Most people can complete 8-12 controlled repetitions with about 75% of their maximum resistance or 1 rep max. The higher the resistance, the lower the number of repetitions that can be completed; the lower the resistance, the greater the number of repetitions that are possible. The number of reps you should do depends on what your goals are. In general, 8-12 reps is a good median number.
Here is a chart that gives you an idea of how many reps you should do.
| Muscle endurance gains | Strength gains | |
|
40-60% of max weight >12 reps |
70-80% of max weight 8-12 reps |
85-90% of max weight 2-6 reps |