15/12/2021
PART 1
Bounding exercises such as these (hurdle and drop jumps) are widely used to train the so-called stretch shortening cycle. Because this term is often misinterpreted, exercises to improve this are performed incorrectly.
In a stretch shortening cycle (as in a hurdle jump and in sprinting) one can observe an eccentric moment (flexion) in the ankle, knee and hip just after landing. Followed by a concentric moment (extension of hip, knee, ankle) at take off. Many textbooks draw the conclusion that the muscles endure the same form of contraction as is observable from the outside. This is actually incorrect.
It doesn’t mean that the muscles also work in this way. In fact, in a good bound (single or double leg) the muscles do not lengthen and shorten, but the length change is due to the passive elements (PEC + SEC) in a muscle, which store and return elastic energy.
In order to move well elastically, this can only happen under certain conditions, the so-called constraints. Proper storage and return of elastic energy AT HIGH INTENSITY MOVEMENT is only possible:
1) when the muscle is in isometric state during the so called amortization phase, around its optimum length.
2) the time frame of storage and release is within a certain bandwidth (approx between 90-200 milliseconds).
If the contact time becomes longer, more energy will “get lost” in heat, and there comes a point where isometric-elastic movement is no longer possible. Muscles will work eccentric-concentrically. See video athlete 1 & 2.
This is also called a phase transition in movement. There is no relationship between the 2 as they require a fundamentally different motor organization. Transfers will therefore not or hardly occur between the 2 forms.
Potential negative effects should not be ignored either. More on this in part 2.
Video:
Poor ex*****on (athlete 1 & 2) to good ex*****on (athlete 3 & 4). Between 3 and 4 there is a phase transition.
