Low force contractions induce fatigue consistent with muscle mRNA expression in people with spinal cord injury

Physiol Rep, 2014 · DOI: 10.1002/phy2.248 · Published: February 1, 2014

Spinal Cord Injury Genetics Musculoskeletal Medicine

Simple Explanation

This study investigates how low-intensity muscle stimulation affects paralyzed muscles in people with spinal cord injury (SCI). The researchers compared muscle fatigue and gene activity in individuals with and without SCI after a low force stimulation protocol. The study found that low-force stimulation caused fatigue in paralyzed muscles, which was linked to specific changes in gene expression. These changes suggest that a low force exercise approach might help improve muscle health in people with SCI. The findings suggest that this type of stimulation may offer a safer way to exercise paralyzed muscles and improve their metabolic function without causing harm to the weakened bones common in individuals with SCI.

Study Duration

Not specified

Participants

29 subjects: 9 with SCI and 20 without SCI

Evidence Level

Original Research

Key Findings

1
Low force stimulation (3 Hz) caused fatigue in chronically paralyzed quadriceps muscles of people with SCI, while the quadriceps of people without paralysis were not fatigued.
2
The paralyzed muscle showed a progressive increase in peak force during repetitive activation 5 minutes after the muscle was fatigued, indicating post-activation potentiation.
3
Gene expression analysis showed that genes related to muscle atrophy and fast-twitch muscle fibers were upregulated in the SCI group, while genes related to oxidative metabolism and slow-twitch fibers were downregulated.

Research Summary

This study demonstrated that a low force single twitch stimulation protocol fatigued the human chronically paralyzed muscle. The fatigue index, the potentiation index, and speed properties responded in a manner consistent with the mRNAs expressed for several genes known to regulate the physiological response to repetitive stimulation. Because individuals with SCI develop (1) severe osteoporosis, (2) have limited muscle activity, (3) impaired muscle glucose utilization, and (4) diabetes, this low force activation protocol may present a novel strategy to mitigate the incidence of metabolic disease in a convenient and safe manner.

Practical Implications

Safe Exercise Strategy

Low-force stimulation protocols may provide a safer method for individuals with SCI to exercise and maintain muscle health without risking fractures.

Metabolic Health Improvement

Regular low-force stimulation may help to improve glucose utilization and overall metabolic health in individuals with SCI.

Gene Regulation for Muscle Adaptation

Low-force stimulation can induce gene expression changes that promote a shift from fast-twitch glycolytic muscle fibers to more oxidative and fatigue-resistant fibers.

Study Limitations

1
Small sample size for muscle biopsy and gene expression analysis.
2
Lack of longitudinal data on the long-term effects of low force stimulation training.
3
The study focused on specific genes, and a broader analysis of the transcriptome could provide more insights.

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