To provide the maximum stimulus for muscle growth, intensity wins over duration every time. Let’s see why this is so and how you can tailor your training to make the most of this principle.
The basis for high intensity training originates with research on stress and adaptation conducted by Dr. Hans Selye (1907-1982).
According to the acclaimed Hungarian endocrinologist, if you place your muscles under stress, and then allow them to recover, they will at some point rebuild themselves and become slightly larger and stronger.
This is an ingenious adaptation of evolution, allowing us to cope with stress, convert it to our advantage and become better able to respond to similar challenges in the future.
The key point in terms of muscle growth is the relationship between the intensity of the stress and the body’s response. Relatively low stress levels result in relatively small adaptations.
This makes perfect sense, of course. In the absence of a large amount of stress, there’s no need for the body to adapt in a meaningful way.
On the other hand, higher intensity exercise puts muscles into a “crisis” mode, thus bringing about greater adaptations. The more stress you put on your muscles, the more they are forced to respond and adapt.
Lifting a higher portion of your maximum weight requires the involvement of a greater number of motor units and thus a greater number of muscle fibers. The more fibers that are stressed, the more of them adapt and the greater the gain in strength will be.
Oddly enough, duration of exercise is a less potent producer of muscular adaptations for a number of reasons. Primary among them: the duration of a workout is inversely proportional to its intensity.
In other words, the longer your workout, the less intense it must be. And as we’ve already seen, intensity is the key to stimulating the greatest amount of adaptation to training.
Another factor that works against the duration model of training for building muscle is that continuous exercise for long periods of time stimulates the release of the stress hormone cortisol.
Cortisol has a catabolic function, meaning it helps break down muscle tissue, which is the exact opposite of what you’re trying to achieve.
Excess cortisol has also been linked to increased blood pressure, cardiovascular problems and higher levels of obesity.
So, when designing your training program, keep in mind that high intensity, short term exercise will stimulate greater gains than longer routines that will, of necessity, be lower in intensity.
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