It's been, what, 115 years since Sandow got this whole sub-culture really going? You'd think that, by this time, we'd have a pretty good handle on exactly how the muscles work and we'd have gotten this information disseminated down to every gym, to every personal trainer and to every gym rat. By now, I thought we'd have no more issues about how many reps it takes to get big and strong... or just strong... or just big.
There's still Smoke and there's still mirrors in the muscle-building world. It still pays to keep people in the dark, occasionally throwing them just enough scraps of decent information to keep them coming back. I've rarely work out in a gym and I've never gotten any instruction from a personal trainer. I'd love to know what the hell goes on when people get personally trained? Doesn't the whole thing about rep ranges get discussed? I guess not because I still get people asking about how many reps to a set does it take to get big and strong. Or, even worse, I see them doing 30 reps with a puny weight expecting to get some serious pythons.
So, that's why I thought I'd discuss it. After all, two family members recently asked me about this and I didn't have a chance to answer. Rep range isn't as concrete as everyone would like to think. The most boiler-plate answer is 3-5 reps to a set for max strength, 8-10 for muscle growth, and anything over 15-20 is just strength endurance and conditioning. It's not that simple. Take a handstand push-up. Is 8 reps the same on that as 8 reps on a squat? The body's moving a lot more distance on a squat than it is the former. So, it takes longer.
This is where we start getting somewhere: the length of time that the muscle is contracting. Muscles contract and move because of this beautiful molecule:
Adenosine Triphosphate, aka ATP. The muscles have two ways of making this little gem: The Oxygen-based aerobic respiration and Glycosis. Muscles also store ATP via creatine phosphate, ready for immediate use. The last two ATP mechanisms are the ones we want to concern ourselves with at the moment. These two are the ones associated with muscular max strength, explosive strength, and hypertrophy. In other words, they are the fuel for creating power and bulk.
Muscle cells have about 15 seconds worth of ATP stored up and are capable of making ATP anaerobically via glycosis for an additional 45 seconds (these numbers may not be exact but you get the idea). So, any exercise set that fatigues the muscle to the point of stopping in less than 60 seconds is going to build the most power and muscle mass. Since they're the creators of power, the muscle adapts to the demand by becoming stronger and thicker. VOILA! Bigger muscles!
See where rep ranges for size and strength can be a little faulty? Let's go back to the handstand push-up/squat comparison. A handstand push-up moves the source of the resistance about 12 inches. Contrast that to squats, which have over 24 inches of movement. So, it's possible to do more handstand push-ups in 30 seconds than squats because the lesser distance to move the resistance. So, relying on rep ranges can be faulty logic.
Speed must also be taken into consideration too. Sprinters conclusively prove that moving as fast as possible can build some muscular bulk. It may not build as much, or build it as fast, as lifting a ridiculously heavy object but it still works. After all, moving the body (or a weight)at balls-to-the-wall speed requires a lot of muscular recruitment and contraction. The muscle has to thicken up to deal with the strain. If the exercise you're working on can go on longer than a minute at a time without stopping from fatigue, then the muscles switch over to the aerobic respiration. This more efficient method involves using oxygen to create ATP. If you're trying to build bulk, then this isn't the way to go. Since the muscles aren't contracting intensely, they're not going to thicken and build up. There's no need since thick muscles are more inefficient for such a task.
So, you could use the guidelines for rep ranges that I described above as a starting point in building your routine. Just keep in mind that if the movement is shorter in distance or faster in speed, then you might be able to fit in more reps. Generally speaking, a set that lasts 30 seconds or less builds more strength while a 30-60 second set builds more muscle bulk. Any more than 60 seconds and, from a muscle and power-building stand point, you're wasting your time.