Strength

Strength isn't a single concept. Different expressions exist: maximal strength (the heaviest load you can lift for one rep), explosive strength (the ability to generate force quickly) and strength endurance (the ability to maintain force production over time). In the weight room, when people say 'strength training' they almost always mean maximal strength.

Strength gains depend on two main factors. The first is neural: the nervous system learns to recruit more muscle fibers simultaneously and coordinate them better. This explains why a beginner gets stronger week after week without yet seeing major muscular changes. The second is structural: the more muscle you have, the more strength potential you have.

To train maximal strength, the classic protocol calls for heavy loads (80-95% of max), low reps (1-5 reps), long rests (3-5 minutes) and compound exercises. Squat, bench press and deadlift are the three lifts traditionally used to measure strength in powerlifting.

Strength and hypertrophy aren't opposing goals: they feed each other. The more muscle you have, the more strength you can express. The more strength you have, the more load you can use to stimulate hypertrophy. For most people training in the gym, a program that trains both qualities is the better choice.