(Work=Force X Distance) = (Work=Force X Time)

(a x SETS) + (b x REPS) + (c x WEIGHTS) = (d x INJURY)

Many studies have been conducted with varying combinations of sets, repetitions and weights. At the extremes, high amounts of weight and low reps per set – possibly done to fatigue – build size and strength. Low weight and high reps per set – also possibly done to fatigue – build strength, endurance and tone, not dramatic size.

What may not be as well known is that injuries can be limited by introducing another variable – TIME.  The length of your arms or legs is 

a constant, therefore you cannot change Distance.  However, you can exchange Distance for Time in the equation. Timing is a three-count positive contraction and nine count negative (eccentric) contraction. The slower the count, the longer the muscle must work. Now you can use fewer repetitions (with no more than three sets) and much less weight to achieve the same results (size and strength or endurance and strength). You can reduce the weight by 30 percent if working on size and strength and by 50 percent for strength and endurance. With less weight and less repetitions, you have now limited your chances for injury.