Final answer:
The major physical change during middle adulthood includes a decline in physical functioning, along with weight gain, the graying of hair, and the appearance of wrinkles.
Step-by-step explanation:
During middle adulthood, which generally lasts from the mid-30s to the mid-60s, several significant physical changes occur. One of the major changes is a decline in physical functioning. This includes a decrease in visual acuity, a reduction in physical strength, slower reaction times, and eventually, a decline in maximal heart rate and aerobic performance.
However, it's also a normal part of this stage for individuals to experience weight gain, with men tending to gain weight around the abdominal area and women around the hips and thighs. Changes in hair color and skin elasticity also become more apparent; hair begins to thin and turn gray, while skin starts showing wrinkles. Moreover, the risk for chronic diseases like type 2 diabetes, cardiovascular disease, and cancer increases during middle adulthood.