![]() The stiffness of the spring, typically referred to as ‘leg spring’, is determined from the relationship between the magnitude of the ground reaction force and the distance between the centre of mass (CM) and the centre of pressure on the ground. In the search for general principles underlying bouncing gaits, biomechanists have modelled the body as a linear massless spring supporting a point mass equivalent to body mass. the distance between hip and toe) decreases while the ground reaction force increases, and during the second half of the ground contact phase, leg length increases while the ground reaction force decreases. During the first half of the ground contact phase, leg length (i.e. Legs behave like compression springs during bouncing gaits such as running and hopping. ![]() Instead, we speculated, subjects are using a simple control strategy that results in smooth movements and a decrease in leg stiffness with hopping height. Correspondence between simulated hops and experimental hops was poor when STIM( t) was optimized to minimize mechanical energy expenditure, but good when an objective function was used that penalized jerk of CM motion, suggesting that hopping subjects are not minimizing energy expenditure. Experimental results were reproduced with a model of the musculoskeletal system comprising four body segments and nine Hill-type muscles, with muscle stimulation STIM( t) as only input. Subjects reduced hopping height primarily by reducing the amplitude of muscle activation. Leg stiffness decreased with hopping height, from 350 N m −1 kg −1 at 26 cm to 150 N m −1 kg −1 at 14 cm. Kinematics, ground reaction forces and electromyograms were measured. Variations in leg stiffness were achieved in six subjects by having them hop at maximum and submaximum heights at a frequency of 1.7 Hz. ‘Leg stiffness’ is the slope of the relationship between ground reaction force and displacement of the centre of mass (CM). The purpose of this study was to understand how humans regulate their ‘leg stiffness’ in hopping, and to determine whether this regulation is intended to minimize energy expenditure.
0 Comments
Leave a Reply. |
AuthorWrite something about yourself. No need to be fancy, just an overview. ArchivesCategories |