@Christian_Thibaudeau thanks for the video, it’s quite well produced (and free above all).
The depth jump you show in the video goes against everything I’ve learn by either Yuri Verkhoshandky, his daughter Natalia answers on their forum, Michael Yessis work or the various study around real plyometrics / shock method.
You argue that the energy is stored for up to 2 seconds but that’s not what I found, if the reaction is not extremely quick the elastic energy stored in the tendons dissipate (0,2 seconds maximum I found in the litterature). Could you explain to me where you’ll find out that 2 seconds is actually the upper limit and link me up to the material that explain that mechanism please ?
This is based on a study showing the duration of the potentiation effect of the stretch reflex on performance.
I’m not gonna lie, I saw that study something like 15 years ago when I was working on my second book and I don’t have the reference on hand.
From memory, after 1 second, the potentiation from the stretch reflex was down by 50% and after 2 seconds there was no more potentiation effect.
I might try to dig up that study, but I honestly can’t guarantee you that I have the time to do it or will remember.
I want to mention that the plyometric effect lasts 100 - 200ms only. The storage of potential energy in the muscle/tendon can last longer BUT it then is used to help with voluntary muscle contraction NOT create a plyometric contraction.
I’ll give you an example, doing depth jumps on a hard surface or a soft surface (e.g. grass or a rubber/gymnastic mat) will have a different effect. Depth jumps on a hard surface will favor the plyometric effect (or a reactive force production due to reflex actions from the force absorption) whereas doing it on a soft surface will shift the effort more toward voluntary contraction by the muscles.
To paraphrase French national track and field coach Thierry Blancon (jumps team): “Hard surface jump training is plyometric, jump training on soft surface is strength training”.