Strength-Training Induces Skeletal Muscle Adaptations in Patients with Myotonic Dystrophy Type I

Abstract

PURPOSE: Myotonic dystrophy type 1 (DM1) is the most prevalent inherited neuromuscular disease in adults. This multisystemic disease is characterized by skeletal muscle impairments including muscle wasting. Slowing muscle wasting in this population using strength training seems a promising strategy, but it remains unknown if it would trigger cellular and molecular responses similar to the ones observed in healthy people. The objective of this case study is to evaluate the effect of a strength-training program on skeletal muscle adaptations in a DM1 patient. METHODS: One male with DM1 (age = 36) underwent a 12-week strength-training program, twice a week, consisting of 2 sets of 6 exercises at 6 RM supplemented by functional tasks. Vastus lateralis muscle biopsy samples were obtained pre- and post-training program. The proportion of type I and II myofibers and the cross sectional area (CSA) of each type were determined by immunohistochemistry. The percentage of centrally nucleated fibers (CNF) was obtained following staining with hematoxyline/eosine Two blinded evaluators analyzed the data. RESULTS: Following the 12-week strength-training program, the patient showed an increase in the CSA of type I myofibers evaluated at 46% (p<0.05) by evaluator #1 and 51% (p<0.05) by evaluator #2. For type II myofibers, the increase in CSA was evaluated to 24% (p<0.05) and 29% (p<0.05) by evaluator #1 and #2, respectively. A muscle fiber-type switching was also induced by the 12-week strength-training program as shown by the increase in the proportion of type II myofibers from 29% to 71% (p<0.05) noted by the evaluator #1 and the similar observation noted by evaluator #2 (28% to 72%, p<0.05). No change was observed in the percentage of CNF by both evaluators. CONCLUSIONS: Our results suggest that skeletal muscle of patients with DM1 could undergo adaptations linked to muscle growth as demonstrated by the increase in the CSA of type I and type II myofibers. It also seems that strength-training parameters used in this study could also influence the distribution of myofibers, in favour of type II. Further studies comprising a higher number of participants are needed to validate our findings and determine to which extent and how skeletal muscles of patients with DM1 adapt to strength training stimulus.