Evaluation of neuromuscular electrical stimulation on fibre characteristics and oxidative capacity in equine skeletal muscles



Reasons for performing study: Neuromuscular electrical stimulation (NMES) is used to increase or maintain muscle strength during rehabilitation. Human studies investigating different protocols show that some treatments induce changes in muscle characteristics. Despite the frequent use of NMES in horses, no studies have been published describing its efficacy.

Objectives: To investigate the effects of a NMES protocol on equine fibre types and areas, glycogen concentrations and enzyme activities.

Methods: NMES was administrated to m. gluteus medius and m. longissimus dorsi, on one side of 6 healthy Standardbred horses. The contralateral side of each muscle served as a nonstimulated control. The horses were stimulated at 50 Hz a day, with 21–39 mA, for 45–60 min, 5 days a week for 4 weeks. Needle biopsies were obtained from the muscles on both sides before and after the experimental period. Muscle samples were analysed for fibre type proportions and area using histochemical methods and for glycogen and enzyme activities (citrate synthase, 3-OH-acyl CoA dehydrogenase, hexokinase and lactate dehydrogenase) using biochemical methods. Muscle contractions at the location and depth of the muscle biopsy were confirmed by diagnostic ultrasound. Nonparametric tests (Mann-Whitney, Wilcoxon sign-rank) were used for statistical analysis.

Results: No significant differences were observed in the percentage of types I, IIA or IIX fibres, fibre areas, glycogen levels or enzyme activities either when comparing stimulated and nonstimulated muscles before and after the NMES treatment, or when comparing the left and right muscle samples.

Conclusions: The NMES treatment was well tolerated by the horses, but the present protocol did not induce significant muscle adaptations. Further studies are needed to describe the effect of more intense and/or prolonged NMES treatment protocols on muscles of healthy horses, and to describe if stimulation protocols induce positive changes in atrophied muscles.