1: SAID Principle and Progressive Overload

The fundamental principles of any form of physiological training are SAID and progressive overloading.

SAID: Specific Adaptation to Imposed Demands

Progressive Overload: Gradually increasing stress upon muscles

Essentially, if you want to improve your strength and increase muscular hypertrophy safely, you have to progressively increase the weight. With barbells this is simple. However, for bodyweight exercises, the key lies within the leverage.

2: Leverage

In calisthenics, progressive overload is achieved through decreasing leverage (the mechanical advantage that a muscle has). Decreasing the leverage can be achieved through two methods:

1 - Changing the body position

Both the planche and front lever have changes in body position that make the exercise more difficult. Some of the planche progressions are shown down below:

As the body is extended - from the tuck position to the straddle position, to the straight body position -  the exercise becomes progressively harder. The muscles apply forces to the bones (lever) that rotate around the joints (fulcrums) to move weight against gravity.

In the case of the planche progression above, the center of mass of the body is shifted further away from the shoulder, straightening the body. This increases the torque on the shoulder, which is the force applied around an axis of rotation. In physics, Torque = Force * Distance. Thus, moving the center of mass away from the shoulder will increase the torque. Since our bodies are built on these leverage methods, all forces on the muscles can be thought of in terms of torque on the muscles at certain joint angles. This is the basis of biomechanics.

2 - Changing the muscle length

Muscles are the strongest at their resting length because that is the point where the maximum number of cross-bridges can be formed. Basically, a cross-bridge is formed when the contractile components of a muscle - myosin and actin - overlap, and the myosin mechanically pulls against the actin, which contracts the muscle.

For instance, pull-ups are a prime example to show why it is crucial to complete exercises with a full range of motion. There are many people on the internet who are not utilizing the full range of motion; they barely get their chin over the bar and they do not fully reach a straight-arm hang position at the completion of the movement. The reason why people shorten the range of motion is because the exercise often becomes more difficult at the edges of the range of the exercise (due to the decrease in strength of the muscle whilst not in resting length caused by less myosin - actin overlap). Hence, shortening the range of motion allows them to perform more repetitions, which appears more impressive. However, there is some truth to the notion that people who shorten the range of motion are cheating themselves out of the full benefit of performance, strength, and hypertrophy.

3: Common Training Concepts

I suppose you know the first three if you've come here.

• Repetitions (Reps)
• Sets
• Rests
• Tempo: The speed at which you execute repetitions. This may influence strength and hypertrophy. Typically, the tempo is referred to in an XXXX format such as 3010. Each "X" is a number of seconds per phase of the exercise.
  - First X - Seconds in the initial movement, i.e. eccentric phase where the muscle lengthens;
  - Second X - Seconds held at the terminal position;
  - Third X - Seconds in the counter movement, i.e. concentric phase where the muscle shortens;
  - Fourth X- Seconds held at the initial position before the next repetition.

• Intensity/Load: It is the amount of physical power (expressed as a percentage of the maximal oxygen consumption) that the body uses when performing an activity. Essentially, it's the difficulty of the exercise. (read more about intensity on: https://en.wikipedia.org/wiki/Exercise_intensity, for scientific articles I wouldn't recommend Wikipedia, but it gives a very nice overview of the subject matter.)
• Volume: Total amount of exercises performed in a workout. Usually calculated as Reps * Sets * Weight = Volume
• Frequency: How often an exercise or a workout is performed.
• Attribute: A particular quality that is being trained. The main three attributes are strength, hypertrophy, and endurance.
• Failure: The point at which you cannot perform another repetition with good form.
• Deload: A planned period where various factors of a routine are reduced in order to give the body time to recover and increase strength, hypertrophy, endurance or other attributes.
• Plateau: A stagnation or a plateau in progress is when an athlete on a specific routine has stopped improving performance - in any of the above-mentioned or other attributes.

4: The Repetition Continuum

There are two ends of the spectrum. One end is strength, the other is endurance. Low reps, higher intensity or higher weight leads to strength. Whereas endurance is attained through higher reps and lower intensity or lower weight.

1. Strength and endurance can't be developed equally proficiently at the same time since they require different training regimens.
2. Developing maximal strength increases the potential for maximum endurance. The way strength modulates endurance is through greater efficiency in the contraction of the muscles. For example, fatigue occurs much more slowly in endurance runners if they've increased strength because they are using a lower percentage of their strength with each stride.
3. Strength takes longer to develop than endurance and conditioning.

Therefore, in order to succeed in strength-biased sports, one should prioritize strength training. Whereas, for endurance sports, one should simultaneously train strength and endurance.

Generally, an 80/20 split is good enough. If you want to prioritize one side, train that side 80% of the time (or of the intensity) and train the other side 20%. For strength athletes; 4 strength, 1 endurance workouts, and vice versa for endurance athletes.