Answer:
The number of reps you should do depends on where you are in your training (new, experienced, coming back from a long layoff) and your goals. To become as strong and as big as your body type will allow, do fewer than 8 or 10 reps per set. To tone your muscles and develop the type of strength you need for everyday life — moving furniture or shoveling snow — aim for 10 to 12 repetitions. Doing dozens of reps with ultralight weights (weights you can barely even feel) doesn’t bring good results of any kind, because you’re not stressing your muscles enough.