Neural Adaptation Analysis of Muscle Isometric Maximum Voluntary Contraction Resistance Training at Different Joint Angles / 医用生物力学

Objective To study the characteristics of neural adaptation for resistance training of maximum voluntary contraction (MVC) of muscles at different joint angles. Methods Thirty healthy male college students were randomly divided into 3 groups, and each group was subjected to MVC isometric contraction resistance training at elbow joint angles of 45°, 90°, and 135°. Surface electromyography (sEMG) signals of the biceps brachii were measured before and after training, and the root mean square (RMS) and median frequency (MF) of the sEMG signals were also analyzed. ResultsThere were significant differences in normalized RMS of sEMG for the biceps brachii before and after training at 45°, 90°, and 135° elbow joints. Comparison of the RMS between different angles after training showed that 45° was significantly different from 90° and 135°. There were no significant differences between 90° and 135°. After training, no significant differences were found in normalized MF at all angles. Conclusions The RMS of sEMG shows angle-specific changes, while the MF of sEMG does not have angle-specific changes. When the biceps brachii is at the middle and large elbow joint angles, the neural adaptation effect produced by isometric resistance training is better.

Neuromuscular adaptations induced by low load resistance training method with skin cooling / 体力科学

Loss of muscle strength is not only associated with loss of muscle mass, but also affected by neural factors. It is well known that facilitatory and inhibitory responses of spinal motor neurons occur with cutaneous stimulation via spinal interneurons. The purpose of this study was to examine the neural adaptations associated with low load resistance training utilizing skin cooling (SC). 10 men trained both legs and each side was randomly assigned to SC training (SC-T) and non SC training (NSC-T). Subjects performed 30 isometric ankle dorsiflexion repetitions at 35% maximum voluntary contraction (MVC) 3 times weekly for 6 weeks. The skin cooling condition was defined as when skin temperature was 25°C while repetitive resistance training was being performed. Dorsiflexor MVC significantly increased in both SC-T (n = 9) and NSC-T (n = 9) by 12.8 and 3.8%, respectively. A significant increase in root mean square of EMG (rmsEMG) was observed for 30 isometric ankle dorsiflexion repetitions in SC-T both pre- and post-training. Lower leg girths did not significantly increase post-training. Therefore, the results of this study suggest that muscle strength might increase via changes in neural activation and that SC-T may lead to greater increases in muscle strength compared with NSC-T because of improved muscle activation during resistance training with SC. Therefore, we suggest that low load resistance training with SC is an effective method to increase muscle strength.

Effects of Tai Chi Chuan combined with vibration training on the reflex activity of peripheral neuron / 医用生物力学

Objective To investigate the effects of Tai Chi Chuan combined with vibration training on the excitability of α-motorneuron pool and γ-reflex arc. Methods 55 healthy college students were divided into Tai Chi Chuan + vibration training (TAV) group, Tai Chi Chuan training (TAI) group, vibration training (VB) group, and control group (CON) for 8 weeks with 3 times training per week. Each time at pre-and post-training, H-reflex and M-wave were recorded by electrical stimulus induced on soleus muscle. T-reflex was also collected by knocking on the Achill tendon. Results After 8-week training, the ratios of Hmax/Mmax and T-reflex/Mmax in VB group were significantly decreased (P<0.05), while the ratio of T-reflex/Mmax in TAV group was significantly increased (P<0.05), and the change percentage of T-reflex/Mmax was significantly higher than that in VB group (P<0.05). Conclusions Although the vibration training could decrease the resting excitability of α-motorneuron pool, the Tai Chi Chuan combined with vibration training could give the muscle spindle stronger excitement so as to further induce the high excitability of γ-reflex arc. It indicated that the Tai Chi Chuan combined with vibration training is feasible since the neural adaptation around peripheral neuron system could be induced after such kind of training.