progressive resistive exercise
/ PRE, said "P-R-E" /
A muscle is a frugal tenant: it keeps only as much strength as its daily life seems to demand, and lets the rest waste away. To make a weakened muscle grow stronger, you must repeatedly ask it to do a little more than it is comfortable with — and then, as it rises to the challenge, ask for a little more again. That steady raising of the bar is what "progressive" means in progressive resistive exercise.
The method is straightforward. The muscle works against a resistance it can only just manage — a weight, an elastic band, a machine, even the limb's own weight — for a set number of repetitions. As the muscle adapts and that load starts to feel easy, the resistance is nudged up so the muscle is once again challenged. This is the training principle of overload (you must exceed the usual demand) wedded to progression (the demand must keep rising). Classic schemes such as the DeLorme programme build through sets at increasing fractions of a person's maximum, but the core idea is simply: make it hard, then make it harder. Unlike passive range-of-motion work, here the muscle itself does the work, so here is where real strength is built.
In rehabilitation this is the workhorse for rebuilding strength lost to disuse, injury, surgery, or nerve damage — the quadriceps that withered after knee surgery, the grip that faded after a wrist fracture. It demands a muscle that can actually contract, so it is matched to the person: someone too weak to lift against gravity starts with assisted or gravity-eliminated movement and only graduates to added resistance once they can. The honest limit: strengthening can restore a muscle's power, but it cannot regrow a severed nerve or replace a muscle the nervous system can no longer command.
Three weeks after knee surgery, a patient does leg lifts with a 1 kg cuff weight, 10 repetitions, 3 sets. When that becomes easy a fortnight later, the therapist swaps in a 2 kg cuff — the load progresses so the muscle keeps being challenged.
Without the regular bump in load, the muscle adapts and then simply stops getting stronger.
Resistance work can strengthen a muscle but cannot "reconnect" it: if the nerve supplying a muscle is dead, no amount of effort restores it — the muscle must first be able to contract.