May 2019

EXCERPT: Foot Orthoses Alter Lower-limb Biomechanics in Basketball Players—Flat Feet or Normal Arch

Figure 4: Hip, knee and ankle moment curves during propulsion phase by foot type and orthosis

By Malia Ho, Pui Wah Kong, Lowell Jia-Yee Chong, and Wing-Kai Lam

Flat-footed persons are believed to have poorer jump performance compared to those who have a normal arch. Foot orthoses are commonly used to support the deformed foot arch and improve normal foot function. However, it is unclear if use of foot orthoses affects jump performance in athletes. Our study sought to investigate if foot type or a foot orthosis influences countermovement jump (CMJ) and standing broad jump (SBJ) performance and lower-limb biomechanics.

Methods

Twenty-six male basketball players were classified as normal-arched (n = 15) or flat-footed (n = 11) using the Chippaux-Smirak index, navicular drop test, and resting calcaneal angle measurement. They performed jumps with and without prefabricated foot orthoses. We measured jump height and distance for CMJ and SBJ, respectively. We also measured hip, knee and ankle joint angles; angular velocities; moments; and powers during take-off.

Results

There was no difference in jump height or jump distance regardless of foot types and foot orthoses. For CMJ, the flat-footed group exhibited less ankle plantarflexion (F1,24 = 8.407, p = 0.008, ηp2 = 0.259 large effect) and less peak hip-joint power (F1,24 = 7.416, p = 0.012, ηp2 = 0.244 large effect) than the normal-arched group. Foot orthoses reduced ankle eversion in both groups (F1,24 = 6.702, p = 0.016, ηp2 = 0.218 large effect). For SBJ, the flat-footed group produced lower peak hip angular velocity (F1,24 = 7.115, p = 0.013, ηp2 = 0.229 large effect) and generated lower horizontal ground reaction force (GRF) (F1,24 = 5.594, p = 0.026, ηp2 = 0.189 large effect) than the normal-arched group. Wearing a foot orthosis reduced ankle eversion (F1,24 = 5.453, p = 0.028, ηp2 = 0.185 large effect), peak horizontal GRF (F1,24 = 13.672, p = 0.001, ηp2 = 0.363 large effect) and frontal-plane ankle moment (F1,24 = 4.932, p = 0.036, ηp2 = 0.170 large effect).

Discussion

Our main results were (Figure):

  • There was no difference in jump height or jump distance regardless of foot type or foot orthosis.
  • In CMJ, the flat-footed group displayed less plantarflexion and peak hip-joint power than the normal-arched group; foot orthoses reduced ankle eversion at take-off compared to a flat, neutral insole.
  • In SBJ, the flat-footed group produced less peak horizontal GRF and lower hip angular velocity than the normal-arched group; foot orthoses reduced ankle eversion, peak horizontal GRF, and ankle frontal plane moment at take-off, compared to flat neutral insoles.

Effect of foot type: It would seem that flat-footed persons can perform just as well as their normal-arched counterparts. The differences in biomechanics of the lower extremity may indicate that flat-footed persons have to work harder to achieve the same performance and may infer that flat-footed persons may experience fatigue earlier than their normal-arched counterparts. Foot type accounted for 25.9% variance in ankle plantarflexion, 24.4% variance in hip-joint power and 22.9% variance in hip angular velocity (large effect) at CMJ, while accounting for 18.9% variance in peak horizontal GRF (small effect) at SBJ. Further studies need to be conducted to investigate the impact of these biomechanical changes on their clinical implications, such as muscle use.

Effect of foot orthosis: Foot orthoses are hypothesized to provide medial arch support and reduce rearfoot eversion. Our results in CMJ and SBJ support the contention that, when prefabricated orthoses were used, the ankle was in a more inverted position during take-off. Our findings showed that the use of foot orthoses resulted in a reduction between 1° and 3° of ankle eversion for all participants during CMJ and SBJ. Our results show that an increase in ankle stability would not relate to jumping performance and is consistent with another study in which ankle stability was increased by using collar height and heel counter stiffness of footwear. The foot orthoses used in our study provide support primarily in the rearfoot and midfoot areas, which may have caused changes in the shape and biomechanics on these regions of the foot. Foot orthoses accounted for large effect sizes in ankle eversion (21.8% variance) in CMJ and accounted for large effect in ankle eversion (18.5% variance) and peak ankle frontal moment (17% variance) at SBJ. Although the magnitude of change was small, the large effect sizes found in this study would encourage future longitudinal studies to ascertain the impact of these biomechanical differences to potentially improve movement analyses to tailor training strategies to improve jump performances.

Conclusion

Foot type and the use of foot orthoses influence take-off biomechanics, but not actual CMJ and SBJ performance, in basketball players. Compared to normal-arched athletes, flat-footed athletes generated smaller propulsion GRF and lower hip-flexion velocity and power, which suggests possible compensatory movement strategies to maximize jump performance. Future studies may investigate whether these altered biomechanics—taking into consideration their respective magnitude and effect sizes—may have implications for lower-limb injury. The use of foot orthoses resulted in biomechanical changes in both the normal-arched and flat-footed groups, but does not enhance jumping performance.

This article has been summarized and excerpted from “Foot orthoses alter lower limb biomechanics but not jump performance in basketball players with and without flat feet,” which appeared in the Journal of Foot and Ankle Research (2019:12:24), by the same authors. References and methodological details have been removed for brevity. Use is per the Creative Commons Distribution 4.0 International License. Read the full article at https://jfootankleres.biomedcentral.com/articles/10.1186/s13047-019-0334-1.

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