Tadashi Muramatsu

Length Change of Human Gastrocnemius Aponeurosis and Tendon during Passive Joint Motion

The extent of elongation and slackness of aponeurosis and tendon, and muscle fiber length of human medial gastrocnemius muscle are determined in vivo using ultrasonography. The ankle joint is passively moved at 5°/s within the joint range of –36 to 7° (0° = neutral anatomic position; positive values for dorsiflexion) by a dynamometer while the length change of the aponeurosis and tendon is determined using ultrasonography (n = 8 men). Strain is calculated as the length change relative to the reference length of aponeurosis and tendon when the passive joint moment is 0. Elongation (positive strain values) of aponeurosis and tendon at 7° are 2.1 ± 1.1 and 2.4 ± 1.0%, respectively. The extent of slackness (negative strain values) of aponeurosis and tendon at –36° are –1.8 ± 1.1 and –3.5 ± 1.6%, respectively, and there is a significant difference between them (p < 0.05). This may be related to the existence of muscle fibers that attach to the aponeurosis over its whole length and do not allow it to fold. The results indicate that the length change of aponeurosis and tendon of medial gastrocnemius muscle occurs over the range of ankle joint positions even during passive joint motions.

Superficial aponeurosis of human gastrocnemius is elongated during contraction: implications for modeling muscle-tendon unit

Two questions were addressed in this study: (1) how much strain of the superficial aponeurosis of the human medial gastrocnemius muscle (MG) was obtained during voluntary isometric contractions in vivo, (2) whether there existed inhomogeneity of the strain along the superficial aponeurosis. Seven male subjects, whose knees were extended and ankles were flexed at right angle, performed isometric plantar flexion while elongation of superficial aponeurosis of MG was determined from the movements of the intersections made by the superficial aponeurosis and fascicles using ultrasonography. The strain of the superficial aponeurosis at the maximum voluntary contraction, estimated from the elongation and length data, was 5.6+/-1.2%. There was no significant difference in strain between the proximal and distal parts of the superficial aponeurosis. Based on the present result and that of our previous study for the same subjects (J. Appl. Physiol 90 (2001) 1671), a model was formulated for a contracting uni-pennate muscle-tendon unit. This model, which could be applied to isometric contractions at other angles and therefore of wide use, showed that similar strain between superficial and deep aponeuroses of MG contributed to homogeneous fascicle length change within MG during contractions. These findings would contribute to clarifying the functions of the superficial aponeurosis and the effects of the superficial aponeurosis elongation on the whole muscle behavior.

Differences In Fat-free Mass And Muscle Thicknesses At Various Sites According To Performance Level Among Judo Athletes

The purpose of this study was to investigate differences in fat-free mass and thicknesses of various muscles among judo athletes of different performance levels. The subjects were 69 male judo athletes of 3 different performance levels. Group A was composed of athletes who participated in the Olympic Games or Asian Games (n = 13). Groups B(n = 21) and C (n = 35) were composed of judo athletes at a university who did or did not participate in intercollegiate competitions (including qualifying matches), respectively. Muscle and fat thicknesses were measured by B-mode ultrasound at 9 sites. Fat percentage was calculated from fat thicknesses using a previously reported equation. Fat-free mass was calculated from fat percentage and body weight. Muscles thicknesses were normalized to the height of the individual. Group A had significantly larger fat-free mass than Group C (p < 0.05). The normalized thicknesses of the elbow extensor and flexor muscles were significantly larger in Group A than in Group C. The normalized thickness of the elbow flexor muscle was significantly larger in Group A than in Group B. The results of this study showed that judo athletes with low performance levels such as those in Group C had lower fat-free mass, and the degree of development of the brachialis muscles differed according to performance level.

Geometric and Elastic Properties of in vivo Human Achilles Tendon in Young Adults

The purpose of this study was to clarify whether the major determinant of the extendibility of the Achilles tendon in young adults was the geometric properties of the tendon. The subjects were 38 healthy young adults (26 male, 12 female; 26 ± 5 years). The subjects developed maximum voluntary isometric plantar flexion (MVIP) torque while the displacement of the distal myotendinous junction of the medial gastrocnemius and ankle joint rotation was determined using a B-mode ultrasonograph and a goniometer, respectively. The tendon force (F) was calculated from MVIP torque and the moment arm of Achilles tendon. The elongation of the Achilles tendon (ΔX) was obtained from the tendon displacements and ankle joint rotation. Achilles tendon stiffness (k) was calculated by dividing F by ΔX. The specific stiffness of the Achilles tendon (ks) was obtained from k normalized to the Achilles tendon length at rest. The cross-sectional area of the Achilles tendon (CSA) was measured at 5, 10, and 15% of the lower leg length proximal to the insertion of the Achilles tendon using a B-mode ultrasonography. The results showed that more distal portion of the Achilles tendon had a larger CSA, and that there was a strong correlation between the average and minimum Achilles tendon CSA. ΔX was 9.9 ± 2.5 mm. k and ks were 330 ± 77 N/mm and 63 ± 20 kN, respectively. No significant correlation was seen between CSA and ks (r = 0.15, p > 0.05). It was suggested that a stiffer Achilles tendon did not necessarily have a thicker shape, which might indicate that the major determinant of the extendibility of the Achilles tendon was not its geometric properties in young adults.

Effects of muscle cooling on the stiffness of the human gastrocnemius muscle in vivo

Background/Aims: The effects of muscle cooling on the stiffness of the human gastrocnemius muscle (GAS) were examined in vivo. Methods: The knee joint was passively extended from 90 to 0° (0° = full knee extended position) with a constant ankle angle of 10° dorsiflexed position (0° = the sole of the foot is approximately perpendicular to the anterior margin of the shaft of the tibia) in a control condition (room temperature of 18–23°C) and a cooling condition (muscle temperature decreased by 5.8 ± 1.7°C after cooling using a cold water bath at a temperature of 5–8°C for 60 min). The change in passive Achilles tendon force, muscle fascicle length of GAS and muscle temperature were measured (n = 6) during the motion. Results and Conclusion: GAS stiffness was significantly greater in the cooling condition (20 ± 8 N/mm) than the control condition (18 ± 8 N/mm). There was no cooling effect on the muscle slack length, beyond which passive muscle force arises. The maximum passive Achilles tendon force significantly increased by 19 ± 20% after cooling. These results suggested that cooling increased the passive muscle force due to the increase in the muscle stiffness rather than the shift of the muscle slack length.

In vivo Mechanical Properties of Proximal and Distal Aponeuroses in Human Tibialis Anterior Muscle

Load-strain characteristics of distal (deep) and proximal (superficial) aponeuroses were determined in vivo for human tibialis anterior muscle (TA). Seven male subjects exerted isometric dorsiflexion torque from relaxation to voluntary maximum while elongation of both aponeuroses of TA was determined by ultrasonography. Two positions (end of the muscle belly and a proximal part) and one position (distal part) were scanned for the deep and superficial aponeuroses, respectively, and tendinous movements of the respective positions were determined. Based on the tendinous movements, elongation of each aponeurosis was determined. Both aponeuroses were elongated significantly, and there was no significant difference in strain between the deep (3.3 ± 0.8%) and superficial (3.0 ± 0.5%) aponeuroses. In addition, there was a significant linear relationship between strain of deep and superficial aponeuroses. It was suggested that both aponeuroses similarly act as an elastic component in pennate muscles.