Force-velocity relationship models of nine skeletal muscles

Abstract

s-International Society of Biomechanics XIV Congress 1993 639 FORCE-VELOCITY RELATIONSHIP MODELS OF NINE SKELETAL MUSCLES R. V. Baratta, M. Solomonow, R. Best, & R. D’Ambrosia Bioengineering Laboratory, Department of Orthopaedics Louisiana State University Medical Center, New Orleans, Louisiana 70112 A muscle’s force-velocity relationship is one of its most fundamental dynamic propertiesThis study was directed at exploring the similarities and differences that exist among several muscles in the cat’s hindlimb. It was performed as part of an effort to develop a comprehensive dynamic model of muscle performance. A constant load system was used to measure the force-maximal velocity relationships in nine muscles. Each load was applied to resting muscle and allowed to equilibrate in a passive state. A tetanic pulse train was then applied, exciting the muscle and causing it to shorten against the load. The maximum velocity attained during the contraction was used to plot against the load, producing load-velocity curves which were fitted using Hill’s model by a least squares algorithm. Loads were used through the physiologic range of each muscle, starting at lOOg, and increasing until each muscle was no longer able to produce more than 1 m m of shortening during the contraction. It was found that large variations exist between the force-velocity relationships of the various muscles tested. Regression analysis between Hill’s model parameters and architectural parameters showed a clear correlation between the maximal unloaded velocity of each muscle and the length of active elongation combined with its fiber composition. It was also found that the fiber composition is the most important determinant of the curvature of the relationship. MODELS OF LENGTH-FORCE RELATIONSHIPS IN NINE SKELETAL MUSCLES R.V. Baratta, M. Solomonow, T. Vance, R. Best, R. D’Ambrosia Bioengineering Laboratory, Department of Orthopaedics Louisiana State University Medical Center, New Orleans, Louisiana 70112 The length-force relationship of muscle is perhaps its most fundamental performance characteristic. It has been traditionally determined under isometric conditions. The purpose of this study was to examine this relationship under a load moving scheme and compare the results to those obtained using traditional methods. The significance of this comparison is that muscles performing useful contractions are not held isometrically, but move loads. A constant load apparatus was used to measure the load moving length force relationship of nine muscles in the cat’s hindlimb. A variety of loads was applied and allowed to equilibrate with the muscle in a passive state. In this condition defined the passive length at that load was defined. A stimulus pulse train was then applied, causing the muscle to shorten. The length attained at active equilibrium was used to define the total length-force curve. Once the passive and total force curves were constructed, their difference was calculated to obtain the active force curve. These relationships were also obtained through traditional isometric methods. The results indicate that the tibialis anterior and the medial gastrocnemius exhibit bicompartmental behavior in isometric conditions. In load moving contractions, the extensor digitomm longus exhibits similar behavior as well. In general a slight shift in the optimal length of muscles is observed in direct comparison tests, as well as a significant decrease in the maximal force. The results provide warning that it is inaccurate to use isometric length-force curves when predicting the force output of moving muscle. THE MINIMAL PASSIVE MUSCLE FIBRES LENGTH AND THE EXTRACELLULAR CONNECTIVE COMPONENTS J. Paul Delage, J. Augustin-Lucille, A. Belagoun and C. Guillon UFR STAPS Universite de Bordeaux II Domaine Universitaire 33405 Talence Cedex France. Passive shortening of nine muscles from the leg and thigh of cadavers were observed over the full range of joint flexion. Taking account of the architecture of the each muscle we studied the whole process of shortening for each bundle of muscle fibres. In the case of the Vastus medialis, Vastus intermedius, Vastus lateralis and Adductor longus muscles, bundles shortened by only 53 % or 59 % of their maximal length, the bundles of the Rectus femoris, Semitendinosus, Biceps femoris, Soleus and Gastrocnemius muscles, bundles shortened by 76 % or 89 %. In the second group, it was shown by both dissection and electron microscopy that the bundles reached their shortest position at 53 % or 59 % of their maximal length. Beyond the corresponding articular position, they assumed a curved configuration and were devoid of passive strain. We provide a model of the extracellular connective components which could explain the fact that the minimal length remains constant. After stress, the bundles shorten under the combined action of the tendinous sheet, the connective bundle walls and the extracellular matrix components. Since the cellular volume remains constant, after active shortening the bundles return to the minimal length at rest through the action of the extracellular matrix components.