Final answer:
Heel contact is the initiation of the stance phase within the gait cycle and occurs at approximately 0% of the gait cycle, marking the beginning of the phase.
Step-by-step explanation:
Heel contact marks the beginning of the stance phase in the gait cycle, and it occurs at approximately 0% of the gait cycle. This is the point when the heel of the leading foot touches the ground, initiating the stance phase, which will continue until the foot lifts off the ground again. The choices provided (A. 10%, B. 20%, C. 30%, D. 40%) do not accurately represent the percentage of the gait cycle at which heel contact occurs. It is essential to understand that in terms of percentage, the heel strikes immediately upon beginning the stance phase, effectively making it 0% of the gait cycle. From strike to toe-off, the stance phase accounts for about 60% of the entire cycle, with the remaining 40% being the swing phase where the foot is not in contact with the ground.