Separate Lifting From Cardio or HIIT
Why not put them together? If you do the energy systems work after the lifting workout you risk decreasing muscle growth by inhibiting mTOR via the increase in AMPK from the energy systems work.
Without going into too much complex science, mTOR is the trigger for protein synthesis (muscle growth) while AMPK is increased when you expend a lot of energy, and it can inhibit mTOR. So raising AMPK right after lifting might partially inhibit the muscle growth stimulated by lifting.
If you have no choice but to do both types of exercise in the same workout then you should do loaded energy systems work like sets of farmer's walks, Zercher carries, or pushing the Prowler. The loading will also raise mTOR which might compensate for the increase in AMPK.
So in order of effectiveness:
- Do energy systems work in the morning (not totally fasted), and lift in the afternoon or evening if you can train twice per day.
- Do cardio and lifting on separate days. In this case the whole workout would be about energy systems. You'd start with an easy warm-up (like stationary biking 10 minutes) then you'd do a high intensity medley, for example farmer's walk for 60 meters, then 30 seconds rest, then Prowler pushing 60 meters, then 60 seconds rest. Do 4-6 sets and finish with low to moderate intensity steady state cardio for 20-40 minutes.
- Lift then do loaded energy systems work. Here you'd do sets lasting 30-60 seconds on the farmer's walk, Prowler pushing, rowing ergometer or Assault Bike for example. Do 6-8 sets with a 1:1 work to rest ratio.