For muscle building, the best protein sources include lean meats, fish, eggs, dairy products, legumes, and plant-based options like quinoa and tofu. These sources provide essential amino acids necessary for muscle repair, growth, and recovery. Whey protein is particularly effective due to its fast absorption rate, making it ideal for post-workout supplementation. Athletes should aim for a balanced intake of protein throughout the day, targeting approximately 1.2 to 2.0 grams per kilogram of body weight based on their level of activity and body composition goals.