Final answer:
Strength declines by approximately 15-20% between the ages of 20 and 50, due in part to a decrease in the body's metabolic rate and muscle mass loss.
Step-by-step explanation:
Strength generally declines about 15-20% between 20 and 50 years of age. This decline is partly attributable to the decrease in the body's metabolic rate, which falls nearly 2 percent per decade after age 30. Furthermore, during this period, especially from 50 to 70 years of age, there is a significant loss of muscle mass, which corresponds to reduced strength.
To maintain strength and counteract aging effects, it's essential to remain active through proper exercise, nutrition, and an active lifestyle.