Eric, thriving under the iron:

Some would have you believe that fitness, even strength, can be achieved with minimal weight and a plethora of calisthenic and gymnastic movements. Push-ups, pull-ups, dips, sit-ups, unweighted squats, etc... definitely, these exercises have a place in a well-rounded program. We prescribe them in quantities that would appear enormous to most people.

We also use light-weight implements to devastating affect.

In order to affect lasting adaptation of the most important motor units in the body, though, time must be spent under the iron. There is simply no way to avoid the truth that muscles will adapt to specific loads.... the weight being moved in a push-up will hardly ever change. However, a bench-press inherently has a nearly infinite range of weight. Speed of movement may be increased, but there exists a limited horizon for this type of adaptation.

If you want to become stronger, more powerful, and faster; you must spend some time under the iron.