Building muscle and strength requires manipulating five key variables: exercise selection, intensity, volume, rest intervals, and training frequency. Dr. Andy Galpin explains how to optimize each for your specific goal—whether you want pure strength gains, hypertrophy, power, or endurance—and reveals why soreness is a terrible metric for workout quality. Progressive overload through modifiable variables (exercise choice, intensity, volume, rest, frequency) is the only way to continue improving; doing the same workout indefinitely produces zero adaptation. Strength training requires 85%+ of one-rep max with 2-4 minute rest intervals and 5 or fewer reps per set, while hypertrophy requires 10-25 working sets per muscle per week at any rep range between 5-30, taken close to muscular failure.