Effects of fatiguing exercise on high‐energy phosphates, force, and EMG: Evidence for three phases of recovery

Abstract

Experiments were designed to evaluate the relative contribution of impulse propagation failure, high-energy phosphate depletion, lowered pH, and impaired excitation-contraction coupling to human muscle fatigue and recovery. 31P nuclear magnetic resonance spectroscopy measurements were made on adductor pollicis muscle, together with simultaneous measurements of M-wave, force, and rectified integrated EMG (RIEMG). During fatigue, maximum voluntary contraction force (MVC) fell by 90%, pH fell from 7.1 to 6.4, and phosphocreatine was almost totally depleted. Neuromuscular efficiency (NME = force/RIEMG) was reduced to 40% of control at the end of the fatiguing contraction, and the M wave was reduced in amplitude and prolonged in duration. Following exercise, the M wave returned to normal within 4 minutes. pH, high-energy phosphates, and MVC recovered within 20 minutes. By contrast, neuromuscular efficiency did not recover within 60 minutes. These findings indicate three different components of fatigue. The first is reflected by the altered M wave and indicates impaired muscle membrane excitation and impulse propagation. The second, associated with reduced MVC, correlates with the metabolic state of the muscle (PCr and pH). The third, indicated by reduced NME, is independent of changes in high-energy phosphates and pH and is probably due to impaired excitation-contraction coupling.

EMG and metabolite-based prediction of force in paralyzed quadriceps muscle under interrupted stimulation

“…Rest spectrum of 31 P metabolites indicates that energetically a paralyzed muscle is similar to a normal muscle. Under isometric FES as well as during the subsequent rest period, the acquired 31 P spectra were metabolically similar to those obtained for maximal voluntary contraction [22]. The above similarity could be expected since no injury was caused directly to the muscle cells and to the peripheral nervous system.…”

Age‐related Effects of Fatigue and Recovery From Fatigue in Rat Medial Gastrocnemius Muscle

“…However, in the present experiments the level of phosphocreatine was restored with a much faster time course during recovery from fatigue than the slow phase of isometric force recovery and thus seems unlikely to explain this longer term element of fatigue (Figs 7 and 8;Fitts & Holloszy, 1976). According to Miller, Giannini, Millner-Brown, Layser, Koretsky, Hooper & Werner (1987) recovery of phosphocreatine, inorganic phosphate and muscle pH have similar time courses. The high phosphocreatine concentration reattained early in recovery (Fig.…”

Muscle Na-K-pump and fatigue responses to progressive exercise in normoxia and hypoxia

“…However, in contrast to the previous studies where M-wave characteristics were measured concurrently with fatigue, initially, we assessed these properties only 4 -5 min after exercise. It would be expected that some recovery in M-wave properties would occur during the period after exercise when the volunteers were being prepared for stimulation, as a result of recovery or partial recovery of selected intracellular metabolic by-products (40) and restoration of transmembrane Na ϩ and K ϩ gradients (41). To investigate whether or not significant recovery had occurred, we have performed a separate set of experiments measuring the M-wave properties during the progressive exercise task itself.…”