Strength Training, Proteins, Carbs and Fats Muscle is harder to build and maintain as we age. In fact, most of us start losing muscle between ages 30 to 35. Physically inactive people are at particular risk and can experience anywhere from a 3% to 8% loss of lean muscle mass every decade after that. This is due to lower testosterone levels in men and lower estrogen levels in women — both hormones that help build muscle. Changes in nerve and blood cells and how the body conve