Drinking milk or its isolated proteins alone won't result in big muscles. You need to strength train diligently to build lean muscle mass. The International Society of Sports Nutrition recommends that you follow a strength-training program for at least 10 to 12 weeks that consists of three to five days per week of lifting. Use compound exercises for both the upper and lower body during this exercise protocol. Compound exercises are those that activate multiple joints at one time, such as squats and presses. Consume the whey or casein and whey protein powder within 45 to 90 minutes of finishing each session for optimal uptake and use of the amino acids.