Postfatigue potentiation of the paralyzed soleus muscle: evidence for adaptation with long-term electrical stimulation training

J Appl Physiol, 2006 · DOI: 10.1152/japplphysiol.00099.2006 · Published: August 1, 2006

Simple Explanation

This study investigates how paralyzed muscles respond to repeated stimulation after fatigue, focusing on a phenomenon called postfatigue potentiation, where muscle strength temporarily increases after a period of fatigue. The research compares this response in individuals with recent paralysis versus those with long-term paralysis, and it also examines the impact of regular electrical stimulation training on muscle behavior. The findings suggest that electrical stimulation training can help maintain the muscle characteristics observed in the early stages of paralysis, potentially improving the effectiveness and predictability of functional electrical stimulation (FES) systems.

Study Duration

2 Years

Participants

15 men with complete SCI and 10 additional subjects enrolled within the first 6 mo after SCI

Evidence Level

Not specified

Key Findings

1
Chronically paralyzed muscles show significant postfatigue potentiation, while acutely paralyzed muscles do not.
2
Long-term electrical stimulation training preserves the potentiation characteristics of acutely paralyzed muscles.
3
Untrained limbs of individuals with SCI develop postfatigue potentiation over time, similar to chronically paralyzed muscles.

Research Summary

The study quantified postfatigue potentiation in acutely and chronically paralyzed soleus muscles and determined the effect of long-term electrical stimulation training on potentiation characteristics. Chronic SCI subjects demonstrated significant postfatigue potentiation, while acute SCI subjects did not; however, electrical stimulation training preserved the early postinjury potentiation characteristics. Postfatigue potentiation is a characteristic of fast-fatigable muscle and can be prevented by timely neuromuscular electrical stimulation training.

Practical Implications

FES Design

Potentiation is an important consideration in the design of functional electrical stimulation control systems for people with SCI.

Training Regimen

Early implementation of electrical stimulation training can preserve muscle characteristics and prevent undesirable potentiation.

Muscle Health

Maintaining muscular and skeletal integrity may be important to the overall health of individuals with SCI.

Study Limitations

1
Longitudinal training studies are difficult to control and require substantial commitment from subjects.
2
Routine laboratory assessments of the untrained limb included only one bout (not 4 bouts).
3
It is conceivable that the untrained limb benefited, via segmental cross-education, from the training that occurred on the contralateral side.

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