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The Effects of Dietary Creatine Supplements on the Contractile Properties of Rat Soleus and Extensor Digitorum Longus Muscles
Author(s) -
McGuire M.,
Bradford A.,
MacDermott M.
Publication year - 2001
Publication title -
experimental physiology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.925
H-Index - 101
eISSN - 1469-445X
pISSN - 0958-0670
DOI - 10.1113/eph8602131
Subject(s) - isometric exercise , creatine , medicine , contraction (grammar) , endocrinology , chemistry , soleus muscle , tetanic stimulation , muscle contraction , stimulation , muscle relaxation , anatomy , long term potentiation , skeletal muscle , receptor
Daily creatine supplements (0.258 g kg −1 ) were administered to adult male Wistar rats ( n = 7) in the drinking water. Age matched rats ( n = 6) acted as controls. After 5‐6 days, contractile properties were examined in soleus and extensor digitorum longus (EDL) muscle strips in vitro at 30 °C. In soleus muscles, creatine supplements decreased the half‐relaxation time of the isometric twitch from 53.6 ± 4.3 ms in control muscles to 48.4 ± 5.5 ms but had no effect on twitch or tetanic tension or on twitch contraction time. In EDL muscles twitch tension, tetanic tension, twitch contraction and half‐relaxation times were all unaffected by creatine supplements. Creatine supplements increased the fatigue resistance of the soleus muscles but had no effect on that of the EDL muscles. After a 5 min low‐frequency fatigue test, tension (expressed as a percentage of initial tension) was 56 ± 3% in control soleus muscles, whereas that in the creatine‐supplemented muscles was 78 ± 6% ( P < 0.01). In the EDL muscles, the corresponding values were 40 ± 2% and 41 ± 9%, respectively. The force potentiation which occurred in the EDL muscles during the initial 20‐30 s of the fatigue test was 170 ± 10% of initial tension in the control muscles 24 s after the initial stimulus train but was reduced ( P < 0.01) to 130 ± 20% in the creatine‐supplemented muscles. In conclusion, soleus muscle endurance was increased by creatine supplements. EDL endurance was unaffected but force potentiation during repetitive stimulation was decreased.