Ortega Justus O, Lindstedt Stan L, Nelson Frank E, Jubrias Sharon A, Kushmerick Martin J, Conley Kevin E
Department of Kinesiology & Recreation Administration, Humboldt State University, Arcata, CA 95521, USA Department of Radiology, University of Washington Medical Center, Seattle, WA 98195, USA.
Department of Biological Sciences, Northern Arizona University, South Beaver Street, Flagstaff, AZ 86001, USA
J Exp Biol. 2015 Jul;218(Pt 13):2075-82. doi: 10.1242/jeb.114512. Epub 2015 May 11.
Muscle produces force by forming cross-bridges, using energy released from ATP. While the magnitude and duration of force production primarily determine the energy requirement, nearly a century ago Fenn observed that muscle shortening or lengthening influenced energetic cost of contraction. When work is done by the muscle, the energy cost is increased and when work is done on the muscle the energy cost is reduced. However, the magnitude of the 'Fenn effect' and its mirror ('negative Fenn effect') have not been quantitatively resolved. We describe a new technique coupling magnetic resonance spectroscopy with an in vivo force clamp that can directly quantify the Fenn effect [E=I+W, energy liberated (E) equals the energy cost of isometric force production (I) plus the work done (W)] and the negative Fenn effect (E=I-W) for one muscle, the first dorsal interosseous (FDI). ATP cost was measured during a series of contractions, each of which occurred at a constant force and for a constant duration, thus constant force-time integral (FTI). In all subjects, as the FTI increased with load, there was a proportional linear increase in energy cost. In addition, the cost of producing force greatly increased when the muscle shortened, and was slightly reduced during lengthening contraction. These results, though limited to a single muscle, contraction velocity and muscle length change, do quantitatively support the Fenn effect. We speculate that they also suggest that an elastic element within the FDI muscle functions to preserve the force generated within the cross-bridges.
肌肉通过形成横桥并利用ATP释放的能量来产生力量。虽然力量产生的大小和持续时间主要决定能量需求，但近一个世纪前芬恩观察到肌肉缩短或伸长会影响收缩的能量消耗。当肌肉做功时，能量消耗增加；当对肌肉做功时，能量消耗减少。然而，“芬恩效应”及其镜像效应（“负芬恩效应”）的大小尚未得到定量解决。我们描述了一种将磁共振波谱与体内力钳相结合的新技术，该技术可以直接量化一块肌肉——第一背侧骨间肌（FDI）的芬恩效应[E=I+W，释放的能量（E）等于等长力量产生的能量消耗（I）加上所做的功（W）]和负芬恩效应（E=I-W）。在一系列收缩过程中测量ATP消耗，每次收缩都在恒定的力和持续时间下进行，因此力-时间积分（FTI）恒定。在所有受试者中，随着FTI随负荷增加，能量消耗呈比例线性增加。此外，当肌肉缩短时，产生力量的消耗大幅增加，而在拉长收缩过程中略有减少。这些结果虽然仅限于一块肌肉、收缩速度和肌肉长度变化，但确实在定量上支持了芬恩效应。我们推测，它们还表明FDI肌肉内的一个弹性元件起到了保存横桥内产生的力量的作用。
