Department of Evolution, Ecology, and Organismal Biology, University of California, Riverside, Riverside, CA 92521, USA.
J Exp Biol. 2022 Dec 1;225(23). doi: 10.1242/jeb.244083. Epub 2022 Dec 9.
A trade-off between locomotor speed and endurance occurs in various taxa, and is thought to be underpinned by a muscle-level trade-off. Among four replicate high runner (HR) lines of mice, selectively bred for voluntary wheel-running behavior, a negative correlation between average running speed and time spent running has evolved. We hypothesize that this trade-off is due to changes in muscle physiology. We studied the HR lines at generation 90, at which time one line (L3) is fixed for the mini-muscle phenotype, another is polymorphic (L6) and the others (L7, L8) lack mini-muscle individuals. We used in situ preparations to quantify the contractile properties of the triceps surae muscle complex. Maximal shortening velocity varied significantly, being lowest in mini-muscle mice (L3 mini=25.2 mm s-1, L6 mini=25.5 mm s-1), highest in normal-muscle mice L6 and L8 (40.4 and 50.3 mm s-1, respectively) and intermediate in normal-muscle L7 mice (37.2 mm s-1). Endurance, measured both as the slope of the decline in force and the proportion of initial force that could be sustained, also varied significantly. The slope was shallowest in mini-muscle mice (L3 mini=-0.00348, L6 mini=-0.00238), steepest in lines L6 and L8 (-0.01676 and -0.01853), and intermediate in L7 (-0.01145). Normalized sustained force was highest in mini-muscle mice (L3 mini=0.98, L6 mini=0.92) and lowest in L8 (0.36). There were significant, negative correlations between velocity and endurance metrics, indicating a muscle-level trade-off. However, this muscle-level trade-off does not seem to underpin the organismal-level speed and endurance trade-off previously reported as the ordering of the lines is reversed: the lines that run the fastest for the least time have the lowest muscle complex velocity and highest endurance.
在各种分类单元中，运动速度和耐力之间存在权衡，据认为这是由肌肉水平的权衡所支撑的。在四个经过选择性繁殖的高跑（HR）小鼠品系中，选择了自愿轮跑行为，平均跑步速度和跑步时间之间存在负相关。我们假设这种权衡是由于肌肉生理学的变化所致。我们在第 90 代研究了 HR 品系，此时一条线（L3）固定为迷你肌肉表型，另一条线（L6）是多态的，其他两条线（L7、L8）缺乏迷你肌肉个体。我们使用原位制剂来量化三腿肌复合物的收缩特性。最大缩短速度差异显著，迷你肌肉小鼠（L3 迷你=25.2mm/s，L6 迷你=25.5mm/s）最低，正常肌肉小鼠 L6 和 L8（分别为 40.4 和 50.3mm/s）最高，正常肌肉 L7 小鼠（37.2mm/s）居中。耐力，通过力下降斜率和初始力可持续比例来衡量，也有显著差异。斜率在迷你肌肉小鼠中最浅（L3 迷你=-0.00348，L6 迷你=-0.00238），在 L6 和 L8 线中最陡峭（-0.01676 和-0.01853），在 L7 线中居中（-0.01145）。正常化的持续力在迷你肌肉小鼠中最高（L3 迷你=0.98，L6 迷你=0.92），在 L8 中最低（0.36）。速度和耐力指标之间存在显著的负相关，表明存在肌肉水平的权衡。然而，这种肌肉水平的权衡似乎并没有支撑以前报道的生物体水平的速度和耐力权衡，因为线条的排序是相反的：跑得最快的线在最短的时间内具有最低的肌肉复合体速度和最高的耐力。
