Shortening of muscle relaxation time after creatine loading

Abstract

The effect of creatine (Cr) supplementation on muscle isometric torque generation and relaxation was investigated in healthy male volunteers. Maximal torque (Tmax), contraction time (CT) from 0.25 to 0.75 of Tmax, and relaxation time (RT) from 0.75 to 0.25 of Tmax were measured during 12 maximal isometric 3-s elbow flexions interspersed by 10-s rest intervals. Between the pretest and the posttest, subjects ingested Cr monohydrate (4 x 5 g/day; n = 8) or placebo (n = 8) for 5 days. Pretest Tmax, CT, and RT were similar in Cr and placebo groups. Also in the posttest, Tmax and CT were similar between groups. However, posttest RT was decreased consistently by approximately 20% (P < 0.05) in the Cr group from the first to the last of the 12 contractions. In addition, the mean decrease in RT after Cr loading was positively correlated with pretest RT (r = 0.82). It is concluded that Cr loading facilitates the rate of muscle relaxation during brief isometric muscle contractions without affecting torque production.

Contractile properties, fatigue and recovery are not influenced by short-term creatine supplementation in human muscle

“…Since the relaxation process accounts for an important fraction of total energy consumption (Bergstrom & Hultman, 1988) during repeated muscle contraction there might be a performance benefit if relaxation time were decreased. Van Leemputte et al (1999) suggested that the mechanism facilitating relaxation was the rise in PCr concentration which enabled the sarcoplasmic Ca¥-ATPase to operate at a higher thermodynamic efficiency or at a higher rate of cross-bridge detachment (van Leemputte et al 1999). Changes in EMG in response to Cr supplementation have not been assessed extensively and comparisons between studies are difficult since different techniques have been employed.…”

“…Indeed, it has been shown that following Cr supplementation in rats, twitch and tetanic half-relaxation times (HRT) are decreased (Wakatsuki et al 1994). In human elbow flexors relaxation time of voluntary contractions is also less (van Leemputte et al 1999).…”

“…In part, it seems the disparity in the findings occurs because of differences in the exercise model employed, or the intensity, duration, and frequency of the task, and the level of fitness of the subjects. Most studies have adopted cycling, swimming, or dynamic isotonic contractions, but few studies have employed an isometric model (van Leemputte et al 1999). Compared with a dynamic task, the isometric model offers greater ability to assess in a controlled situation, the effects of various neural and contractile factors which might be affected by Cr supplementation.…”

“…Also, it has been proposed that Cr supplementation alters muscle relaxation through changes in local PCr concentration. Increases in PCr may optimize sarcoplasmic reticulum (SR) Ca¥-ATPase activity, thereby facilitating muscle relaxation (van Leemputte et al 1999) by promoting enhanced re-uptake of Ca¥. Indeed, it has been shown that following Cr supplementation in rats, twitch and tetanic half-relaxation times (HRT) are decreased (Wakatsuki et al 1994).…”

“…Although it is unlikely that there would be significant protein synthesis in 5 days, cell swelling might alter muscle architecture (pennation angle) which could affect contractile properties (Lieber, 1992). Although a few studies have examined isometric voluntary force changes following Cr supplementation (Harridge et al 1994;Maganaris & Maughan, 1998;van Leemputte et al 1999), stimulated contractile properties and maximal voluntary force have not been assessed concurrently in nonfatigued and fatigued muscle. Thus, the purpose of this investigation was to determine whether short-term creatine supplementation (5 days) in young men would alter electrically evoked contractile characteristics of muscle, and induce a performance benefit in maximal voluntary force, time to fatigue, or rate of recovery in a submaximal isometric elbow flexion endurance task.…”