In healthy adults over 65 years of age, combining heavy-load resistance training three times per week with daily whey protein supplementation significantly increases quadriceps muscle size by approximately 1.68 cm² and improves dynamic and isometric knee extensor strength by 18.4 Nm and 23.9 Nm, respectively, over one year compared to protein supplementation alone.

Lifting heavy weights pulls on muscle fibers, which turns on a molecular switch that tells the muscle to build more contractile proteins. Drinking whey protein at the same time provides the raw materials needed for this process. Together, they cause muscle fibers to grow thicker, making the muscle bigger and stronger. Light weights only improve how well the nerves signal the muscle to contract, but they don't make the muscle grow.