Cromie Lear Melinda J, Millard Matthew, Gleiss Adrian C, Dale Jonathan, Dimitrov Marina, Peiros Elizabeth, Block Barbara
1 Mechanical Engineering, Stanford University, California.
2 Hopkins Marine Station, Stanford University, California.
Physiol Biochem Zool. 2020 May/Jun;93(3):185-198. doi: 10.1086/708247.
In tunas, the slow-twitch red muscle, which has an elevated temperature, powers thunniform locomotion, a stiff-bodied swimming style. The anatomical placement and operating temperatures of red muscle vary widely among teleosts: in tunas, the red muscle is located centrally in the body, adjacent to the spine, and maintains an elevated temperature. In the majority of ectothermic teleosts, red muscle is located laterally in the body, adjacent to the skin, and operates at ambient temperature. The specialized physiology and biomechanics of red muscle in tunas are often considered important adaptations to their high-performance pelagic lifestyle; however, the mechanics of how muscular work is transmitted to the tail remains largely unknown. The red muscle has a highly pennate architecture and is connected to the spine through a network of bones (epicentral bones) and long tendons (posterior oblique tendons). The network of long tendons has been hypothesized to enhance the power transmitted to the tail. Here, we investigate the morphology and biomechanics of the tuna's red muscle and tendons to determine whether elasticity is exploited to reduce the cost of transport, as is the case in many terrestrial vertebrates. To address this question, we evaluate two hypotheses: (1) tendons stretch during red-muscle-actuated swimming and (2) tendons comprise the primary load transmission pathway from the red muscle to the spine. To evaluate these hypotheses, we measured the mechanical properties of the posterior oblique tendons and performed novel dissections to estimate the peak force that the red muscle can generate. The force-generating capacity of the red muscle is calculated to be much greater than the load-bearing capacity of the posterior oblique tendons. Thus, the long tendons likely stretch under force from the red muscle, but they are not strong enough to be the primary force transmission pathway. These results suggest that other pathways, such as serial load transmission through the red muscle myomeres to the great lateral tendon and/or the anterior oblique tendons to the skin, transmit appreciable force to the tail.
在金枪鱼中，温度较高的慢肌红肌为典型的硬体游泳方式——梭形运动提供动力。硬骨鱼的红肌在解剖学上的位置和工作温度差异很大：在金枪鱼中，红肌位于身体中央，靠近脊柱，并保持较高的温度。在大多数变温硬骨鱼中，红肌位于身体侧面，靠近皮肤，并在环境温度下工作。金枪鱼红肌的特殊生理和生物力学特性通常被认为是对其高性能远洋生活方式的重要适应；然而，肌肉做功如何传递到尾部的机制在很大程度上仍然未知。红肌具有高度羽状的结构，并通过骨骼网络（中枢骨）和长肌腱（后斜肌腱）与脊柱相连。有人推测，长肌腱网络可增强传递到尾部的力量。在这里，我们研究了金枪鱼红肌和肌腱的形态和生物力学，以确定是否像许多陆生脊椎动物那样利用弹性来降低运输成本。为了解决这个问题，我们评估了两个假设：（1）在红肌驱动游泳时肌腱会伸展；（2）肌腱构成了从红肌到脊柱的主要负荷传递途径。为了评估这些假设，我们测量了后斜肌腱的力学性能，并进行了新颖的解剖，以估计红肌能够产生的峰值力。计算得出红肌的力产生能力远大于后斜肌腱的承载能力。因此，长肌腱可能会在红肌的作用力下伸展，但它们的强度不足以成为主要的力传递途径。这些结果表明，其他途径，如通过红肌肌节到外侧大肌腱的串联负荷传递和/或通过前斜肌腱到皮肤的串联负荷传递，会将可观的力传递到尾部。
