Final answer:
The loss of strength after age 45 is attributed to sarcopenia, which is the gradual decrease in the ability to maintain skeletal muscle mass that occurs in later adulthood. This condition is caused by a decline in muscle fibers and their replacement with connective tissue and adipose tissue. Sarcopenia is primarily caused by a reduction in fast-twitch muscle fibers and a decrease in the size of motor units.
Step-by-step explanation:
Loss of strength after age 45 is attributed to a condition called sarcopenia, which is the gradual decrease in the ability to maintain skeletal muscle mass that occurs in later adulthood.
As people age, there is a decline in the number of muscle fibers, and they are replaced by connective tissue and adipose tissue. This muscle atrophy results in a loss of strength, including the strength required for posture and mobility.
Sarcopenia is primarily caused by a reduction in fast-twitch muscle fibers responsible for short, powerful contractions, and a decrease in the size of motor units, which leads to less muscle tension being produced.