The 15's aren't going to give you much hypertrophy, if any. If you actually read up on the HST program, you'll see that the main point of the 15's is to flush the muscles with lactate, which functions like low-level rehab. If you're not old, or you have no joint problems, you can skip the 15's or simply do them for one week.
The 10's are pretty useless, from what I've seen. Some people can gain during the 10's, but I honestly don't see a reason for them. I'd do the 15's, then drop to the 5's right away. I actually am doing a routine that originated as an HST one.
If you know a lot about the program, and if you ever read on the forums, you'll learn that frequency is one of the best variables to increase for hypertrophy. Frequent training (AM/PM splits, especially) helps with a summation effect, increasing protein synthesis and nutrient partitioning, among other things. It also makes it much easier on the CNS to cope with volume.
Anyways, I am now training Monday through Saturday, AM/PM. That's right, 12x a week. The split is AM: Incline bench, seated OHP, pullup, squat, incline curl. PM: Dips, shrugs, bentover row, good mornings, closegrip bench.
I do one set for each exercise, each session. This gives me 12 sets for chest, legs and back weekly, and 6 sets for triceps, biceps, traps and shoulders. There's very little pure isolation work. Despite the extremely frequent training bouts, the overall weekly volume totals 60 sets. The 5x5 routine typically landed around 45-50 sets. I do, of course, throw in some core work (bridges, side bridges and full crunches) as well as grip work.
Rather than determine my 5 RMs and ramp to them as HST would have me do, I simply pick a weight a good deal (about 70%) of my known 5 RM (thanks to the 5x5 routine). I then increase the weight every other day (so, Monday, Wednesday, and Friday) as per a typical HST routine. The days following (Tuesdays, Thursdays and Saturdays) keep the same weights as the preceeding day.
Though it seems like a lot, it's so easily managed on the body. I couple this with my physically demanding warehouse job for 15+ hours a week or constant, heavy box lifting, moving and tossing.
My plan is to continue to increase the weights until I stall with 5 reps. Once I fail, I'll drop the volume by going down to 3 reps. From here, I will continue until I stall out once more. When this happens, I'll take a week off from lifting. When I come back to it, I'll start at 70% of my new 5 RM, and ramp from there.
It's very...different, and I'm skeptical as to its effectiveness, but I honestly have a good feeling about it. The principles of hypertrophy exist, and there's no reason I wouldn't gain strength with this approach.
It's fun training this often.
