Abstract
High-load isometric exercise is considered an effective countermeasure against muscle atrophy, but therapeutic electrical stimulation for muscle atrophy is often performed without loading. In the present study, we investigated the combined effectiveness of electrical stimulation and high-load isometric contraction in preventing muscle atrophy induced by hindlimb unloading. Electrical stimulation without loading resulted in slight attenuation of muscle atrophy. Moreover, combining electrical stimulation with high-load isometric contraction enhanced this effect. In electrical stimulation without loading, inhibition of the overexpression of calpain 1, calpain 2, and MuRF-1 mRNA was confirmed. On the other hand, in electrical stimulation with high-load isometric contraction, inhibition of the overexpression of cathepsin L and atrogin-1 mRNA in addition to calpain 1, calpain 2, and MuRF-1 mRNA was confirmed. These findings suggest that the combination of electrical stimulation and high-load isometric contraction is effective as a countermeasure against muscle atrophy.
Highlights
Skeletal muscle atrophy results from a variety of conditions such as hindlimb unloading [1, 2], joint immobilization [3, 4], denervation [5, 6], and spinal cord injury [7,8,9]
Because hindlimb unloading was applied for 14 days in the present study, it was hypothesized that the increase in protein degradation was related closely rather than the decrease in protein synthesis to the atrophied tibialis anterior muscle
Electrical stimulation in isotonic contraction slightly attenuated muscle atrophy induced by hindlimb unloading, the combination of electrical stimulation and high-load isometric contraction inhibited increases in all 3 protein degradation pathways linked to muscle atrophy and enhanced the effect of electrical stimulation to prevent muscle atrophy
Summary
Skeletal muscle atrophy results from a variety of conditions such as hindlimb unloading [1, 2], joint immobilization [3, 4], denervation [5, 6], and spinal cord injury [7,8,9]. Resistance exercise training is performed as an effective therapeutic intervention to prevent muscle atrophy induced by these diverse conditions. Isometric contraction exercise confers greater protection against muscle atrophy because isometric contraction is a higher-intensity activity than isotonic contraction [11, 12]. In performing different types of muscle contraction, it is reported that electrical stimulation in isometric contraction is more effective in preventing muscle atrophy than that in isotonic contraction [7, 16]
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