The effect of foot orthoses on sprinting biomechanics on flat footed individuals

Introduction: Sprinting involves running at near maximum speeds. Sprinting produces high ground reaction forces (GRF) and loading rates which predisposes sprinters to injuries. Compared to non-flatfooted individuals, flatfooted individuals exhibit different lower extremity biomechanics during locomotion which are associated with an increased risk of overuse injuries. Flat-footed individuals are therefore possibly more susceptible to sprint injuries. Foot orthoses are usually prescribed to flatfooted individuals to better control the rearfoot and reduce GRF. However, there is a lack of studies investigating the efficacy of foot orthoses during sprinting. This study investigated the effects of foot orthoses on GRF in flatfooted individuals during sprinting. In addition, the comfort perception of foot orthoses were evaluated. Method: Ten flatfooted university male athletes (age 24.9 ± 1.10 years, Body Mass 70.45 ± 8.89 kg) ran on an instrumented treadmill at three different speeds (5m/s, 6m/s and 7m/s) under two different orthoses conditions (prefabricated foot orthoses and flat control insoles). The order of running speed and orthotic conditions were randomized. The GRF of the last eight complete steps of each trial were collected. Comfort perception was measured using a 150mm visual analogue scale after completion of the entire trial. A two-way repeated ANOVA was performed on GRF variables. A paired sample t-test was performed on the comfort perception ratings. Results: There was no significant interaction effect between speed and foot orthosis conditions for the GRF variables (P > 0.05). Compared to flat control insoles, the prefabricated foot orthoses were found to reduce the time to peak vertical GRF by 12% resulting in a corresponding increase in loading rate by 32.3% (P < 0.05) while peak propulsive force was reduced by 3.93% (P < 0.05). The participants responded that the prefabricated orthotics provided better arch support but poorer overall comfort compared to the flat control insoles (P < 0.05). Discussion: The findings suggest that the prefabricated foot orthoses do not reduce shock at foot strike. Therefore, no inference can be made regarding the potential for prefabricated orthosis to prevent impact related injuries during sprints. The poor overall comfort perceived when using the prefabricated foot orthoses may be due to minimal wear-in time. In conclusion, this study shows that there is no clear beneficial effect of foot orthosis in flat-footed individuals during sprinting.