Muscle for Life

Clap your hands if you’ve heard this one before: “Muscles don’t know weight, only tension.” It’s an old bodybuilding saw that’s been around for decades, and it’s shorthand for the theory that the key driver of muscle growth is how long your muscles are working (contracting) during your workouts. For example, if you do one set of 8 reps and each rep takes about 5 seconds, your time under tension for that set is 40 seconds (8 x 5). If you do three sets of the exercise, your total time under tension is 120 seconds (40 x 3). According to proponents of this idea, the more time under tension you rack up over days, weeks, months, and years of training, the more muscle you’ll gain more or less regardless of any other training variable (intensity, frequency, volume, etc.). Is this true, though? Is time under tension really the biggest lever you can pull to build muscle? Not really. You see, time under tension is an important element of the training stimulus that produces muscle growth, but it’s best to think of it as