(C) PLOS One
This story was originally published by PLOS One and is unaltered.
. . . . . . . . . .



Surface effects on kinematics, kinetics and stiffness of habitual rearfoot strikers during running [1]

['Wenxing Zhou', 'Key Laboratory Of Exercise', 'Health Sciences', 'Shanghai University Of Sport', 'Ministry Of Education', 'Shanghai', 'School Of Exercise', 'Health', 'Lulu Yin', 'Jiayi Jiang']

Date: 2023-05

This study compared the running biomechanics and lower-limb stiffness of habitual rearfoot strike runners on a runway covered with three different surfaces (artificial grass, synthetic rubber, or concrete). The lower-limb joint moments were lower when running on artificial grass or synthetic rubber, except for the knee flexion and internal rotation moments. This finding partially supports our initial hypothesis. The braking force (17%–36% of the stance phase) and mediolateral GRF were significantly greater when running on a soft surface (artificial grass or synthetic rubber) than on a hard surface, and the lower-limb stiffness, the vertical GRF, the loading rates, and the lower-limb joint motion showed no significant differences among the three surfaces, which are inconsistent with our original hypothesis.

The runners did not show any differences in lower-limb joint motion when running on the three surfaces. However, previous studies reported that runners were observed to modify their running kinematics according to the road stiffness. Shen et al. [ 16 ] reported a lower peak ankle dorsiflexion and hip flexion for the plastic track (softer) than the asphalt road (harder); Pinnington et al. [ 33 ] indicated an increased peak knee flexion angle when running on a soft, dry sand surface compared with that when running on a firm, wooden floor surface. In our study, the runners did not adjust their running postures, which may be due to the insufficient differences in road stiffness among the three artificial runways. In the current study, we added different materials (artificial grass, synthetic rubber, concrete) on the top of the original pavement without making more changes to its internal structure, which may explain the unchanged running kinematics.

Running kinetics

Theoretically, running on different road surfaces would generate different landing impacts, especially in the vertical direction. However, in the current study, we demonstrated no differences in the vertical GRF and loading rates when running on the three overground surfaces. Consistent to our finding, Yamin et al. [7] concluded that GRF was not in correlation with the surface hardness when running in minimally or heeled shoe. Dixon et al. [12] reported no differences in peak impact force among conventional asphalt surface, rubber-modified asphalt surface and acrylic sports surface. Yet, discrete parameters (i.e., peak GRF by Yamin et al. and peak impact force by Dixon et al.) were compared in their study. Unlike the two aforementioned studies, the current study compared the entire vertical GRF curves as well as loading rates (AVLR and IVLR). Thus, our findings may provide further evidence to support that the vertical GRF was typically not influenced by the change in surface [7, 12].

Researchers still have different views regarding the surface effects on the vertical GRF and loading rates. Some studies [12, 34–36] demonstrated that surface stiffness did not affect the vertical GRF during running. Other studies reported that the vertical GRF changed with surfaces stiffness [7, 14]. When the plantar pressure values instead of the vertical GRF values were compared, current evidence suggests that softer surfaces yield lower [4, 5, 15] or similar [17] magnitudes of peak plantar pressure values compared to harder surfaces. Shen et al. [16] found the AVLR was not different when running on asphalt road or plastic track, whereas Dixon et al. [12] reported greater vertical loading rates when running on hard surfaces. The surface effect on landing impact during running seems remain inconclusive. Therefore, besides surface stiffness, further studies are required to unveil the potential relationship by considering many factors, such as surface structures, runners’ footstrike patterns, shoe conditions, and quantification methods.

We did not observe any difference in the lower-limb stiffness measurements (e.g., k leg , k vert , or k joint ) when the habitual rearfoot strikers ran on the three different surfaces. These results can be explained by the unchanged lower-limb joint kinematics and vertical GRF. Inconsistent to our study, scholars demonstrated that runners subconsciously adjusted their lower-limb stiffness based on the perception of different surface hardness [37]. Indeed, runners were previously found to increase their leg stiffness and decrease the knee and ankle joint stiffness when running on softer surfaces [6, 13, 14]. However, in the current study, as the running speed was close to participant’s comfortable speeds, they did not need to modify their running postures to maintain performance.

The braking force at initial contact (0%–2% of stance phase) was significantly lower when running on artificial grass compared with running on synthetic rubber or concrete surface but became greater during the middle of the braking stage (17%–36% of stance phase). This phenomenon indicates the different braking mechanisms of habitual rearfoot strikers when running on different surfaces. Particularly, the forward acceleration was reduced slowly when running on artificial grass instead of decelerating suddenly like they did during running on synthetic rubber or concrete surface. In addition, the propulsion force at the end (94%–100%) of the stance phase was lower when running on artificial grass than that when running on the other surfaces. The greater propulsion force means that the runners could push off the ground more forcefully when running on synthetic rubber or concrete surface than on artificial grass. Horizontal GRF was rarely investigated. Only one study by Karamanidis et al. [35] compared anteroposterior GRF when running on three surfaces with different compliance. However, they reported no differences in the braking and propulsion forces when running on road surfaces with different stiffness. It seems that, besides the surface stiffness, other features of the running road (i.e., surface coefficient of friction) may also play a role, which should be investigated in the future.

Regarding the mediolateral GRF, the medial force in the early stance phase and the lateral force during the late stance phase were greater when running on artificial grass than concrete surface. The mediolateral GRF allows the quantification of the path of the center of mass (COM) in the frontal plane [38] and is related to the gait stability during running. The excessive transition of COM from medial to lateral (or lateral to medial) during running requires a great force to stabilize the runners’ posture in the frontal plane [38]. Accordingly, the dynamic postural stability was lower when running on softer surfaces (e.g., woodchip trail) [39]. Therefore, the mediolateral GRF of our habitual rearfoot strikers running on artificial grass were high.

Although we did not observe any differences in lower-limb kinematics, stiffness and vertical GRF when our habitual rearfoot strikers ran on the three different surfaces, their ankle joint moments were greater when running on concrete surface than the other two surfaces. The hip extension, hip abduction and knee abduction moments were also greater when running on the harder surface. Generally, the external joint moments give a net estimate of the loading imposed on the biological structures surrounding a joint, such as muscles, tendons and ligaments. In our study, increased ankle joint moments mostly occurred during the propulsion phase (65%-100%) when the foot pushed the body forward, which increases more stress for plantar flexors and subtalar joint invertors when running on the harder surface. Increased knee and hip joint moments occurred at the end of propulsion phase for the frontal plane movement when running on the harder surface, which may result in greater retropatellar stress through greater contributions from the vastus lateralis, extensions of the iliotibial band, or both [40]. In addition, previous studies have attempted to decrease frontal hip or knee joint moments through training program to reduce running-related overuse injuries [41]. Willwacher et al. [10] recently observed that running barefoot on harder surfaces increased the ankle joint moments and decreased knee joint moments. They explained it to a more plantar flexed footstrike patterns, which are usually associated with barefoot running or running on harder surfaces. Unlike our study, their subjects adopted a more plantarflexed footstrike behavior. In a word, our findings may demonstrate that the habitual rearfoot strikers may continuously expose to a higher risk of running-related overuse injuries when running on the harder surface.

Two limitations should be noted. First, only male runners were recruited in this study, which may prevent the generalization our findings because of gender differences in shock attenuation when running on different surfaces [42]. Second, the running tests were conducted on a short constructed laboratory runway (15 m), and they can run relatively limited steps before landing on the force plates. Meantime, relative short time was provided to each runner to familiraze themselves with the three new running surfaces. It is necessary to conduct an outdoor running test to further investigate the surface effects on running biomechanics.

[END]
---
[1] Url: https://journals.plos.org/plosone/article?id=10.1371/journal.pone.0283323

Published and (C) by PLOS One
Content appears here under this condition or license: Creative Commons - Attribution BY 4.0.

via Magical.Fish Gopher News Feeds:
gopher://magical.fish/1/feeds/news/plosone/

You are viewing proxied material from magical.fish. The copyright of proxied material belongs to its original authors. Any comments or complaints in relation to proxied material should be directed to the original authors of the content concerned. Please see the disclaimer for more details.