Relationship of contraction capacity to metabolic changes during recovery from a fatiguing contraction.
The relationship between changes in muscle metabolites and the contraction capacity was investigated in humans. Subjects (n = 13) contracted (knee extension) at a target force of 66% of the maximal voluntary contraction force (MVC) to fatigue, and the recovery in MVC and endurance (time to fatigue) were measured. Force recovered rapidly [half-time (t 1/2) less than 15 s] and after 2 min of recovery was not significantly different (P greater than 0.05) from the precontraction value. Endurance recovered more slowly (t 1/2 approximately 1.2 min) and was still significantly depressed after 2 and 4 min of recovery (P less than 0.05). In separate experiments (n = 10) muscle biopsy specimens were taken from the quadriceps femoris muscle before and after two successive contractions to fatigue at 66% of MVC with a recovery period of 2 or 4 min in between. The muscle content of high-energy phosphates and lactate was similar at fatigue after both contractions, whereas glucose 6-phosphate was lower after the second contraction (P less than 0.05). During recovery, muscle lactate decreased and was 74 and 43% of the value at fatigue after an elapsed period of 2 and 4 min, respectively. The decline in H+ due to lactate disappearance is balanced, however, by a release of H+ due to resynthesis of phosphocreatine, and after 2 min of recovery calculated muscle pH was found to remain at a low level similar to that at fatigue.(ABSTRACT TRUNCATED AT 250 WORDS)
Sahlin
K
K
Department of Clinical Physiology, Karolinska Institute, Huddinge University Hospital, Sweden.
Ren
J M
JM
D000244:Adenosine Diphosphate / Q000032:analysis; D000249:Adenosine Monophosphate / Q000032:analysis; D000255:Adenosine Triphosphate / Q000032:analysis; D000328:Adult; D001706:Biopsy; D005221:Fatigue; D005958:Glucosephosphates / Q000032:analysis; D006801:Humans; D007773:Lactates / Q000032:analysis; D008297:Male; D009119:Muscle Contraction; D009132:Muscles / Q000378:metabolism* / Q000473:pathology; D010725:Phosphocreatine / Q000032:analysis; D013997:Time Factors
D005958:Glucosephosphates; D007773:Lactates; D010725:Phosphocreatine; D000249:Adenosine Monophosphate; D000244:Adenosine Diphosphate; D000255:Adenosine Triphosphate