Force generation, in muscles

In summary, therefore, solution and fiber biochemistry have provided some idea about how ATP is used by actomyosin to generate force. Currently, it seems most likely that phosphate release, and also an isomerization between two AM.ADP.Pj states, are closely linked to force generation in muscle. ATP binds rapidly to actomyosin (A.M.) and is subsequently rapidly hydrolyzed by myosin/actomyosin. There is also a rapid equilibrium between M. ADP.Pj and A.M.ADP.Pj (this can also be seen in fibers from mechanical measurements at low ionic strength). The rate limiting step in the ATPase cycle is therefore likely to be release of Pj from A.M.ADP.Pj, in fibers as well as in solution, and this supports the idea that phosphate release is associated with force generation in muscle. 

Takagi, Y. Shuman, H. Goldman, Y.E. Coupling between phosphate release and force generation in muscle actomyosin. Philos. Trans. R. Soc. Lond. B. Biol. Sci. 2004, 359, 1913-1920. 

Huxley, A.F., Simmons, R. Proposed mechanism of force generation in striated muscle. Nature 233 533-538, 1971. 

The second of these steps, the rate of hydrolysis at 12 °C, measured by analysis of the ADP content in fibers rapidly frozen at different times after ATP release from caged-ATP, is 40-60 s (Ferenczi, 1986) which is similar to the rate of active force increase at 20°C once the difference in temperature has been accounted for. This rate is similar to that measured in solution however, and is not rate limiting in solution. Therefore, force generation in the caged-ATP experiments could be limited by hydrolysis, or more likely, by a step following hydrolysis such as Pj release. The idea that release of phosphate is linked to force production in muscle... 

Kawai, M., and Halvorson, H. R. (1991). Two step mechanism of phosphate release and the mechanism of force generation in chemically skinned fibers of rabbit psoas muscle. Biophys. J. 59, 329-342. 

Tesi, C., Colomo, F., Nencini, S., Piroddi, N., and Poggesi, C. (2000). The effect of inorganic phosphate on force generation in single myofibrils from rabbit skeletal muscle. Biophys.J. 78, 3081-3092. 

Hibberd MG, Dantzig JA, Trentham DR, Goldman YE (1985) Phosphate release and force generation in skeletal muscle fibers. Science 228 1317-1319 Hidaka, H, Asano M, I wadare S, Matsumoto I, Totsuka T, Aoki N(1978)A novel vascular relaxing agent, N-(6-aminohexyl)-5-chloro-l-naphtalenesulfonamide which affects vascular smooth muscle actomyosin. J Pharmacol Exp Ther 207 8-15... 

The force generated by muscle contraction is transmitted to bone by tendons, with the muscle-tendon-bone combination forming a functional unit which can be referred to as the musculoskeletal chain. There are important differences between the child, the young adult and the mature adult which account for the different injury patterns that are encountered (Harris 1981). In children, the weak links in the musculoskeletal chain are at the bone-tendon interface and at the growth plate, which accounts for the high occurrence of apophyseal avulsion injuries... 

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