Originally posted by Bryan Haycock to the HST forums
There is very LITTLE difference between 1RM and 5RM. The level of recruitment is practically equal. The only difference is how many times the weight moves.
Please understand that ALL slow motor units are activated at relatively low force output. Fast fibers begin to act fully at only 30-50% of your 1RM. Motor units are all utilized but they are not recruited all at once (rate coding etc). This doesn't happen all at once until the load goes up, or motor units begin to fail (fatigue). When a muscle begins to shake it is because recruitment patterns are beginning to synchronize in an effort to accommodate fatigue.
Fatigue of muscle fibers cause LESS microtrauma, not more. If the fibers are not forcefully contracting they are not going to be stimulated to grow.
The load and speed of movement determines what fibers are "worked". Worked is not a good term. "Recruited" is more accurate. 4-6 reps on bench using "10 pounds" moving slowly will likely NOT recruit your fast fibers. Push that same 10 pounds as fast as you can and you will recruit nearly all of your fast twitch fibers.
4-6 reps on bench using "300 lbs" will likely recruit ALL your fast twitch fibers. No matter what the speed. The weight usualy moves slowly because it is heavy, not because your fibers aren't contracting as quickly as they can. Fibers have no control over how fast the contract. They are either 100% ON or 100% OFF, there is no dimmer switch.
Muscle tissue does not distinguish between rep ranges. There is not a special number of contractions that "triggers" a hypertrophic response. The only thing that triggers hypertrophy is sarcolemma distortion and subsequent microtrauma and to a lesser extent, metabolic activity. These pathways of mechanotransduction have been mapped and are not in question. Yes, there are always more details to be ironed out, but the pathways are now established that go from mechanical load to muscle cell growth.
In order to adhere to the principles of training induced muscle hypertrophy we must have progressive load. Progressive load sufficient to cause hypertrophy will limit the number of times the muscle can successfully contract against the resistance. There are several old studies that narrowed it down to a range of perhaps 20 reps (if the muscle is deconditioned) all the way up to 120% of your 1RM. So, depending on how conditioned the muscle is, you can use any rep range between 20 reps and negatives.
While using HST, your reps decrease simply because the load is increasing. Itís that simple. There is no magic number, though others might have you believe there is.