Strength or Resistance Training is any type of exercise in which your muscles are working against a force. Examples include using free weights, weight machines, a resistance band, or even gravity.
Strength training should ideally be done 2-4 days per week–allowing for a 48 hour rest period before working the same muscle groups again.
A typical strength training program involves performing 10-15 repetitions in 2-3 sets, with a few minutes rest in between sets. However, any amount of resistance training can be beneficial.