FUNCTION OF MONOARTICULAR AND BIARTICULAR MUSCLES IN RUNNING

In this study the function of leg muscles during stretch-shortening cy cles in fast running (6 m.s-1) was investigated. For a single stance p hase, kinematics, ground reaction forces, and EMG were recorded. First , rough estimates of muscle force, obtained by shifting the EMG curves +90 ms, were correlated with origin-to-insertion velocity (V(OI)). Se cond, active state and internal muscle behavior were estimated by usin g a muscle model that was applied for soleus and gastrocnemius. High c orrelations were found between estimates of muscle force and V(OI) tim e curves for mono-articular hip, knee, and ankle extensor muscles. The correlation coefficients for biarticular muscles were low. The model results showed that active state of gastrocnemius was high during incr ease of origin-to-insertion length (L(OI)), whereas active state of so leus was low during the start of increase of L(OI) and rose to a plate au at the time lengthening ended and shortening started. It seems that the difference in stimulation between gastrocnemius and soleus is a c ompromise between minimizing energy dissipation and using the stretch- shortening cycle optimally. Furthermore, it was found that the net pla ntar flexion moment during running reached a value of 302 Nm, which wa s 158% and 127% higher than the peak values reached in maximal jump an d sprint push-offs, respectively. It was argued that the higher mechan ical output in running than in jumping could be ascribed to the utiliz ation of the stretch-shortening cycle in running. The higher values in running compared with sprinting, however, may lie in a difference in muscle stimulation.