Thanks for all the responses guys, you have given me many ideas.
My goals at the moment are a bit cloudy. My primary goal is strenght, while I want to work on my conditioning as well. Also, in the process im hoping to have a shift in body comp towards less fat. Im not looking to lose weight, and instead want to maintain weight or even increase gradually. So the purpose of my HIIT and VHIIT sessions will not be energy expenditure. Im more looking to it for the metabolic adaptations primarily and some of the neural adaptations (like speed)
I feel im an ecto, although im at around 15% BF, but I think higher intensities are what I need the most. Ive decided to do 4 Interval sessions per week, 2 upper body, and 2 lower body.
For uppper body:
Push press 8 x 5-10 reps /(45-60sec) treadmill walk
Row 8 x 10-20 reps /(45-60sec) elliptycal
For Lower body:
Hill sprint 8 x 10-30 sec work / 45-90 rest walking down
DB swings 8 x 30reps / 30-60 sec bike rest
Jump squat(BW) 8 x 10-20 reps / 30-60 inc treadmill walk
So probably something along those lines. Ive been reading around on interval training, and its really hard to find clear answers as to what works. I imagine if you are training for sport, its much easier, as you would have the intervals resemble the sport.
But for hypertrophy and fat loss, I think I may have figured out a few of the main factors. Assuming you are working at higher intensities 90-100%
WORK duration seems to be the biggest factor. You simply cant recruit maximal MU's for much longer than 10-15 seconds, and thus an all out sprint lasting 10-15 seconds will probably be the best WORK duration for hypertrophy. (This is not to say that a 30 second 90% sprint wont be good for hypertrophy, but it will just be targeting less of the fast twitch MU's)
Also, a short work duration can be optimal for fat loss as well. You might think at first that if 10-15 seconds is best for hypertrophy, then fat loss must be on the other end of the spectrum at 1-2 minutes work. But I would have to disagree.
I think 30 seconds of work, maybe up to 45 sec is the best duration for fat loss. Anything longer, and the intensity will have to drop too much. But in addition to doing 30 sec work durations, shorter ones of 10-15 sec can be very beneficial as well. But in order to gear these shorter sprints for fat loss, REST should be reduced.
REST, rest seems to be equally important to work durations for intervals. A long rest will be optimal for hypertrophy, because it will allow greater intensities during the work phases. Now obviously if you do a 10 second sprint, you dont need to rest 3 minutes (IF YOUR GOAL IS HYPERTROPHY), but for hypertrophy a work to rest ratio of 1:3-1:5 might be good.
For fat loss, shorter rest is what is needed. This range might be 2:1-1:2
Asside from these two primary factors, I would think that intensity and volume would be very important as well.
As for INTENSITY, not only is it going to be dependant work durations, but also on rest durations.
You could do a 15sec all out sprint for hypertrophy with a 45 sec recovery period. You could also do a 15 sec 90% sprint for fat loss, and pair it with a 30 sec recovery. (the shorter rest duration requires less intensity to b used)
As for VOLUME, im not too sure here. Part of me wants to think that BOTH hypertrophy and fat loss will benefit best from higher volumes, but I dont think this can be correct.
I think for hypertrophy, greater volume should be emphasized but while avoiding fatigue. (I have seen coaches like Staley suggest that intervals be terminated when there is a 10% decrease in speed or performance)
For fat loss, less volume should be the goal but greater fatigue. A drop in performance should be expected.
Other than all of this, I guess you could say that if hyperttrophy is the goal its good to error on the side of TOO MUCH rest, but greater volume, while if fat loss is the the goal its better to error on the side of TOO LITTLE rest, but shorter workouts.
So im not really sure if this is all correct, but these will probably be the guidelines I will be following. And since my current goals are more well rounded instead of just fat loss, or just hypertrophy, i'll follow all forms of progression. (I'll increase intensity on my push presses, i'll decrease rest durations on my rows, i'll increase the duration of the sprints or decrease the rest, etc. And for everything i'll build from 8 rounds up to probably about 12, at which point I would decrease back down to 6-8 and increase the intensity once again.)
Thanks again guys.