For the most part, we want to move the weight in perfect form to ensure proper recruitment of the targeted muscles as well as training injury free. However, if you are an experienced lifter then there are times that you may sacrifice form (somewhat) to go a little heavier with the weight you are using. By sacrificing form or “cheating” you can handle more weight, you don’t want to go overboard with this technique though. Here are two examples of cheating. One is acceptable and the other is not.
Lets say you are doing a barbell curl and the weight is a little more than you can move in perfect form. It is acceptable to sway the body a little bit at the start of the movement to get the bar moving upward. The minor cheat will enable you to get the weight moving past your sticking point so you can stress the muscle more than you would with a more manageable weight.
It is not acceptable to swing the weight up with a huge rocking motion and arching of your body. The major cheat will only increase your chance of injury and incorporate so many other muscles that you will not hit your targeted muscles as effectively.
You want to be able to feel the muscle go through its range of motion at all times during the lift. You want to feel it engage and contract as you lift the weight and you want to feel it stretch while under resistance as you lower the weight. Basically, that’s all you do as you lift weight, contract and stretch under controlled resistance.
It is very important to train a muscle through its full range of motion (ROM). You have to feel the muscle stretch on the negative portion of the lift and fully contract on the positive portion of the lift. Only by training the full ROM, can you strengthen and develop the muscle to its full potential.
Now there may be times when you don’t want to do this. One time that comes to mind, is when you may have some sort of injury. I have had many clients with bad shoulders who can perform a shoulder press but if their upper arm goes any lower than parallel to the floor, it causes them great discomfort. If this is the case, it is fine to just bring your arms parallel to the floor. You are getting the majority of the benefit of this exercise by doing so.
It is one thing to slightly decrease your ROM due to injury but it is another to decrease it due to laziness. Remember, you always want to make an exercise harder not easier. Don’t sacrifice your ROM to make the movement easier. It is only sacrificed when the risk outweighs the benefit.