Waseda University · Medicine
Professor Yasuo Kawakami's research lab specializes in human muscle physiology and biomechanics, focusing on the architectural and functional properties of skeletal muscles in vivo. Using advanced imaging techniques such as ultrasonography and MRI, the lab investigates muscle-tendon unit mechanics, fascicle dynamics, and the effects of training, disuse, and aging on muscle structure and function. Key research directions include muscle fiber pennation, joint angle and muscle length effects on force production, and the physiological adaptations to resistance training and immobilization. The lab also explores neuromuscular control and muscle fatigue through electromyography and dynamic movement analysis.
Figures are computed from collected data and may differ slightly.
Architectural properties of the triceps surae muscles were determined in vivo for six men. The ankle was positioned at 15 degrees dorsiflexion (-15 degrees) and 0, 15, and 30 degrees plantar flexion, with the knee set at 0, 45, and 90 degrees. At each position, longitudinal ultrasonic images of the medial (MG) and lateral (LG) gastrocnemius and soleus (Sol) muscles were obtained while the subject was relaxed (passive) and performed maximal isometric plantar flexion (active), from which fascicle
Muscle-fiber pennation angles were measured in vivo with the use of ultrasonography to investigate the relationship between fiber pennation and muscle size for 32 male subjects (from untrained subjects to highly trained bodybuilders). From the image of a B-mode ultrasonogram, fiber pennation angles and thickness of triceps brachii were determined, the former as angles between echoes from the interspaces of fascicles and from the aponeurosis of long and medial heads of triceps and the latter as t
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 ga
Nine healthy men (22-45 yr) completed 100 repetitive maximal isometric contractions of the ankle plantar flexor muscles in two knee positions of full extension (K0) and flexion at 90 degrees (K90), positions that varied the contribution of the gastrocnemii. Electromyographic activity was recorded from the medial and lateral gastrocnemii and soleus muscles by using surface electrodes. Plantar flexion torque in K0 was greater and decreased more rapidly than in K90. The electromyographic amplitude
Five healthy men carried out a program of head-down bed rest (BR) for 20 days. Before and after BR, a series of cross-sectional scans of the thigh were performed using magnetic resonance imaging, from which volumes of the quadriceps muscles were determined and physiological cross-sectional areas (PCSA) were calculated. Muscle thickness and pennation angles of the triceps brachii, vastus lateralis, and triceps surae muscles were also determined by ultrasonography. During BR, subjects performed un
Results suggest that extensibility of the muscle-tendon unit of the Achilles tendon for the most part is related to passive ankle plantar flexion joint torque.
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