SOME ADVANCES IN INTEGRATIVE MUSCLE PHYSIOLOGY

Integrative muscle physiology has evolved from black box correlations to an understanding of how muscular systems are designed at the molecu lar level. This paper traces some of the obstacles facing integrative muscle physiology and some of the intellectual and technological break throughs which led to the field's development. The ability to determin e (1) which fiber types are active, (2) over what sarcomere lengths an d velocities they shorten during locomotion and (3) their respective f orce-velocity relationships, enabled us to show that many muscular sys tems are designed so that muscles operate at optimal myofilament overl ap and at optimal V/V-max (where maximum power is generated). The abil ity to impose the in vivo length change and stimulation pattern on iso lated muscle has further showed that fish muscle has a relatively slow relaxation rate, and thus rather than generating maximum power during swimming, the muscle appears designed to generate power efficiently. By contrast, during the single shot jump, frog muscle remains maximall y activated during shortening and generates maximum power. Recently bi ophysical techniques have shown that relaxation rate can be altered du ring evolution by changing (1) Ca2+ transient duration; (2) Ca2+ -trop onin kinetics, and (3) crossbridge kinetics. New technologies will soo n enable us to better appreciate how different animal designs evolved. (C) 1998 Published by Elsevier Science Inc. All rights reserved.