 46%). This study demonstrated that variation of physical performance in youth soccer players could be explained by a combination of both functional movement screen scores and maturation.     

Effects of plyometric training on maximal-intensity exercise and endurance in male and female soccer players

In a randomised controlled trial design, effects of 6 weeks of plyometric training on maximal-intensity exercise and endurance performance were compared in male and female soccer players. Young (age 21.1 ± 2.7 years) players with similar training load and competitive background were assigned to training (women, n = 19; men, n = 21) and control (women, n = 19; men, n = 21) groups. Players were evaluated for lower- and upper-body maximal-intensity exercise, 30 m sprint, change of direction speed and endurance performance before and after 6 weeks of training. After intervention, the control groups did not change, whereas both training groups improved jumps (effect size (ES) = 0.35–1.76), throwing (ES = 0.62–0.78), sprint (ES = 0.86–1.44), change of direction speed (ES = 0.46–0.85) and endurance performance (ES = 0.42–0.62). There were no differences in performance improvements between the plyometric training groups. Both plyometric groups improved more in all performance tests than the controls. The results suggest that adaptations to plyometric training do not differ between men and women.     

纵跳中关节功率及其与人体疲劳的关系

考察了纵跳中关节功率及其与人体疲劳的关系。 2次纵跳分别在功率自行车上蹬踏 30 s之前和之后进行。纵跳动作用摄像机摄录下来 ,并在运动解析仪上加以分析。纵跳中的地面反力用测力台测量。根据采集的数据计算了关节功率。通过比较 2组数据计算了各关节处关节功率的变化 ,从而得到了对人体疲劳的一种定量描述     

Analysis of elbow muscle strength parameters in Brazilian jiu-jitsu practitioners

Upper-body dynamic and isometric maximum strength are essential components for success in Brazilian jiu-jitsu (BJJ). This study was aimed at analysing strength parameters in the elbow flexor and extensor muscles of BJJ practitioners. Participants (n = 28) performed maximum isometric contractions of elbow flexors and extensors to determine peak torque (PT), rate of force development (RFD), and the torque–angle (T–A) relationship at elbow angles of 45°, 60°, 75°, 90°, 105°, and 120°. Additionally, concentric and eccentric PTs were measured at 1.04 rad·s^-1. Student t-test and ANOVA were performed using α = 0.05. Elbow flexors were stronger isometrically (P < 0.001, ES = 1.23) but weaker concentrically (P < 0.05, ES = 0.54) than extensor muscles, possibly because of the extensive grip disputes and pushing of opponents in BJJ. The T–A relationship had an inverted “U”-shape. Torque differences across elbow angles were moderate (ES = 0.62) for the extensor and large (ES = 0.92) for the flexor muscles. Isometric torque was greatest for elbow angles of 105° and 75° and smallest for 45° and 120° for extensor and flexor muscles, respectively. Elbow flexors had a greater RFD than extensors, regardless of elbow angle. The present study provides comprehensive results for elbow muscle strength in BJJ practitioners.     

The physical profile of adult male basketball players: Differences between competitive levels and playing positions

This study examined the physical differences in adult male basketball players of different competitive level and playing position using a large cohort. In the middle of the regular season, 129 players from four different Divisions completed a Yo-YoIR1 and, after 3-to-8 days, they performed a 6-min continuous running test (Mognoni’s test), a counter-movement jump (CMJ) test and a 5-min High-intensity Intermittent running test (HIT). Magnitude-based inferences revealed that differences in HIT were very likely moderate between Division I and II and likely small between Division II and III. The differences in absolute peak power and force produced during CMJs between Division I and II and between Division II and III were possibly small. Differences in Yo-YoIR1 and Mognoni’s test were very likely-to-almost certain moderate/large between Division III and VI. We observed possibly-to-likely small differences in HIT and Mognoni’s test between guards and forwards and almost certainly moderate differences in absolute peak power and force during CMJs between guards and centres. The ability to sustain high-intensity intermittent efforts (i.e. HIT) and strength/power characteristics can differentiate between competitive level, while strength/power characteristics discriminate guards from forwards/centres. These findings inform practitioners on the development of identification programs and training activities in basketball.     

排球运动员急停起跳动作中跖趾关节的生物力学分析

以20名女排队员急停起跳动作中的跖趾关节为研究对象,通过三维测力台、高速摄像机和肌电仪多机同步测试来收集运动员急停起跳中跖趾关节的运动学、动力学以及肌电数据。结果表明：1）排球运动员在急停起跳动作中,跖趾关节角度变化幅度在50°~60°之间时,运动员的起跳高度较高。建议排球运动员将急停起跳动作中的跖趾关节进行专项化训练,并采用50°~60°的跖趾关节角度变化幅度;2）排球运动员在急停起跳动作初采用足尖着地能够取得较好的起跳高度。建议排球运动员在训练及比赛中进行急停起跳动作初采用足尖着地;3）训练中,应利用跖趾关节力量训练器进行针对性训练,提高趾长伸肌、第三腓骨肌、拇长伸肌的力量值,提高跖趾关节的活化程度,进而提高运动员的起跳高度。     

Upper extremity bone mineral content asymmetries in tennis players: A systematic review and meta-analysis

The aim of this study was to examine the magnitude of upper extremity bone mineral content (BMC) asymmetries in tennis players. Furthermore, the influence of sex (male versus female versus mixed), chronological age (juniors: < 18 years; adults: 18–39 years and seniors: ≥ 40 years) and starting age (early starters: < 14 years and late starters: > 18 years) on these asymmetries were examined. Two databases were searched for scientific articles that examined upper extremity BMC in tennis players. Pooling of the individual study effect sizes was conducted using the random-effects model. Three subgroup analyses were performed based on sex, chronological age and starting age. Out of the 15 included studies 24 effect sizes were extracted resulting in a significant difference in BMC value between the dominant and nondominant upper extremity of the tennis players (Standardised Mean Difference: 0.85 [95% CI: 0.67–1.03]). The three subgroup analyses all showed medium to strong effect sizes and significant intergroup differences. To conclude, BMC was significantly higher in the dominant upper extremity compared to the nondominant upper extremity in tennis players. Nevertheless, the influence of training volume and playing experience on these asymmetries are yet to be examined.     

Relationship between skeletal muscle contractile properties and power production capacity in female Olympic rugby players

This study aimed to determine which contractile properties measured by tensiomyography (TMG) could better differentiate athletes with high- and low-power values, as well as to analyse the relationship between contractile properties and power production capacity. The contractile properties of the vastus medialis (VM), rectus femoris (RF) and vastus lateralis (VL) of an Olympic women’s Rugby Sevens team (n?=?14) were analysed before a Wingate test in which their peak power output (PPO) was determined. Athletes were then divided into a high-power (HP) and a low-power (LP) group. HP presented an almost certainly higher PPO (9.8?±?0.3 vs. 8.9?±?0.4 W kg^?1, ES?=?3.00) than LP, as well as a very likely lower radial displacement (3.39?±?1.16 vs. 5.65?±?1.50?mm, ES?=?1.68) and velocity of deformation (0.08?±?0.02 vs. 0.13?±?0.03 mm ms^?1, ES?=?1.87) of the VL. A likely lower time of delay was observed in HP for all analysed muscles (ES?>?0.60). PPO was very largely related to the radial displacement (r?=??0.75, 90% CI?=??0.90 to ?0.44) and velocity of deformation (r?=??0.70, 90% CI?=??0.87 to ?0.34) of the VL. A large correlation was found between PPO and the time of delay of the VL (r?=??0.61, 90% CI?=??0.84 to ?0.22). No correlations were found for the contractile properties of RF or VM. These results highlight the importance of VL contractile properties (but not so much those of RF and VM) for maximal power production and suggest TMG as a practical technique for its evaluation.