ADIABATIC TRANSFORMABILITY HYPOTHESIS OF HUMAN LOCOMOTION

It is hypothesized that metabolic and mechanical changes in human loco motion associated with changes in speed v are constrained by two attra ctive strategies: Q(metab) = 1 and Delta Q/(metab)/Delta v = a positiv e definite constant. Q(metab) = Delta E(k) s(-1)/ml O-2 s(-1) where De lta E(k) s(-1) is the summed increments and decrements per unit time i n the translational and rotational kinetic energies of the body's segm ents and ml O-2 s(-1) is the rate at which chemical energy is dissipat ed. The expected constancy of Delta Q(metab)/Delta v was derived from an extension of Ehrenfest's adiabatic hypothesis by which transformati ons (increases, decreases) in locomotion v can be considered as adiaba tic, even though the biological conditions are nonconservative and non -rate-limited. The expected significance of Q(metab) = 1 was derived f rom stability considerations of the symmetry per stride of stored and dissipated energy. An experimental evaluation was provided by collecti ng metabolic and mechanical measures on walking (10 subjects) and runn ing (9 subjects) at progressively greater treadmill speeds but within the aerobic limit. Results revealed that walking was restricted to Q(m etab) less than or equal to 1, with a nonlinear trajectory in v x Q(me tab) coordinates shaped by Q(metab) = 1 (primarily) and the constancy of Delta Q(metab)/Delta v. Running satisfied Q(metab) > 1, with a line ar trajectory in v x Q(metab) coordinates conforming to Delta Q(metab) /Delta v = a constant, with the constant predicted from invariants in the mechanical space v x Delta E(k) s(-1). Results also suggested that the metabolic costs of running might be predictable from measures mad e in the v x Delta E(k) s(-1) space.