Loss of muscle mass and strength contribute to frailty and are associated with falls, mobility limitations and fractures. Men lose more muscle mass and strength than women as they age, suggesting that sex steroids, and testosterone in particular, may contribute to body composition and physical function changes.  Erin LeBlanc, from Kaiser Permanente Northwest (Oregon, USA), and colleagues analyzed data collected on 1,183 men, ages 65 years and older, following the subjects for 4.5 years. Body composition was measured using dual energy x-ray absorptiometry (DXA) scans and physical performance was measured through a series of exercises that assessed grip strength, lower extremity power, walking speed and the ability to rise from a chair without the use of arms. The team found that higher levels of testosterone were associated with reduced loss of lean muscle mass in older men, especially in those who were losing weight. In these men, higher testosterone levels were also associated with less loss of lower body strength.  The study authors conclude that: “Higher endogenous testosterone is associated with reduced loss of lean mass and lower extremity function in older men losing weight. Endogenous testosterone may contribute to healthy aging.”