Ploutz-Snyder L L, Tesch P A, Crittenden D J, Dudley G A
Department of Biological Sciences, Ohio University, Athens 45701, USA.
J Appl Physiol (1985). 1995 Jul;79(1):168-75. doi: 10.1152/jappl.1995.79.1.168.
Exercise-induced spin-spin relaxation time (T2) shifts in magnetic resonance (MR) images were used to test the hypothesis that more muscle would be used to perform a given submaximal task after 5 wk of unweighting. Before and after unilateral lower limb suspension (ULLS), 7 subjects performed 5 sets of 10 unilateral concentric actions with the quadriceps femoris muscle group (QF) at each of 4 loads: 25, 40, 55, and 70% of maximum. T2-weighted MR images of the thigh were collected at rest and after each relative load. ULLS elicited a 20% decrease in strength of the left unweighted QF and a 14% decrease in average cross-sectional area (CSA) with no changes in the right weight-bearing QF. Average CSA of the left or right QF showing exercise-induced T2 shift increased as a function of exercise intensity both before and after ULLS. On average, 12 +/- 1, 15 +/- 2, 18 +/- 2, and 22 +/- 1 cm2 of either QF showed elevated T2 for the 25, 40, 55, and 70% loads, respectively, before ULLS. Average CSA of the left but not the right QF, showing elevated T2 after ULLS, was increased to 16 +/- 2, 23 +/- 3, 31 +/- 7, and 39 +/- 5 cm2, respectively. The results indicated that unweighting increased exercise-induced T2 shift in MR images, presumably due to greater muscle mass involvement in exercise after than before unweighting, suggesting a change in motor control.
运动诱导的磁共振（MR）图像自旋-自旋弛豫时间（T2）变化，被用于检验以下假设：在失重5周后，执行给定的次最大任务时会使用更多肌肉。在单侧下肢悬吊（ULLS）前后，7名受试者对股四头肌（QF）进行了5组，每组10次的单侧向心动作，动作在4种负荷下进行，分别为最大负荷的25%、40%、55%和70%。在休息时以及每个相对负荷后，采集大腿的T2加权MR图像。ULLS使左侧失重QF的力量下降了20%，平均横截面积（CSA）下降了14%，而右侧负重QF没有变化。ULLS前后，显示运动诱导T2变化的左侧或右侧QF的平均CSA均随运动强度增加。ULLS前，对于25%、40%、55%和70%的负荷，平均分别有12±1、15±2、18±2和22±1平方厘米的QF显示T2升高。ULLS后，左侧而非右侧QF显示T2升高，其平均CSA分别增加到16±2、23±3、31±7和39±5平方厘米。结果表明，失重增加了MR图像中运动诱导的T2变化，可能是由于失重后参与运动的肌肉量比失重前更多，这表明运动控制发生了改变。
