1.) Initial Momentum Phase IIMP): This first phase is known as the Initial Momentum Phase (IMP), where the body is moving due to previously created kinetic energy, accumulated from a preceding action. This could be a jump of some sort, a run, sprint, or a drop of some kind. If we do not have this phase, the movement as a whole cannot be considered plyometric.
2.) Pre-Activation Phase (PaP): Due to profound research around the area, the IMP could also include a pre-activation/anticipation phase (PaP) of the lower legs just prior to landing. PaP has been found to bring about generalised muscle stiffness and research suggests that in some cases the lower extremity musculature may be 40-80% activated at the time that the foot touches the ground (Hewett et al, 2005; Nigg and Wakeling, 2001). This anticipation in the body comes from wanting to hit the ground actively, so that tissue structures are ready to withstand high levels of force.
3.) Electromechanical Delay Phase (EDP): The EDP is based on how long it takes for the brain to register and understand force. It initiates electrical signals sent to begin mechanical contraction in a muscle when we first come into contact with the ground. Some may define this phase to include the lengthening of the series elastic component (SEC). There is also an intricate relationship between the PaP and EDPhase. If there is an effective pre-activation prior to landing, the delay may not be as prominent.
4.) Amortization Phase (AP): The Amortisation Phase (AP) is the momentary isometric contraction that bridges the coupling effect of the eccentric and concentric phases. This isometric contraction transitions kinetic energy into high levels of tonic (static) muscular tension, through into the concentric contraction. The AP is where the individual has to deal with the highest levels of force, as the body has to slow down the lengthening process by breaking and transitioning into the shortening phase. The initial ideas around a GCT threshold of <0.25s originated from Verkhoshansky, suggesting that the AP must be completed in under 0.15s for a movement to be considered plyometric. Due to the difficulties of measuring this, whole GCT are taken to categorize movements.
5.) Rebound Phase (RP): This phase marks the release of elastic energy from the SEC, together with the involuntary concentric muscle contraction. This is the result/response of the previous phases and the subsequent final concentric ‘push’ that enables us to get off the ground – and to produce the desired movement.
6.) Final Momentum Phase (FMP): When the concentric contraction is complete, and the body continues to move by means of kinetic energy from the Rebound Phase. This phase will then restart the cycle in preparation for the next movement. This is the resultant airborne phase which is influenced by the preceding phases and in particular, the EDP.
The Plyometric Landing Sequence should be your go to model for determining whether a movement is plyometric or not.
This may seem arbitrary or simplistic, but the model can further provide clarity to categorising movements and importantly understanding what’s happening during airtime phases and grounded phases.
A deeper understanding of the model can then help you indicate which phases may be hampering performance, to then remedy any issues and/or improve upon.
Reference List:
- Gehri, D., Ricard, M., Kleiner, D. and Kirkendall, D. (1998). A Comparison of Plyometric Training Techniques for Improving Vertical Jump Ability and Energy Production. The Journal of Strength and Conditioning Research, 12(2), p.85.
- Verkhoshansky, Y. and Siff, M. (2009). Supertraining. Rome, Italy: Verkhoshansky.
