Seebacher Frank, Tallis Jason A, James Rob S
School of Biological Sciences A08, University of Sydney, Sydney NSW 2006, Australia
Department of Biomolecular and Sport Sciences, Faculty of Health and Life Sciences, Coventry University, Coventry CV1 5FB, UK.
J Exp Biol. 2014 Jun 1;217(Pt 11):1940-5. doi: 10.1242/jeb.101147. Epub 2014 Mar 13.
Metabolic energy (ATP) supply to muscle is essential to support activity and behaviour. It is expected, therefore, that there is strong selection to maximise muscle power output for a given rate of ATP use. However, the viscosity and stiffness of muscle increases with a decrease in temperature, which means that more ATP may be required to achieve a given work output. Here, we tested the hypothesis that ATP use increases at lower temperatures for a given power output in Xenopus laevis. To account for temperature variation at different time scales, we considered the interaction between acclimation for 4 weeks (to 15 or 25°C) and acute exposure to these temperatures. Cold-acclimated frogs had greater sprint speed at 15°C than warm-acclimated animals. However, acclimation temperature did not affect isolated gastrocnemius muscle biomechanics. Isolated muscle produced greater tetanus force, and faster isometric force generation and relaxation, and generated more work loop power at 25°C than at 15°C acute test temperature. Oxygen consumption of isolated muscle at rest did not change with test temperature, but oxygen consumption while muscle was performing work was significantly higher at 15°C than at 25°C, regardless of acclimation conditions. Muscle therefore consumed significantly more oxygen at 15°C for a given work output than at 25°C, and plastic responses did not modify this thermodynamic effect. The metabolic cost of muscle performance and activity therefore increased with a decrease in temperature. To maintain activity across a range of temperature, animals must increase ATP production or face an allocation trade-off at lower temperatures. Our data demonstrate the potential energetic benefits of warming up muscle before activity, which is seen in diverse groups of animals such as bees, which warm flight muscle before take-off, and humans performing warm ups before exercise.
向肌肉供应代谢能量（ATP）对于支持活动和行为至关重要。因此，可以预期，在给定的ATP使用速率下，会有强烈的选择压力来最大化肌肉功率输出。然而，肌肉的粘度和刚度会随着温度降低而增加，这意味着可能需要更多的ATP来实现给定的功输出。在这里，我们测试了这样一个假设：在非洲爪蟾中，对于给定的功率输出，低温下ATP的使用会增加。为了考虑不同时间尺度上的温度变化，我们考虑了4周的驯化（至15或25°C）与急性暴露于这些温度之间的相互作用。冷驯化的青蛙在15°C时的冲刺速度比热驯化的动物更快。然而，驯化温度并未影响离体腓肠肌的生物力学性能。离体肌肉在25°C时比在15°C急性测试温度下产生更大的强直收缩力、更快的等长力产生和松弛，并且产生更多的功环功率。离体肌肉在静息时的耗氧量不会随测试温度而变化，但无论驯化条件如何，肌肉做功时的耗氧量在15°C时显著高于25°C。因此，对于给定的功输出，肌肉在15°C时比在25°C时消耗的氧气显著更多，并且可塑性反应并未改变这种热力学效应。因此，肌肉性能和活动的代谢成本随着温度降低而增加。为了在一系列温度范围内维持活动，动物必须增加ATP的产生，否则在低温下将面临分配权衡。我们的数据证明了活动前预热肌肉在能量方面的潜在益处，这在各种动物群体中都有体现，比如蜜蜂在起飞前预热飞行肌肉，以及人类在运动前进行热身。
