Final answer:
The change in body composition in the elderly is characterized by a reduction in lean muscle mass and a decline in metabolic rate. This decrease in muscle mass is most significant between the ages of 50 and 70.
Step-by-step explanation:
The change in body composition in the elderly is characterized by a reduction in lean muscle mass, which is responsible for a decline in metabolic rate. This decrease in muscle mass and metabolism is most significant between the ages of 50 and 70. The loss of muscle mass is equivalent to reduced strength, which can hinder seniors from engaging in sufficient physical activity. This leads to a positive-feedback system where reduced activity results in even more muscle loss, further reducing metabolism.