Neuromuscular Strategies in Stretch–Shortening Exercises with Increasing Drop Heights: The Role of Muscle Coactivation in Leg Stiffness and Power Propulsion

Abstract

When applying drop jump exercises, knowing the magnitude of the stimulus is fundamental to stabilize the leg joints and to generate movements with the highest power. The effects of different drop heights on leg muscles coactivation, leg stiffness and power propulsion were investigated in fifteen sport science students. Drop jumps from heights of 20, 30, 40, 50, and 60 cm in a random order were performed on a force platform. During each drop jump, the ground reaction force, knee angle displacement, and synchronized surface-electromyography root-mean-square (sEMGRMS) activity (vastus lateralis, VL; vastus medialis, VM; rectus femoris, RF; biceps femoris, BF; tibialis anterior, TA and lateral gastrocnemius, LG) were recorded. The coactivation in the pre-contact phase, between VL and BF, VM and BF as well as RF and BF, was dependent on the drop height (p < 0.01; effect size (ES) ranged from 0.45 to 0.90). Leg stiffness was dependent on the drop height (p < 0.001; ES = 0.27–0.28) and was modulated by the coactivation of VM–BF (p = 0.034) and RF–BF (p = 0.046) during the braking phase. Power propulsion was also dependent on the drop height (p < 0.001; ES = 0.34); however, it was primarily modulated by the coactivation of LG–TA during the braking phase (p = 0.002). The coactivation of thigh muscles explains leg stiffness adjustments at different drop heights. On the contrary, the coactivation of shank muscles is mostly responsible for the power propulsion.

Methodological considerations for determining the volume and intensity of drop jump training. A systematic, critical and prepositive review

“…According to this principle, the way the athlete performs the plyometric activity will determine the training effect (Walshe et al, 1998). Furthermore, the higher the FH, the higher -up to a certain limit -the levels of neuromuscular pre-activation (Taube et al, 2012;Di Giminiani et al, 2020), the higher the speed that can be achieved in the eccentric phase, and thus the higher the contractile potentiating mechanisms of the muscle spindles and the elastic energy contribution by the tendons (Flanagan and Comyns, 2008). These mechanisms also depend on the individual's strength level, associated with maintaining active stiffness during the movement.…”

“…Among the most classic exercises are the Depth Jump (DeJ) and the Drop Jump (DJ), where the athlete stands upright on a box, and keeps his hands on his hips, determines the starting leg, and then performs a free fall in order to provoke a high force against the ground and take off in the shortest possible time in the case of the DJ, but reach a greater jump height (JH) in the case of the DeJ (Clutch et al, 1983) The differences between these tasks are presented in appendix 1. During the free fall, the neuromuscular system prepares to counteract the effects of gravity, a phase in which neuromuscular pre-activation (Taube et al, 2012;Di Giminiani et al, 2020) and proprioceptive receptors which are integrated into the central nervous system (Taube et al, 2012) intervene to ensure an effective landing. The athlete then comes into contact with the ground, where the stretch-shortening cycle (SSC) takes place (Dietz et al, 1979;Schmidtbleicher and Haralambie, 1981;Horita et al, 2003;Turner and Jeffreys, 2010;Pedley et al, 2022).…”

Neuromuscular Characteristics of Unilateral and Bilateral Maximal Voluntary Isometric Contractions following ACL Reconstruction

“…The CI index between the knee extensors and the flexors was determined using the following equation [ 40 , 41 , 42 ]: where i is the sample number and n is the number of data samples in the interval. A lower EMGi is the minimum value of the muscle during electromyography, whereas a higher EMGi is the maximum value of the muscle.…”

Effects of plyometric training on different 8‐week training intensity distributions in well‐trained endurance runners

“…Plyometric exercise consists in a form of resistance training that emphasizes the loading of muscles during an eccentric muscle contraction, which is immediately (<0.2 s) followed by a rebound concentric contraction 7–9 . Typical exercises consist of hopping, skipping, jumping, and other movements' patterns; these have been shown to develop properties related to the stretch–shortening cycle function and the aforementioned neuromuscular adaptations 8,10 . The purpose of plyometrics is to reach maximum strength as fast as possible, hence increasing the power of subsequent movements by using the whole muscle tendon units and stretch reflex 11 .…”

“…[7][8][9] Typical exercises consist of hopping, skipping, jumping, and other movements' patterns; these have been shown to develop properties related to the stretch-shortening cycle function and the aforementioned neuromuscular adaptations. 8,10 The purpose of plyometrics is to reach maximum strength as fast as possible, hence increasing the power of subsequent movements by using the whole muscle tendon units and stretch reflex. 11 From a practical point of view, plyometric exercise must be done at maximum speeds since sub-maximal efforts will produce sub-maximal results.…”