Abstract：
OBJECTIVE: While muscle mass and skeletal muscle fibers phenotype have been shown atypical in constitutional thinness (CT), force production capacities and its architectural determinants have never been explored. The present study compared muscle functionality and architecture between participants with CT and their normal-weight (NW) counterparts.
METHODS: Anthropometry, body composition (Dual-X-ray Absorptiometry), physical activity/sedentary behavior (ActiGraph wGT3X-BT), ultrasound recording of the Vastus Lateralis (2D-ultrasound system), and functional capacities at maximal isometric and isokinetic voluntary contractions (MVCISO and MVCCON) during knee extension (isokinetic dynamometer chair Biodex) have been measured in 18 women with CT (body mass index < 17.5 kg/m2) and 17 NW women.
RESULTS: A lower fat-free mass (ES: -1.94, 95%CI: -2.76 to -1.11, p < 0.001), a higher sedentary time, and a trend for a lower time spent at low-intensity physical activity, were observed in CT vs NW participants. While absolute MVCISO, MVCCON, rate of torque development (RTD), and torque work were all markedly lower in CT, these differences disappeared when normalized to body or muscle mass. Muscle thickness and fascicle length were found lower in CT (ES: -1.29, 95%CI: -2.03 to -0.52, p < 0.001; and ES: -0.87, 95%CI: -1.58 to -0.15, p = 0.02, respectively), while pennation angle was found similar.
CONCLUSIONS: Despite lower absolute strength capacities observed in CT, present findings support the hypothesis of physiological adaptations to the low body and muscle mass than to some intrinsic contractile impairments. These results call for further studies exploring hypertrophy-targeted strategies in the management of CT.
METHODS: Anthropometry, body composition (Dual-X-ray Absorptiometry), physical activity/sedentary behavior (ActiGraph wGT3X-BT), ultrasound recording of the Vastus Lateralis (2D-ultrasound system), and functional capacities at maximal isometric and isokinetic voluntary contractions (MVCISO and MVCCON) during knee extension (isokinetic dynamometer chair Biodex) have been measured in 18 women with CT (body mass index < 17.5 kg/m2) and 17 NW women.
RESULTS: A lower fat-free mass (ES: -1.94, 95%CI: -2.76 to -1.11, p < 0.001), a higher sedentary time, and a trend for a lower time spent at low-intensity physical activity, were observed in CT vs NW participants. While absolute MVCISO, MVCCON, rate of torque development (RTD), and torque work were all markedly lower in CT, these differences disappeared when normalized to body or muscle mass. Muscle thickness and fascicle length were found lower in CT (ES: -1.29, 95%CI: -2.03 to -0.52, p < 0.001; and ES: -0.87, 95%CI: -1.58 to -0.15, p = 0.02, respectively), while pennation angle was found similar.
CONCLUSIONS: Despite lower absolute strength capacities observed in CT, present findings support the hypothesis of physiological adaptations to the low body and muscle mass than to some intrinsic contractile impairments. These results call for further studies exploring hypertrophy-targeted strategies in the management of CT.
摘要：
目的：虽然肌肉质量和骨骼肌纤维表型在体质变薄（CT）中显示不典型，部队生产能力及其建筑决定因素从未被探索过。本研究比较了CT参与者与正常体重（NW）参与者之间的肌肉功能和结构。
方法：人体测量法，身体成分（双X射线吸收法），身体活动/久坐行为（ActiGraphwGT3X-BT），股外侧肌的超声记录（2D超声系统），在18名CT女性（体重指数<17.5kg/m2）和17名西北女性中，测量了膝盖伸展（等速测力计椅Biodex）期间最大等距和等速自愿收缩（MVCISO和MVCCON）的功能能力。
结果：无脂肪质量较低（ES：-1.94，95CI：-2.76至-1.11，p<0.001），久坐时间较长，以及低强度体力活动时间减少的趋势，在CT和NW参与者中观察到。而绝对的MVCISO，MVCCON,扭矩发展率(RTD)，在CT中扭矩功均明显较低，当与身体或肌肉质量归一化时，这些差异消失了。在CT中发现肌肉厚度和束长度较低（ES：-1.29，95CI：-2.03至-0.52，p<0.001；ES：-0.87，95CI：-1.58至-0.15，p=0.02），而忏悔角度被发现类似。
结论：尽管在CT中观察到较低的绝对强度容量，目前的发现支持以下假设：对低身体和肌肉质量的生理适应，而不是对某些内在收缩损伤的适应。这些结果要求进一步研究探索CT管理中的肥大靶向策略。
方法：人体测量法，身体成分（双X射线吸收法），身体活动/久坐行为（ActiGraphwGT3X-BT），股外侧肌的超声记录（2D超声系统），在18名CT女性（体重指数<17.5kg/m2）和17名西北女性中，测量了膝盖伸展（等速测力计椅Biodex）期间最大等距和等速自愿收缩（MVCISO和MVCCON）的功能能力。
结果：无脂肪质量较低（ES：-1.94，95CI：-2.76至-1.11，p<0.001），久坐时间较长，以及低强度体力活动时间减少的趋势，在CT和NW参与者中观察到。而绝对的MVCISO，MVCCON,扭矩发展率(RTD)，在CT中扭矩功均明显较低，当与身体或肌肉质量归一化时，这些差异消失了。在CT中发现肌肉厚度和束长度较低（ES：-1.29，95CI：-2.03至-0.52，p<0.001；ES：-0.87，95CI：-1.58至-0.15，p=0.02），而忏悔角度被发现类似。
结论：尽管在CT中观察到较低的绝对强度容量，目前的发现支持以下假设：对低身体和肌肉质量的生理适应，而不是对某些内在收缩损伤的适应。这些结果要求进一步研究探索CT管理中的肥大靶向策略。
