Popularised by Arthur Jones in the 1970s, High Intensity Training (HIT) is a safe, efficient and effective way to achieve many of the positive adaptations associated with exercise. During a HIT workout you perform safe, joint-friendly strength exercises, at a controlled tempo, to momentary-muscular-failure. One set per exercise is often all that is needed.
The intense nature of each exercise sends a strong signal to your body which triggers all the positive adaptations in your muscles and supporting systems. Long recovery periods are encouraged between workouts. This allows your body to fully recover and recharge before coming back fitter and stronger for the following session. For a beginner this might mean a few days, for a more advanced lifter a week or longer!