Assuming your current goal right now is to simply get better and get out of this chronic fatigue funk you’re experiencing, your best bet is probably a training frequency of 2-3x/week.
There are multiple splits you could use for this purpose but the best ones imo would be:
Full body: you don’t really have a choice here because you’re only training 2x/week. If your recovery is really bad and you feel like shit all the time, then simply go with the minimalist plan from CT. One upper body and one lower body compound exercise done for 3-4 sets of 6-8 with plenty of rest in between sets (something like to 3-4 minutes). If you want to reduce neurological stress even further you could pick compound movements on machines or in the smith machine that reduce the need for stability. When you start to feel better you could add 2 isolation exercises to these workouts for lagging muscles or vanity muscles for 3 sets of 8-12.
Option 1: upper/lower (2x upper, 1x lower body because lower body sessions are usually more demanding from a recovery perspective). Pick one main lift per workout done for 3-4 sets of 6-8, the assistance work should be minimal and low stress (machines and cables). 2-3 exercises for assistance work done for 2-3 sets each for 8-12 reps should be sufficient. Take full rest in between sets. 3-4 minutes for compound movements, 2 minutes for isolation movements.
Option 2: modified push/pull split. This is a modified full body workout where you train your push muscles (quads, pecs, front delts, triceps) on one day and your pull muscles (calves, hamstrings, glutes, lower/upper back, rear delts, biceps) on the other day. Do 1 lower body exercise per workout, the other 2-3 exercises are upper body. One compound exercise for lower/upper body, rest is isolation work. Use the same training variables as mentioned in option one (so sets, reps and rest).
Remember, the purpose of these workouts is simply to maintain your current physique while trying to get out of this fatigued state. It’s all about managing cortisol and adrenaline output.
So you want your workouts to be effective but with the least amount of work/stress possible. Therefore there are a few principles you should respect in your training:
Always leave reps in the tank and never go to failure: 2-3 reps in reserve on the compound movements, 1-2 reps in reserve on the isolation movements. Again, the goal is to maintain your current physique and manage fatigue.
Take full rest in between sets: 3-4 minutes for compound movements, 2 minutes for isolation movements.
Don’t do more than 4 weekly workouts and really, stick with 3. Also, train every other day (one day one, one day off) or even every 2 days (one day on, two days off). This is your best option to manage fatigue, optimize recovery and maintain your physique/strength (it might drop a bit but don’t get discouraged, it will come back quickly once you start training hard again).
Keep volume on the lower side as this variable tends to impact cortisol output the most. Somewhere between 10-15 sets is all you need to maintain.
No intensity techniques whatsoever… NONE. Just simple straight sets.
Spend more time on building up your cardiovascular system. Better conditioning improves lactic acid removal, work capacity, mitochondrial density, blood flow and favorable nutrient partitioning. All these physiological adaptations are highly beneficial when you’re suffering from chronic fatigue. Just make sure to keep your sessions short and sweet. Something like 20-30 minutes at a heart rate of 70-80% done 2-3x/week (ideally on off days) is more than enough.
Spend more time on daily walking (ideally in green environments like forests and fields) and active mobility drills like short yoga sessions for example to increase activity of your parasympathetic nervous system and improve recovery even further.
Twice a day training is not something I would recommend in this context. You likely won’t get enough of a stimulus from your training. You could give it a go if it makes you feel better and if you have the time do to it.
Again, recovering from chronic fatigue is all about minimizing work done in the weight room and maximizing recovery outside of it. So really, prioritize good habits like sleep hygiene, daily walks, stretching/yoga/mindfulness protocols, eating quality nutrition (fruits, vegetables, potatoes, lean meats, herbs&spices, wild foods like berries/maple syrup/raw honey), healthy fats like nuts, olive oil, avocados to get all your macro’s, vitamins, minerals, phytonutrients and water to maximize recovery and neutralize inflammation (too much adrenaline from chronically elevated cortisol is inflammatory).
Eat carbs and focus on foods and supplements that elevate your serotonin/gaba levels. I’m not going to repeat these, just visit my profile and look up previous answers I gave on this topic.
Depending on how severe your chronic fatigue is, you might need to cut back on training for 4-8 weeks to really allow yourself to recover. When recovery has improved significantly, slowly build up your tolerance to training. Don’t rush the process or you’ll end up in the hole again.
I’m sorry to intervene if your question was adressed to @Christian_Thibaudeau. I wanted to share my insights because having suffered from chronic fatigue myself, this topic is close to my heart.