Validity of spatiotemporal and ground reaction force estimates during resisted sprinting with a motorized loading device.

We aimed to examine the validity of estimating spatiotemporal and ground reaction force (GRF) parameters during resisted sprinting using a robotic loading device (1080 Sprint). Twelve male athletes (age: 20.9 ± 2.2 years; height: 174.6 ± 4.2 cm; weight: 69.4 ± 6.1 kg; means ± SDs) performed maximal resisted sprinting with three different loads using the device. The step frequency and length and step-averaged velocity, anteroposterior GRF (Fap ), and the ratio of Fap to resultant GRF (RF) were estimated using the velocity and towing force data measured using the device. Simultaneously, the corresponding values were measured using a 50-m force plate system. The proportional and fixed biases of the estimated values against those measured using the force plate system were determined using ordinary least product (OLP) regression analysis. Proportional and fixed biases were observed for most variables. However, the proportional bias was small or negligible except for the step frequency. Conversely, the fixed bias was small for step-averaged velocity (0.11 m/s) and step length (0.04 m), whereas it was large for step frequency (0.54 step/s), Fap (16N), and RF (2.22%). For all variables except step frequency, the prediction intervals in the OLP regression dramatically decreased when the corresponding values were smoothed using a two-step moving average. These results indicate that by using the velocity and force data recorded in the loading device, most of the spatiotemporal and GRF variables during resisted sprinting can be estimated with some correction of the fixed bias and data smoothing using the two-step moving average.

The effect of biological maturity status on ground reaction force production during sprinting.

Sprint ability develops nonlinearly across childhood and adolescence. However, the underpinning ground reaction force (GRF) production is not fully understood. This study aimed to uncover the kinetic factors that explain these maturation-related sprint performance differences in Japanese boys and girls. A total of 153 untrained schoolchildren (80 boys, 73 girls) performed two 50-m maximal effort sprints over a 52-force-platform system embedded in an indoor track. Maturity offset (years from peak height velocity; PHV) was estimated using anthropometric data and used to categorise the children into six-year-long maturation groups (from group 1 [5.5-4.5 years before PHV] to group 6 [0.5 years before to 0.5 years after PHV). Maximum and mean step-averaged velocities across 26 steps were compared across consecutive maturation groups, with further GRF analysis (means and waveforms [statistical parametric mapping]) performed when velocity differences were observed. For boys, higher maximum velocities (effect size ± 90% CI = 1.63 ± 0.69) were observed in maturation group 2 (4.5-3.5 years before PHV) compared to group 1 (5.5-4.5 years before PHV), primarily attributable to higher antero-posterior GRFs across shorter ground contacts. Maximum velocities increased from maturation group 4 (2.5-1.5 years before PHV) to group 5 (1.5-0.5 years before PHV) in the girls (effect size ± 90% CI = 1.00 ± 0.78), due to longer ground contacts rather than higher GRFs per se. Waveform analyses revealed more effective reversal of braking forces and higher propulsive forces (e.g. 14%-77% of stance 4), particularly for comparisons involving boys, which suggested potentially enhanced stretch-shortening ability. Youth sport practitioners should consider these maturation-specific alterations when evaluating young athletes' sprint abilities.

Age-related differences in kinematics and kinetics of sprinting in young female.

This study aimed to investigate the age-related differences in sprinting performance, kinematic and kinetic variables in girls aged between 7.0 and 15.3 years. Step-to-step spatiotemporal variables and ground reaction impulses during sprinting were collected in 94 Japanese girls across a 50 m inground force plate system. From the results, a difference in rate of development in sprinting performance in girls over 12.7 years compared with younger girls (YG) was observed. The older girls (OG) became slightly slower each year (-0.09 m/s/y) compared to the YG (0.24 m/s/y) who increased their running speed. Moreover, height increased by 6.3 cm/y in YG and only 3.6 cm/y in OG, while step length during the maximal speed phase increased by 0.08 m/y in YG and plateaued in OG (0.01 m/y). Propulsive impulse during the initial acceleration phase was the kinetic variable to differ in rate of development between the age groups with an increase of 0.024 Ns/y in the YG compared to -0.010 Ns/y in OG. The development of sprinting ability in Japanese girls was more rapid before age 12.7 years. The difference in rate of development in sprinting ability can be primarily attributed to greater growth rates in YG, contributing to increases in the propulsive impulse during the initial acceleration phase and step length during the maximal speed phase. The limited gains in step length and the propulsive impulse in OG may reflect their reduced growth rate in height and the fact that increases in fat mass with maturation impaired relative force production.

How sprinters accelerate beyond the velocity plateau of soccer players: Waveform analysis of ground reaction forces.

Forces applied to the ground during sprinting are vital to performance. This study aimed to understand how specific aspects of ground reaction force waveforms allow some individuals to continue to accelerate beyond the velocity plateau of others. Twenty-eight male sprint specialists and 24 male soccer players performed maximal-effort 60-m sprints. A 54-force-plate system captured ground reaction forces, which were used to calculate horizontal velocity profiles. Touchdown velocities of steps were matched (8.00, 8.25, and 8.50 m/s), and the subsequent ground contact forces were analyzed. Mean forces were compared across groups and statistical parametric mapping (t tests) assessed for differences between entire force waveforms. When individuals contacted the ground with matched horizontal velocity, ground contact durations were similar. Despite this, sprinters produced higher average horizontal power (15.7-17.9 W/kg) than the soccer players (7.9-11.9 W/kg). Force waveforms did not differ in the initial braking phase (0%-~20% of stance). However, sprinters attenuated eccentric force more in the late braking phase and produced a higher antero-posterior component of force across the majority of the propulsive phase, for example, from 31%-82% and 92%-100% of stance at 8.5 m/s. At this velocity, resultant forces were also higher (33%-83% and 86%-100% of stance) and the force vector was more horizontally orientated (30%-60% and 95%-98% of stance) in the sprinters. These findings illustrate the mechanisms which allowed the sprinters to continue accelerating beyond the soccer players' velocity plateau. Moreover, these force production demands provide new insight regarding athletes' strength and technique training requirements to improve acceleration at high velocity.

Vertical Impulse as a Determinant of Combination of Step Length and Frequency During Sprinting.

This study aimed to clarify the influence of vertical impulse on the magnitude of step length (SL) and frequency (SF) and their ratio during the entire acceleration phase of maximal sprinting. Thirty-nine male soccer players performed 60-m sprints, during which step-to-step ground reaction forces were recorded over a 50-m distance. The mean values of spatiotemporal variables and vertical and anteroposterior impulses for each set of four steps during the acceleration phase until the 28th step were computed to examine relationships among variables in seven sections. When controlling for the influence of running speed, stature and corresponding duration of braking or propulsion, vertical impulses during the propulsive phase at the 1st-4th step section and those during the braking phases in the sections from the 5th-8th to the 25th-28th step were positively correlated with SL and SL/SF ratio and negatively correlated with SF, whereas the anteroposterior impulses were not correlated with SL or SF. In conclusion, the current results demonstrate that vertical impulse during the propulsive phase in the initial acceleration stage and that during the braking phase in the middle and later acceleration stages are the most likely determinants of the combination of SL and SF during sprinting.

Age-Related Differences in Spatiotemporal Variables and Ground Reaction Forces During Sprinting in Boys.

PURPOSE: We aimed to elucidate age-related differences in spatiotemporal and ground reaction force variables during sprinting in boys over a broad range of chronological ages. METHODS: Ground reaction force signals during 50-m sprinting were recorded in 99 boys aged 6.5-15.4 years. Step-to-step spatiotemporal variables and mean forces were then calculated. RESULTS: There was a slower rate of development in sprinting performance in the age span from 8.8 to 12.1 years compared with younger and older boys. During that age span, mean propulsive force was almost constant, and step frequency for older boys was lower regardless of sprinting phase. During the ages younger than 8.8 years and older than 12.1 years, sprint performance rapidly increased with increasing mean propulsive forces during the middle acceleration and maximal speed phases and during the initial acceleration phase. CONCLUSION: There was a stage of temporal slower development of sprinting ability from age 8.8 to 12.1 years, being characterized by unchanged propulsive force and decreased step frequency. Moreover, increasing propulsive forces during the middle acceleration and maximal speed phases and during the initial acceleration phase are probably responsible for the rapid development of sprinting ability before and after the period of temporal slower development of sprinting ability.

Validity of muscle thickness-based prediction equation for quadriceps femoris volume in middle-aged and older men and women.

BACKGROUND: This study examined the validity of muscle thickness (MT)-based prediction equation for the muscle volume of the quadriceps femoris (QFMV) by evaluating the applicability of a prediction equation previously derived from young men and by developing a new prediction equation in middle-aged and older individuals. METHODS: The MT at the midpoint of the thigh anterior and QFMV were determined using ultrasonography and magnetic resonance imaging in 30 men and 30 women aged 51 to 77 years. First, we examined the validity of the MT-based prediction equation previously developed for young men to estimate the QFMV of middle-aged and older individuals. Second, we allocated the subjects to validation or cross-validation group and developed a prediction equation for estimating the QFMV using a stepwise multiple regression analysis. RESULTS: The published equation generated a small but a significant difference between the measured and estimated QFMV, with a systematic error depending on the size of QFMV. A multiple regression analysis for the validation group produced the following equation: QFMV (cm3) = (sex × 267.7) + (MT × 249.3) + (thigh length × 41.1) - 1663.7 (sex: man = 1, woman = 0). R 2 and SEE of the regression equation were 0.888 and 124.4 cm3 (12.0 %), respectively. The developed equation was validated and cross-validated. CONCLUSION: For middle-aged and older individuals, the prediction equation previously derived from young men is not applicable, and the newly developed prediction equation with sex, MT, and thigh length as independent variables is applicable for estimating QFMV.

Muscle shear modulus measured with ultrasound shear-wave elastography across a wide range of contraction intensity.

INTRODUCTION: In this study we examine the repeatability of measuring muscle shear modulus using ultrasound shear-wave elastography between trials and between days, and the association between shear modulus and contraction intensity over a wide range of intensities. METHODS: Shear modulus of the biceps brachii was determined using ultrasound shear-wave elastography during static elbow flexion (up to 60% of maximal contraction) in healthy young adults. RESULTS: The correspondence of shear modulus was confirmed in phantoms between the manufacturer-calibrated values and the shear-wave elastography values. The intraclass correlation coefficient of muscle shear modulus was high: 0.978 between trials and 0.948 between days. Shear modulus increased linearly with elbow flexion torque across contraction intensity, and its slope was associated negatively with muscle strength. CONCLUSIONS: Muscle shear modulus measured with ultrasound shear-wave elastography may be useful for inferring muscle stiffness across a wide range of contraction intensity. In addition, it has high repeatability between trials and between days.

Neuromuscular adaptations following 12-week maximal voluntary co-contraction training.

PURPOSE: The present study examined neuromuscular adaptations following 12-week maximal voluntary co-contraction training. METHODS: Sixteen young men were allocated to training (TG, n = 9) or control (CG, n = 7) group. TG conducted a training program (3 days/week), which consisted of 4-s maximal voluntary contractions of elbow flexors and extensors by simultaneously contracting both muscle groups at 90° of the elbow joint, followed by 4-s muscle relaxation (10 repetitions/set, 5 sets/day) for 12 weeks. In addition to the muscle thicknesses of elbow flexors and extensors, the torque and electromyograms (EMGs) of the two muscle groups during isometric maximal voluntary contraction (MVC) were determined before (Pre), after 4 weeks, and 12 weeks of intervention. RESULTS: After intervention, CG showed no significant changes in all measured variables. In TG, MVC torque significantly increased in both elbow flexors (+13 % at 4 weeks and +15 % at 12 weeks) and extensors (+27 % at 4 weeks and +46 % at 12 weeks) from Pre. Muscle thickness also significantly increased in both elbow flexors (+4 %) and extensors (+4 %) at 12 weeks. Agonist EMG activities during MVC significantly increased in both elbow flexors (+31 % at 4 weeks and +44 % at 12 weeks) and extensors (+27 % at 4 weeks and +40 % at 12 weeks), without changes in antagonist involuntary coactivation level in both muscle groups. CONCLUSION: These results indicate that maximal voluntary co-contraction is applicable as a training modality for increasing the size and strength of antagonistic muscle pairs without increasing involuntary coactivation level.

Kinematic and Kinetic Profiles of Trunk and Lower Limbs during Baseball Pitching in Collegiate Pitchers.

The purpose of this study was to clarify differences in the kinematic and kinetic profiles of the trunk and lower extremities during baseball pitching in collegiate baseball pitchers, in relation to differences in the pitched ball velocity. The subjects were 30 collegiate baseball pitchers aged 18 to 22 yrs, who were assigned to high- (HG, 37.4 ± 0.8 m·s(-1)) and low-pitched-ball-velocity groups (LG, 33.3 ± 0.8 m·s(-1)). Three-dimensional motion analysis with a comprehensive lower-extremity model was used to evaluate kinematic and kinetic parameters during baseball pitching. The ground-reaction forces (GRF) of the pivot and stride legs during pitching were determined using two multicomponent force plates. The joint torques of hip, knee, and ankle were calculated using inverse-dynamics computation of a musculoskeletal human model. To eliminate any effect of variation in body size, kinetic and GRF data were normalized by dividing them by body mass. The maxima and minima of GRF (Fy, Fz, and resultant forces) on the pivot and stride leg were significantly greater in the HG than in the LG (p < 0.05). Furthermore, Fy, Fz, and resultant forces on the stride leg at maximum shoulder external rotation and ball release were significantly greater in the HG than in the LG (p < 0.05). The hip abduction, hip internal rotation and knee extension torques of the pivot leg and the hip adduction torque of the stride leg when it contacted the ground were significantly greater in the HG than in the LG (p < 0.05). These results indicate that, compared with low-ball-velocity pitchers, high-ball-velocity pitchers can generate greater momentum of the lower limbs during baseball pitching. Key pointsHigh-ball-velocity pitchers are characterized by greater momentum of the lower limbs during pitching motion.For high-pitched-ball velocity, stabilizing lower limbs during pitching plays an important role in order to increase the rotation and forward motion of the trunk.Computation of the lower-extremity kinetics and measurement of lower-extremity strength may help clarify the role of muscle strength in determining knee and hip function in baseball pitching.

Trunk muscle activities during abdominal bracing: comparison among muscles and exercises.

Abdominal bracing is often adopted in fitness and sports conditioning programs. However, there is little information on how muscular activities during the task differ among the muscle groups located in the trunk and from those during other trunk exercises. The present study aimed to quantify muscular activity levels during abdominal bracing with respect to muscle- and exercise-related differences. Ten healthy young adult men performed five static (abdominal bracing, abdominal hollowing, prone, side, and supine plank) and five dynamic (V- sits, curl-ups, sit-ups, and back extensions on the floor and on a bench) exercises. Surface electromyogram (EMG) activities of the rectus abdominis (RA), external oblique (EO), internal oblique (IO), and erector spinae (ES) muscles were recorded in each of the exercises. The EMG data were normalized to those obtained during maximal voluntary contraction of each muscle (% EMGmax). The % EMGmax value during abdominal bracing was significantly higher in IO (60%) than in the other muscles (RA: 18%, EO: 27%, ES: 19%). The % EMGmax values for RA, EO, and ES were significantly lower in the abdominal bracing than in some of the other exercises such as V-sits and sit-ups for RA and EO and back extensions for ES muscle. However, the % EMGmax value for IO during the abdominal bracing was significantly higher than those in most of the other exercises including dynamic ones such as curl-ups and sit-ups. These results suggest that abdominal bracing is one of the most effective techniques for inducing a higher activation in deep abdominal muscles, such as IO muscle, even compared to dynamic exercises involving trunk flexion/extension movements. Key PointsTrunk muscle activities during abdominal bracing was examined with regard to muscle- and exercise-related differences.Abdominal bracing preferentially activates internal oblique muscles even compared to dynamic exercises involving trunk flexion/extension movements.Abdominal bracing should be included in exercise programs when the goal is to improve spine stability.

Effects of body mass-based squat training in adolescent boys.

The purpose of this study was to determine the effects of body mass-based squat training on body composition, muscular strength and motor fitness in adolescent boys. Ninety-four boys (13.7 ± 0.6 yrs, 1.60 ± 0.09 m, 50.2 ± 9.6 kg) participated in this study and were randomly assigned to training (n = 36) or control (n = 58) groups. The training group completed body mass-based squat exercise training (100 reps/day, 45 sessions) for 8 weeks. Body composition and muscle thickness at the thigh anterior were determined by a bioelectrical impedance analyzer and ultrasound apparatus, respectively. Maximal voluntary knee extension strength and sprint velocity were measured using static myometer and non-motorized treadmill, respectively. Jump height was calculated using flight time during jumping, which was measured by a matswitch system. The 8-wk body mass-based squat training significantly decreased percent body fat (4.2%) and significantly increased the lean body mass (2.7%), muscle thickness (3.2%) and strength of the knee extensors (16.0%), compared to control group. The vertical jump height was also significantly improved by 3.4% through the intervention. The current results indicate that body mass-based squat training for 8 weeks is a feasible and effective method for improving body composition and muscular strength of the knee extensors, and jump performance in adolescent boys. Key pointsAn 8-wk body mass-based squat exercise training decreased percent body fat in adolescent boys.The body mass-based squat exercise training increased muscle size and strength capability of the knee extensors in adolescent boys.The squat exercise training improves vertical jump height in adolescent boys.

Effects of Different Isometric Training Programs on Muscle Size and Function in the Elbow Flexors.

It remains unknown whether a regimen of a combination of high- and low-intensity resistance training increases muscle size and maximal voluntary isometric contraction (MVC) simultaneously. This study aimed to clarify the effect of the combination of high- and low-intensity resistance training on muscle size and neuromuscular function in the elbow flexors. Sixteen male adults participated in a 9-week isometric training regimen in elbow joint flexion of each arm. We randomly assigned two different training regimens to left and right arms: one aiming to strengthen maximal strength (ST) and the other aiming to develop muscle size as well as maximal strength, which consists of one contraction to volitional failure with 50% of MVC added to ST (COMB). Following the 3-week training to volitional failure as familiarization, the participants conducted the 6-week ST and COMB training in each arm. Before the intervention, and at the third (Mid) and ninth (Post) weeks, MVC and muscle thickness in the anterior part of the upper arm (ultrasound) were measured. Muscle cross-sectional area (mCSA) was derived from the obtained muscle thickness. From Mid to Post, the relative change in MVC was similar in both arms. The COMB regimen increased muscle size, but no significant change was found in ST. Following the 3-week isometric training to volitional failure, the 6-week training regimen for developing maximal voluntary and muscle hypertrophy increased MVC, with increasing mCSA, and the training-induced change in MVC was similar to that for developing maximal voluntary strength alone.

Influence of horizontal resistance loads on spatiotemporal and ground reaction force variables during maximal sprint acceleration.

This study aimed to elucidate the influence of horizontal resistance loads on the spatiotemporal and ground reaction force (GRF) variables during maximal sprint acceleration. Nine male sprinters (20.2 ± 1.2 years; 175.3 ± 4.5 cm, 69.7 ± 6.1 kg) performed sprint-running with six loading conditions of one unresisted and five resisted loads of 4, 6, 8, 10, and 12 kg using a resistance training device with intelligent drag technology. During the trials, the GRFs for all steps were determined using a 50-m force plate system. The spatiotemporal and GRF variables at running velocity of every 0.5 m/s were obtained and compared across the loading conditions. The maximal running velocity under 0, 4, 6, 8, 10, and 12 kg loading conditions were 9.84 ± 0.41, 8.55 ± 0.41, 8.09 ± 0.33, 7.62 ± 0.34, 7.11 ± 0.31, and 6.71 ± 0.29 m/s, respectively. ANOVA revealed significant main effects of load on the measured variables (η2 = 0.236-0.715, p < 0.05), except for stance-averaged anteroposterior GRF and braking impulse. However, the observed differences between the loading conditions were small, with approximately 4% (1.3-7.5%) for the GRF variables and approximately 9% (1.2-22.3%) for the spatiotemporal variables. The present study indicates that horizontal resistance load in sprint acceleration has little impact on the spatiotemporal and GRF variables at a given running velocity. In contrast to a general recommendation, one should adopt a heavy load in resisted sprint aiming to improve performance in the earlier stage of maximal sprint acceleration.

Knee extensor strength is associated with Mini-Mental State Examination scores in elderly men.

The present study examined whether the strength capability of knee extensor muscles is associated with global cognitive function, assessed by Mini-Mental State Examination (MMSE), in non-disabled elderly men. Isometric torques during maximal voluntary knee extension, plantar flexion, and elbow flexion and MMSE scores were determined in 39 non-disabled men aged 61-79 years and used for the cross-sectional analysis examining the associations among the measured variables. Moreover, 27 of the subjects participated in a training program consisted of body mass-based exercises (sitting down onto and standing up from a chair, hip joint extension and flexion, calf raises, side leg raises, and trunk flexion and extension) 6 days a week for 3 months. Isometric torques and MMSE scores were determined after the intervention. Among the data before intervention, only knee extension torque (KET) and KET relative to body mass (KET/BM) significantly correlated to the MMSE scores: r = 0.579 (P < 0.0001) for KET and r = 0.520 (P < 0.001) for KET/BM. After the intervention, KET and KET/BM increased significantly, but MMSE score did not. However, the absolute change in MMSE scores was significantly associated with that in KET (r = 0.381, P < 0.05) and KET/BM (r = 0.422, P < 0.05). These findings indicate that the strength capability of knee extensors is associated with global cognitive function in non-disabled elderly men, and provide a new perspective to a general concept that exercises strengthening knee extensor muscles should be included in resistance training programs for elderly individuals.

Differences between junior and senior male sprinters in physiological variables associated with sprint performance.

BACKGROUND: The physiological variables associated with sprint performance have been extensively studied. However, little information is available on how the corresponding physiological variables differ between junior and senior sprinters. This study aimed to examine this subject. METHODS: In addition to the maximal running velocity achieved while sprinting over 60-m, body composition, muscle thicknesses of the trunk and lower limbs, performance scores of four jumping tasks (countermovement, rebound, standing long, and standing five-step jumps), and 10-s maximal anaerobic pedaling power were determined in 17 junior and 22 senior male sprinters. RESULTS: In the junior and senior sprinters, most of the measured variables were significantly correlated with the maximal running velocity. Analysis of covariance showed that only the maximal pedaling power relative to the body mass was significantly different between the two groups in the regression equation slope of the relationship with maximal running velocity (0.20 for junior and 0.64 for senior sprinters). Additionally, multiple regression analysis revealed that while the standing five-step jump distance (40%) and the size of the psoas major muscle (23%) were selected as explanatory factors for maximal running velocity in the junior sprinters, maximal pedaling power relative to the body mass (63%) was selected in the senior sprinters. CONCLUSIONS: This study suggests that the following physiological factors associated with sprint running performance differ between the junior and senior sprinters: the ability of repetitive jumping in the horizontal forward direction and muscularity of hip flexors in the junior sprinters versus the anaerobic capacity in senior sprinters. Therefore, coaches and athletes need to take into consideration that the physiological variables to be focused on are different for each generation.

Force-velocity relationship profile of elbow flexors in male gymnasts.

BACKGROUND: The theoretical maximum force (F0), velocity (V0), and power (Pmax) of athletes calculated from the relationship between force and velocity (F-V relationship) and the slope of the F-V relationship, reflect their competitive and training activity profiles. Evaluating the F-V relationship of athletes facilitates categorizing the profiles of dynamic muscle functions in relation to long-term sport-specific training. For gymnastics, however, no studies have tried to examine the profiles of F-V relation and power output for upper limb muscles in relation to the muscularity, while the use of the upper extremities in this sport is very unique as described earlier. PURPOSE: It was hypothesized that the F-V relationship of the elbow flexion in gymnasts might be characterized by low capacity for generating explosive force, notably in terms of the force normalized to muscle size. METHODS: The F0, V0, and Pmax derived from the force-velocity relationship during explosive elbow flexion against six different loads (unloaded condition, 15, 30, 45, 60, and 75% of maximal voluntary isometric elbow flexion force (MVFEF)) for 16 gymnasts (GYM) and 22 judo athletes (JD). F0 and Pmax were expressed as values relative to the cross-sectional area index (CSAindex) of elbow flexors (F0/CSAindex and Pmax/CSAindex, respectively), which was calculated from muscle thickness in the anterior upper arm. The electromyogram (EMG) activities of the biceps brachii (BB) during the maximal isometric and dynamic tasks were also determined. RESULTS: There were no significant differences in CSAindex of elbow flexors between GYM and JD. MVFEF/CSAindex for GYM was significantly lower than that for JD. Force was linearly associated with velocity in the dynamic elbow flexion for all the participants (r =  - 0.997 to -0.905 for GYM, r =  - 0.998 to -0.840 for JD). F0, F0/ CSAindex, V0, Pmax, Pmax/CSAindex, and MVFEF were significantly lower in GYM than in JD. The activity levels of BB during the dynamic tasks tended to be lower in GYM than in JD at load of <45%MVC. CONCLUSION: Gymnasts cannot generate explosive elbow flexion force corresponding to their muscle size. This may be due to low neuromuscular activities during the maximal dynamic tasks against relatively low loads.

A new approach to quantify angles and time of changes-of-direction during soccer matches.

BACKGROUND AND AIMS: Soccer players frequently perform change-of-directions (CODs) at various speeds during matches. However, tracking systems have shown limitations to measure these efforts. Therefore, the aim of the present study was to propose a new approach to measure CODs using a local positioning system (LPS), and clarify position-related difference in profile of CODs by using the approach. METHODS: The x- and y-coordinate data for each soccer player were measured with a local positioning system. Speed, acceleration, jerk, and direction of speed were derived from the coordinate data. Based on accelerations of above 2 m/s2, the onsets and ends of CODs derived from jerk were identified (COD duration). Changes of direction of speed (θCOD) were determined for the corresponding period. Six collegiate male soccer players performed CODs according to 13 set angles (0-180°; every 15°) so that differences between θCOD and set angle could be determined (Exp. 1). Relative frequency distributions of θCOD and number of CODs were determined in 79 collegiate and amateur male soccer players during 9 soccer matches (Exp. 2). RESULTS: In Exp. 1, θCOD was positively related to set angle (r = 0.99). Each θCOD was smaller than the corresponding set angle, and the difference became greater with increasing COD angle. In Exp. 2, The number of CODs in a match was 183 ± 39 across all positions. There were no significant position-related differences in the number of CODs. The duration of a COD was 0.89 ± 0.49 s across all positions. The relative frequency distribution of θCOD revealed that the number of CODs at 0-15° and 105-135° tended to be higher than those at other angles during soccer matches. Further, θCOD was affected by the speed at the onset of COD during soccer matches (Exp. 2). CONCLUSIONS: The current findings demonstrate that θCOD derived from direction of speed and jerk may be a new indicator for evaluating COD during soccer matches.

Comparison of available equations to estimate sit-to-stand muscle power and their association with gait speed and frailty in older people: Practical applications for the 5-rep sit-to-stand test.

OBJECTIVES: This study aimed i) to compare relative sit-to-stand power (STSrel) values yielded by the different equations reported in the literature; ii) to examine the associations between STSrel, derived from the equations, and age, sex, frailty and habitual gait speed (HGS); and iii) to compare the ability of the different STSrel equations to detect frailty and low HGS in older adults. METHODS: 1568 participants (>65 years) were included. STSrel was calculated according to four validated equations. Frailty was assessed using the Frailty Trait Scale and HGS as the time to complete 3 m. ANOVA tests, regression analyses and receiver operator characteristic curves were used. RESULTS: There were significant differences among the STSrel values yielded by all the equations, which were higher in men compared to women and negatively associated with age (r = -0.21 to -0.37). STSrel was positively and negative associated to HGS and frailty, respectively, in both men (r = 0.29 to 0.36 and r = -0.18 to -0.45) and women (r = 0.23 to 0.45 and r = -0.09 to -0.57) regardless of the equation used. Area under the curve values varied between 0.68 and 0.80 for Alcazar's, 0.67-0.80 for Ruiz-Cárdenas's, 0.51-0.65 for Smith's, and 0.68-0.80 for Takai's equations. Low STSrel indicated an increased probability of having both low HGS and frailty (OR [95%CI] = 1.6 to 4.5 [1.21 to 5.79]) for all equations with the exception of Smith's equations for frailty in women. CONCLUSIONS: All the equations presented adequate criterion validity, however, the Alcazar's equation showed the highest level of clinical relevance according to its ability to identify older people with frailty and low HGS.

Elderly oarsmen have larger trunk and thigh muscles and greater strength than age-matched untrained men.

To evaluate whether regularly performed rowing exercise affects the trunk muscles size and function, and to examine the effect of rowing exercise on thigh muscle size and function in elderly rowers, we compared the cross-sectional area (CSA) and strength of these muscles in elderly male rowers and in age-matched untrained men. Participants were 16 elderly rowing-trained men (ROW age, 67.8 +/- 2.3 years) and 18 elderly untrained men (CON 66.2 +/- 3.0 years). CSA was measured by MRI in the trunk and thigh muscles. Isometric trunk flexion force and leg extension power were measured. ROW had a 20% larger total trunk muscle CSA than CON (P < 0.01); rectus abdominis was 27% larger, psoas major 64% larger, and erector spinae 14% larger in ROW than in CON (P < 0.05-0.001). Isometric trunk flexion force was related to the CSA of the rectus abdominis (r = 0.777, P < 0.001) and psoas major (r = 0.694, P < 0.001), and was 42% larger in ROW than in CON (P < 0.001). However, force adjusted for the CSA of the muscles did not differ significantly between CON and ROW. In ROW, the CSA was 13% larger in the total thigh muscles (P < 0.01), and leg extension power was 43% higher than in CON (P < 0.001). These results suggest that rowing exercise is a favorable training modality for the trunk muscles, especially psoas major and that it improves thigh muscle size and function in elderly men.