Cheating

Cheating works like this: you perform your reps with correct technique until concentric failure. At that point, instead of ending the set, you use a slight body swing, torso oscillation, or recruitment of other muscle groups to get past the concentric phase. Once past it, you control the eccentric phase with the target muscle. It's in that slowed-down eccentric that the additional stimulus concentrates, because the muscle can still resist a load it could no longer lift.

The classic example is the barbell curl. You reach failure after 8 clean reps, then use a slight hip extension to generate momentum and complete 2-3 additional reps, slowly controlling the descent. The same principle applies to upright rows, lateral raises, and other isolation exercises.

Cheating is a legitimate technique when used with judgment. The problem is that most people use it from the very first rep, turning every exercise into a weight toss. In that case you're not doing cheating as an intensity technique: you're simply using a load that's too heavy with terrible technique. The rule is simple: first you reach failure with perfect form, then you use cheating to squeeze out a few more reps. If you can't do at least 6-8 clean reps before introducing momentum, the weight is too heavy. And remember: cheating increases stress on tendons and joints. Use it sparingly and only on exercises where the risk is manageable.