Data reduction
Ground reaction force data were normalized to body
weight and then the impact force (if present) from the vertical
ground reaction force component was recorded. The
operational definition of the impact force was a local
maximum that occurred within 50 milliseconds of ground
contact. One participant was dropped from the analysis
entirely because there was an overall absence of impact
force for any condition. This resulted in nine participants
being retained for analysis. Ground contact was determined
as the time of first vertical force > 20 N. Stance time was
calculated as the time difference between ground contact and
toe off (time of 1st force < 20 N at the end of the stance
phase). The peak force (aka F2) was the second maximum
vertical ground reaction force that was observed near midstance.
This discrete variable was always referred to as the
peak force regardless of the magnitude, as compared to the
impact force.