Repeated high‐intensity exercise modulates Ca²⁺ sensitivity of human skeletal muscle fibers

Abstract

The effects of short-term high-intensity exercise on single fiber contractile function in humans are unknown. Therefore, the purposes of this study were: (a) to access the acute effects of repeated high-intensity exercise on human single muscle fiber contractile function; and (b) to examine whether contractile function was affected by alterations in the redox balance. Eleven elite cross-country skiers performed four maximal bouts of 1300 m treadmill skiing with 45 min recovery. Contractile function of chemically skinned single fibers from triceps brachii was examined before the first and following the fourth sprint with respect to Ca(2+) sensitivity and maximal Ca(2+) -activated force. To investigate the oxidative effects of exercise on single fiber contractile function, a subset of fibers was incubated with dithiothreitol (DTT) before analysis. Ca(2+) sensitivity was enhanced by exercise in both MHC I (17%, P < 0.05) and MHC II (15%, P < 0.05) fibers. This potentiation was not present after incubation of fibers with DTT. Specific force of both MHC I and MHC II fibers was unaffected by exercise. In conclusion, repeated high-intensity exercise increased Ca(2+) sensitivity in both MHC I and MHC II fibers. This effect was not observed in a reducing environment indicative of an exercise-induced oxidation of the human contractile apparatus.

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

“…In addition, the reducing agent dithiothreitol has been shown to blunt the increase in myofibrillar Ca 2+ sensitivity of both slow‐ and fast‐twitch human skinned fibres following high‐intensity exercise (Gejl et al . ). This suggests that oxidative events are also involved in the modulation of Ca 2+ sensitivity in slow‐twitch fibres.…”

“…Interestingly, human skeletal muscle fibres fatigued in vivo and subsequently studied in skinned fibre preparations have demonstrated increases in myofibrillar Ca 2+ sensitivity following high‐intensity exercise (Gejl et al . ), as well as differences between fast‐ and slow‐twitch fibres regarding fatigue‐induced changes in myofibrillar Ca 2+ sensitivity following prolonged endurance exercise (Hvid et al . ).…”

Reactive oxygen/nitrogen species and contractile function in skeletal muscle during fatigue and recovery

“…) and some skinned fibre experiments show increased rather than decreased myofibrillar Ca 2+ sensitivity after fatiguing contractions (Gejl et al . ; Watanabe et al . ).…”

Molecular Basis for Exercise-Induced Fatigue: The Importance of Strictly Controlled Cellular Ca2+Handling

“…However, the effects of ROS/RNS are highly complex and the results of some studies even imply that reducing ROS/RNS during fatigue would impair rather than improve performance. For instance, acute exogenous application of H 2 O 2 results in a transient increase in myofibrillar Ca 2þ sensitivity (Andrade et al 1998(Andrade et al , 2001Cheng et al 2015) and some skinned fiber experiments show increased rather than decreased myofibrillar Ca 2þ sensitivity after fatiguing contractions (Gejl et al 2015;Watanabe et al 2015).…”