Project 451631

The concept of declining function with age requires a better understanding of whether it is an immutable characteristic of aging or whether it can be mitigated. When we age, we lose muscle. However, we are uncertain whether declines in muscle mass directly contribute to declining physical mobility with age. This loss of muscle is referred to as sarcopenia, a term that was simply a loss of muscle when it was originally coined. More recent redefinitions of sarcopenia have framed it as the loss of muscle mass AND physical function (strength and walking speed, for example). Importantly, sarcopenia in older persons is associated with increased adverse outcomes, including falls, functional decline, frailty, and mortality. Sarcopenia has recently received recognition as a treatable condition with the receipt of a code for billing by physicians in certain jurisdictions. Despite being able to bill for diagnosing and treating sarcopenia, it can be defined as a treatable condition in several ways. Thus, its diagnosis is decidedly complex. Importantly, our team showed that various ways of diagnosing sarcopenia result in various people having sarcopenia and others not, whereas another definition reverses the previous diagnosis. With confusion around how to diagnose sarcopenia, its use in clinical situations becomes tenuous at best. Our main assertion is that the biological substrate of sarcopenia, skeletal muscle, has not been accurately measured. This lack of accurate measurement has led to confusion about whether measuring muscle is clinically relevant in sarcopenia. Our main idea is that skeletal muscle mass, when accurately measured, is a powerful predictor of functional declines in older men and women. We will use a novel method to measure skeletal muscle in a large cohort of older men and women and track them for two years. We plan to show that our method of measuring muscle will show a strong association between change in muscle mass and decline in mobility.