Smith S A, Montain S J, Matott R P, Zientara G P, Jolesz F A, Fielding R A
Department of Health Sciences, Sargent College of Health and Rehabilitation Sciences, Boston University, Boston, 02215, Massachusetts, USA.
J Appl Physiol (1985). 1998 Oct;85(4):1349-56. doi: 10.1152/jappl.1998.85.4.1349.
Young [n = 5, 30 +/- 5 (SD) yr] and middle-aged (n = 4, 58 +/- 4 yr) men and women performed single-leg knee-extension exercise inside a whole body magnetic resonance system. Two trials were performed 7 days apart and consisted of two 2-min bouts and a third bout continued to exhaustion, all separated by 3 min of recovery. 31P spectra were used to determine pH and relative concentrations of Pi, phosphocreatine (PCr), and beta-ATP every 10 s. The subjects consumed 0.3 g . kg-1 . day-1 of a placebo (trial 1) or creatine (trial 2) for 5 days before each trial. During the placebo trial, the middle-aged group had a lower resting PCr compared with the young group (35.0 +/- 5.2 vs. 39.5 +/- 5.1 mmol/kg, P < 0.05) and a lower mean initial PCr resynthesis rate (18.1 +/- 3.5 vs. 23.2 +/- 6.0 mmol . kg-1 . min-1, P < 0.05). After creatine supplementation, resting PCr increased 15% (P < 0.05) in the young group and 30% (P < 0.05) in the middle-aged group to 45.7 +/- 7.5 vs. 45.7 +/- 5.5 mmol/kg, respectively. Mean initial PCr resynthesis rate also increased in the middle-aged group (P < 0.05) to a level not different from the young group (24.3 +/- 3.8 vs. 24.2 +/- 3.2 mmol . kg-1 . min-1). Time to exhaustion was increased in both groups combined after creatine supplementation (118 +/- 34 vs. 154 +/- 70 s, P < 0.05). In conclusion, creatine supplementation has a greater effect on PCr availability and resynthesis rate in middle-aged compared with younger persons.
年轻男性和女性（n = 5，年龄30±5岁（标准差））以及中年男性和女性（n = 4，年龄58±4岁）在全身磁共振系统内进行单腿膝关节伸展运动。两次试验间隔7天，每次试验包括两组2分钟的运动回合，第三回合持续至力竭，各回合之间有3分钟的恢复时间。每隔10秒用31P光谱测定pH值以及无机磷（Pi）、磷酸肌酸（PCr）和β-三磷酸腺苷（β-ATP）的相对浓度。在每次试验前，受试者连续5天每天服用0.3 g·kg-1·天-1的安慰剂（试验1）或肌酸（试验2）。在安慰剂试验期间，中年组的静息PCr水平低于年轻组（35.0±5.2 vs. 39.5±5.1 mmol/kg，P<0.05），平均初始PCr再合成率也较低（18.1±3.5 vs. 23.2±6.0 mmol·kg-1·min-1，P<0.05）。补充肌酸后，年轻组的静息PCr增加了15%（P<0.05），中年组增加了30%（P<0.05），分别达到45.7±7.5和45.7±5.5 mmol/kg。中年组的平均初始PCr再合成率也有所增加（P<0.05），达到与年轻组无差异的水平（24.3±3.8 vs. 24.2±3.2 mmol·kg-1·min-1）。补充肌酸后，两组合并的力竭时间增加（118±34 vs. 154±70秒，P<0.05）。总之，与年轻人相比，补充肌酸对中年人的PCr可用性和再合成率有更大影响。
