I am not aware of any studies that mention the strict planche, front lever, or any other advanced calisthenic movement. If anybody is, please share it, I would love to read it. Studies typically focus on regular resistance training such as bench, squat, and deadlift numbers. All we can do for now is try to draw conclusions from data that looks relevant.
How can I structure a training program aimed at hypertrophy using calisthenics skills such as planche and front lever?
How to maximize hypertrophy: The most recent research suggests that volume is the most important factor for muscle growth in the gym. The classic 1-3 reps for strength and 8-12 for hypertrophy seems to be falling apart as more rep ranges seem to be producing the same results. A 2019 meta analysis states:
The American College of Sports Medicine (ACSM) recommends 1−3 sets per exercise of 8−12 repetitions with 70−85% of one repetition maximum (1RM) for novice and 3−6 sets of 1−12 repetitions with 70−100% 1RM for advanced individuals [13]. However, the recent literature shows a much wider range of training options. Several studies have found that training with low-loads (30−60% 1RM) results in similar hypertrophy to training with moderate and high-loads (>60% 1RM) when volitional fatigue occurs [11,14,15,16]. Moreover, reaching volitional fatigue at all times is not necessary to make significant gains in hypertrophy [17], especially when training with high-loads is considered [18]. Evidence indicates that significant muscle growth occurs when the majority of training sets are performed with ~3–4 repetitions in reserve (with moderate to high-loads) [19].
It concluded:
In summary, foundations for individuals seeking to maximize muscle growth should be hypertrophy-oriented RT consisting of multiple sets (3−6) of six to 12 repetitions with short rest intervals (60 s) and moderate intensity of effort (60−80% 1RM) with subsequent increases in training volume (12–28 sets/muscle/week) [20].
Meta analysis after meta analysis say the same thing over and over. More volume is one of the main driving factors behind hypertrophy. So how much volume is actually optimal? A general range that I am seeing is 6-8 sets per muscle group, per session is the max you would want. This varies greatly by person though, so you need to find your own volume ceiling through trial and error. Most studies say somewhere in the range of 12-18 sets per week per muscle group is ideal. So you could hit each muscle group 3x a week with 4-6 sets with something like a full body split 3 days a week. Or hit each muscle group 2x of 6-8 sets if you were doing 4-6 days a week in a push pull legs split.
Something I learned while researching this, is that going to failure might not be the best idea either. If you know how many reps in reserve you have, it might be best to stop a couple early. Nearly the same results in muscle mass, but the last two reps were disproportionately fatiguing.
Thus, it seems that as long as RT is carried to a point of significant fatigue (likely only 1 to 2 repetitions shy of failure), increases in muscle activation and mass will be similar to those of RT performed to failure.
This studies results draws my mind to greasing the groove.
Applying This Data to Calisthenics
Splits: Working out the same muscle group multiple times a week makes it easier to reach your weekly volume. Since the movements you are performing are highly taxing, I would recommend, in this order, a push pull legs split 6 days a week, a push pull with legs split between the two for 4 times per week, or full body 2-3 times per week. Just make sure that you have 48 hours between working the same muscle group. Calisthenics is very upper body heavy, so this might be a bit tricky, but at the end of the day listen to your body and you should be fine. Rest if you need it.
Movements: You should start with the hardest movements first, or whatever you want to train specifically while you are fresh. After you are unable to perform those with good technique, move down to the progressions or use bands and strengthen those fundamentals. Perhaps something like straddle planche for 1-2 sets of 4 seconds. Then progressively use a heavier and heavier band on your feet for your last sets so you can maintain the proper form and still get your volume in. One of the big problems with training exclusively calisthenics is that it is hard to progressively overload, and bands and weight vests are perfect for this. If you feel like ascending to another level, try ankle weights on the planche or lever.
I identify myself as an beginner/intermediate in calisthenics skills.
Because there is such a small community it is often hard to measure where we are. The skills you say you have are quite advanced and only a small percentage of people who train calisthenics can do planche or the front lever. A redditor attempted to figure out some averages roughly a year ago. Even in the group with the biggest advantage (short males), there were still only 4% claiming to be able to do the planche increasing to about 8% if you include straddle planche and 12% for the front lever. Keep in mind these numbers are likely inflated due to people claiming they can do movements they cannot, and only basic filtering was performed, so take this data with a grain of salt.
A final note, all the exercise in the world is irrelevant without the proper diet and sleep.