The plank progression works these muscles isometrically (where the length of the muscle worked does not change) whereas leg raises develop them both concentrically and eccentrically.
These progressions will ultimately lead to such exercises as the dragon flag (a favourite of Bruce Lee), the hanging dragon flag and –from gymnastics- floor L-holds.
Unless otherwise indicated, you should be aiming to complete 6 sets of 6 repetitions of the given exercise within a workout.
The first set is a warm up set: go back two or three levels in the progression and perform that variation for 6 reps.
Perform each following set ‘to failure’ (e.g. 6,6,5,5,4).
In each new workout, you should aim to improve on the number of reps you performed previously by at least 1, e.g.: (6,6,5,5,4) → (6,6,6,5,4)
Once you manage 6 sets of 6 reps, you are ready to move on to the next variation in the progression.
If you find yourself not progressing any longer, take a few rest days, then resume training.
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