5 Reasons Your Legs Are NOT Growing

The most common reason for atrophy to occur in the legs is disuse. Lack of activity for any reason — illness, injury, seated desk job, sedentary lifestyle — can lead to loss of leg muscle. Alcoholism and malnutrition can also inhibit muscle growth and cause the body to use muscle proteins for energy.Focus on aerobic activities that use the legs, such as walking, running, bicycling, elliptical training or stair climbing. Strength exercises that focus on the quadriceps, hamstrings and calf muscles will build muscle mass in the legs.

https://www.livestrong.com/article/347887-leg-muscle-atrophy/