Smith-Ryan Abbie E, Ryan Eric D, Fukuda David H, Costa Pablo B, Cramer Joel T, Stout Jeffrey R
1Department of Exercise and Sport Science, University of North Carolina Chapel Hill, Chapel Hill, NC; 2Sport and Exercise Science, University of Central Florida, Orlando, FL; 3Department of Kinesiology, California State University-San Bernardino, San Bernardino, CA; and 4Department of Nutrition and Health Sciences, University of Nebraska-Lincoln, Lincoln, NE.
Med Sci Sports Exerc. 2014;46(5):990-7. doi: 10.1249/MSS.0000000000000194.
This study aimed to examine the effects of intermittent isometric fatigue on maximal voluntary contraction (MVC) strength, percent voluntary activation (%VA), peak twitch force (PTF), peak rate of force development (PRFD), half relaxation time (HRT), and maximal compound action potential (M-wave) amplitude of the soleus and medial gastrocnemius muscles before and after creatine (Cr) loading.
Using a double-blinded, placebo-controlled, randomized design, 12 women were assigned to a Cr (n = 6; mean age ± SD = 23.3 ± 3.0 yr) or placebo (PL; n = 6; mean age ± SD = 21.3 ± 1.6 yr) group. Participants supplemented four times daily for 5 d with 5 g of Cr + 10 g of fructose or 10 g of fructose. At baseline and after testing, an isometric MVC and the twitch interpolation procedure were used before and after a 4-min isometric fatigue protocol of the plantarflexor muscles, which consisted of six intermittent duty cycles per minute (7-s contraction, 3-s relaxation) at 70% MVC.
There were no interactions between the Cr and PL groups (P > 0.05) for any dependent variable. The fatigue protocol reduced voluntary strength (-17.8%, P < 0.001) and %VA (-3.7%, P = 0.005). Baseline PTF (P < 0.005) and PRFD (P < 0.001) values were less than those of all respective time points, but PTF value decreased from 3 min to 4 min and after testing (P < 0.005). HRT increased from baseline to minutes 1 and 2 and then returned to baseline at minutes 3 and 4 and after testing. The M-wave did not change (P > 0.05).
Five days of Cr loading did not influence isometric force, %VA, evoked twitch properties, or the central and peripheral aspects of fatigue measured in this study.
本研究旨在探讨肌酸（Cr）负荷前后，间歇性等长疲劳对比目鱼肌和腓肠肌最大自主收缩（MVC）力量、自主激活百分比（%VA）、峰值抽搐力（PTF）、力量发展峰值速率（PRFD）、半松弛时间（HRT）以及最大复合动作电位（M波）幅度的影响。
采用双盲、安慰剂对照、随机设计，将12名女性分为Cr组（n = 6；平均年龄±标准差 = 23.3 ± 3.0岁）或安慰剂（PL）组（n = 6；平均年龄±标准差 = 21.3 ± 1.6岁）。参与者每天补充4次，持续5天，分别补充5克Cr + 10克果糖或10克果糖。在基线和测试后，在跖屈肌进行4分钟等长疲劳方案（包括每分钟6个间歇性工作周期，7秒收缩，3秒放松，强度为70%MVC）前后，使用等长MVC和抽搐插值程序。
对于任何因变量，Cr组和PL组之间均无交互作用（P > 0.05）。疲劳方案降低了自主力量（-17.8%，P < 0.001）和%VA（-3.7%，P = 0.005）。基线PTF（P < 0.005）和PRFD（P < 0.001）值低于所有相应时间点的值，但PTF值从3分钟到4分钟以及测试后下降（P < 0.005）。HRT从基线增加到第1和第2分钟，然后在第3和第4分钟以及测试后恢复到基线。M波未发生变化（P > 0.05）。
5天的Cr负荷并未影响本研究中测量的等长力量、%VA、诱发抽搐特性或疲劳的中枢和外周方面。
