Your genes, your patterns of exercise, your workout consistency, and, to a small degree, your nutrition levels, determine the largest muscle size you will ever be able to achieve.

You can go a step further by using anabolic drugs such as testosterone, Growth
Hormone, IGF-1, and insulin, but there is a limit to the amount of help you’ll receive from those drugs too.

Biological systems can adapt to only a specific amount of stress before they break down. This is an example of hormesis, which is not to be confused with homeostasis.

Hormesis is the theory that a stressor, such as exercise, can force a system to adapt in a positive manner. The amount of stress compared to the level of benefit, however, is not a linear relationship. It is a curved relationship.

There is an amount of exercise that is just right – and there are amounts that are too small and too great. In order to stimulate muscle growth, you need to be in the “just right” zone.

As you get stronger, the location of the zone changes. You need to exercise often and at an increasing level in order to grow. But a limit is eventually reached, at which point, the entire system breaks down. This isn’t an issue for most people. Most individuals never reach the limit.

The goal should be to push to the top of the “just right” zone without going over it in order to stimulate maximum muscle growth.

The amount of rest time needed between bouts of exercise has not yet been determined.

We do know that muscle soreness peaks between 24 and 48 hours after exercising and can take up to a week to dissipate. We also know that it’s not necessary to wait a full week before returning to an exercise routine.

Muscle soreness is caused by a number of factors, including swelling, the release of noxious chemicals in the muscle cells, the stimulation of pain receptors, and inflammation.

“Lactic acid” has nothing to do with muscle soreness. Only people who don’t understand exercise physiology say this.

Muscle soreness we experience occasionally following workouts tends to be more closely linked to the negative, or eccentric, phase of each rep rather than the push, or concentric, phase.

Even when you don’t intentionally do “eccentric” exercises, most exercises with heavy weights require a controlled eccentric contraction as well as a concentric push.

You can continue exercising when you’re experiencing muscle soreness, but it’s possible that, because of the soreness, you might not generate enough force to make your workout worthwhile.

Here is a good rule of thumb: Train through mild to moderate soreness (a pain level of 1-6), but don’t train during bad periods of soreness (level 7 or higher). When your soreness returns to a manageable level, you can resume training.