title: Function of mono- and biarticular muscles in running.
abstract: In this study the function of leg muscles during stretch-shortening cycles in fast running (6 m.s-1) was investigated. For a single stance phase, 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 (VOI). Second, active state and internal muscle behavior were estimated by using a muscle model that was applied for soleus and gastrocnemius. High correlations were found between estimates of muscle force and VOI time 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 increase of origin-to-insertion length (LOI), whereas active state of soleus was low during the start of increase of LOI and rose to a plateau at the time lengthening ended and shortening started. It seems that the difference in stimulation between gastrocnemius and soleus is a compromise between minimizing energy dissipation and using the stretch-shortening cycle optimally. Furthermore, it was found that the net plantar flexion moment during running reached a value of 302 Nm, which was 158% and 127% higher than the peak values reached in maximal jump and sprint push-offs, respectively. It was argued that the higher mechanical output in running than in jumping could be ascribed to the utilization of the stretch-shortening cycle in running. The higher values in running compared with sprinting, however, may lie in a difference in muscle stimulation.
authors.affiliation: Department of Functional Anatomy, Faculty of Human Movement Sciences, Vrije Universiteit, Amsterdam, The Netherlands.
authors.forename: R
authors.initials: R
authors.lastname: Jacobs
authors.forename: M F
authors.initials: MF
authors.lastname: Bobbert
authors.forename: G J
authors.initials: GJ
authors.lastname: van Ingen Schenau
mesh_terms: D000328:Adult; D001696:Biomechanical Phenomena; D004548:Elasticity; D004576:Electromyography / Q000379:methods; D006801:Humans; D007596:Joints / Q000502:physiology; D007866:Leg / Q000502:physiology*; D008297:Male; D008954:Models, Biological; D009068:Movement / Q000502:physiology; D009119:Muscle Contraction / Q000502:physiology; D009132:Muscles / Q000502:physiology*; D012420:Running / Q000502:physiology*