Sometime in your early forties, something shifts. The muscle you built in your twenties and thirties becomes harder to maintain. Recovery takes longer. The composition of your body changes, even when your weight stays the same. You are not imagining it. This is sarcopenia: the age-related, progressive loss of skeletal muscle mass and function that begins silently in your thirties and accelerates with each decade thereafter. For men and women over 40, building strength is no l