Mechanical demand and multijoint control during landing depend on orientation of the body segments relative to the reaction force
Introduction
Multijoint control of moments induced by large reaction and intersegmental forces experienced during landing presents a significant challenge to the neuromuscular system prior to and during contact with the supporting surface. The neuromuscular system prepares for the impending load after foot contact by activating muscles prior to contact (McKinley and Pedotti, 1992; Sidaway et al., 1989). After contact, the muscle tendon units must generate sufficient force to stabilize the joints, control joint flexion, and reduce total body momentum. The set of muscles an individual chooses to control the reaction force will likely influence the mechanical loading experienced by the lower extremity during the landing and their ability to modify control, if perturbed.
Landings of gymnastics elements performed by the same gymnast provide a set of practised, goal directed multijoint movements that allow us to examine the influence of diverse initial momentum conditions on multijoint strategies individuals use to control the reaction force after contact. The mechanical objective of these landings is to reduce the total body momentum to zero at contact with a single placement of the feet. This requires the foot to be positioned beyond the TBCM in the direction of travel so that adequate impulse can be generated during the landing phase. Failure to achieve this mechanical objective during competition results in a reduction in performance score that often influences the outcome of the competition (McNitt-Gray, 1992).
Although the mechanical objective of gymnastics landings is the same at the total body level, we hypothesized that the mechanical demand imposed on the lower extremity would be significantly different between landings that require initial foot positions anterior (e.g. front salto landing) or posterior (e.g. back salto landing) relative to the TBCM. We anticipated that ankle plantar flexor net joint moments (NJM) would be needed to control the toe-heel foot contact pattern common to all gymnastics landings. However, we expected that the direction of the knee and hip NJMs would be different between tasks because of between task differences in segment angles and reaction force direction. We anticipated that gymnasts would use a common impedance-like control strategy (Hogan, 1984) to provide adequate joint stability and satisfy the NJM demand during this period of high loading. However, we also hypothesized that lower extremity muscle activation would scale to accommodate for between task differences in mechanical demand. We expected that biarticular muscles would actively contribute to knee and hip net joint moments (Prilutsky, 2000), particularly during the impact phase when knee and hip NJMs act in opposite directions (McNitt-Gray, 1993).
Section snippets
Methods
Six male collegiate gymnasts volunteered to participate in accordance with the Institutional Review Board. The gymnasts were currently competing on a competitive team placed in the top five of all collegiate teams within the United States. The mean height of the gymnasts was 164 cm (±6 cm) and the mean weight was 597.5 N (±57.7 N).
The gymnasts were asked to land three tasks (DROP, FRONT, BACK) without taking a step or hop as commonly done during competition. DROP landings were initiated by stepping
Results
Successful performance of all the three landing tasks required the gymnasts to initiate contact with the feet positioned beyond the TBCM in the direction of travel so that adequate linear and angular impulse could be generated during the landing phase. Significantly greater angular orientation of the R angle position vector, from the center of pressure to the TBCM (R angle), were observed at contact for the FRONT as compared to the DROP and BACK landings (Fig. 1). Achievement of this narrow
Discussion
Landings are complex multidegrees of freedom tasks involving impact. Identification of control strategies implemented during landings performed under diverse initial conditions has revealed how affordances and restrictions imposed by the task and orientation of the physical plant may influence motor behavior and mechanical loading.
In this study, competition style landings of drop jumps, front saltos, and back saltos were performed by male collegiate gymnasts from a platform onto landing mats.
Acknowledgments
This project was funded in part by the United States Olympic Committee, USA Gymnastics, Carolina Gym Supply, American Athletics, Inc., Speith, and Intel.
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2023, Human Movement ScienceCitation Excerpt :Shifts in relative contributions of the knee and hip NJMs involved in controlling the lower extremity during impulse generation serve as a mechanism to redirect the RF (van Ingen Schenau et al., 1992), reorient the CoM via controlling trunk motion (Mathiyakom et al., 2005), and control the relative orientation between the CoM and RF (Mathiyakom, McNitt-Gray, & Wilcox, 2006a,b; Mathiyakom et al., 2021; McNitt-Gray et al., 2001;Mathiyakom & McNitt-Gray, 2008; Pijnappels et al., 2004, 2005). These results are consistent with previous studies demonstrating that segment orientation, the magnitude and orientation of the RF relative to the segment, and the adjacent NJMs are the primary determinants affecting the NJMs (Mathiyakom, McNitt-Gray, & Wilcox, 2006a,b; Mathiyakom et al., 2021; McNitt-Gray et al., 2001; Pijnappels et al., 2004, 2005; Mathiyakom & McNitt-Gray, 2008). Interestingly, the oscillation of NJMs during the impact interval followed by a more sustained NJMs during the push interval, as observed in this study, were also similar to those observed during the impact and post-impact phase of landing tasks (McNitt-Gray et al., 2001) and initial contact of the stepping leg during fall-recovery tasks (Pijnappels et al., 2004, 2005; Mathiyakom & McNitt-Gray, 2008).
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