Geng Luo

Improved footwear comfort reduces oxygen consumption during running

Footwear comfort has been shown to have an influence on injuries, but it was unknown whether comfort was related to performance. The current study examined the effects of footwear comfort on running economy. Thirteen male participants rated five pairs of shoes on perceived comfort. Oxygen consumption was assessed during steady state runs in the least and most comfortable shoes at slightly above the aerobic threshold. A paired t-test was used to compare running economy in the most versus the least comfortable shoe conditions. The findings of the study indicated a significant improvement in running economy, 0.7% on average, in the most comfortable shoe condition. It is suggested that future study of kinematic and kinetic reactions to footwear of different comfort will help to understand the mechanism for the observed performance improvement.

Identification of critical traction values for maximum athletic performance

The purpose of this study was to investigate the relationship between mechanically available footwear traction and performance in top-speed curved sprint running and maximum effort linear acceleration. Based on results from previous studies, it was hypothesized that performance would increase as available traction increased but only to a point after which performance would plateau and further increases in available traction would not affect performance. The goal of this study was to identify such critical traction values. Thirty-two recreational athletes performed maximum effort 2.3 m radius curve sprints and linear accelerations from a standing start using four identical mid-cut basketball shoes differing only in outsole traction. Available traction was modified by manipulating the outsole material. The traction coefficients of the test shoes, quantified with a portable traction tester on the actual test surface, were 0.26, 0.54, 0.82 and 1.13. Ground reaction forces and three-dimensional kinematics were quantified during the tests. Greater amounts of traction (both peak and average) were utilized as the mechanically available traction increased. Increases in available traction from 0.26 to 0.54 to 0.82 provided systematic performance advantages for both curved sprinting and linear acceleration. However, no further performance enhancements were detected when the available traction increased beyond 0.82. Increases in the use of available traction beyond a threshold of 0.82 were reflected in the peak but not the average utilized traction or overall ground reaction impulse generation.

Footwear traction and lower extremity noncontact injury

PURPOSE Football is the most popular high school sport; however, it has the highest rate of injury. Speculation has been prevalent that foot fixation due to high footwear traction contributes to injury risk. Therefore, the purpose of the study was to determine whether a relationship exists between the athletes specific footwear traction (measured with their own shoes on the field of play) and lower extremity noncontact injury in high school football. METHODS For 3 yr, 555 high school football athletes had their footwear traction measured on the actual field of play at the start of the season, and any injury the athletes suffered during a game was recorded. Lower extremity noncontact injury rates, grouped based on the athletes specific footwear traction (both translational and rotational), were compared. RESULTS For translational traction, injury rate reached a peak of 23.3 injuries/1000 game exposures within the midrange of translational traction, before decreasing to 5.0 injuries/1000 game exposures in the high range of traction. For rotational traction, there was a steady increase in injury rate as footwear traction increased, starting at 4.2 injuries/1000 game exposures at low traction and reaching 19.2 injuries/1000 game exposures at high traction. CONCLUSIONS A relationship exists between footwear traction and noncontact lower extremity injury, with increases in rotational traction leading to a greater injury rate and increases in translational traction leading to a decrease in injury. It is recommended that athletes consider selecting footwear with the lowest rotational traction values for which no detriment in performance results.

Wear influences footwear traction properties in Canadian high school football

Primary objective: To determine the range of translational and rotational traction that exists in cleated footwear of athletes, on the surface of play in Canadian high school football. Research design: Field study. Methods and procedures: The shoes of 106 athletes were tested on the field of play using a portable robotic testing machine. The machine measured translational and rotational traction on all shoes. Shoes were compared based on their shape, wear and cleat arrangement; fin, edge, stud. Main outcome and results: Translational and rotational traction ranged from 0.49 to 1.01 and 15.1 to 57.2 Nm, respectively. Fin shoes had significantly lower rotational traction compared to both the edge and stud shoe. Wear resulted in large variability of the cleated traction. Conclusions: The influence of wear has been shown to affect footwear traction, and must be taken into account. Therefore more accurate estimates of traction may occur when testing is completed using players’ actual footwear.

Limb force and non-sagittal plane joint moments during maximum-effort curve sprint running in humans

SUMMARY Compared with running straight, when human runners sprint along a curve, the ability of the inside leg to generate force is compromised. This decreased force generation has been suggested to limit the overall performance of the runner. One theory for this force loss is that the large non-sagittal plane joint moments of the inside leg reach their operating limits, thus prohibiting further generation of the performance-related sagittal plane joint moments. We investigated the inside leg force generation and the ankle and knee joint moments when 13 subjects sprinted with and without an additional mass of 12.4 kg along a curve of 2.5 m radius. The increase in the subjects’ mass evoked a significant increase in the resultant ground reaction force. The peak non-sagittal plane moments increased significantly for both the ankle and knee joints. This observation suggests that when sprinting normally with maximum effort, the non-sagittal plane joint moments are not operating at their limits. The large increases in ground reaction force were associated with greater extension moments generated at the knee joint. In contrast, the peak ankle plantarflexion moment remained unchanged across conditions. It is possible that for the specific joint configuration experienced, the overall ability to generate plantarflexion moment reaches the limit. Future studies with interventions increasing the ability of the muscle-tendon units to generate plantarflexion moment may provide an experimental opportunity to further examine this speculation.

Ankle moment generation and maximum-effort curved sprinting performance.

Turning at high speed along acute curves is crucial for athletic performance. One determinant of curved sprinting speed is the ground reaction force that can be created by the supporting limb; the moment generated at the ankle joint may influence such force generation. Body lean associated with curved sprints positions the ankle joints in extreme in-/eversion, and may hinder the ankle moment generation. To examine the influence of ankle moment generation on curved sprinting performance, 17 male subjects performed maximum-effort curved sprints in footwear with and without a wedge. The wedged footwear was constructed with the intention to align the ankle joints closer to their neutral frontal-plane configuration during counter-clockwise curved sprints so greater joint moments might be generated. We found, with the wedged footwear, the average eversion angle of the inside leg ankle was reduced, and the plantarflexion moment generation increased significantly. Meanwhile, the knee extension moment remained unchanged. With the wedged footwear, stance-average centripetal ground reaction force increased significantly while no difference in the vertical ground reaction force was detected. The subjects created a greater centripetal ground reaction impulse in the wedged footwear despite a shortened stance phase when compared to the control. Stance-average curved sprinting speed improved by 4.3% with the wedged footwear. The changes in ankle moment and curved sprinting speed observed in the current study supports the notion that the moment generation at the ankle joint may be a performance constraint for curved sprinting.

Validation of a mechanical method for golf footwear stability measurement

Golf swings are performed primarily in the frontal plane, and have been associated with a lateral shift of the body center of mass (Williams and Cavanagh 1983). Using high-speed cinematography, Williams and Cavanagh (1983) showed that, during the followthrough phase after ball impact, as the body center of mass continues travelling laterally toward the target, the front ankle of the golfer experiences a large amount of inversion. Thus, the authors suggested stability as an important feature for golf footwear. Footwear properties can be assessed using mechanical devices or human subjects. The advantages of using mechanical devices over human subjects are the higher repeatability and lower cost. However, in order to provide externally valid measurements, the outcome from a mechanical test must be verified using results from human assessments. To the authors’ knowledge, a validated mechanical testing device to evaluate the stability of golf footwear does not currently exist. Thus the purposes of the current study were to: (1) propose a mechanical device to measure the stability of golf footwear; (2) verify whether differences in footwear stability, measured during human testing, can be reproduced using this mechanical device.

Traction properties of footwear in Canadian high school football

Aerts, P., Vinaya, A.S., Van Gheluwe, B., De Clercq, D., and D’Août, K., 2007. Plantar pressure and foot shape in habitual barefoot walkers. Am. J. Phys. Anthropol., 132 (S44), 60–61. Morton, D.J., 1935. The human foot. Its evolution, physiology and functional disorders. Columbia University Press. Pataky, T.C., 2008. Assessing the significance of pedobarographic signals using random field theory. J. Biomech., 41, 2465–2473. Pataky, T.C. and Goulermas, J.Y., 2008. Pedobarographic statistical parametric mapping (pSPM): A pixel-level approach to foot pressure image analysis. J. Biomech., 42, 2136–2143.

Footwear traction and lower extremity non-contact injury

The knee and ankle joint are two of the most frequently injured joints in the body with most of these injuries occurring without contact between players (Malone et al. 1992). Recent studies have concluded that the traction between the shoe and surface may be one of the major factors affecting non-contact injuries (Lambson et al. 1996). Previous studies have examined the relationship between footwear traction and injury; these studies used sample shoes and surfaces for their traction measurement with only a small range of tractions tested. Research into the actual relationship between an athlete’s footwear traction and injury over the entire range of traction actually used in sport is not available.

Limb Force Generation as a Limiting Factor for Maximum-Effort Acceleration Performance

Sprint acceleration is important in various sports. The current study examined whether acceleration performance is limited by strength, more specifically the peak limb force generation. We tested this idea by altering the mechanical demand for the supporting limb, and then determining if the peak limb force is constantly operating at its maximum level across conditions. Thirteen athletes performed maximum-effort sprint acceleration with and without an additional mass equivalent to 17 % of their body mass. We found the athletes were capable of generating a greater limb force when sprinting with the mass compared to the control. This observation suggests that acceleration performance might not be limited by the ultimate magnitude of limb force generation. It remains puzzling why the athletes would not fully utilize their limb force for propulsion. Future studies are needed to further explore other potential limiting factors for acceleration performance, such as kinematic constraints for body lean.