What sets and reps to use in your workout
By now I'll assume you have a full exercise program planned out with what exercises you're going to do on which days and in what order. Now you just have to decide how many sets and how many reps you want to use for each exercise.
Stupid things you probably think you know
I just want to get these out of the way quickly:
1. 3×10 is the best for building mass/strength/endurance/curing cancer
Everyone loves 3 sets of 10 reps for every exercise (written as 3×10). Why? Who knows… It's not a magic number, there are none. It's probably just an arbitrary number that is popular because it's a round number (10 is easy to remember for intelligent gym-goers) and it works for most people. But so would 3×9, or 3×11, or 4×9, or 4×11.
2. Do low reps with heavy weight to get big, do high reps with light weight to get really cut
This is dumber than 1. Why? Briefly, because being "cut" is about having low body fat, not so much about the kinds of weights you lift. There are other reasons for why this is a stupid idea but that's enough for a whole new article.
Maybe you should just start with 3x10 for now...
Sets and reps for beginners
Remember above where I said doing 3×10 is stupid? Well re-read it, because I didn't. Stop putting words in my mouth, alright? I said it's stupid to say that's the best number of sets and reps for any given goal. It may well work but it's a fairly arbitrary middle of the road sort of rep scheme. But one instance when I think it is useful, and when I do recommend it, is for beginners, for exactly that reason – it is middle of the road. It allows beginners to use weights heavy enough to get a feel for weight training, and to get some size and strength improvements, but it doesn't allow them to go so heavy that they will injure themselves. Beginners need a bit of time with moderate weight training (for which 3×10 is perfect) to condition their muscles and joints to deal with the stresses of lifting maximal weights.
So, if you are new to weight training, start with something moderate like 3×10 for a few weeks to get a feel for it, and then start gradually mixing up your sets and reps according to the rest of this article.
The rep range continuum
When reading the descriptions of the different rep ranges, keep in mind that nothing is cut and dry. Rather than specific categories it is more like a continuum from 1-infinity reps, and all the rep ranges will train most attributes to some extent. Further, the extent to which any given attribute will be trained increases or decreases depending on which way along the continuum you are moving. So in short, remember that this is a rough guide.
A good example of the low rep-range in use.
Low reps (1-3)
This is the high intensity, maximal strength and power range. This range is very good for training those attributes, but is very draining on your CNS (central nervous system) so you can't do a lot of sets. You will also need a fair bit of experience before you start effectively training in this range. This rep range is targeted more at developing maximal strength/power, and less at hypertrophy (making your muscles bigger), though this doesn't make it worthless to bodybuilders – by making you stronger, you can lift more weight overall and as a general rule, more weight = more muscle. I find such low reps to be only worthwhile for big compound exercises like deadlifts, squats, benchpress, etc. If you have a while of weight training under your belt you can use this on the biggest exercise of any given day, but I wouldn't use it for more than one exercise each day, and only on your biggest compound exercise.
Low-medium reps (4-7)
This rep range is still good for developing maximal strength, but with a bit more hypertrophy added in there as well. Think of it as a middle-ground between low and medium-high reps, because that's exactly what it is. Remember how I said this was a continuum? This rep range can be used for either big compound exercises or assistance or isolation exercises. "Assistance exercises" refers to any exercises, either compound or isolation (e.g. close grip bench press, or triceps extension), that are done after your main lift (bench press) in order to help improve it.
Medium-high reps (8-12)
This rep range is targeted more towards hypertrophy than maximal strength or power. Of course you can get stronger with this rep range and many people do. I find this rep range less effective for larger compound movements like deadlifts, squats, benchpress, etc, and more effective for smaller isolation/assistance exercises like curls.
Too many reps won't do much for your bodybuilding... this includes endless pushups.
High reps (15+)
If you do many more than 15 reps the weights are necessarily so low that it's effectively strength-endurance training. You'll get a decent pump, and it's useful for glycogen depletion (if you don't know what that is, forget it for now) but in terms of improving strength or putting on muscle, it's hardly ideal. As for using higher reps for getting "cut", unless you're using it specifically for glycogen depletion, there's not much point. And if you're using high reps for glycogen depletion in order to get to extremely low body fat levels, that is way beyond the scope of this article and you probably wouldn't be reading it, so again: forget it.
This depends on two things; how heavy the weight is, and how many reps you're doing. It's related to total work load, which is “sets x reps x weight”. The total workload you can manage decreases as the intensity (i.e. weight) increases, so this isn't useful to you as a formula to be calculated, but more as a principle.
Suppose you can do 5 sets x 5 reps x 100kgs in any given exercise. The total workload is 2500kgs. If you want to increase the sets, you need to decreases the reps or weight, or both. You can increase the reps, and then you have to decrease the sets or weight, or both. Lastly you can increase the weight, which will require you to do fewer sets of fewer reps.
It's less important that you get your sets and reps and weights worked out perfectly, and more important that you always strive to increase one or all of those things, preferably without decreasing the others. Read this article on progressive overload for a better explanation.
Now you should have a rough understanding of what sets and reps to use, here's a quick summary:
Lower reps are targeted more towards strength/power, with higher reps more for hypertrophy, but go above 15 and you're mainly training strength endurance
Do lower reps with your bigger compound exercises, and higher reps with your smaller compound and isolation exercises
Do lower rep exercises before higher rep exercises
Remember that total workload = sets x reps x weight, so they are all interrelated
If you're a beginner, start with 3×10 for a few weeks and ease into other rep ranges.