In any given rep or set structure, it isn’t just about how many reps you do, that determines how hard a muscle works. What you’re really looking at is Time Under Tension (TUT) which is the total time that your muscle is under tension in the concentric, isometric and eccentric phases. If you have a 1-second concentric contraction, a half-second isometric and a 2-second eccentric, then your TUT per rep would be 3 ½ seconds. If you take the number of reps and multiply it by the TUT, you get the total Time Under Tension for the set.
If we look at the TA2 program, in Sets #2 and #3, we have a rep speed of approximately 3 ½ seconds, multiplied by 10 reps, which gives us a TUT for that set of roughly 35 seconds. The ideal TUT for muscle size and strength gains (hypertrophy) the ideal range is 30-70 seconds. In Set #4, although we have 15 reps as opposed to 10, our TUT is very similar. Let’s compare: Using an explosive rep speed of less than 1-second on the eccentric and concentric, and no pause on the isometric, we have a TUT per rep of less than 2-seconds. Multiply that by our 15-reps and we have roughly 30 seconds. As you can see, although we’re doing more reps, our TUT is less, but still in that ideal range for building muscle.
One of the peripheral benefits of Set #4 is that we’re also driving more blood into the muscle. Besides the fact that we all like the way a good muscle pump feels, it also serves a muscle building purpose. By driving more blood into the muscle, along with it comes muscle building nutrients like glucose and amino acids.