The Investigation of Metabolic and Cardiovascular Responses to Fatiguing Static Effort.
SAINT LOUIS UNIV MO SCHOOL OF MEDICINE
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In the animal experiments a new method of stimulating muscles was developed in the laboratory to mimic voluntary contractions. Cat muscles were stimulated to fatigue at various constant tensions. The soleus muscle slow twitch did not fatigue unless the tension exceeded 30 of maximal strength whereas the plantaris muscle fast-twitch fatigued at all tensions above 3 of maximal strength. Fatigue was not attributable to failure of the neuromuscular junction. Fatiguing contractions of the soleus muscle did not elicit an increase in blood pressure whereas fast-twitch muscles did so, just as in voluntary contractions in man. In human studies, women held given fractions of maximal strength longer than men. But because men are stronger than women, transposing the same data into absolute tension shows that the men have a longer isometric endurance for any given tension examined. Electromyographic studies show that the integrated amplitude increases as contractions are held to fatigue by about the same amount, irrespective of the tension held. The frequency of the electromyogram fell by an absolute amount all tensions. This kind of analysis may be used as a tool to detect fatigue. Extensive studies of the control of muscle blood flow showed that during intermittent isometric exercise, local metabolites were responsible for dilating the vessels but that that effect could be opposed, in part, by neural vasoconstriction. Author
- Anatomy and Physiology
- Stress Physiology