T. Fukunaga

In vivo muscle fibre behaviour during counter-movement exercise in humans reveals a significant role for tendon elasticity

Six men performed a single ankle plantar flexion exercise in the supine position with the maximal effort with counter movement (CM, plantar flexion preceded by dorsiflexion) and without counter movement (NoCM, plantar flexion only) produced by a sliding table that controlled applied load to the ankle (40 % of the maximal voluntary force). The reaction force at the foot and ankle joint angle were measured using a force plate and a goniometer, respectively. From real‐time ultrasonography of the gastrocnemius medialis muscle during the movement, the fascicle length was determined. The estimated peak force, average power, and work at the Achilles’ tendon during the plantar flexion phase in CM were significantly greater than those in NoCM. In CM, in the dorsiflexion phase, fascicle length initially increased with little electromyographic activity, then remained constant while the whole muscle‐tendon unit lengthened, before decreasing in the final plantar flexion phase. In NoCM, fascicle length decreased throughout the movement and the fascicle length at the onset of movement was longer than that of the corresponding phase in CM. It was concluded that during CM muscle fibres optimally work almost isometrically, by leaving the task of storing and releasing elastic energy for enhancing exercise performance to the tendon.

Ultrasonography gives directly but noninvasively elastic characteristic of human tendon in vivo

To obtain an insight into tendon elasticity during human movement, a real-time ultrasonography was applied to the contracting tibialis anterior muscle. The insertion point of fascicles onto the aponeurosis was clearly visualized, and its position relative to a fixed marker on the skin moved proximally (Δ1) according to the increasing dorsiflexion force (ΔF) with a fixed ankle joint. Notably, the Δ1 − ΔF relationship in the tendon was found to be quadratic in nature (ΔF = cΔ12; c=1.48 ∼ 2.24, r=0.985 ∼ 0.992, n=9) as has been reported in the isolated tendon, although the ΔF − Δ1 curves were slightly underestimated in comparison with the stiffness constant estimated from tendon architecture. This underestimation might be caused by changes in the height of the foot arch with the application of force.

Comparison of muscle cross-sectional area and strength between untrained women and men

The cross-sectional areas (CSA) of fat, muscle and bone tissues of the limb as well as maximal voluntary isokinetic strength were measured in untrained men (n=27) and women (n=26) aged 18–25 years. Anatomical CSA of the three tissues were determined by ultrasound on the upper arm and thigh. The isokinetic strength of the elbow and knee extensor and flexor muscles were measured by an isokinetic dynamometer (Cybex 11) at 1.05 rad · s−1. The women had significantly (P<0.001) larger fat CSA and smaller bone and muscle CSA than the men in both the upper arm and thigh. Among tissue CSA, the largest difference between the women and men was found in fat CSA regardless of the measurement sites. The sex differences in bone and muscle CSA were found largely in the upper arm compared to the thigh, even when expressed per unit second power of the limb length. Regression analyses of the data for respective samples for the men and women showed significant correlations (r=0.411−0.707, P < 0.05−P < 0.001) between CSA and strength in all muscle groups except for the elbow extensors of the men (r=0.328, P>0.05) and the elbow flexors of the women (r=0.388, P>0.05). No significant difference between sexes was observed when strength was expressed per unit of muscle CSA (F · CSA−1) for the elbow flexors and extensors. However, the men showed significantly higher F · CSA−1 than the women for the knee flexors and extensors (P < 0.001). These results would indicate that, although the difference between sexes in muscle CSA is smaller in the thigh than in the upper arm, differences in the ability to develop dynamic strength proportional to the CSA appeared mainly in the thigh muscles compared to the upper muscles.

Estimation of active force-length characteristics of human vastus lateralis muscle.

The length and angles of fascicles were determined for the vastus lateralis muscle (VL) using ultrasonography in 6 subjects performing ramp isometric knee extension. The subject increased torque from zero (relax) to maximum (MVC) with the knee positioned every 15 degrees, from 10 degrees to 100 degrees flexion (0 degrees = full extension). As the knee was positioned closer to extension, fascicle length was shorter [116 +/- 4.7 (mean +/- SEM) mm at 100 degrees vs. 88 +/- 4.1 mm at 10 degrees (relax)]. The fascicle length of the VL decreased with increasing torque at each knee position [116 +/- 4.7 (relax) to 92 +/- 4.3 mm (MVC) at 100 degrees]. On the other hand, fascicle angles increased with an increase in torque. These changes reflected the compliance of the muscle-tendon complex which increased as the knee reached a straight position. The estimated muscle force of the VL was maximal (2,052 +/- 125 N) for a fascicle length of 78 +/- 2.7 mm (i.e. optimum length) with the knee positioned at 70 degrees of flexion. The relationship between muscle force and fascicle length indicated that the VL uses the ascending (knee < 70 degrees), plateau (70 degrees), and descending regions (> 70 degrees) of the force-length curve.

VALIDITY OF BIOELECTRICAL IMPEDANCE AND ULTRASONOGRAPHIC METHODS FOR ESTIMATING THE MUSCLE VOLUME OF THE UPPER ARM

Abstract The present study aimed to investigate the validity of bioelectrical impedance and ultrasonographic methods for predicting the muscle volume of the upper arm. Bioelectrical impedance of the right upper arm and the thickness of elbow flexor and extensor muscles were measured from 26 healthy young adult men using a specially designed bioelectrical impedance data acquisition system and brightness-mode ultrasound apparatus, respectively. As reference data, the muscle volume (MVMRI) of the right upper arm was determined using a magnetic resonance imaging method. The impedance index was calculated as L2/Z, where L is the upper arm length and Z is the impedance of the shoulder to the elbow. The muscle volume (MVULT) was calculated as π·(d/2)2·L, where d is muscle thickness. L2/Z and MVULT were significantly correlated with MVMRI with correlation coefficients of 0.971 and 0.962, respectively. In these relationships, the standard errors of estimation were 44.2 cm3 (6.3%) for L2/Z and 50.7 cm3 (7.2%) for MVULT. There was no significant difference between the absolute errors of muscle volumes estimated by L2/Z and MVULT: 36.2 (4.8, SEM) cm3 for L2/Z versus 40.3 (5.8) cm3 for MVULT. The present results suggest that both bioelectrical impedance and ultrasonographic methods may be useful for predicting the muscle volume of the upper arm.

Measurement of viscoelastic properties of tendon structures in vivo

The purpose of this study was to investigate the viscoelastic properties of tendon structures in humans. Elongation of the tendon and aponeurosis of medial gastrocnemius muscle (MG) was directly measured by ultrasonography, while subjects (n=19) performed ramp isometric plantar flexion up to the voluntary maximum, followed by a ramp relaxation. The relationship between tendon elongation (L) and estimated muscle force (Fm) was fitted to a linear regression, the slope of which was defined as compliance of the tendon structures. The hysteresis was calculated as the ratio of the area within the L‐Fm loop (elastic energy dissipated) to the area beneath the load portion of the curve (elastic energy input). The resulting L‐Fm relationship was non‐linear in form, as previously reported on animal and human tendons in vitro. The mean compliance was 4.5±1.1  ·  10−2 mm/N. However, there was a considerable inter‐subject variability (2.9 to 7.2  ·  10−2 mm/N). The Youngs modulus, i.e., the slope of the stress–strain curve, was 280 MPa, which tended to be lower than the previously reported values for human tendons. It was also found that the strain of the tendon structures was homogeneously distributed along their length. The mean hysteresis (energy dissipation) was 22.2±8.8%. However, again there was a considerable inter‐subject variability (9.7 to 37.2%). The present results indicated that the tendon structures of human MG were considerably compliant and their hysteresis was in accordance with previously reported values.

Strength and cross-sectional area of knee extensor muscles in children

Iksokinetic strength and cross-sectional area (CSA) of knee extensor muscles were examined in 60 boys and girls, aged 6–9 years, and in 71 young adult men and women to investigate the influences of age and gender on the strength capabilities in relation to muscle size. A single anatomical CSA of quadriceps femoris at the right mid-thigh was measured by using a B-mode ultrasonic apparatus. Isokinetic strength produced at three kinds of constant velocity, 1.05, 3.14, and 5.24 rad · s−1, was significantly correlated to the product of CSA and thigh length (TL) in separate samples by age and gender. In both genders, however, young adults had significantly higher ratios of strength to CSA · TL (ST · CSA−1 · TL−1) than children at all measurement velocities. Relative differences in ST · CSA−1 · TL−1 between children and young adults became larger with increasing test velocity. Within the same generation, men had significantly higher ST · CSA−1 · TL−1 than women at all measurement velocities except for the ratio in children at 1.05 rad · s−1. These results indicate that the ability to produce strength proportional to muscle size is lower in children than in young adults, regardless of gender, and lower in women than in men within the same generation.

A cross-sectional study of the size and strength of the lower leg muscles during growth.

The influences of age and sex on the cross-sectional area (CSA) and isometric strength of the ankle dorsiflexors and plantarflexors (PF) were investigated in four age groups of 121 boys and 121 girls aged: 7–9, 10–12, 13–15, and 16–18 years. A single anatomical cross-section was determined at 30% of the distance from the articular cleft between the femur and tibiacondyles by using an ultrasonic apparatus. In both sexes, the increase in age was associated with significant increases in the CSA and strength (ST) of these opposing muscle groups. The sex differences became apparent in the 13–15 year group for CSA and in the 16–18 year group for ST but the differences reduced considerably when CSA and ST were expressed per unit of the second power of the lower leg length (CSA·LL−2) and the product of CSA and the lower leg length (ST·CSA−1·LL−1), respectively. However,CSA·LL−2 of both muscles had a tendency to be increased at and over the age of 10–12 years, and was the highest at 16–18 years, andST·CSA−1·LL−1 of PF showed higher values in the older boys than in the younger. Thus, it appeared that, at least in the reciprocal muscle groups of the ankle joint, the sex differences in muscle CSA and ST during growth could be accounted for by differences in LL and muscle mass, respectively. However, other factors must also be involved to explain completely the age differences in these variables.

Morphological and functional differences in the elbow extensor muscle between highly trained male and female athletes

Abstract The purpose of this study was to investigate the difference in the morphological and functional aspects of the triceps brachii muscle between highly trained male and female athletes who were members of the 1996 Japanese Olympic teams in each of three different events: soccer, gymnastics and judo. The thickness (TBmt) and fibre pennation angle (TBpen) of the triceps brachii muscle and force output during elbow extensions were determined using a B-mode ultrasound apparatus and an isokinetic dynamometer, respectively. The TBmt and its value relative to upper arm length (TBmt/lua) were significantly larger in the men than in the women in all the events except judo. In all the subjects, a significant correlation was found between TBmt/lua) and TBpen (r= 0.721, P < 0.05). The existence of the sex difference in TBpen within the same event was in agreement with that observed in TBmt/lua except for the soccer players. The TBpen of the soccer players were similar in both sexes although a significant sex differences was found in TBmt/lua. The isokinetic forces measured using the two velocities 60°· s−1 (F60) and 180°· s−1 (F180) were significantly correlated to the cross-sectional area (CSA) of the triceps brachii muscle estimated from TBmt (r= 0.702, P < 0.05 for F60, and r= 0.776, P < 0.05 for F180). No significant sex differences were found in either F60/CSA or F180/CSA in any of the events. From these results, it could be assumed, at least in the Olympic athletes tested in this study, that the fibre angulation of the triceps brachii muscle was almost the same in the two sexes if allowance was made for the difference in the muscle size, and the sex difference in force generation capability of the triceps brachii muscle could in the main be attributed to the difference in CSA rather than in the architectural characteristics.

Sex difference in force generation capacity during repeated maximal knee extensions

AbstractThe force generation capacity, during 50 repeated maximal knee extensions with a constant velocity of 3.14 rad · s−1, and cross-sectional area (CSA) of the quadriceps femoris muscles were determined for untrained women (n = 36) and men (n = 27) aged from 18 to 25 years. As force scores in the maximal repetitions, the mean values of force (