The bouncing mechanism of running against hindering and aiding traction forces

Abstract Situations where a subject is running on level ground without any additional factors influencing his gait are rather infrequent. Much like running on a slope, running against a horizontal traction force which either hinders or aids the forward motion of running will create a shift in the positive and negative work being done by the muscles which in turn modifies the bouncing mechanism of running. We aimed to investigate (1) the changes in energy of the centre of mass during running associated with speed and increasing hindering and aiding traction forces, (2) study the storage and release of energy throughout the step, (3) compare these changes brought about horizontally to vertical changes observed when running up a slope. Ground reaction forces were measured on 8 subjects running on an instrumented treadmill against different traction forces at different speeds. Results suggest that (1) running against a hindering traction force will increase positive horizontal work and decrease negative work, by increasing pushing time and decreasing contact time thus containing the force required to maintain forward motion against traction, (2) against an aiding force, the shift tends towards negative horizontal work due to an increase in braking time and increased aerial time thus containing the power required to reset the limbs each step. Furthermore, when compared to slope running results show various similarities kinetically.