For example, during a forward trip, the backward-directed component of the GRF, acting on the tripping leg, passes posterior to the COM and contributes to the forward angular impulse about the COM (Figure 1).
Successful balance recovery by way of a stepping strategy uses angular impulse generated by the swing leg during both the swing and contact phases immediately following the perturbation.
During this interval, the GRF is essentially aligned with the COM  and results in minimal angular impulse generation (Figure 2(b)).
In trials with successful forward fall recovery using a single step, younger adults and older adult nonfallers generated sufficient backward angular impulse to neutralize the forward angular momentum of the body induced by the trip.
Collectively, these results suggest that improvements in muscle strength and rate of muscle force development may give older adult fallers the muscular capacity to regulate angular impulse during the push-off phase.
To counteract the backward angular momentum induced by the perturbation, the body must generate forward angular impulse during interaction with the environment.