Abstract
BackgroundCreatine supplementation can improve performance during high intensity exercise in humans and improve muscle strength in certain myopathies. In this present study, we investigated the direct effects of acute creatine incubation on isolated mouse fast-twitch EDL muscles, and examined how these effects change with fatigue.Methods and ResultsThe extensor digitorum longus muscle from mice aged 12–14 weeks was isolated and stimulated with field electrodes to measure force characteristics in 3 different states: (i) before fatigue; (ii) immediately after a fatigue protocol; and (iii) after recovery. These served as the control measurements for the muscle. The muscle was then incubated in a creatine solution and washed. The measurement of force characteristics in the 3 different states was then repeated. In un-fatigued muscle, creatine incubation increased the maximal tetanic force. In fatigued muscle, creatine treatment increased the force produced at all frequencies of stimulation. Incubation also increased the rate of twitch relaxation and twitch contraction in fatigued muscle. During repetitive fatiguing stimulation, creatine-treated muscles took 55.1±9.5% longer than control muscles to lose half of their original force. Measurement of weight changes showed that creatine incubation increased EDL muscle mass by 7%.ConclusionAcute creatine application improves force production in isolated fast-twitch EDL muscle, and these improvements are particularly apparent when the muscle is fatigued. One likely mechanism for this improvement is an increase in Ca2+ sensitivity of contractile proteins as a result of ionic strength decreases following creatine incubation.
Highlights
The ingestion of supplementary creatine can increase intramuscular creatine and improve performance, during maximally fatiguing exercise [1,2]
The creatine(Cr)/phosphocreatine(PCr) cycle acts as a temporal buffer of ATP during the first seconds of intense skeletal muscle contraction before glycolysis and mitochondrial mechanisms can respond to the increased demand for ATP
To see whether creatine incubation affects the diameter of muscle fibres, single enzymatically isolated flexor digitorum brevis (FDB) fibres were viewed under a Nikon inverted microscope at 6600, while perfused with oxygenated Krebs solution
Summary
The ingestion of supplementary creatine can increase intramuscular creatine and improve performance, during maximally fatiguing exercise [1,2]. The creatine(Cr)/phosphocreatine(PCr) cycle acts as a temporal buffer of ATP during the first seconds of intense skeletal muscle contraction before glycolysis and mitochondrial mechanisms can respond to the increased demand for ATP. MM-CK, the M-line isoform, is localised to the M-line of the A-band of the contractile apparatus and is functionally coupled to glycolysis [9] This means that myosin ATPase preferentially uses ATP supplied by CK rather than cytosolic ATP [10]. At the sarcomeres, where large amounts of ATP are hydrolyzed during repetitive contractions, the MM-CK allows for the immediate phosphorylation of ADP This maintains a low ADP concentration, reducing the ADP-mediated leak of Ca2+ from the SR, which would reduce the releasable Ca2+ and reduce the force output of the muscle [13]. We investigated the direct effects of acute creatine incubation on isolated mouse fast-twitch EDL muscles, and examined how these effects change with fatigue
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