"Cheating" when weight lifting is really common. Look around the gym and no doubt you will see people sacrificing their lifting technique to pump out a few more repetitions. Is this an effective method of training?
Possibly for muscle growth in specific circumstances. The jury is still out as to whether or not having "textbook" form is more effective than cheating with your weight lifting form. There is no solid scientific evidence to date that proclaims cheating more effective than having strict form with absolute certainty. There are many people who would swear black and blue one way or another, but the science just isn't there to conclusively prove either point.
One benefit to cheating is that you can obtain additional repetitions. This is of use especially if you are training with an eccentric, or negative phase focus. You are much stronger on the negative phase of any exercise than on the positive (or concentric phase). Therefore if you cheat on the concentric, you may still be able to control the eccentric phase and thus obtain the benefits associated with eccentric training - including hypertrophy and strength development.
One problem with cheating with your lifting technique is that you take the load of the muscles you are targeting, at least on the concentric phase. Consider bicep curls - if you swing, you will recruit your legs more than your biceps. Alternatively on seated shoulder presses, if you move your hips forward you may recruit more chest muscle tissue than is desired, thus taking the load off the deltoids (the shoulder muscles).
If you are cheating just to obtain more reps, or lift more weight, without any other reasons (such as focusing on the eccentric phase), then in all likelihood you are taking the load off the targeted muscles are thus reducing the effectiveness of that exercise.
The other major issue associated with poor form is the significantly heightened risk of injury. As soon as you begin to throw weights around without particular consideration of correct lifting technique, you do run the risk of hurting yourself. Injuries can come in all shapes and sizes from a minor muscle tear, to chronic tendinitis or an acute back injury. If you have minimal weight lifting experience (less than a few years) and do not have a specific reason for cheating with your technique, then I would very strongly advise to drop the weights back and focus on correct weight lifting technique. It just isn't worth the risk.
Finally, if you are cheating just to lift more weight because you feel that:
- This is more effective because you are lifting more weight
- This impresses other people
- Your self confidence is improved
Drop the weight back - no question about it:
- Lifting more weight whilst sacrificing your technique is dangerous if you do not know what you are doing for the reasons explained above.
- Other people don't really evaluate your worth as a human being based on the amount of weight you can lift.
- The amount of weight you lift should not be a function of your self confidence. If you feel that it is, you will need to do some internal work on how you feel about yourself. I'm no psychologist, but training to boost your own ego is an accident waiting to happen.