Yasuo Kawakami

In vivo behaviour of human muscle tendon during walking.

In the present study we investigated in vivo length changes in the fascicles and tendon of the human gastrocnemius medialis (GM) muscle during walking. The experimental protocol involved real–time ultrasound scanning of the GM muscle, recording of the electrical activity of the muscle, measurement of knee– and ankle–joint rotations, and measurement of ground reaction forces in six men during walking at 3 km h–1 on a treadmill. Fascicular lengths were measured from the sonographs recorded. Musculotendon complex length changes were estimated from anatomical and joint kinematic data. Tendon length changes were obtained combining the musculotendon complex and fascicular length–change data. The fascicles followed a different length–change pattern from those of the musculotendon complex and tendon throughout the step cycle. Two important features emerged: (i) the muscle contracted near–isometrically in the stance phase, with the fascicles operating at ca. 50 mm; and (ii) the tendon stretched by ca. 7 mm during single support, and recoiled in push–off. The behaviour of the muscle in our experiment indicates consumption of minimal metabolic energy for eliciting the contractile forces required to support and displace the body. On the other hand, the spring–like behaviour of the tendon indicates storage and release of elastic–strain energy. Either of the two mechanisms would favour locomotor economy.

Training-induced changes in muscle architecture and specific tension

Five men underwent unilateral resistance training of elbow extensor (triceps brachii) muscles for 16 weeks. Before and after training, muscle layer thickness and fascicle angles of the long head of the triceps muscle were measured in vivo using B-mode ultrasound, and fascicle lengths were estimated. Series anatomical cross-sectional areas (ACSA) of the triceps brachii muscle were measured by magnetic resonance imaging, from which muscle volume (Vm) was determined and physiological cross-sectional area (PCSA) was calculated. Elbow extension strength (isometric; concentric and eccentric at 30, 90 and 180°·s−1) was measured using an isokinetic dynamometer to determine specific tension. Muscle volumes, ACSA, PCSA, muscle layer thickness and fascicle angles increased after training and their relative changes were similar, while muscle and fascicle length did not change. Muscle strength increased at all velocities; however, specific tension decreased after training. Increase in fascicle angles, which would be the result of increasedVm and PCSA, would seem to imply the occurrence of changes in muscle architecture. This might have given a negative effect on the force-generating properties of the muscles.

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.

Prediction equations for body composition of Japanese adults by B‐mode ultrasound

A total of 117 Japanese subjects (62 men and 55 women) volunteered for the study. Subcutaneous adipose tissue (AT) and muscle thicknesses were measured by B‐mode ultrasonography at nine sites of the body. Body density (BD) was determined the hydrodensitometry. Reproducibility of thickness measurements by ultrasonography was high (r = 0.96–0.99). Correlations between AT thickness and BD ranged from −0.46 (gastrocnemius) to −0.87 (abdomen) for males and −0.46 (gastrocnemius) to −0.84 (abdomen) for females. A higher negative correlation (r = −0.89) was observed for the sum of AT thicknesses (forearm, biceps, triceps, abdomen, subscapula, quadriceps, hamstrings, gastrocnemius, and tibialis anterior) both in males and in females. Slightly lower coefficients were observed between muscle thickness and LBM (r = 0.36 to r = 0.70 for males and r = 0.44 to r = 0.55 for females). Prediction equations for BD and LBM from AT and muscle thickness were obtained by multiple regression analysis. Cross‐validation on a separate sample (33 men and 44 women) showed an accurate prediction for BD. The present findings suggest that B‐mode ultrasonography can be applied in clinical assessment and field surveys.

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.

Changes in muscle size, architecture, and neural activation after 20 days of bed rest with and without resistance exercise.

Abstract Nine healthy men carried out head-down bed rest (BR) for 20 days. Five subjects (TR) performed isometric, bilateral leg extension exercise every day, while the other four (NT) did not. Before and after BR, maximal isometric knee extension force was measured. Neural activation was assessed using a supramaximal twitch interpolated over voluntary contraction. From a series cross-sectional magnetic resonance imaging scans of the thigh, physiological cross-sectional areas (PCSA) of the quadriceps muscles were estimated (uncorrected PCSA, volume/estimated fibre length). Decrease in mean muscle force after BR was greater in NT [−10.9 (SD 6.9)%, P < 0.05] than in TR [0.5 (SD 7.9)%, not significant]. Neural activation did not differ between the two groups before BR, but after BR NT showed smaller activation levels. Pennation angles of the vastus lateralis muscle, determined by ultrasonography, showed no significant changes in either group. The PCSA decreased in NT by −7.8 (SD 0.8)% (P < 0.05) while in TR PCSA showed only an insignificant tendency to decrease [−3.8 (SD 3.8)%]. Changes in force were related more to changes in neural activation levels than to those in PCSA. The results suggest that reduction of muscle strength by BR is affected by a decreased ability to activate motor units, and that the exercise used in the present experiment is effective as a countermeasure.

Muscle and tendon interaction during human movements

FUKUNAGA, T., Y. KAWAKAMI, K. KUBO, and H. KANEHISA. Muscle and tendon interactions during human movements. Exerc. Sport Sci. Rev., Vol. 30, No. 3, pp. 106–110, 2002. Muscle and tendon interaction was estimated in vivo by real-time ultrasonography. Differences between muscles in internal muscle-fiber shortening during isometric actions are due to the elastic properties of tendon. Compliant human tendons allow muscles to contract isometrically during many human movements for efficient force generation.

Specific tension of elbow flexor and extensor muscles based on magnetic resonance imaging

Series cross-section images of the upper extremity were obtained for four men by magnetic resonance imaging (MRI) and anatomical cross-sectional areas (ACSA) of elbow flexor muscles [biceps brachii (BIC), brachialis (BRA), brachioradialis (BRD)] and extensor muscles [triceps brachii (TRI)] were measured. Physiological cross-sectional area (PCSA) was calculated from the muscle volume and muscle fibre length, the former from the series ACSA and the latter from the muscle length multiplied by previously reported fibre/muscle length ratios. Elbow flexion/extension torque was measured using an isokinetic dynamometer and the force at the tendons was calculated from the torque and moment arms of muscles measured by MRI. Maximal ACSA of TRI was comparable to that of total flexors, while PCSA of TRI was greater by 1.9 times. Within flexors, BRA had the greatest contribution to torque (47%), followed by BIC (34%) and BRD (19%). Specific tension related to the estimated velocity of muscle fibres were similar for elbow flexors and extensors, suggesting that the capacity of tension development is analogous between two muscle groups.

Elastic properties of muscle-tendon complex in long-distance runners.

Abstract The purpose of this study was to investigate the elastic properties of muscle-tendon complex (MTC) in knee extensor muscles and the capacity for elastic energy utilization in long-distance runners (LDR) by comparing with data obtained from untrained individuals (CON). The elongation (L) of the tendon and aponeurosis of vastus lateralis muscle during isometric knee extension was determined by real-time brightness mode ultrasonography, while the subjects developed a gradually increasing torque from 0 (relaxed) to maximal effort (MVC) within 7 s. In addition, performances in two kinds of maximal vertical jumps, i.e. squatting (SJ) and counter-movement jumps (CMJ), were measured. The relationship between L muscle and force (F ) was curvilinear and consisted of an initial region (toe region), characterized by a large increase in L with increasing F, immediately followed by a linear region. The slope of the regression equation for the L-F relationship in the range 50%–100% of MVC was defined as an index of MTC compliance, where the rate of the changes in L to that in muscle F at every 10% of MVC became almost constant. The maximal L (Lmax) and MTC compliance were significantly lower in LDR than in CON: 29.9 (SD 3.9) mm in LDR compared to 33.3 (SD 5.5) mm in CON for Lmax and 1.55 (SD 0.25) × 10−2 mm · N−1 in LDR compared to 1.88 (SD 0.82) × 10−2 mm · N−1 in CON for MTC compliance. Also, LDR showed significantly less elastic energy absorption (Ee) than CON, defined as the area below the L-F relationship curve from 0 to 100% of MVC. Not only jump heights but also the differences between the heights in SJ and CMJ, expressed as the percentage of the height in SJ, were significantly lower in LDR than in CON. The augmentation with counter-movement was significantly correlated to either MTC compliance (r = 0.554, P < 0.05) or Ee (r = 0.563, P < 0.05). Thus, the present results would indicate that MTC of vastus lateralis muscle is less compliant and its potential for energy storage during MTS lengthening is lower in LDR than untrained individuals. These elastic profiles of vastus lateralis muscle in LDR may be associated with their lower performances during CMJ.

Differences in activation patterns in elbow flexor muscles during isometric, concentric and eccentric contractions.

SummaryTo investigate the relative activation of the synergistic muscles during three different types of muscle contraction, the electromyograms (EMG) of two elbow flexor muscles, the biceps brachii (BB) and the brachioradialis (BR), have been compared. To accomplish this eight healthy human subjects performed the following elbow flexions against the same load — concentric, eccentric and isometric contractions. The isometric contractions were performed at three elbow angles: 10, 45 and 90° (0° equal to full expension). The EMG were recorded by bipolar surface electrodes, and the relative activation between the two muscles was evaluated as the quotient of mean EMG activities (BR/BB). For the isotonic elbow flexions, BR/BB were calculated at three angle divisions: 0–30°, 30–60° and 60–90°. Results indicated that the relative activation of the BR during the concentric contractions was higher than that of the eccentric contraction, particularly at the extended elbow angles, i.e. the BR/BB of the concentric contractions for the elbow joint angles ranging from 0–30° and 30–60° were significantly greater (P<0.05) than those of the eccentric contractions. During the isometric and eccentric contractions, the BR/BB at the flexed joint angles tended to be greater than those at the extended angles. In contrast, there were no angle-dependent BR/BB variations during the concentric elbow flexions. Further, changing patterns in the EMG power spectra due to the type of contraction were different between BB and BR. These results indicated that the activation pattern in the two elbow flexor muscles varied with the muscle contraction pattern.