Changes in Impact Signals and Muscle Activity in Response to Different Shoe and Landing Conditions

Abstract

Few rigorous scientific studies have investigated how the corresponding neuromuscular activity in the lower extremity occurs during different landing control movements in response to different impact signals. This study aimed to determine the potential shoe effects on impact signals, neuromuscular responses and their possible interactions in different human landing movements. Twelve male basketball players were required to wear high-cushioned basketball shoes (BS) and minimally cushioned control shoes (CC) to perform active drop jump landings (DJL) and passive landings (PL). Ground reaction forces and EMG amplitude (root mean square, EMGRMS) of the leg muscles within 50 ms before and after the landing movements were collected simultaneously. No shoe effect was found on the characteristics of impact signals and neuromuscular activity during the contact phase of DJL. By contrast, for PL, the values of maximal ground reaction force and the peak loading rate were evidently lower in the BS condition than in the CC condition (p < 0.05). Meanwhile, the EMGRMS of all muscles demonstrated a significant decrease in the BS condition compared with the CC condition within 50 ms after contact (p < 0.05). These findings suggest that under the condition in which related muscles are activated improperly, a neuromuscular adaptation occurs in response to different impact signals. Key words: vertical ground reaction force; EMG amplitude; drop landing. IntroductionDuring two-footed landings from vertical jumps, the peak magnitude of vertical reaction forces has been found to range from 3.5 to 6 times BW (Gross and Nelson, 1988). Previous investigations reported a close relationship between the great shock in strenuous landings and lower-limb injuries, that is, repetitive excessive loading can induce acute injuries (Beynnon et al., 2005;McNitt-Gray, 1993) and overuse damages (Agel et al., 2007;Borowski et al., 2008). Thus, to prevent sports injuries in athletic activities, footwear manufacturers have been focusing on designing shoes that can attenuate a shock wave, and thus the concept of cushioning has been widely used since the 1970s (Clarke et al., 1983).Current investigations into impact forces have focused not only on the magnitude, timing and the loading rate, but also on the reactions and muscular responses of the musculoskeletal system (Brüggemann et al., 2011). A series of concepts about the effects of impacts has been provided during the past ten years (Boyer and Nigg, 2007;Nigg and Wakeling, 2001). Impacts are regarded as input signals into the human locomotor system, which produce a shock wave and meantime initiate the vibrations of lower extremity soft tissues. These signals are sensed and the central nervous system responds by adjusting, if necessary, the activation of the relevant major muscle groups (Nigg and Wakeling, 2001 (Frederick and Hagy, 1986;Hamill et al., 1983), different lower limb postures (Derrick et al., 2002), and/or the hardness (or material) of the shoe midsole (Clarke et al., 1983). Theoretically, dif...

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