Many studies have demonstrated that the firing behavior of single motor units varies in a nonlinear manner to the exerted torque during gradual muscle contraction and relaxation. However, it is unclear whether @entity2146 has such a hysteresis-like feature. In this study, we examined @entity2146 using transcranial magnetic stimulation (TMS) during gradual muscle contraction and relaxation for torque regulation in elbow flexor muscles. Eight healthy male subjects performed two different @entity14978 , namely, sinusoidal and tonic torque exertion tasks. In the sinusoidal task, the subjects sinusoidally increased and decreased the isometric elbow flexion torque (range of 0-15% of maximum @entity2472 ) at three different frequencies (0.33, 0.17, and 0.08 Hz). For each ascending (contraction: CON) and descending (relaxation: @entity4632 ) period of the exerted torque, a single TMS was applied at 5 phases. In the tonic task, the elbow flexion torque was tonically exerted at 7 levels in a similar range as that in the sinusoidal task. EMG activities were recorded from the agonists, the biceps brachii (BB) and brachioradialis (BRD) muscles, and an antagonist, the @entity427 ( @entity427 ) muscle. The results demonstrated that the EMG activities of both the agonists and antagonist were larger in the CON period than the @entity4632 period, even when the exerted torque was the same. However, there were no significant differences in EMG activation profiles among the different frequencies of contraction. In BB and BRD, the motor-evoked potential (MEP) elicited by the TMS was also greater in the CON period than in the @entity4632 period. This CON- @entity4632 difference of MEP amplitudes was still observed when corrections were made for the increased EMG activities; that is, the MEP amplitudes to the identical EMG activities were greater in the CON period than in the @entity4632 period, and this phenomenon was more pronounced at higher frequencies. In addition, the degree to which sinusoidal MEPs exceeded tonic MEPs in the CON period and were smaller than tonic MEPs in the @entity4632 period became more pronounced at higher frequencies. On the other hand, there were significant correlations between the BB and BRD MEP amplitudes and the rate of change of elbow flexion/extension torque. These results indicate that @entity2146 during muscle contraction and relaxation has a neural hysteresis to the muscle activity, i.e., spinal motoneuronal activity, according to the rate of change of the exerted torque, i.e., muscle tension. This suggests that @entity2146 modulation depends not only on concurrent spinal motoneuronal activity and muscle tension but also on the time-series pattern of their changes during muscle contraction and relaxation.

Hysteresis in XXXX during gradual muscle contraction and relaxation in humans.

@entity14978 :: ('MESH:C566973', 'Disease') :: ['isometric elbow flexion tasks'] @entity2146 :: ('MESH:D011595', 'Disease') :: ['corticospinal excitability'] @entity4632 :: ('5966', 'Gene') :: ['REL'] @entity427 :: ('MESH:D012021', 'Disease') :: ['triceps brachii', 'TB'] @entity2472 :: ('MESH:C536214', 'Disease') :: ['voluntary contraction']
@entity2146 :: (MESH:D011595,Disease) :: ['corticospinal excitability']
