What is the difference between a passive and active ground reaction force?

Question

Trying to revise biomechanics and its spinning me out...

Answer 1

Active ground reaction force, in the example of say, a runner, is any ground reaction force which is directly the result of muscular activity under the conscious control of the individual (for example, pushing off from the floor to continue running).

However, at the point where the heel comes down and hits the ground again, the muscle latency means that during the first 30-75ms (approx) of contact, the body has to respond passively (passive deformation) - as the muscles have not had time to react - this can cause serious damage.

Essentially passive ground reaction force is a force acting on the body before the muscles have time to react to it, which, if high enough, can cause serious damage. Active force is the force the body is expecting when it exerts force on the ground, such as jumping up - the athlete pushes down on the ground in order to be propelled upwards - this upward ground reaction force is ACTIVE because it occured solely due to the muscles under the conscious control of the individual.