Electromechanical stimulation ameliorates inactivity-induced adaptations in the medial gastrocnemius of adult rats

Abstract

The efficacy of high-load, short-duration isometric contractions, delivered as one vs. two sessions per day, on blunting inactivity-induced adaptations in the medial gastrocnemius (MG) were compared. Adult rats were assigned to a control (Con) or spinal cord-isolated (SI) group where one limb was stimulated (SI-Stim) while the other served as a SI control (SI-C). One bout of stimulation (BION microstimulator) consisted of a 100-Hz, 1-s stimulus, delivered every 30 s for 5 min with a 5-min rest period. This bout was repeated six times consecutively (SI-Stim1) or with a 9-h rest interval after the third bout (SI-Stim2) for 30 consecutive days. MG weights (relative to body weight) were 63, 72, and 79% of Con in SI-C, SI-Stim1, and SI-Stim2, respectively. Mean fiber size was 56% smaller in SI-C than in Con, and it was 19 and 31% larger in SI-Stim1 and SI-Stim2, respectively, compared with SI-C. Maximum tetanic tension was 42, 60, and 73% of Con in SI-C, SI-Stim1, and SI-Stim2, respectively. Specific tension was 77% of Con in SI-C, and at Con levels in both SI-Stim groups. SI increased the percent IIb myosin heavy chain composition (from 49 to 77%) and IIb+ fibers (from 63 to 79%): these adaptations were prevented by both Stim paradigms. These results demonstrate that 1) brief periods of high-load isometric contractions are effective in reducing inactivity-induced atrophy, functional deficits, and phenotypic adaptations in a fast hindlimb extensor, and 2) the same amount of stimulation distributed in two compared with one session per day is more effective in ameliorating inactivity-related adaptations.

Chronic α-hydroxyisocaproic acid treatment improves muscle recovery after immobilization-induced atrophy

“…However, it is noteworthy that Wistar rats of this age regained muscle mass relatively quickly. In general, limb immobilization has been reported to decrease muscle mass and fiber diameter in mice, rats, and humans (24,35,37,40,54,61). This disuse atrophy is caused by an imbalance between rates of protein synthesis and degradation.…”

Automatic classification of motor unit potentials in surface EMG recorded from thenar muscles paralyzed by spinal cord injury

“…12), the analysis yields the times the tracked motor units were active. This can be expanded to investigate activity differences between awake and asleep time, to investigate the amounts of neuromuscular activity required to sustain muscle and motor unit properties (Kernell et al, 1987; Kim et al, 2007) or to evaluate whether medications dampen activity. Muscle spasms are a quality of life issue for spinal cord injured individuals, for example by disrupting sleep.…”

“…For example, they can be used to investigate the concept that only small amounts of neuromuscular activity are required to sustain muscle and motor unit properties (Kernell et al, 1987; Kim et al, 2007). They could also be used to evaluate whether medications dampen activity.…”

Recovery of control of posture and locomotion after a spinal cord injury: solutions staring us in the face

“…Using the rat model of spinal cord isolation, we have initiated studies to determine the minimum number of contractions required to maintain the properties of a muscle. As little as 1 min of brief, high-load isometric contractions per day was sufficient to significantly ameliorate the loss of mass and maximum tetanic tension, and the shift from slower-to-faster phenotypes in the otherwise inactive medial gastrocnemius muscle (Kim et al, 2007). In addition, delivering the same amount of activity during two sessions per day was more effective than one session per day (Fig.…”