What is the definition or description of: strength training?

To improve muscle: Strength training is to improve muscle mass. This can come from lifting weights, yoga, circuit training, etc. It is great at all ages but definitely needed to stop age related muscle loss.

Strength Training: A method of improving muscular strength by gradually increasing the ability to resist force through the use of free weights, machines, or the person's own body weight. Strength training sessions are designed to impose increasingly greater resistance, which in turn stimulates development of muscle strength to meet the added demand.