@jamierite74 My couple of cents:
- If you use any cardio device like an elliptical machine that counts calories then you can conveniently progress by burning a little more calories each session. Good autoregulation because it's agnostic to intensity; HIIT one day and high/low-intensity steady state the next are fully comparable for progression. Also, different devices or modalities as long as you can keep track of burned calories. Impatience also works in my favor for once, as I got to up the intensity to finish faster.
- Shortening rest breaks between sets is an investment. The negative effect of short breaks on hypertrophy is nullified by being conditioned to short breaks,
according to studies. It's an investment because it allows for (maintaining intensity over) higher volume in the same session, or for cashing out the investment in shorter sessions; good for adherence.
- Circuits maximize local muscle recovery for the rest taken between sets, which allows shorter breaks, which allows more systemic conditioning with a relatively smaller impact on performance. For example, instead of: Bench press > two min rest > bench press, I do (with the same bar) bench press > one min rest > BB row > one minute rest > bench press, etc. Even though the rest time between sets is half, there is more rest time on the level of the muscle. Other circuits I really like are: pull-ups > recover breath> dips > recover breath > pull-ups etc, and the super enjoyable ez-bar curl > recover > ez-bar overhead shoulder press > recover > ez-bar overhead triceps extensions, etc. I circuit exercises that I can use the same bar and load for while being within the 5-15 rep range.