RESUMO
OBJECTIVE: The aim of this article is to review the basic research concerned with force and fatigue induced by electrical stimulation. Specific reports on human and animal models are covered. Articles dealing with specific afflictions of the neuromuscular system are also reviewed. DATA SOURCES: The main sources for article retrieval were the classic bibliographic data bases in the exercise, rehabilitation and physiological science fields such as Index Medicus and Medline. Indexing terms used included human and animal in conjunction with electrical stimulation, force and fatigue. Language and time constraints limited the search to French and English texts of this century. Proceedings of different electrical stimulation conferences were also covered. STUDY SELECTION: All authors had to approve the selection of the articles to be included in this review. The narrow scope of the review made it possible to include most of the articles investigated. Redundancy of information was the only rejection criterion. DATA EXTRACTION: Initially, the first author collated the articles and extracted the relevant data. This collation was then verified with respect to the original information and approved by all authors. DATA SYNTHESIS: Possible sites of the fatigue mechanisms may include the central nervous system, the peripheral nervous system, the neuromuscular junction, and the muscle excitation-contraction coupling. Even though not unanimous, data gathered from normal muscles seem to support that the major contributor to fatigue is the muscle fiber and not the nervous system or the neuromuscular junction. Other work involving paralyzed muscles suggest that electrically induced exercise alters the contractile properties of the muscle more specifically. CONCLUSIONS: It appears that muscle intracellular processes dominate the force decrease associated with muscular fatigue. Accordingly, when dealing with a problem involving loss of force and hyperfatigability, the metabolic aspects and muscle physiology should be prime considerations in choosing a therapeutic approach. The nervous and/or neuromuscular implications are, however, not to be discarded.
