Effect of Compression Garments on Controlled Force Output After Heel-Rise Exercise.

Kato, E, Nakamura, M, and Takahashi, H. Effect of compression garments on controlled force output after heel-rise exercise. J Strength Cond Res 32(4): 1174-1179, 2018-The purpose of this study was to elucidate the effects of compression garments (CG) on controlled force output after strenuous exercise. Sixteen healthy volunteers completed trials both with CG and without CG (control trial: CON) on 2 separate, random days which were at least 1 month apart. Both trials required participants to perform heel-rise exercises from maximal dorsiflexion to maximal plantar flexion 20 times with a single leg. The subjects repeated 3 sets of the exercise and took a rest for 2 minutes between sets. Before and after the heel-rise exercise, mechanical (stiffness) and architectural properties of the gastrocnemius medialis muscle were evaluated using the ultrasound method. Also, isometric maximal voluntary contraction (MVC) of plantar flexion was measured, and the subjects maintained 20% MVC of plantar flexion torque for 20 seconds as steadily as possible (steadiness task) as an index of force control. Repeated 2-way analysis of variance analysis (CG/CON × time) indicated that all the parameters declined immediately after heel-rise exercise in both CG and CON trials. Maximal voluntary contraction did not show different tendencies between CG and CON trials, but muscle stiffness and steadiness declined less in CG than CON (p < 0.05). In conclusion, CG are considered to positively benefit controlled force output after strenuous exercise.

Muscle Thickness and Passive Muscle Stiffness in Elite Athletes: Implications of the Effect of Long-Term Daily Training on Skeletal Muscle.

To examine the effect of long-term daily training on athletes' skeletal muscle, this study determined the relation between their muscle thickness and passive muscle stiffness, and compared the muscle thickness and muscle stiffness between athletes and non-athletes. Participants were elite Japanese athletes (278 men, 200 women) from various sports and non-athletes (35 men, 35 women). Rectus femoris (RF) muscle thickness was measured using B-mode ultrasonography and was normalized to the total body mass (muscle thickness/body mass1/3). RF passive muscle stiffness (shear modulus) was assessed by ultrasound shear-wave elastography. There was a negligibly significant correlation between muscle thickness and muscle stiffness in male athletes (p=0.003; r=-0.18) but not in female athletes (p=0.764; r=0.02). Among men, muscle thickness was significantly greater in athletes than non-athletes (p<0.001), whereas muscle stiffness was significantly less in athletes than non-athletes (p=0.020). Among women, muscle thickness was significantly greater in athletes than non-athletes (p<0.001), whereas muscle stiffness did not differ significantly between athletes and non-athletes (p=0.412). These results suggest that the effect of long-term daily training performed by athletes on muscle stiffness is more complicated than that on muscle thickness.

Validity of ultrasound muscle thickness measurements for predicting leg skeletal muscle mass in healthy Japanese middle-aged and older individuals.

BACKGROUND: The skeletal muscle mass of the lower limb plays a role in its mobility during daily life. From the perspective of physical resources, leg muscle mass dominantly decreases after the end of the fifth decade. Therefore, an accurate estimate of the muscle mass is important for the middle-aged and older population. The present study aimed to clarify the validity of ultrasound muscle thickness (MT) measurements for predicting leg skeletal muscle mass (SM) in the healthy Japanese middle-aged and older population. FINDINGS: MTs at four sites of the lower limb and the bone-free lean tissue mass (LTM) of the right leg were determined using brightness-mode ultrasonography and dual-energy X-ray absorptiometry (DXA), respectively, in 44 women and 33 men, 52- to 78-years old. LTM was used as a representative variable of leg skeletal muscle mass. In the model-development group (30 women and 22 men), regression analysis produced an equation with R2 and standard error of the estimate (SEE) of 0.958 and 0.3 kg, respectively: LTM (kg) = 0.01464 × (MTSUM×L) (cm2) - 2.767, where MTSUM is the sum of the product of MTs at four sites, and L is length of segment where MT is determined. The estimated LTM (7.0 ± 1.7 kg) did not significantly differ from the measured LTM (7.0 ± 1.7 kg), without a significant systematic error on a Bland-Altman plot. The application of this equation for the cross-validation group (14 women and 11 men) did not yield a significant difference between the measured (7.2 ± 1.6 kg) or estimated (7.2 ± 1.6 kg) LTM and systematic error. CONCLUSION: The developed prediction equation may be useful for estimating the lean tissue mass of the lower extremity for the healthy Japanese middle-aged and older population.

Differences in spring-mass characteristics between one- and two-legged hopping.

Although many athletic activities and plyometric training methods involve both unilateral and bilateral movement, little is known about differences in the leg stiffness (K(leg)) experienced during one-legged hopping (OLH) and two-legged hopping (TLH) in place. The purpose of this study was to investigate the effect of hopping frequencies on differences in K(leg) during OLH and TLH. Using a spring-mass model and data collected from 17 participants during OLH and TLH at frequencies of 2.0, 2.5, and 3.0 Hz, K(leg) was calculated as the ratio of maximal ground reaction force (F(peak)) to the maximum center of mass displacement (ΔCOM) at the middle of the stance phase measured from vertical ground reaction force. Both K(leg) and F(peak) were found to be significantly greater during TLH than OLH at all frequencies, but type of hopping was not found to have a significant effect on ΔCOM. These results suggest that K(leg) is different between OLH and TLH at a given hopping frequency and differences in K(leg) during OLH and TLH are mainly associated with differences in F(peak) but not ΔCOM.

Sex differences in relationship between passive ankle stiffness and leg stiffness during hopping.

The goal of this study was to examine the hypothesis that the relationships between passive ankle stiffness and leg stiffness would be different between males and females. 10 males and 10 females performed hopping in place on two legs at three frequencies of 2.0, 2.5, and 3.0 Hz. Based on a spring-mass model, leg stiffness, which is defined as the ratio of maximum ground reaction force to maximum center of mass displacement at the middle of the stance phase, was calculated using the vertical ground reaction force. Further, passive ankle stiffness was calculated as the slope of the passive ankle torque-angle relationship, which results from controlled passive ankle dorsiflexion. There was no significant difference in the leg stiffness between males and females at three hopping frequencies; however, females displayed less passive ankle stiffness than males. Further, significant positive linear relationships were found between the passive ankle stiffness and the leg stiffness for females at all hopping frequencies; however, there were no significant correlations between the passive ankle stiffness and the leg stiffness in males for all hopping frequencies. These results suggest that the relationship between the passive ankle stiffness and the leg stiffness are not the same between males and females, which may lead to a greater risk of anterior cruciate ligament injuries in females.

Acute effects of static stretching on leg-spring behavior during hopping.

Despite the fact that a stiffer leg spring is prerequisite for achieving a better performance during sports activities, effects of various types of warm-up on the leg stiffness is not well-known. The purpose of this study was to determine if static stretching influences the leg stiffness during two-legged hopping. Fourteen male subjects performed two-legged hopping at 2.2 Hz before and after a 3-min passive stretching of the triceps surae (dorsiflexion of 30°). Based on a spring-mass model, we calculated leg stiffness, which is defined as the ratio of maximal ground reaction force to maximum center of mass displacement at the middle of the stance phase. It was found that there was no significant difference in leg stiffness after passive static stretching. These results suggest that 3-min passive static stretching does not affect the leg-spring behavior and stiffness regulation during two-legged hopping. Finally, possible explanations for the invariant leg stiffness after the passive stretching are discussed.

Acute effect of muscle stretching on the steadiness of sustained submaximal contractions of the plantar flexor muscles.

This paper examines the acute effect of a bout of static stretches on torque fluctuation during an isometric torque-matching task that required subjects to sustain isometric contractions as steady as possible with the plantar flexor muscles at four intensities (5, 10, 15, and 20% of maximum) for 20 s. The stretching bout comprised five 60-s passive stretches, separated by 10-s rest. During the torque-matching tasks and muscle stretching, the torque (active and passive) and surface electromyogram (EMG) of the medial gastrocnemius (MG), soleus (Sol), and tibialis anterior (TA) were continuously recorded. Concurrently, changes in muscle architecture (fascicle length and pennation angle) of the MG were monitored by ultrasonography. The results showed that during stretching, passive torque decreased and fascicle length increased gradually. Changes in these two parameters were significantly associated (r(2) = 0.46; P < 0.001). When data from the torque-matching tasks were collapsed across the four torque levels, stretches induced greater torque fluctuation (P < 0.001) and enhanced EMG activity (P < 0.05) in MG and TA muscles with no change in coactivation. Furthermore, stretching maneuvers produced a greater decrease (∼15%; P < 0.001) in fascicle length during the torque-matching tasks and change in torque fluctuation (CV) was positively associated with changes in fascicle length (r(2) = 0.56; P < 0.001), MG and TA EMG activities, and coactivation (r(2) = 0.35, 0.34, and 0.35, respectively; P < 0.001). In conclusion, these observations indicate that repeated stretches can decrease torque steadiness by increasing muscle compliance and EMG activity of muscles around the joint. The relative influence of such adaptations, however, may depend on the torque level during the torque-matching task.

Development of an equation to predict muscle volume of elbow flexors for men and women with a wide range of age.

The present study examined the age-related changes in muscle thickness (MT) and volume (MV) of elbow flexors and developed a prediction equation of the MV based on the MT applicable to men and women with a wide range of age. The MT and MV were determined from a single ultrasonographic image and multiple magnetic resonance imaging scans, respectively, in 72 men and 75 women aged 19-77 year. As a result of examining the age-MT and age-MV relationships by calculation of partial correlation coefficients with the control variable of gender, MV was decreased with aging whereas the corresponding decline in MT was not significant. The subjects were randomly separated into either a validation (38 men and 42 women) or a cross-validation (34 men and 33 women) group, and a multiple regression equation to estimate MV using not only MT but also upper arm length (L), age and gender as independent variables [MV (cm(3)) = 60.8 x MT (cm) + 6.48 x L (cm) - 0.709 x age (year) + 51.4 x gender (0 women, 1 men) - 187.4] was validated and cross-validated. Thus, the prediction equation for MV of elbow flexors newly developed was shown to be applicable to men and women with a wide range of age.

Variability of limb muscle size in young men.

The purpose of this study was to determine the interindividual variability of the upper and lower limb muscle size in young men. Subjects were 655 Japanese men aged 18-39 years. They were sedentary and mildly to highly active individuals, including college athletes of various sports. Muscle thicknesses at each of the anterior and posterior portions of the upper arm, thigh, and lower leg were measured using B-mode ultrasonography. Interindividual variability of muscle thickness was evaluated by coefficients of variation (CVs). The CVs of muscle thicknesses were found to be in the order of upper arm posterior (17.7%), thigh anterior (14.8%), thigh posterior (12.6%), upper arm anterior (12.2%), lower leg anterior (9.8%), and lower leg posterior (9.4%). The CVs were significantly different between each pair of measurement sites except for those of upper arm anterior-thigh posterior and lower leg anterior-posterior. These differences remain significant even when the muscle thicknesses were normalized to the segment length. The observed differences in the size variability can be interpreted as muscle-related differences in hypertrophic responsiveness to resistance training. The muscle-dependent size variability may be related to the differences in the fiber-type composition and/or muscle usage in daily life among examined muscle groups.

Relationships between muscle strength and indices of muscle cross-sectional area determined during maximal voluntary contraction in middle-aged and elderly individuals.

The present study examined how muscle cross-sectional area (CSA) indices determined at rest and during maximal voluntary contraction (MVC) are related to muscle strength in middle-aged and elderly individuals (22 men and 36 women, 51-77 years). The muscle thickness (MT) of elbow flexors and circumference (C) at the level 60% distal to the upper arm was measured by ultrasonography and a measuring tape, respectively, both at rest and during isometric MVC of elbow flexion. The muscle strength (F) of elbow flexors was calculated by dividing the torque developed during MVC by the forearm length of each subject. The product of MT and C (MTxC) and the square of MT (MT) were defined as the muscle CSA indices. The F was significantly correlated with MTxC during MVC (r = 0.905, p < or = 0.001) and at rest (r = 0.778, p < or = 0.001), with the former relationship significantly stronger than the latter (p < or = 0.001). Similarly, F was significantly correlated with MT both during MVC (r = 0.896, p < or = 0.001) and at rest (r = 0.780, p < or = 0.001), and there was also a significant difference between the correlation coefficients (p < or = 0.01). These findings show that, in middle-aged and elderly individuals, muscle strength is more closely related to muscle CSA indices during MVC than at rest. It is concluded that the present muscle CSA indices taken during MVC enable easy and practical evaluation of the muscle strength per size of elbow flexors in middle-aged and elderly individuals.