2000-04-03
15:15 at SWU B11 (in Schlieren)

Muscle Mechanics: From Sarcomeres to Muscle

David A. Morgan

Departments of Electrical and Computer Systems Engineeringand Physiology,Monash University, Clayton, Australia

 Stretch of active muscle: sarcomeres to training effects. Morgan, D L, U Proske, R Lynn, J Talbot, C Brockett, N Whitehead   T Allen. Departments of Electrical and Computer Systems Engineering and Physiology, Monash University, Clayton, Australia Stretch of active muscle, known as eccentric contraction, especially at long muscle lengths, produces a wide range of observations that are difficult to explain with the usual assumption that the stretch is uniformly distributed among the sarcomeres. Histology shows grossly non-uniform sarcomeres. Physiological experiments show "permanent extra tension", and changes to the length-tension and the stimulation rate-tension relationships. Unaccustomed eccentric exercise leads to "Delayed Onset Muscle Soreness", the muscle damage and tenderness peaking one to two days later. Postulating grossly non-uniform stretch of sarcomeres provides explanations for a wide range of these observations and their characteristics. Such on-uniformity is predicted by the descending limb of the length-tension relation and the presence of a yield point in the force-velocity relation. The extra tension is explained by the non-uniform sarcomere length distribution. The shift of the length-tension curve is explained by the added compliance of disrupted sarcomeres, which may also explain much of the stimulation rate-tension changes. Accumulation of over-stretched sarcomeres leading to tearing of membranes can explain the loss of calcium ion homeostasis that occurs early in the damage process that leads to DOMS. The rapid training effect can be caused by growth of extra sarcomeres to avoid operation on the descending limb. New results show that eccentric training of human hamstring muscles leads to a maintained shift in the angle-torque curve for knee flexion to longer muscle lengths, supporting the growth of sarcomeres as the training mechanism. Bibliography: D.L. Morgan, et al. Morgan, D. L. (1990). New insights into the behavior of muscle during active lengthening. Biophysical Journal 57, 209-221. Morgan, D. L., Claflin, D. R.   Julian, F. J. (1991). Tension as a function of sarcomere length and velocity of shortening in single skeletal muscle fibres of the frog. Journal of Physiology 441, 719-732. Wood, S. A., Morgan, D. L.   Proske, U. (1993). Effects of repeated eccentric contractions on structure and mechanical properties of toad sartorius muscle. American Journal of Physiology 265, C792-C800. Lynn, R.   Morgan, D. L. (1994). Decline running produces more sarcomeres in rat vastus intermedius muscle fibres than incline running. Journal of Applied Physiology 77, 1439-1444. Morgan, D. L. (1994). An explanation for residual increased tension in striated muscle after stretch during contraction. Experimental Physiology 79, 831-838. Talbot, J. A.   Morgan, D. L. (1996). Quantitative analysis of sarcomere non-uniformities in active muscle following a stretch. Journal of Muscle Research and Cell Motility 17, 261-268. Morgan, D. L., Claflin, D. R.   Julian, F. J. (1996). The effects of repeated active stretches on tension generation and myoplasmic calcium in frog single fibres. Journal of Physiology 497, 665-674. Jones, C., Allen, T., Talbot, J. A., Morgan, D. L.   Proske, U. (1997). Changes in the mechanical properties of human and amphibian muscle after eccentric exercise. European Journal of Applied Physiology and Occupational Physiology 76, 21-31. Lynn, R., Talbot, J. A.   Morgan, D. L. (1998). Differences in rat skeletal muscles after incline and decline running. Journal of Applied Physiology 85, 98-104. (http://jap.physiology.org/cgi/content/abstract/85/1/98) Talbot, J. A.   Morgan, D. L. (1998). The effects of stretch parameters on eccentric exercise induced damage to toad skeletal muscle. Journal of Muscle Research and Cell Motility 19, 237-245.