Spinal Cord Injury Muscle Research Articles

Myogenesis contributes to functional electrical stimulation (fes)‐induced recovery of myofiber excitability and mass of human long‐term denervated muscles in spinal cord injury (SCI)

Many months after SCI, when an irreversible injury involves lower motoneurons, severe atrophy of human muscle is complicated by fibrosis and fat substitution (denervated, degenerated muscle, DDM). We will describe the effects of long‐term lower motoneuron denervation on human muscle and present the structural results of muscle trained using FES. Antibody for embryonic myosin demonstrates that sustained myogenesis occurs in human DDM. By electron microscopy we studied: a) the overall structure of fibers and myofibrils in long‐term DDM, including the effects of FES, and b) the structure and localization of calcium release units, or triads, the structure deputed to activate muscle contraction during excitation‐contraction coupling (ECC). The poor excitability of human long‐term DDM fibers during the first stages of FES training could be explained in terms of spatial disorder of both the ECC and contractile apparati. The structural studies are extremely encouraging since they demonstrate that FES training is effective in reverting long‐term DDM atrophy and in maintaining the trophic state of the recovered myofibers.

Effect of training on contractile and metabolic properties of wrist extensors in spinal cord-injured individuals.

Paretic human muscle rapidly loses strength and oxidative endurance, and electrical stimulation training may partly reverse this. We evaluated the effects of two training protocols on the contractile and metabolic properties of the wrist extensor in 12 C-5/6 tetraplegic individuals. The wrist extensor muscles were stimulated for 30 min/day, 5 days/week, for 12 weeks, using either a high-resistance (Hr) or a low-resistance (Lr) protocol. Total work output was similar in both protocols. The nontrained arm was used as a control. Maximum voluntary torque increased in the Hr (P < 0.05) but not the Lr group. Electrically stimulated peak tetanic torque at 15 HZ, 30 HZ, and 50 HZ were unchanged in the Lr group and tended to increase only at 15 HZ (P < 0.1) in the Hr group. Resistance to fatigue, however, increased (P < 0.05) in both Hr (42%) and Lr (41%) groups. Muscle metabolism was evaluated by (31)P nuclear magnetic resonance spectroscopy ((31)P-NMRS) during and following a continuous 40-s 10-HZ contraction. In the Hr group the cost of contraction decreased by 38% (P < 0.05) and the half-time of phosphocreatine (PCr) recovery was shortened by 52% (P < 0.05). Thus, long-term electrically induced stimulation of the wrist extensor muscles in spinal cord injury (SCI) increases fatigue resistance independent of training pattern. However, only the Hr protocol increased muscle strength and was shown to improve muscle aerobic metabolism after training. Muscle Nerve 27: 72-80, 2003