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Impaired sarcoplasmic reticulum Ca2+ release is the major cause of fatigue‐induced force loss in intact single fibres from human intercostal muscle

Changes in intramuscular Ca2+ handling contribute to development of fatigue and disease‐related loss of muscle mass and function. To date, no data on human intact living muscle fibres have been described. We manually dissected intact single fibres from human intercostal muscle and simultaneously measured force and myoplasmic free [Ca2+] at physiological temperature. Based on their fatigue resistance, two distinct groups of fibres were distinguished: fatigue sensitive and fatigue resistant. Force depression in fatigue and during recovery was due to impaired sarcoplasmic reticulum Ca2+ release in both groups of fibres. Acidification did not affect force production in unfatigued fibres and did not affect fatigue development in fatigue‐resistant fibres. The current study provides novel insight into the mechanisms of fatigue in human intercostal muscle.