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.

No Association of Plantar Aponeurosis Stiffness with Medial Longitudinal Arch Stiffness.

Lower stiffness of the medial longitudinal arch is reportedly a risk factor for lower leg disorders. The plantar aponeurosis is considered essential to maintaining the medial longitudinal arch. It is therefore expected that medial longitudinal arch stiffness is influenced by plantar aponeurosis stiffness. However, this has not been experimentally demonstrated. We examined the relationship between the plantar aponeurosis stiffness and medial longitudinal arch stiffness in humans in vivo. Thirty young subjects participated in this study. The navicular height and shear wave velocity (an index of stiffness) of the plantar aponeurosis were measured in supine and single-leg standing positions, using B-mode ultrasonography and shear wave elastography, respectively. The medial longitudinal arch stiffness was calculated based on body weight, foot length, and the difference in navicular height between the supine and single-leg standing conditions (i. e., navicular drop). Shear wave velocity of the plantar aponeurosis in the supine and single-leg standing positions was not significantly correlated to medial longitudinal arch stiffness (spine: r=-0.14, P=0.45 standing: r=-0.16, P=0.41). The findings suggest that the medial longitudinal arch stiffness would be strongly influenced by the stiffness of foot structures other than the plantar aponeurosis.

Characteristics of Relative Age Effects and Anthropometric Data in Japanese Recreational and Elite Male Junior Baseball Players.

BACKGROUND: The mechanisms underlying the relative age effect (RAE), a biased distribution of birth dates, in sport events have been investigated for more than two decades. The present study investigated the characteristics of the RAE in baseball and anthropometric data (height and weight) among recreational junior baseball players as well as elite players, using data extracted from national surveys. METHODS: Birth and anthropometric data were obtained from 4464 Japanese students as elementary school, junior high school, and high school players. RESULTS: Significant RAEs were noted in recreational junior high school and high school players, but not in elementary school players, and the effect size became larger with increasing grade (0.063 in elementary school players, 0.151 in junior high school players, and 0.227 in high school players). We also observed a significant RAE for elite elementary, junior high, and high school players. However, the effect size of elite players became smaller with increasing grade (0.563 in elementary school players, 0.358 in junior high school players, and 0.343 in high school players). Height and weight values were significantly larger in elite elementary and junior high school players than in recreational elementary and junior high school players, but height was almost the same between recreational and elite high school players. CONCLUSION: The characteristics of RAEs differed between recreational and elite junior baseball players. Anthropometric data were also different, depending on birth data, and between recreational and elite baseball players in elementary and junior high school students.

Association between toe grasping strength and accelerometer-determined physical activity in middle-aged and older women.

[Purpose] To test the hypothesis that toe grasping strength is associated with daily physical activity in older adults. [Subjects] Fifty-seven Japanese women, aged 52-78 years, volunteered. [Methods] Toe grasping and knee extension strength were measured. Physical activity was also measured, using an accelerometer, and the total duration of each level of exercise intensity (light, moderate, and vigorous) and average step counts were calculated. Subjects were separated into two groups on the basis of accelerometer-determined step counts: LOW (n=28, <8000 steps/day) and HIGH (n=29, ≥8000 steps/day). [Results] Body mass index and body composition (% fat and fat-free mass) were similar between the two groups. Absolute and relative toe grasping strengths (divided by body weight) were greater in HIGH than in LOW. However, both absolute and relative knee extension strength were similar between the groups. Relative toe grasping and knee extension strength correlated with all 3 intensities of physical activity and average step count. After adjusting for age, the duration of light plus moderate physical activity and average step counts correlated to toe grasping strength but not to knee extension strength. [Conclusion] Our results suggest that toe grasping strength may be associated with the amount of light intensity daily physical activity.

Association between forearm muscle thickness and age-related loss of skeletal muscle mass, handgrip and knee extension strength and walking performance in old men and women: a pilot study.

Very little information is available concerning the relationship between handgrip strength and muscle size in the upper and lower extremities, especially the forearm muscle itself. To investigate the relationships among ultrasound-measured forearm muscle thickness from the radius and ulna bone interface with handgrip strength, knee extension strength, walking speed and absolute/relative total skeletal muscle mass (TMM), 32 Japanese men and 21 Japanese women ages 70-83 years had muscle thickness (MT) measured by ultrasound. In the forearm, two MTs (forearm-radius and forearm-ulna MT) were measured. TMM was estimated from an ultrasound-derived prediction equation. Handgrip-strength was significantly correlated with forearm-ulna MT in both men and women. There were no significant correlations between forearm MT and walking speed in either sex. In men, both forearm-radius and forearm-ulna MT were significantly correlated with TMM and TMM index. In women, a significant correlation was only observed between forearm-ulna MT and TMM index. Our results suggest that forearm-ulna MT may be a useful parameter for evaluating handgrip strength and TMM index in older Japanese men and women.

Association between site-specific muscle loss of lower body and one-leg standing balance in active women: the HIREGASAKI study.

AIM: To test the hypothesis that static balance is associated with site-specific loss of muscle mass in older adults. METHODS: A total of 57 active women aged 52-83 years had their muscle thickness (MTH) measured by ultrasound at four sites on the anterior and posterior aspects of their upper- and lower-leg. MTH ratios were calculated to assess the site-specific muscle loss. One-leg standing balance with eyes open and maximum isometric knee extension/flexion strength were measured. Daytime physical activity was also measured. The participants were separated into three groups based on achieved timed one-leg balance test: less than 60 s (n = 19, G1), 60-120 s (n = 12, G2) and over 120 s (n = 26, G3). RESULTS: Age was inversely correlated to the upper-leg (A50 : P70) MTH ratios (r = -0.389, P < 0.001), but not lower-leg ratio (r = 0.047), thus site-specific muscle loss was observed in the upper-leg. Total muscle mass was similar among the groups. A50 : P70 MTH ratio and absolute and relative knee flexion strength were lower in G1 than in G3. Step counts and durations of moderate and vigorous exercise were lower in G1 and G2 than in G3. There were significant correlations between one-leg balance and A50 : P70 MTH ratio (r = 0.271, P < 0.05) and physical activity level (r = 0.357-0.481, P < 0.01). After adjusting for step count, one-leg balance was only correlated significantly with duration of vigorous exercise (r = 0.319, P < 0.05). CONCLUSION: Higher physical activity could have more impact on balance regulation, as the influence of site-specific muscle loss was weak in active women.

Is muscle strength ratio a criterion for diagnosis of site-specific muscle loss?

AIM: Recently, data have questioned the homogenous model of sarcopenia, and suggest that the loss of muscle mass could occur in a site-specific manner. It is unclear, however, whether a muscle strength ratio can be used to assess age-related, site-specific muscle loss. The purpose of the present study was to investigate the relationship between the age-related loss of thigh muscle, muscle function and gait performance. METHODS: A total of 55 men aged 18-79 years had muscle thickness (MTH) measured by ultrasound at three sites on the anterior (30% and 50% of thigh length) and posterior (70% of thigh length) aspects of the thigh. MTH ratios were calculated to assess the site-specific muscle loss (anterior 30% : posterior 70% MTH [A30:P70] and anterior 50% :posterior 70% MTH [A50:P70]). Walking performance, maximum isometric knee extension/flexion, toe-grasping and handgrip strength were measured. RESULTS: Age was inversely correlated with the ratios of A30:P70 (r=-0.332) and A50:P70 (r=-0.466). There were no significant correlations between the A30:P70 and A50:P70 ratios, and height and bodyweight. The A30 : P70 and A50 : P70 ratios were also not correlated with maximal walking speed. However, the A50:P70 ratio was significantly correlated with zig-zag walking (r=-0.350) and handgrip strength (r=0.334). In addition, these MTH ratios were also correlated with knee extension (r=0.309 and r=0.405), flexion (r=0.306 and r=0.412) and toe-grasping strength (r=0.265 and r=0.336). After adjusting for physical activity, the MTH ratios were still not correlated with ratio of muscle strength. CONCLUSION: Strength ratios did not correlate with MTH ratios. Our cross-sectional analysis suggests that age-related site-specific muscle loss could assess the decrease in absolute muscular strength, but not the ratio of muscle strength.

Lower body site-specific sarcopenia and accelerometer-determined moderate and vigorous physical activity: the HIREGASAKI study.

BACKGROUND AND AIMS: It is unknown if the site-specific muscle loss of ageing muscle is associated with accelerometer-determined daily step count and/or intensity of physical activity. The purpose of this study was to examine the relationships between accelerometer- determined physical activity and lower body muscle size in women. METHODS: Forty-eight women aged 52 to 76 years had their muscle thickness (MTH) measured by B-mode ultrasound at seven sites on the anterior and posterior aspects of their upper- and lower-leg. Daytime physical activity was measured using an accelerometer on 30 consecutive days and the total duration of each level of exercise intensity (light-PA, moderate-PA and vigorous-PA), average step count, and physical activity-related energy expenditure were calculated. RESULTS: Age was inversely correlated with anterior 30% upper-leg MTH (r=-0.296, p<0.05), but not with other measured MTH sites. Light-PA was not significantly (p>0.05) correlated with measured lower body MTH. However, moderate-PA was correlated (p<0.05) with lower-leg MTH, while vigorous-PA was correlated (p<0.05) with lower-leg and anterior 30% upper- leg MTH. Following adjustment for confounding factors, the anterior and posterior lower-leg MTH was positively correlated (p<0.05) with duration of moderate- PA and vigorous-PA, as well as average step count. CONCLUSIONS: Thus daily moderate and vigorous physical activity was associated with higher muscle mass in the lower leg, but not in the upper-leg muscle, suggesting that the site-specific upper-leg muscle loss may not be prevented or attenuated by daily physical activity.

Relationship between site-specific loss of thigh muscle and gait performance in women: the HIREGASAKI study.

Sarcopenia is observed as a site-specific loss of skeletal muscle mass, however, it is unknown whether the site-specific sarcopenia is associated with development of physical disability. The purpose of this study was to examine the relationship between age-related thigh muscle loss and gait performance. Fifty-three women aged 52-83 years had their thigh muscle thickness (MTH) measured by ultrasound at five sites on the anterior (30%, 50%, and 70% of thigh length) and posterior (50% and 70% of thigh length) aspects of their thigh. Maximum and normal walking speeds, zig-zag walking time, and maximal voluntary isometric knee extension and flexion strength were measured. Age was inversely correlated to the anterior and posterior MTH ratio (e.g., anterior 50%:posterior 70% MTH ratio [r=-0.426, p=0.002]), thus the site-specific muscle loss of the thigh was observed in the present sample. There were no significant correlations between the anterior/posterior MTH ratio and maximum and normal walking speeds. However, the ratios of anterior 50%:posterior 70% MTH (r=-0.430) and anterior 30%:posterior 70% MTH (r=-0.444) were correlated (p=0.001) to zig-zag walking test. After adjusting for age, height and weight, the anterior 30%:posterior 70% MTH (r=-0.292, p=0.040) was inversely correlated to zig-zag walking performance. Isometric knee extension strength was also inversely correlated to zig-zag walking. Our results suggest that an age-related loss of adductor/quadriceps muscles may be associated with a decrease in a relatively difficult task performance such as zig-zag walking.

Ultrasound assessment of adductor muscle size using muscle thickness of the thigh.

CONTEXT: Previous studies investigated the relationship between ultrasound-derived anatomical muscle thickness (MTH) and individual muscle cross-sectional area (CSA) and muscle volume in several limb and trunk muscles; however, the adductor muscle that contributes to hip adduction and pelvic stabilization, as well as balance ability, has not been studied. OBJECTIVE: To examine the relationship between MTH of the lower, middle, and upper thigh measured by B-mode ultrasound and the muscle CSA and volume of adductor muscle obtained by magnetic resonance imaging (MRI) to confirm the possibility of predicting adductor muscle CSA/volume using ultrasound-derived MTH. SETTING: University research laboratory. SUBJECTS: 10 men and 10 women (20-41 y old) volunteered to participate in this study. MAIN OUTCOME MEASURES: A series of continuous muscle CSAs along the thigh were measured by MRI scans (1.5-T scanner, GE Signa). In each slice, the anatomical CSA of the adductors was analyzed, and the muscle volume was calculated by multiplying muscle CSA by slice thickness. Thigh MTH was measured by B-mode ultrasound (Aloka SSD-500) at 5 sites (anterior 30%, 50%, and 70% and posterior 50% and 70% of thigh length). RESULTS: A strong correlation was observed between anterior 30% MTH and 30% adductor CSA in men (r = .845, P < .002) and women (r = .952, P < .001) and in both groups combined (r = .922, P < .001). Anterior 30% MTH was also strongly correlated to adductor muscle volume when combined with thigh length (n = 20, r = .949, P < .001). However, there were moderate or nonsignificant correlations between anterior and posterior 50% and 70% MTH and adductor muscle CSA/volume. CONCLUSIONS: The results suggest that MTH in the upper portion of anterior thigh best reflects adductor muscle CSA or muscle volume, while the lower portions of the anterior and posterior sites are least likely to predict adductor muscle size.

Effect of pressure intensity of graduated elastic compression stocking on muscle fatigue following calf-raise exercise.

The purpose of the present study was to examine the effects of wearing a graduated elastic compression (EC) stocking, with different pressure profiles during a fatiguing calf-raise exercise session, on the torque generating capacity after exercise. Fourteen subjects performed 15 sets of 10 repetitions of calf-raise exercise, wearing one of three stockings of different compression pressure profiles: two kinds of EC stockings (one (EC30) with 30mmHg at the ankle, 21-25mmHg at the calf, and 10mmHg below the knee, and the other (EC18) with 18, 12-14, and 7mmHg at the same regions, respectively) and a non-EC sport stocking as a control (CON). Before and after the exercise, torque and electromyographic (EMG) signals of medial gastrocnemius and soleus muscles were recorded during an evoked triplet contraction and the maximal voluntary contraction (MVC). All stockings had no effect on the decline of the MVC torque whereas the reduction of the evoke triplet torque in EC30 stocking condition was significantly smaller compared with that in CON (-6.4±8.5% for EC30 and -16.5±9.0% for CON, P<0.05). The reduction of the mean power frequency of EMG during MVC in the EC30 condition was significantly smaller than that in CON (-4.4±10.9Hz for EC30 and -18.7±7.9Hz for CON, P<0.05). These results suggest that the EC stocking with adequate pressure at the calf region relieves muscle fatigue of the triceps surae induced by calf-raise exercise.

Fatigue-induced changes in synergistic muscle force do not match tendon elongation.

This study aimed to investigate whether fatigue-induced changes in synergistic muscle forces match their tendon elongation. The medial gastrocnemius muscle (MG) was fatigued by repeated electrical stimulation (1 min x 5 times: interval 30 s, intensity: 20-30% of maximal voluntary plantar flexion torque) applied at the muscle belly under a partial occlusion of blood vessels. Before and after the MG fatigue task, ramp isometric contractions were performed voluntarily, during which tendon elongations were determined by ultrasonography, along with recordings of the surface EMG activities of MG, the soleus (SOL) and the lateral gastrocnemius (LG) muscles. The tendon elongation of MG and SOL in post-fatigue ramp was similar, although evoked MG forces dropped nearly to zero. In addition, for a given torque output, the tendon elongation of SOL significantly decreased while that of LG did not, although the activation levels of both muscles had increased. Results suggest that the fatigue-induced changes in force of the triceps surae muscles do not match their tendon elongation. These results imply that the tendons of the triceps surae muscles are mechanically coupled even after selective fatigue of a single muscle.

Joint angle dependence of intermuscle difference in postactivation potentiation.

The purpose of this study was to examine the effect of ankle joint angle on the intermuscle difference in postactivation potentiation (PAP) between the medial gastrocnemius (MG) and soleus (SOL) muscles. At the neutral position of joint angle, dorsiflexion of 20 degrees , and plantarflexion of 20 degrees , twitch responses were evoked by stimulating the posterior tibial nerve with supramaximal intensity before and after a 10-s maximal voluntary plantarflexion at each joint angle. Mechanical properties of the MG and SOL muscles were assessed simultaneously and separately by using mechanomyography (MMG), and the extent of potentiation of each muscle was evaluated by peak-to-peak amplitude of the MMG signal. The MG showed greater potentiation than the soleus after the conditioning MVC in the neutral and dorsiflexion position, while in the plantarflexion position no significant difference was found in PAP between MG and SOL. These results suggest that the difference in the magnitude of PAP between synergistic muscles is determined by a combination of the joint angle- and fiber composition-dependence of PAP.

Fatigue-related changes in fascicle-tendon geometry over repeated contractions: difference between synergist muscles.

Fatigue-induced changes in force production of synergist muscles were evaluated through observation of fascicle-tendon geometry and electromyography (EMG). Seven subjects performed 60 maximal isometric plantar flexions intermittently. No statistically significant intermuscle difference was observed in the decrease of mean EMG amplitudes or mean power frequency for the medial gastrocnemius (MG) and soleus (SOL) muscles. The tendon elongation of MG significantly decreased after the 19th contraction, and MG fascicle length increased after the 29th contraction, while SOL fascicle and tendon length did not change except for the last contraction. The declines in torques were highly correlated with the increase of MG fascicle length and decrease in tendon elongation in each subject, while no consistent relationship was found for SOL. These results suggest that changes in force-production of MG and SOL over repeated contractions differ, which is reflected in fascicle-tendon geometry.

The influence of fascicle behavior on the lack of velocity dependence in eccentric joint torque in humans: in vivo observation.

To investigate the relationship between fascicle behavior and joint torque, the fascicle behavior of the triceps surae during isometric and eccentric (30 and 60 deg/s) plantar flexion by maximal voluntary and submaximal electrical activation (MVA and SEA) was measured by realtime ultrasonography. Eccentric torque at 30 and 60 deg/s was significantly higher than isometric torque under SEA, but not under MVA. However, fascicle length did not significantly differ between isometric and eccentric trials under either condition. Therefore, the difference in developed torque by MVA and SEA cannot be explained by fascicle behavior. Under both MVA and SEA conditions, eccentric torque at 30 and 60 deg/s was equivalent. Similarly, fascicle lengthening velocities at 30 and 60deg/s did not show any significant difference. Such fascicle behavior can be attributed to the influence of tendinous tissue and pennation angle, and lead to a lack of increase in eccentric torque with increasing angular velocity.