Final answer:
Single-leg support accounts for approximately 40% of the gait cycle during normal walking. This balances the body on one leg while the other advances. To enhance stability, humans lower their center of gravity and expand their base of support.
Step-by-step explanation:
The gait cycle is a crucial function of bipedal locomotion, where stability is a vital factor. During normal walking, each foot is in contact with the ground for about 50% of the gait cycle, and of that time, single-leg support accounts for approximately 40% of the gait cycle. This phase is when one leg (the stance leg) supports the body while the other (the step leg) is swinging forward. Additionally, stability during the gait cycle is enhanced through various means, such as widening the base of support and lowering the center of gravity. For instance, when a football player prepares to catch a ball or brace for impact, they may bend their knees, which lowers their center of gravity and increases stability.
To maintain stability, particularly during single-leg support, the muscles work extensively to keep the body balanced, as described in Figure 9.16 and Figure 9.18. When both feet are on the ground, stability is also improved by expanding the base and reducing the center of gravity, as depicted. These strategies are part of our evolutionary development that allows us to walk efficiently and without falling over, showing how the anatomy of bipedal organisms has adapted to ensure stability during locomotion.