So here's something to consider.

Since the nascent days of the modern fitness industry, the exhortation to "use good form" when you lift weights (and run, and cycle and swim and so on) has been repeated so many times you barely hear it anymore. Doing a set a barbell curls? Stand rigid and move only at the elbow joints. Better still, do it against a wall. Minimize your postural sway and work the biceps. Doing a chin-up? Stretch the lats fully and work from a dead hang on each rep. Keep the body still throughout the movement. For the love of God, don't cheat!

The approach, of course, stems from the muscle-isolation idea that in order to "work our [pecs, lets, deltoids, etc]," we need to bend and twist and contort our bodies, performing weird, counter-intuitive movements in order to optimally stimulate the various body parts so that they grow.

All well and good. It's the ubiquitous bodybuilding model, with its laser-like focus on aesthetics at all costs. And in many cases, the "strict form" idea is useful and accurate. Barbell squatting or dead lifting with lousy form, of course, is just plain stupid. Learning to bench press in a shoulder-sparing way, and to do core exercises safely are basic skills that any beginning exerciser should acquire.

But think about cheating for a moment. When you try to curl too much weight, you sway your body and use momentum to swing the bar up--in a way that resembles a kind of rudimentary power clean movement. When you try to eke out more chin-ups, you swing your body back and forth and undulate the spine, again, turning to momentum to help with the movement. You're trying to recruit other muscle groups--larger, more powerful, usually the more centrally located muscle groups surrounding the pelvis--to help you perform the exercise.

And that makes perfect physiological sense, because your muscles are foot-soldiers, not all-knowing four-star generals. They only understand the assignment: if you're doing a barbell curl, for example, the body just knows "move bar from point A to point B." Why you'd want to call on this small, weak division of foot-soldiers (the biceps) and not that large, strong division of foot-soldiers (the hips and back) is utterly baffling to the nervous system, so it's everything you can do to stop yourself from doing the totally instinctive thing--using the biggest, strongest muscles to perform the task in the most efficient way possible. Same with the instinct to turn an overhead press into a push-jerk, or to turn a chin-up into a kip-up. You naturally drift towards using your biggest muscle groups whenever possible.

The point I'd like to make here is that's actually a good thing. That's you trying to turn a weird and unnatural movement into an athletic, integrated one.

Among the many other problems with doing too many single-joint isolation movements in a strength-training program, I believe that they encourage poor movement habits by deliberately cutting off the powerhouse portions of the kinetic chain from the rest of the body. Next time you're working out and have the urge to cheat, see if there's a way in which that "cheating" actually improves the movement--makes it more holistic and global in nature.

I'm not a kettlebell expert, but many of those movements--swings of all kinds, for instance--seem to solve this inherent problem with many standard barbell and dumbbell exercises.