Department of Sport, Health and Exercise Science, University of Hull, Cottingham Road, Kingston upon Hull HU67RX, UK.
Exp Physiol. 2010 Jan;95(1):202-10. doi: 10.1113/expphysiol.2009.048967. Epub 2009 Sep 11.
To better understand the effects of pubertal maturation on the contractile properties of skeletal muscle in vivo, the present study investigated whether there are any differences in the specific tension of the quadriceps muscle in 20 adults and 20 prepubertal children of both sexes. Specific tension was calculated as the ratio between the quadriceps tendon force and the sum of the physiological cross-sectional area (PCSA) multiplied by the cosine of the angle of pennation of each head within the quadriceps muscle. The maximal quadriceps tendon force was calculated from the knee extension maximal voluntary contraction (MVC) by accounting for EMG-based estimates of antagonist co-activation, incomplete quadriceps activation using the interpolation twitch technique and magnetic resonance imaging (MRI)-based measurements of the patellar tendon moment arm. The PCSA was calculated as the muscle volume, measured from MRI scans, divided by optimal fascicle length, measured from ultrasound images during MVC at the estimated angle of peak quadriceps muscle force. It was found that the quadriceps tendon force and PCSA of men (11.4 kN, 214 cm(2)) were significantly greater than those of the women (8.7 kN, 152 cm(2); P < 0.01). Both adult groups had greater values than the children (P < 0.01) but there were no differences between boys (5.2 kN, 99 cm(2)) and girls (6.1 kN, 102 cm(2)). Agonist activation was greater in men and women than in girls (P < 0.05), and antagonist activation was greater in men than in boys (P < 0.05). Moment arm length was greater in men than in boys or girls and greater in women than in boys (P < 0.05). The angle of pennation did not differ between the groups in any of the quadriceps heads. The specific tension was similar (P > 0.05) between groups: men, 55 +/- 11 N cm(-2); women, 57.3 +/- 13 N cm(-2); boys, 54 +/- 14 N cm(-2); and girls, 59.8 +/- 15 N cm(-2). These findings indicate that the increased muscle strength with maturation is not due to an increase in the specific tension of muscle; instead, it can be attributed to increases in muscle size, moment arm length and voluntary activation level.
为了更好地理解青春期成熟对活体骨骼肌收缩特性的影响，本研究调查了两性 20 名成年人和 20 名青春期前儿童的股四头肌比张力是否存在差异。比张力定义为股四头肌肌腱力与股四头肌每个头的生理横截面积（PCSA）乘以羽状角余弦的乘积之比。最大股四头肌肌腱力通过考虑基于肌电图的拮抗肌共同激活估计值、使用插值抽搐技术测量不完全股四头肌激活以及基于磁共振成像（MRI）测量髌腱力臂，从膝关节伸展最大随意收缩（MVC）中计算得出。PCSA 计算为 MRI 扫描测量的肌肉体积除以 MVC 期间超声图像测量的最佳肌束长度，以估计股四头肌最大力的角度。结果发现，男性（11.4 kN，214 cm(2)）的股四头肌肌腱力和 PCSA 显著大于女性（8.7 kN，152 cm(2)；P < 0.01）。两组成年人的数值均大于儿童（P < 0.01），但男孩（5.2 kN，99 cm(2)）与女孩（6.1 kN，102 cm(2)）之间没有差异。男性和女性的激动剂激活大于女孩（P < 0.05），男性的拮抗剂激活大于男孩（P < 0.05）。男性的力臂长度大于男孩或女孩，女性的力臂长度大于男孩（P < 0.05）。在任何股四头肌头中，羽状角都没有在组间存在差异。各组的比张力相似（P > 0.05）：男性，55 +/- 11 N cm(-2)；女性，57.3 +/- 13 N cm(-2)；男孩，54 +/- 14 N cm(-2)；女孩，59.8 +/- 15 N cm(-2)。这些发现表明，随着成熟肌肉力量的增加不是由于肌肉比张力的增加所致；相反，它可以归因于肌肉大小、力臂长度和自愿激活水平的增加。
