Effect of electrical stimulation-induced muscle force and streptomycin treatment on muscle and trabecular bone mass in early-stage disuse musculoskeletal atrophy.

OBJECTIVES: The aim was to determine whether daily muscle electrical stimulation (ES) and streptomycin treatment would have positive or negative effects on trabecular bone mass in disuse rats. METHODS: Seven-week-old male F344 rats were randomly divided into five groups of eight animals each: an age-matched control group (CON); a sciatic denervation group (DN); a DN + direct electrical stimulation group (DN+ES); a DN + streptomycin treatment group (DN+SM); and a DN+ES+SM group. The tibialis anterior (TA) muscles in all ES groups were stimulated with 16mA at 10Hz for 30 min/day, six days/week, for one week. Bone volume and structure were evaluated using micro-CT, and histological examinations of the tibiae were performed. RESULTS: Direct ES significantly reduced the disuse-induced trabecular bone loss. Osteoid thickness were also significantly greater in the ES groups than in the DN group. Micro CT and histomorphological parameters were significantly lower in the DN+ES+SM group than in the DN+ES group, while there were no significant differences between the DN and DN+SM groups. CONCLUSIONS: These results suggest that ES-induced muscle force reduced trabecular bone loss, and streptomycin treatment did not induce bone loss, but attenuated the effects of ES-induced muscle force on reducing the loss of disused bone.

Electrical stimulation of denervated rat skeletal muscle retards trabecular bone loss in early stages of disuse musculoskeletal atrophy.

OBJECTIVES: We aimed to determine the intensity of muscle stimulation required to prevent structural failure as well as bone and skeletal muscle loss after denervation-induced disuse. METHODS: Seven-week-old rats (weight, 198-225 g) were randomly assigned to age-matched groups comprising control (CON), sciatic nerve denervation (DN) or direct electrical stimulation (ES) one day later [after denervation] with 4, 8 and 16 mA at 10 Hz for 30 min/day, six days/week, for one or three weeks. Bone architecture and mean osteoid thickness in histologically stained tibial sections and tension in tibialis anterior muscles were assessed at one and three weeks after denervation. RESULTS: Direct ES with 16 mA generated 23-30% maximal contraction force. Denervation significantly decreased trabecular bone volume fraction, thickness and number, connectivity density and increased trabecular separation in the DN group at weeks one and three. Osteoid thickness was significantly greater in the ES16 group at week one than in the DN and other ES groups. Trabecular bone volume significantly correlated with muscle weight. CONCLUSIONS: Relatively low-level muscle contraction induced by low-frequency, high-intensity electrical muscle stimulation delayed trabecular bone loss during the early stages (one week after DN) of musculoskeletal atrophy due to disuse.

Changes over time in structural plasticity of trabecular bone in rat tibiae immobilized by reversible sciatic denervation.

OBJECTIVE: The present study aimed to clarify the structural recovery, and to compare the time course of morphological changes in trabeculae and the process of bone mass change in rat tibiae following temporary immobilization of hind limb by sciatic neurectomy or nerve freezing. METHODS: In 11-week-old male Fischer 344 rats, 4-5 mm of the sciatic nerve was removed (neurectomy group) or frozen by 5-second application of a stainless steel rod immersed in liquid nitrogen (nerve-freezing group). Quantitative changes in cancellous bone were assessed by histomorphometry. RESULTS: The results clarified that: trabecular bone volume (BV/TV) decreases until 3 weeks after denervation, and in the nerve-freezing group, it then increases from week 4, recovering to pre-surgery levels by week 10 (no recovery was seen in the neurectomy group); in the initial phase of bone atrophy, the decrease in BV/TV is more gradual in the nerve-freezing group than in the neurectomy group; and changes in trabecular architecture in the bone atrophy-recovery process are strongly associated with changes in trabecular thickness. CONCLUSION: The findings suggested that after transient injury by nerve freezing and subsequent recovery of neuromuscular function, bone tissue undergoes recovery from bone loss, but that trabeculae may not show complete structural recovery.

Response training shortens visuo-motor related time in athletes.

In the present study, we aimed to determine whether response training shortens visuo-motor related time in athletes performing a simple reaction task. 14 healthy male athletes were included in the study. Subjects were randomly divided into 2 groups: a training group, which underwent response training consisting of a mastication task in response to a visual signal, and a non-training (control) group, which did not undergo response training. Pre-motor time and transcranial magnetic stimulation over the primary motor cortex for recording motor evoked potentials were measured in the control group, and before and after the response training session in the training group. Both pre-motor time and visuo-motor related time, but not motor evoked potential latency, were significantly reduced after response training in the training group. Subjects who had a longer visuo-motor related time before training showed a greater reduction in visuo-motor related time after training. These results suggest that visuo-motor related time before training could be useful as a predictor of the reduction in reaction time following response training.