<div></div><div id="QUOTEHEAD">QUOTE</div><div id="QUOTE">Is that enough rest for the muscle to grow? I thought it was 48 hrs.</div>
The muscle can grow even through constant loading, but this isn't very practical.
HST advises 3x a week training because the anabolic effects of exercise generally last 36-48 hours. So, if you train approximately every other day you should be fine. However, training sooner than that won't compromise your gains in any way. And maybe, just maybe, it can actually help a bit (summation effect).
The muscle itself doesn't need "rest" (as perceived by humans) in order to grow. Our CNS, though, is an entirely different story. We have to balance exercise, frequency and volume with CNS fatigue. Many guys here have actually tried 6x a week or even 12x a week. Nothing wrong with that, as long as it serves your goals.
Keep in mind, though, that high frequency training requires a lot of energy, making it somewhat difficult to bulk. Not that it can't be done, it's just that many guys have problems eating that much and so they stick with 3x a week. If you can grow on 4x a week, 6x a week or whatever that's fine. As they say, only you can manage your own training.
Regards,
Dimitris