Kimitaka Nakazawa

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.

Reconstruction and Tuning of Neural Circuits for Locomotion After Spinal Cord Injury

Because patients with an injured spinal cord face severe functional deficits, novel therapeutic approaches are required to treat this traumatic disorder. Recent advances in molecular biology and electrophysiology have rendered approaches based on these two subjects important in this field. A molecular approach involving tissue engineering is beneficial for preserving or restoring the neural circuit, i.e., the so-called hardware of the spinal cord. On the other hand, the electrophysiological approach has advantages such as modulation and analysis of use-dependent plastic changes in neural functioning of human subjects, which corresponds to the “software” of the spinal cord. Because varied biological processes are triggered after spinal cord injury, we should use either approach, or both, depending on the clinical problem that needs to be solved.