Abstract
In isometric contraction-induced fatigue force loss has been related to mostly myoelectrical
or intramuscular events. However, some factors potentially involved may interfere
at more than one site in these events and it has proven difficult to distinguish between
those influences. The study of the relationships between force generating capacity,
the metabolic state of a muscle and its myoelectrical properties may therefore help
broaden our understanding of the fatigue process. In order to investigate these relationships,
we have evaluated changes in force-generating capacity, NMR-determined metabolic variables,
and myoelectrical activity, as measured from surface EMG, simultaneously in brachial
biceps muscle of healthy subjects, during different types of fatiguing isometric exercise
and during recovery. Factors studied include intramuscular pH, inorganic phosphate
and its diprotonated form concentrations, root-mean square and mean power frequency
of the EMG power spectrum, and neuromuscular efficiency index. Results show that different
mechanisms are likely to contribute to force loss in fatiguing muscle and during different
phases of recovery from fatigue. Indeed, relationships between variables from the
three groups differed according to exercise protocol as well as in fatiguing and recovering
muscle.
Key words
Muscle - electromyography - nuclear magnetic resonance - fatigue - intramuscular pH
