Be sure to get between 7-9 hours rest EACH NIGHT for optimal results.

During a workout, rest for at least 60 seconds and up to 90 seconds between sets for MUSCLE GAIN.

Rest between 2-3 minutes for STRENGTH GAIN.

Not enough rest can cause muscle to breakdown.

Too much rest will allow the muscle to recover nearly 100% energy, meaning you will not be tearing the muscle and forcing it to collect more muscle fibres and grow bigger.

Related Questions:

1. How many sets and reps should I be doing to gain muscle? Do I need to train all muscles the same way?
2. What rep range and set range should I use to build strength? How long should I rest between sets?