Effects of 12-week Tai Chi training on soleus H-reflex and muscle strength in older adults: a pilot study.

The purpose of this study was to determine the effects of 12-week Tai Chi (TC) training on the soleus (SOL) H-reflex modulation and plantarflexion muscle strength in older adults. Twenty volunteers were assigned into training (N = 14; 72.2 ± 3.7 years of age) and control (N = 6; 74.2 ± 6.1 years of age) groups. The participants in the TC group practiced Yang style TC 1 h per session, 3 sessions per week, for 12 weeks, guided by a qualified TC instructor. The ratio of the maximal peak-to-peak amplitude of SOL H-reflex (H (max)) to M-wave (M (max)) was determined during bipedal standing under four sensory conditions: stable surface and eyes open (SO), stable surface and eyes closed (SC), unstable surface and eyes open (UO), and unstable surface and eyes closed (UC). The maximal isometric plantarflexion muscle strength was also assessed by using a dynamometer. The results showed that the SOL H (max)/M (max) ratio increased significantly after the 12 weeks of TC training under the SC (37.0%), UO (33.3%) and UC (36.0%) conditions (P < 0.05). The maximal plantarflexion strength also improved significantly after training (19.8%; P < 0.05). In contrast, the control group showed no significant changes in all measurements after the 12 weeks.

Effects of electromyostimulation on knee extensors and flexors strength and steadiness in older adults.

It is known that electromyostimulation (EMS) alone or superimposed over voluntary contraction (EV) can effectively improve muscle strength. However, the effect of this type of training on the ability to control force production at submaximal levels is unknown. The authors examined the effects of EV training on steadiness in force production of knee extensors and flexors in older adults. Forty participants, including 20 men and 20 women, 60-77 years of age, were randomly allocated into a control group (CG) and an electromyostimulation superimposed over voluntary contraction (EVG) group. The EVG performed 30 bilateral isometric knee extension and flexion contractions per session, 3 training sessions per week, for 6 weeks. The variations in force production, expressed in absolute (standard deviation [SD]) and relative (coefficient of variation [CV]) terms, were assessed in isometric contractions at 5%, 15% and 25% maximal voluntary contraction (MVC) levels. Results indicated that MVC increased in knee extension and flexion in EVG (p < .05) after the training; steadiness CV also improved at 15% MVC in knee flexion (p < .05) but no significant changes were found in knee extension and steadiness SD. The training-induced changes in MVC were not correlated to steadiness CV that might indicate different mechanisms underlying these adaptations.

Test-retest reliability of the soleus H-reflex is affected by joint positions and muscle force levels.

The purpose of this study was to determine the test-retest reliability of the soleus (SOL) H-reflex during rest and isometric contractions at 10%, 30%, and 50% of the maximal voluntary force (MVC) at the ankle joint angles of neutral (0 degrees), plantarflexion (20 degrees), and dorsiflexion (-20 degrees) respectively, in a sitting position. Ten healthy participants, with mean age of 24.9+/-5.0 (SD) years, height 168.3+/-8.8 cm, weight 62.7+/-12.3 kg, were tested for the SOL H-reflex (H(max)) on two separate occasions within 7 days. The intraclass correlation coefficient (ICC) for the test-retest of the SOL H-reflex during rest was found to be high at ankle joint angle of neutral (ICC=0.92) and plantarflexion (0.96), and moderate at dorsiflexion (0.75). Inconsistent ICC values (range from 0.62 to 0.97) were found during the submaximal voluntary contractions at the three ankle joint positions. High ICCs were also found in H(max)/M(max) ratio at neutral (0.86), plantarflexion (0.96), and dorsiflexion (0.84) positions. It was concluded that the test-retest reliability of the SOL H-reflex was affected by the intensity of voluntary contraction and ankle joint position. The H-reflex demonstrated a higher reliability at the neutral and plantarflexion positions than that at the dorsiflexion position during rest, and a higher reliability at 10% MVC than that at 30% and 50% MVC.

Effects of unilateral electromyostimulation superimposed on voluntary training on strength and cross-sectional area.

In this study we investigate the effects of unilateral voluntary contraction (VC) and electromyostimulation superimposed on VC (EV) training on maximal voluntary (MVC) force and cross-sectional area (CSA), as assessed by magnetic resonance imaging of knee extensors. Thirty young men were randomly assigned to either a control group (CG), VC group (VG), or EV group (EVG). The VG and EVG trained the right leg isometrically three sessions per week for 6 weeks. After training, MVC increased in the right leg in the VG and in both legs in the EVG, and EVG was significantly different from CG (all P < 0.01). Increased CSA was found only in the right leg in the VG and EVG (P < 0.01), and correlated with improvements of MVC (r = 0.49, P = 0.01). It appeared that the EV training was equally effective as VC at increasing MVC and CSA, while having a greater cross-education effect. Increased strength without muscle hypertrophy in the unexercised leg of the EVG indicated that neural adaptation was responsible for the cross-education effect.