Re: Tips to increase energy and endurance?
Everyone makes good points. But let me add my thoughts (and politely disagree on a couple of points...)
Everybody is different. You have to find what works for you.
Sustained duration makes a huge difference. In the hard labor world (a place I lived during my twenties and occasionally revisit with a home pro project), it is customary to take a break (morning/lunch/afternoon) every 2 hours (+/- 15 minutes) to give the muscles/system a chance to recharge otherwise you become exhausted mentally and physically - a dangerous and unproductive state that takes hours to recover from once it occurs. While a small snack and/or caffeine will help you get past glycogen depletion in a training session lasting longer than 2 hours, a 15 minute break (with snack or without) in the middle is actually better. I could write an entire post just about how training 2-3 hours with only a short 5 minute break is VERY counterproductive but I'll just note that in passing here. That is a very bad training paradigm in my experience of 35+ years of fitness training/labor. I've never seen evidence you can "train" this exhaustion effect away.
I actually don't think calories are that critical (except that small snack for a long training session). When I was a hard laborer, in the summer, I ate only two meals a day. Breakfast was a cup of black coffee. In the winter, I required 5 meals a day because the body burns tons of calories to stay warm. Regular daily vigorous exercise probably requires maybe 500 extra calories... A beer and a serving of chips or nuts after the workout. Done.
Good breathing technique can be critical. The intercostal muscles (ribcage) can become rapidly fatigued from constant hard chest breathing leading to poor oxygen intake and accelerating the body to the exhaustion state that requires sustained rest. Good diaphragmatic breathing is more sustainable over a long session of exercise and helps stave off exhaustion.
For a fit person, 20 - 25 hours of physical training per week doesn't seem that unsustainable to me if managed properly, although the body definitely needs time to acclimate to a hard routine.
Fundamentally, exercise should be invigorating - not exhausting. Properly balanced exercise should give you more energy and vigor - that is the benefit. I think you need to experiment to find the right balance that works for you. Maybe one less Aikido session - or only doing 1-2 hours on some days instead of 2-3 is what you need. And/or better diet. And/or more breaks. And/or improved breathing.