Weijie Fu

Effects of local elastic compression on muscle strength, electromyographic, and mechanomyographic responses in the lower extremity

The purpose of this study was to investigate the effect of elastic compression on muscle strength, electromyographic (EMG), and mechanomyographic (MMG) responses of quadriceps femoris during isometric and isokinetic contractions. Twelve participants performed 5s isometric maximal voluntary contractions (MVC) and 25 consecutive and maximal isokinetic knee extensions at 60 and 300°/s with no (control, CC), medium (MC), and high (HC) compression applied to the muscle. The EMG and MMG signals were collected simultaneously with muscle isometric and isokinetic strength data. The results showed that the elevated compression did not improve peak torque, peak power, average power, total work, and regression of torque in the isometric and isokinetic contractions. However, the root mean squared value of EMG in both HC and MC significantly decreased compared with CC at 60 and 300°/s (p<0.01). Furthermore, the EMG mean power frequency in HC was significantly higher than that in CC at 60°/s (p<0.05) whereas no significant compression effect was found in the MMG mean power frequency. These findings provide preliminary evidence suggesting that the increase in local compression pressure may effectively increase muscle efficiency and this might be beneficial in reducing muscle fatigue during concentric isokinetic muscle contractions.

How Joint Torques Affect Hamstring Injury Risk in Sprinting Swing-Stance Transition

ABSTRACT Purpose The potential mechanisms of hamstring strain injuries in athletes are not well understood. The study, therefore, was aimed at understanding hamstring mechanics by studying loading conditions during maximum-effort overground sprinting. Methods Three-dimensional kinematics and ground reaction force data were collected from eight elite male sprinters sprinting at their maximum effort. Maximal isometric torques of the hip and knee were also collected. Data from the sprinting gait cycle were analyzed via an intersegmental dynamics approach, and the different joint torque components were calculated. Results During the initial stance phase, the ground reaction force passed anteriorly to the knee and hip, producing an extension torque at the knee and a flexion torque at the hip joint. Thus, the active muscle torque functioned to produce flexion torque at the knee and extension torque at the hip. The maximal muscle torque at the knee joint was 1.4 times the maximal isometric knee flexion torque. During the late swing phase, the muscle torque counterbalanced the motion-dependent torque and acted to flex the knee joint and extend the hip joint. The loading conditions on the hamstring muscles were similar to those of the initial stance phase. Conclusions During both the initial stance and late swing phases, the large passive torques at both the knee and hip joints acted to lengthen the hamstring muscles. The active muscle torques generated mainly by the hamstrings functioned to counteract those passive effects. As a result, during sprinting or high-speed locomotion, the hamstring muscles may be more susceptible to high risk of strain injury during these two phases.

Segment-interaction and its relevance to the control of movement during sprinting

The aims of this study were to investigate the functions of muscle torque and its relation to other torque components during sprinting stance and swing phases. Three-dimensional kinematics and ground reaction force data were collected from eight elite male sprinters performing maximal-effort sprinting on a synthetic track. Intersegmental dynamics approach (ISD) was used to quantify lower extremity joint torque and their components during one gait cycle of the maximal speed phase during sprinting. Specifically, a modified version of the ISD was used to determine the relationship among the active muscle torque (MST), passive motion-dependent torque (MDT), ground reaction torque (EXT), gravitational torque (GTT), and net joint torque (NET) during stance and swing phases. The contribution of each torque component to lower extremity joint motion was quantified. Our results revealed that the active MST functioned to counteract EXT during stance phase. EXT acted to accelerate knee extension and hip flexion, meanwhile the muscles across these joints produced flexion torque at the knee and extension torque at the hip. During swing phase, MDT at the knee and hip joints was mainly produced by leg angular acceleration which was very significant at the moment when leg swing from forward to backward, active MST counterbalanced the effect of MDT. In summary, muscle torque functions mainly to push the ground to counter ground reaction force for controlling the movement during stance phase. However, the role of muscle torque changes during swing phase to mainly counteract the effect of MDT to control the movement direction of the lower extremity at both the hip and knee joints.

Research Advancements of Compression Equipments in Sports Science

The utilization of sports compression equipments has widely attracted the attention of researchers with the need to maintain muscle functions, reduce sport injuries, and improve athletic performance. It has become a heated issue in research field of sportswear since the beginning of the new century. Methods of literature review, logic analysis and mathematical statistics were used to analyze the study of compression garments from hardcopy journals and online databases. Although a series of studies showed the benefits of compression garments, however, the underlying mechanisms have not been confirmed yet. Moreover, no research referring compression equipments have been conducted in China, which also restricts our native people from getting a further understanding about the potential mechanism of compression apparel. Based on more advanced compression materials, the future study of compression garments will focus on the vibration characteristics of muscle (soft tissue), especially on proprioceptive sensation, neuromuscular control, injury prevention, and performance enhancement.

The Role of Footwear on Impact Forces and Soft Tissue Vibrations during Active and Passive Landings

The aim of this study was to explore the effect of basketball shoes on impact forces, soft tissue vibrations, and their possible interactions during active landing (drop jump, DJ) and passive landing (PL). Six male basketball players wore two types of shoes (basketball shoe vs. control shoe) to execute 5 trials of double-leg landing in each of 6 testing conditions from a manual tiltable platform (i.e., 2 landing styles × 3 heights: 30 cm, 45 cm, and 60 cm). Kinematics of the lower extremity, ground reaction force data, and accelerations of the quadriceps femoris were collected simultaneously. The results showed that there was no significant shoe effect on the input signal for both the time domain and the frequency domain during DJ. However, during PL, the amplitude of impact and loading rate in basketball shoe were obviously smaller at each height (p<0.05); meanwhile, input frequency was also significantly lower for the basketball shoe condition than the control at 45 cm height (p<0.05). Furthermore, input frequency would move towards soft tissue vibration frequency and created a resonance situation (below 25 Hz). Findings of this study indicated that under the condition of related muscles were not be activated properly, the basketball shoe reduced the magnitude of impact, changed the input frequency, and kept away from the resonance frequency, which may further be enlightened and developed in performance and fatigue.

Shoe cushioning reduces impact and muscle activation during landings from unexpected, but not self-initiated, drops

OBJECTIVES To date, few rigorous scientific studies have been conducted to understand the impact mechanics and muscle activation characteristics of different landing tasks and the influence of shoe properties. The aim of this study was to examine the effects of shoe cushioning on impact biomechanics and muscular responses during drop landings. DESIGN A single-blinded and randomized design. METHODS Twelve male collegiate basketball players performed bipedal landings from self-initiated and unexpected drops (SIDL and UDL) from a 60-cm height wearing highly-cushioned basketball shoes (Bball) and less cushioned control shoes (CC). Sagittal plane kinematics, ground reaction forces (GRF), accelerations of the shoe heel-cup, and electromyography (EMG) of the tibialis anterior (TA), lateral gastrocnemius, rectus femoris (RF), vastus lateralis (VL), and biceps femoris (BF) were collected simultaneously. RESULTS In SIDL, no significant differences were observed in peak vertical GRF, peak heel acceleration, or EMG amplitude (root mean square, EMGRMS) for all muscles between the two shoe conditions. In UDL, however, both peak vertical GRF and heel acceleration were significantly lower in Bball compared to CC. Furthermore, the EMGRMS of TA, RF, VL, and BF muscles showed a significant decrease in Bball compared to CC within the 50ms after contact. CONCLUSIONS These observations suggest that shoe cushioning may make only a limited contribution to reducing landing impact forces provided that neuromuscular adjustments occur properly, as in SIDL. However, in the situation where pre-planned neuromuscular activity is reduced or absent, as in UDL, wearing a highly-cushioned shoe decreases peak impact and muscle activation in the 50ms after ground contact.

Do Strike Patterns or Shoe Conditions Have a Predominant Influence on Foot Loading

Abstract This study aimed to explore the effects of strike patterns and shoe conditions on foot loading during running. Twelve male runners were required to run under shoe (SR) and barefoot conditions (BR) with forefoot (FFS) and rearfoot strike patterns (RFS). Kistler force plates and the Medilogic insole plantar pressure system were used to collect kinetic data. SR with RFS significantly reduced the maximum loading rate, whereas SR with FFS significantly increased the maximum push-off force compared to BR. Plantar pressure variables were more influenced by the strike patterns (15 out of 18 variables) than shoe conditions (7 out of 18 variables). The peak pressure of midfoot and heel regions was significantly increased in RFS, but appeared in a later time compared to FFS. The influence of strike patterns on running, particularly on plantar pressure characteristics, was more significant than that of shoe conditions. Heel-toe running caused a significant impact force on the heel, whereas wearing cushioned shoes significantly reduced the maximum loading rate. FFS running can prevent the impact caused by RFS. However, peak plantar pressure was centered at the forefoot for a long period, thereby inducing a potential risk of injury in the metatarsus/phalanx.

Joint Torque and Mechanical Power of Lower Extremity and Its Relevance to Hamstring Strain during Sprint Running

The aim of this study was to quantify the contributions of lower extremity joint torques and the mechanical power of lower extremity muscle groups to further elucidate the loadings on hamstring and the mechanics of its injury. Eight national-level male sprinters performed maximum-velocity sprint running on a synthetic track. The 3D kinematic data and ground reaction force (GRF) were collected synchronously. Intersegmental dynamics approach was used to analyze the lower extremity joint torques and power changes in the lower extremity joint muscle groups. During sprinting, the GRF during the stance phase and the motion-dependent torques (MDT) during the swing phase had a major effect on the lower extremity movements and muscle groups. Specifically, during the stance phase, torque produced and work performed by the hip and knee muscles were generally used to counteract the GRF. During the swing phase, the role of the muscle torque changed to mainly counteract the effect of MDT to control the movement direction of the lower extremity. Meanwhile, during the initial stance and late swing phases, the passive torques, namely, the ground reaction torques and MDT produced by the GRF and the inertial movement of the segments of the lower extremity, applied greater stress to the hamstring muscles.

Effects of shoe collar height on sagittal ankle mechanics during weight-bearing dorsiflexion movement and lay-up jump

This study aims to investigate the effects of wearing high-top and low-top basketball shoes on the ankle joint kinematics, kinetics and performance in the sagittal plane during weight-bearing dorsiflexion (WB-DF) movement and lay-up jump. Twelve subjects performed WB-DF movement and lay-up jumps (LU) in two shoe conditions. Wearing HS can significantly reduce ankle joint excursion in WB-DF. No significant differences were found in jumping height and kinematics between the two shoes. In LU, peak plantarflexion torque and power were significantly lower in HS. The high-top shoes adopted in this study did not restrict the ankle dorsiflexion performance during actual jumping. But it is suggested that the greater power in LS during LU may have a greater potential in the actual game with different conditions, such as the distance of the shot and opposition. Thus, high shoe collar height would be applied to practical with the caution of affecting the partial kinetic characteristics of the ankle joint in the sagittal plane.

Shoe cushioning changes impact and landing-related muscle responses during passive, but not active, drop jumps

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