The hypertrophy guide.
Hypertrophy is the technical word for growing muscle. The thing makes the muscle bigger; everything else is detail. Most lifters know this. Most lifters still get the detail wrong.
What hypertrophy is
Muscle grows when the fibers are challenged hard enough, often enough, and over enough time. The body sees a stress it can't handle comfortably, decides it needs more tissue to handle that stress next time, and adds it. The adaptation isn't fast. But it's reliable, given the right inputs.
The three pillars
- Mechanical tension. The muscle has to work hard against meaningful resistance. Light weight moved easily doesn't grow anything. Heavy weight moved with intent does.
- Volume. Total hard work, usually counted as challenging sets per muscle per week. Most muscles respond well to ten to twenty hard sets a week. Below that, you're undershooting. Above that, you're paying for it in recovery.
- Progression. The work has to get harder over time. Same weight, same reps, forever, equals same muscle, forever.
The rep range question
For decades the answer was "eight to twelve." The current answer is broader: anywhere from six to thirty reps grows muscle, as long as the set is taken close enough to failure. What matters more than the rep number is the intensity — meaning, how few reps you had left in the tank when you racked the weight.
That said, lower reps (six to ten) tend to be more efficient for compound lifts; higher reps (twelve to twenty) for isolation work and machines.
How Checkfit programs it
Checkfit picks rep ranges per exercise based on what that exercise is good for. Compounds get heavier rep targets. Isolations get higher. Every set has a target intensity — how hard the last rep should feel — and the next session's weight is calculated from how close you actually got to that target.
The volume per muscle is balanced across the week so nothing is overworked and nothing is forgotten. You don't have to count sets. You don't have to pick rep ranges. The math is on your side.
