It is proposed that the series elastic (tendinous) elements can amplify the peak power output of the muscle-tendon unit (MTU) in the takeoff phase of a jump. The second theory takes into account the series elastic element. Therefore, this theory may neglect the potential role played by the tendon found in some of the leg extensor muscles.
The ‘optimal contractile conditions’ theory was derived based on observations on the frog semimembranosus (SM) muscle which has no appreciable tendon.
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In particular, the presence/absence of series elasticity (e.g., extra-muscular free tendon, denoted as tendon hereon) may affect the ability for power production. However, the frog has more than fifteen leg extensor muscles that vary in architecture. In this theory all leg extensor muscles must work optimally, and therefore produce an equal power output per volume of muscle. In the first theory, it is proposed that the hind limb muscles are used under optimal contractile conditions, which include operating at lengths across the plateau region of the force-length relationship and shortening at a constant “optimal” speed that maximizes power production for maximally activated muscles. There are two main theories in the literature proposed for explaining the mechanism of the high power generation in frog hind limb muscles during jumping. However, a conclusive explanation of how frogs achieve their jumping feats remains elusive. Such an explosive movement requires a high power output from the frog hind limb muscles. They are capable of jumping a horizontal distance exceeding ~30 times of their body length by accelerating from a stationary initial position to great speed at takeoff in a fraction of a second.
The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.Ĭompeting interests: The authors have declared that no competing interests exist.įrogs have an impressive jumping ability. This is an open access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.ĭata Availability: All relevant data are within the paper and its Supporting Information files.įunding: The work was supported by Natural Sciences and Engineering Research Council (NSERC) of Canada.
Received: OctoAccepted: FebruPublished: March 10, 2017Ĭopyright: © 2017 Moo et al. PLoS ONE 12(3):Įditor: François Hug, Universite de Nantes, FRANCE We also found that the extra-muscular free tendon likely amplifies the peak power output of the PL by modulating fascicle shortening length and shortening velocity for optimum power output, but not by releasing stored energy through recoiling as the tendon only started recoiling after peak PL power had been achieved.Ĭitation: Moo EK, Peterson DR, Leonard TR, Kaya M, Herzog W (2017) In vivo muscle force and muscle power during near-maximal frog jumps. High instantaneous peak power in PL (536 ± 47 W/kg) was achieved by optimizing the contractile conditions in terms of the force-length but not the force-velocity relationship, and by a dynamic catch mechanism that decouples fascicle shortening from muscle-tendon unit shortening. Fifteen near maximal jumps (> 50cm in horizontal distance) were analyzed. In this study, we determined the instantaneous variable power output of the plantaris longus (PL) of Lithobates pipiens (also known as Rana pipiens), by directly measuring the in vivo force, length change, and speed of muscle and fibre shortening in near maximal jumps. As in vivo instantaneous power generation in frog hind limb muscles during jumping has never been measured directly, it is hard to distinguish between the two theories. Two main theories have emerged to explain the high power output of the frog leg extensor muscles, either (i) the contractile conditions of all leg extensor muscles are optimized in terms of muscle length and speed of shortening, or (ii) maximal power is achieved through a dynamic catch mechanism that uncouples fibre shortening from the corresponding muscle-tendon unit shortening. Frogs’ outstanding jumping ability has been associated with a high power output from the leg extensor muscles.
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