Abstract
Skeletal muscle is an integral part of the somatic nervous system and plays a primary role in the performance of physical activities. Because physical activity is vital to countering the effects of aging and age related diseases and is a key component in the maintenance of healthy body composition it is important to understand the effects of use and disuse on skeletal muscle. While voluntary muscle activity provides optimal benefits to muscle and the maintenance of healthy body composition, neuromuscular electrical stimulation may be a viable alternative activity for individuals with paralysis. Body composition with a healthy muscle to fat ratio has been associated with healthy blood lipid and glucose profiles that may decrease the risk of cardiovascular and metabolic diseases.
Highlights
Knowledge of skeletal muscle physiology is important as the various principles that govern muscle health guide the development of rehabilitative and preventive exercise prescriptions
Voluntary muscle action is the natural order of muscle contraction when unavailable, neuromuscular electrical stimulation (NMES) has been proposed as a promising rehabilitative tool for individuals with limited ability to voluntarily activate muscles
The objectives of this paper are to 1) provide a brief overview of skeletal muscle strength, 2) describe the effects of muscle deactivation on muscle size, fiber type and muscle mechanics, 3) discuss the changes in body composition and metabolic profile accompanied with muscle atrophy, and 4) describe the effects of voluntary and externally induced exercise as countermeasures for reversing muscle disuse
Summary
10% increase in muscle mass 2% increase in muscle mass, 22% increase in muscle CSA, 1.9% decrease in fat mass 3.3% increase in muscle mass 63% increase in muscle cross sectional area. Because large twitch fibers rely primarily on glycolysis, these fibers are unable to replenish their glycogen storage capacity during NMES and the idea of reversal recruitment Another theory describes a randomly, synchronous, repeated recruitment of motor units during NMES compared to the orderly, asynchronous recruitment during voluntary exercise (i.e. slow to fast fibers as force is increased) [98]. With NMES repeated random activation of the same slow and fast motor units result in fatigue during submaximal exercise so performance cannot be maintained. Chen and associates found that 6 months of FES-LEC improved the BMD of the distal femur and proximal tibia 6 months after cessation of FESLEC BMD returned to pre-exercise levels [105] These findings demonstrate that the benefits of physical activity [7] are temporary and that long term physical activity is required to achieve long term benefits
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