THE SPRING-MASS MODEL AND THE ENERGY-COST OF TREADMILL RUNNING

During running, the behaviour of the support leg was studied by modell ing the runner using an oscillating system composed of a spring (the l eg) and of a mass (the body mass). This model was applied to eight mid dle-distance runners running on a level treadmill at a velocity corres ponding to 90% of their maximal aerobic velocity [mean 5.10 (SD 0.33) m.s(-1)]. Their energy cost of running (C-r), was determined from the measurement of O-2 consumption. The work, the stiffness and the resona nt frequency of both legs were computed from measurements performed wi th a kinematic arm. The C-r was significantly related to the stiffness (P < 0.05, r = -0.80) and the absolute difference between the resonan t frequency and the step frequency (P < 0.05, r = 0.79) computed for t he leg producing the highest positive work. Neither of these significa nt relationships were obtained when analysing data from the other leg probably because of the work asymmetry observed between legs. It was c oncluded that the spring-mass model is a good approach further to unde rstand mechanisms underlying the interindividual differences in C-r.