| Objective: During running, jumping and other human movements, lower limb exposure to passive impact can affect on human muscle - skeletal system, but that does not mean the impact force is the fundamental causes of sports injuries. Recent studies have shown that the resonance which is created by the overlapped frequency between that of impact forces (10-20Hz) and the natural frequency of soft tissues (5-65Hz) is an essential cause for soft tissue injury. In this study, drop jumps and passive landings which are two common ways were selected as target movements. The aim of this study was to explore the effect of basketball shoes and compression shorts on impact forces, soft tissue vibrations, muscle activity, and their possible interactions during active landing (drop jump, DJ) and passive landing (PL). Including: (1) to discuss the basic biomechanical characteristics and exercise performance by wearing two different sports equipments during two landing activities. (2) to compare the influence of different shoes (amplitude, time-frequency domain features) and lower limb soft tissue characteristics (amplitude, frequency and damping characteristics of the time) effects, and the corresponding muscle's response (pre- activataion and post- activation and co-activation, etc.), we can further quantify the impact of sports shoes for the response and thus affect the lower limb muscle function. (3) to compare the effect of compression shorts on impact, muscle activation, mechanical properties (frequency, damping, etc.) of soft tissues in lower limb and changes in transfer characteristics of vibration. We also determined the interrelationship between compression apparel and adaptation function of muscle, in order to further comprehend the internal mechanisms for reducing energy consumption, affecting muscle fatigue and ultimately improving the performance by wearing compression equipments.Methods: 12 male professional athletes specialized in physical education were selected as subjects. A well-known international brand of basketball shoe was chosen in the testing with strong cushion capacity of shoes. Shoe in control condition (CC) was also arranged. Compression shorts (CS), the products under a well-known international brand, were elected as test equipments, and were also given corresponding control group. Each subject was required to stand on a custom-made device with adjustable height to complete two kinds of drop landings (drop jump and passive landing) from three heights (30 cm, 45 cm and 60 cm). Infrared camera capture system (Vicon, UK), force platform (Kistler, Switzerland), the acceleration signal analysis system (Biovision, Germany), EMG signal analysis system (Biovision), and high-speed camera system (Motion Pro X-4, USA) were synchronously to collected kinematics / dynamics of lower extremity (hip, knee, ankle), impact characteristics (ground reaction force), soft tissue acceleration signal (and the femoral quadriceps muscles), and EMG signals of major muscle groups (tibialis anterior: TA, gastrocnemius lateral head: LG, rectus femoris: RF, vastus lateralis: VL and biceps femoris: BF). Visual3D, DASYLab and other signal analysis software were also applied to process and analyse data.Results: (1) Joint kinematics/dynamics: Ankle angle in Bball group and hip angle in CS group were significantly larger than that of CC during the instantaneous moment of touchdown in DJ; minimum / maximum angle of ankle one in Bball group and hip one in CS showed an obvious increase during DJ from 45 cm and 60cm, and the minimum angle velocity of both ankle and hip joint decreased. However, neither Bball nor CS took effects on takeoff velocity and jump heights during DJs. In addition, no significant changes were found in joint torque, maximum power and stiffness of joints while wearing compression shorts and basketball shoes. (2) Characteristics of impact forces: during DJ, peak impact, maximum load rate and impact frequency were not be influenced by basketball shoes. However, during PL from all heights-30cm, 45cm and 60cm, wearing basketball shoes can significantly reduce the peak impact force, the maximum load rate, input frequency and frequency of the acceleration in heel (fGRF and fshoe). Meanwhile, compared with the CC, the effect of height on impact frequency of Bball group is relatively smaller. (3) Characteristics of soft tissue vibration: a significant decrease of maximum amplitude and vibration damping by wearing compression shorts was found in both landing styles. During DJ60, the resonant frequencies of hamstring muscles in CS condition were significantly greater than those in CC. For DJ45, DJ60, and PL60, the resonance transmissibility (Hmax) of both quadriceps femoris and hamstring muscles in CS condition was significantly lower than that in CC. (4) features of muscle activities: whether in pre-activation or post-activation periods, activation of the muscles in lower limb during PL was obviously less than that in DJ situation from the same drop height. During DJ, a significant decrease in EMG pre- / post-activation, as well as median frequency (MF) of the RF, VL, and BF was found in the CS condition. Meanwhile, a significant decrease in EMG post-activation of TA, LG, as well as RF and BF under certain drop heights was found in the Bball condition. Wearing basketball shoes also showed an influence on the MF of the VL, LG and RF during both pre- and post-activation.Conclusion: (1) Wearing basketball shoes and compression shorts can change partial kinematics results (touchdown angle, the maximum/minimum angle, etc.) of lower extremity joints during drop jumps. However, no significant differences were found in the strength output parameters, such as the variation of moment, stiffness, power output, and rebound height. (2) During active DJs, characteristic parameters of impact force can't be significantly changed by the intervention of basketball shoes; while in condition of passive landing (PL), wearing basketball shoes can remarkably reduce the peak of impact, loading rate, acceleration and impact frequency, in addition, can minimize the effect of height on characteristic parameters of impact force. Reminder: we can highlight the essentiality of basketball shoes when people can't control the motion of landing completely (or minor). In other words, wearing basketball shoes can alter signal features of soft tissue in lower limbs when exert the functions of buffering and anti-vibration. And with basketball shoes, we can also decline the transmissibility to keep the soft tissue away from the region of resonance. By doing this, effects, like reduced vibration, which should be achieved with extra muscle activations could be realized. (3) The intervention of compression shorts showed a significant decrease in vibration amplitude of quadriceps femoris and hamstring muscles, but an increase in damping factors of them. Compared with changing the frequency of vibration system, wearing compression shorts can affect vibration characteristics of soft-tissue via reducing the resonance of system which can also avoid the resonance between repetitive impacts and lower extremity in more cases, what's more, benefit muscle pre- / post-activation, in order to bring in a positive effect on energy consumption, comfort and prevention of sports injuries. |
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