Biewener A A, Konieczynski D D, Baudinette R V
Department of Organismal Biology and Anatomy, The University of Chicago, Chicago, IL 60637, USA.
J Exp Biol. 1998 Jun;201(Pt 11):1681-94. doi: 10.1242/jeb.201.11.1681.
Moderate to large macropodids can increase their speed while hopping with little or no increase in energy expenditure. This has been interpreted by some workers as resulting from elastic energy savings in their hindlimb tendons. For this to occur, the muscle fibers must transmit force to their tendons with little or no length change. To test whether this is the case, we made in vivo measurements of muscle fiber length change and tendon force in the lateral gastrocnemius (LG) and plantaris (PL) muscles of tammar wallabies Macropus eugenii as they hopped at different speeds on a treadmill. Muscle fiber length changes were less than +/-0.5 mm in the plantaris and +/-2.2 mm in the lateral gastrocnemius, representing less than 2 % of total fiber length in the plantaris and less than 6 % in the lateral gastrocnemius, with respect to resting length. The length changes of the plantaris fibers suggest that this occurred by means of elastic extension of attached cross-bridges. Much of the length change in the lateral gastrocnemius fibers occurred at low force early in the stance phase, with generally isometric behavior at higher forces. Fiber length changes did not vary significantly with increased hopping speed in either muscle (P>0.05), despite a 1. 6-fold increase in muscle-tendon force between speeds of 2.5 and 6.0 m s-1. Length changes of the PL fibers were only 7+/-4 % and of the LG fibers 34+/-12 % (mean +/- S.D., N=170) of the stretch calculated for their tendons, resulting in little net work by either muscle (plantaris 0.01+/-0.03 J; gastrocnemius -0.04+/-0.30 J; mean +/- s.d. ). In contrast, elastic strain energy stored in the tendons increased with increasing speed and averaged 20-fold greater than the shortening work performed by the two muscles. These results show that an increasing amount of strain energy stored within the hindlimb tendons is usefully recovered at faster steady hopping speeds, without being dissipated by increased stretch of the muscles' fibers. This finding supports the view that tendon elastic saving of energy is an important mechanism by which this species is able to hop at faster speeds with little or no increase in metabolic energy expenditure.
中等体型至大体型的有袋类动物在跳跃时能够提高速度，而能量消耗几乎没有增加或完全没有增加。一些研究人员认为，这是由于它们后肢肌腱节省了弹性能量。要实现这一点，肌肉纤维必须在长度变化很小或没有长度变化的情况下将力传递给肌腱。为了验证是否如此，我们在活体状态下测量了帚尾岩袋鼠（Macropus eugenii）在跑步机上以不同速度跳跃时，其腓肠外侧肌（LG）和跖肌（PL）的肌肉纤维长度变化和肌腱力。跖肌的肌肉纤维长度变化小于±0.5毫米，腓肠外侧肌的变化小于±2.2毫米，相对于静息长度，分别占跖肌总纤维长度的不到2%和腓肠外侧肌的不到6%。跖肌纤维的长度变化表明，这是通过附着的横桥的弹性伸展实现的。腓肠外侧肌纤维的大部分长度变化发生在站立期早期的低力阶段，在较高力时通常表现为等长收缩。尽管在速度从2.5米/秒增加到6.0米/秒之间时，肌腱力增加了1.6倍，但两种肌肉的纤维长度变化均未随跳跃速度的增加而显著变化（P>0.05）。跖肌纤维的长度变化仅为其肌腱计算伸长量的7±4%，腓肠外侧肌纤维为34±12%（平均值±标准差，N = 170），因此两种肌肉所做的净功都很小（跖肌0.01±0.03焦耳；腓肠肌 -0.04±0.30焦耳；平均值±标准差）。相比之下，肌腱中储存的弹性应变能随着速度的增加而增加，平均比两块肌肉所做的缩短功大20倍。这些结果表明，在后肢肌腱中储存的应变能越来越多，在更快的稳定跳跃速度下能够有效地回收，而不会因肌肉纤维的过度拉伸而耗散。这一发现支持了这样一种观点，即肌腱弹性节能是该物种能够以更快速度跳跃而代谢能量消耗几乎没有增加或完全没有增加的重要机制。
