Key point for hitting and maintaining 6% bodyfat at 42 with increased energy and recovery? Timing is everything. Do your first workout immediately after waking. Then, break fast. Usually you want to do a bodyweight workout in the morning which focuses on mobility, compensation and (muscle) activation to throw on all the neurological switches for the day, get a little bit sweaty to increase the metabolic furnace. Then, do another session but weighted, late afternoon, and within about an hour, eat your meal. (I eat a full meal every 2-4 hours.)
You have a catabolic window to take advantage of in the morning workout which will upshift your metabolism to burn fat all day, if you hit it before eating in the morning. And you have an anabolic window of about an hour after your heavy workouts to eat all of your protein (and your carb and fat to convert the protein) to capitalize on the greatest muscle density increases. (Food quality has a heavy impact here, too.)
Both sessions should be around 20-40 min long, no shorter, and above 40 is bonus UNLESS it requires you to take a day off due to delayed muscle soreness, then it’s too much. Most people won’t commit two half hour sessions, so as a guideline, the morning session is more important, as it’s the recovery, but for those who are my age and offsetting aging’s muscle loss, every 3-4 days, add a weighted afternoon workout.
This approach was critical to how I moved from 15% to 6%BF and sustain it with zero adverse affects, and actual energy increases. I feel lighter, more vibrant, quicker and more responsive, more alert, less stressed, and able to concentrate all day long without fatigue. Optimizing my ability to do my writing and home improvement projects was one of the best side effects of effective meal-to-workout timing.
I’ve been training the wave for a very long time, and have my food quality, meal structure, exercise protocol, compensation and mobility locked in tightly with my recovery from intensity. What may externally seem intense is no longer intense (RPE/HRmax) any longer, but that is because of the years of incremental progression I invested and the rearrangement of my lifestyle for optimization of my family quality time and my quality work productivity, which is the reason I train. Two a day training is no different than the wave, except as I had written, you’re adding a morning compensation/mobility session on the days you do intense conditioning or strength training. Remember you can add more recovery but not more work. My afternoon sessions are often low to moderate intensity, and only high every 3-7 days. It is no different than any of the TACFIT recommendations except for the meal timing.