Which of the following is an example of a high-impact exercise?

High-impact exercises involve activities that cause both feet to leave the ground simultaneously, resulting in greater stress on the joints and bones. Jumping jacks are a classic example of a high-impact exercise because they require jumping and landing with both feet off the ground at the same time, which engages multiple muscle groups and elevates heart rate.

In contrast, walking and swimming are classified as low-impact exercises. Walking keeps one foot grounded at all times, and swimming is performed in a way that minimizes impact on the joints. Stretching typically involves slow, controlled movements that do not involve any jumping or impact, further distinguishing it from high-impact exercises. Thus, jumping jacks stand out as the clear example of high-impact activity among the options provided.