From this NYT article Lifting Lighter Weights Can Be Just as Effective as Heavy Ones:
“A new study finds that people who lift relatively light weights can build just as much strength and muscle size as those who grunt through sessions using much heftier weights.”
If lifting heavy or lighter weights produce the same strength increases you might do well to consider which produces those results in the safest manner. Increasing strength should not be the cause of injuries, but rather it should give you protection from injuries.
Whether the weights lifted are lighter or heavier in both instances the stress imposed on the body needs to be sufficient to affect a positive change. When the body is exposed to more than it’s used to handling, as an act of self-preservation, the body responds by making a positive adaptation if given enough time and resources to recover from the imposed stress.
Lifting a very heavy weight requires force that can be potentially harmful. Additionally, momentum is often required just to have a chance of completing the repetition; momentum is counter-productive as it has the effect of unloading the muscles you are trying to work.
With a lighter weight there will be less force needed to move the weight, and if you slow down the movement just a bit it will be even safer and there will be less momentum – less unloading of the muscles. If a set is taken to volitional failure (you can’t move it) a heavier weight will have a shorter time under load than a lighter weight, but in both instances the muscles will be exposed to more than they can handle producing deep fatigue. The main difference is the potential for injury.
A characteristic of many strength exercise programs is a very high injury rate. Google any strength training program along with the keys words injury rate, and you will likely see a whole lot of hits. With a program with high potential risks you might make 10 steps forward barring injury, but if you are injured you will likely take 10 or more steps backward.
At Austin Personal Trainers and New Orleans Personal Trainers we place a high premium of safety and increasing strength. We use MedX equipment with its special medical rehab features. We can show you how to safely increase your strength and avoid injuries.