Every boxer does bicep curls. Most people who train with weights for a sport do bicep curls. And if you work out in a gym with other people (rather than in your garage or basement by yourself) you’ll see lots of curl cheaters.
These are usually the younger kids in the free weight pit who are trying to curl too much weight. They’ll load up, then stand in front of the mirror and try to sling the weight up to their shoulders, bending their backs and swinging the barbell up in a fairly uncontrolled motion. They let it fall down again, then use the momentum of the backswing to get the weight up for the next repetition.
It’s unsafe, it looks awful, and I cringe when I see it.
But curl cheating can actually be helpful when done right. A slight rocking motion can strengthen the muscles — primarily your back and abs — that support a bicep curl. Every time I’ve seen curl cheating done well, however, the weightlifter was wearing a weight belt for support, and I highly recommend this as a safety measure.
Although I use them regularly, I’m not a big fan of controlled weight machines. They build in so much control that they seem to over-isolate the muscles being trained. This will not help you in your sport, because your muscles function like a team. They are carefully interconnected and need each other to perform at optimum capacity. When you train them in complete isolation, they aren’t as good at functioning together; you see this same effect in All-Star teams when individually good players are thrown together as a team for the first time — it takes them a while to learn to play well together.
So if you are training with machines, be sure to add free weights into the mix and learn to control your weights as you lift them. And if you’re curling with free weights, wear a belt and let your abs and back get into the mix once in a while.
Sometimes it’s okay to cheat!