Every workout is usually four exercises, with three sets per exercise, with each set done to failure. So for example, day 1 would be leg extensions, leg presses, single-leg calf raises, and inclined sit-ups. Rest between sets of the same exercise is minimal, (in the area of 10 - 20 seconds). Then after an exercise is over, I'll rest a minute or two and set up the next exercise. And that's it. It's a get-in-and-get-out kind of workout.
That's a goodly amount but not unreasonable. (Although in direct contradiction to HIT orthodoxy!) Are you keeping track of any key variables (strength, size) as you modify your routine from time to time? If so it would be interesting to hear of any changes from time to time.
These days I focus way more on staying on top of my diet than tracking the progress metrics of the exercise routine. It's just way too easy to derail yourself by screwing up your diet than it is to derail yourself because of the differences between one exercise routine vs. another. And I guess that makes sense because your diet is something you have to wrestle with every moment you're awake, but exercise is only something you need to do in small time intervals periodically throughout the week.
The biggest improvement to my health I think has been in the way of my meditation. I meditate 30 min in the morning and at night. My mediation has transitioned from a place of mindfulness/concentration on a mantra to scanning my body for illnesses/ pain/ emotions and the overall health of the nervous system. I try to make my body be in the para sympathetic state as much as I can. I’ve seen my sex drive increase, sleep better and just overall sense of feeling healthy.
I have to admit, I often (always?) have difficulty with meditation, especially now, since I have stuff going on (which is probably the best time to do it!). I can, however, engage in periodic breathing exercises, where the exhale is longer than the inhale, such as Weil's 4-7-8 method. This also aids in the relaxation response. You work with what you can, eh?
Just as an afterthought, since you have been workout out for years, and to failure on each set, have you ever considered reducing your frequency, at least per muscle group per week? You're younger than I am, of course, but have you never started feeling burned out with your frequency?
When I first started like 3 years ago I lasted 1 minute meditating, then I did 5 and grew from there over time. Now I'm able to mediate for 1-2 hours if I had the time. Just sit there and let your thoughts flow through and concentrate on the breath and your third eye. You don't need to blank your mind just when you start attaching to your thoughts bring it back to the breathe and over time it will just become easier to do. "Mediation as Medicine" is a great read an talks about how breathe, sound vibration etc can help with your health by manipulating the endocrine system which releases hormones and peptides.
I've felt burned out before but usually when I start to feel that way, the best course of action for me has been to just take a week off and do nothing. I was really pushing things hard right up until my 50th birthday because I knew I was going to be gone for a week in the Bahamas. But having that week off without worrying about working out was just so relaxing and enjoyable. And I had plenty of friends with me that made the trip even more worthwhile. So far I'm really liking this over 50 life. Why didn't you guys tell me it was going to be like this?