Foot-orthosis-shoe interactions in cycling

Abstract

In cycling, the foot-shoe-pedal interface is the single propulsive link for power transmission. During pedalling the majority of plantar pressures occur beneath the first metatarsal head and hallux. High and repetitive anteromedial plantar pressures are proposed to result in foot pain and paraesthesia. The use of orthoses in cycling shoes has been suggested to decrease forefoot pressures by distributing them more effectively over a greater plantar surface area through increased conformity to the foot. This thesis investigated interactions between the foot, shoe and orthosis at this interface. Study 1 investigated road cycling shoe comfort as rated on a visual analogue scale (VAS) and the prevalence of foot pain and numbness amongst 53 professional cyclists. Cycling shoes were rated as moderately comfortable (7.09±1.85). 53.8% of cyclists reported experiencing foot pain and 42.3% reported foot numbness when riding. The perception of hotter conditions corresponded to a significant increase in reported foot pain (p<0.001) and numbness (p<0.001). Foot pain corresponded to a decreased rating of shoe comfort overall (p=0.001) and at the forefoot (p=0.001) but numbness had no influence. Study 2 investigated the effect of foot volume change on reported foot pain, numbness and rated shoe comfort amongst 13 professional cyclists during two international level staged races. An increase in foot volume (p=0.001) was noted during racing. Foot volume increase was negatively correlated to overall shoe comfort (p=0.024), but did not impact on foot pain and numbness. Foot pain corresponded to a decreased comfort rating for shoe upper (p=0.006) and arch (p=0.013) and numbness to a decreased comfort of the shoe overall (p=0.024) and forefoot (p=0.005). Studies 3, 4 and 5 investigated the effect of various in-shoe orthosis features on plantar contact area (CA), mean plantar pressure (MP) and perceived comfort and support rated on a VAS. For all studies cyclists performed steady-state, seated cycling at a cadence of 90 rpm. Plantar surface CA and MP were measured using the pedar-X® system (Novel, Munich Germany), determined for discrete plantar regions represented as a percentage of the total CA and MP respectively (CA% and MP%). Study 3 compared a contoured orthosis and a flat insert of similar hardness in 12 cyclists riding at a rating of perceived exertion (RPE) of 12. CA% and MP% were determined for seven discrete regions. The contoured orthosis produced a significantly greater CA% at the medial (p=0.001) and lateral midfoot (p=0.009) and significantly increased MP% at the hallux (p=0.003). Perceived support was significantly greater at the arch (p<0.000) and heel (p=0.013) with the contoured orthoses but comfort was not altered. Study 4 examined the effect of varying power output (PO) on CA% and MP% patterns as well as the changes induced by a contoured orthosis compared to a flat insert. 8 cyclists rode at three POs of 150, 200 and 250 watts (W). Plantar surface CA% and MP% were determined for seven discrete regions. Two testing sessions were performed at least one week apart. No statistically significant interaction or main effects were noted for PO or time. The contoured orthosis produced a significant increase in CA% at the medial midfoot (p=0.001) and decrease at the lateral forefoot (p=0.001) with a significantly increase in MP% at the medial (p<0.000) and lateral midfoot (p=0.001). Study 5 examined the effect of orthosis hardness (soft, hard) and posting (medial rearfoot, medial forefoot and lateral forefoot posting) on plantar surface characteristics and perceived orthosis comfort and support. 23 cyclists rode at an RPE of 12. CA% and MP% were determined for nine discrete regions. Cycling shoe comfort was rated on a VAS. The softer orthosis significantly increased CA% (p=0.014) at the midfoot and heel and decreased it at the forefoot and toes while MP% (p=0.034) was significantly increased at the mid and lateral forefoot and significantly decreased across the midfoot. Both rearfoot and forefoot posting significantly decreased CA% (p=0.018) at the midfoot and heel and increased it through the forefoot with no significant change in MP%. Rearfoot posting significantly influenced both comfort (p=0.036) and support (p=0.018) at the arch and heel but hardness demonstrated no effect. Foot pain and numbness may be a prevalent issue amongst cyclists and appear to be influenced by cycling conditions perceived as hotter. When racing, foot volume increases which influences shoe comfort but does not appear to impact on foot pain and numbness. However, foot pain and numbness appear to correspond to a reduction in shoe comfort. Initial evidence indicates that contoured, soft, non-posted orthoses appear to modulate high forefoot plantar pressures, believed to cause foot pain and numbness, by more effectively distributing pressure over a greater plantar surface area through increased conformity to the foot. Contoured and posted orthoses appear to provide greater perceived support, but do not appear to greatly influence perceived comfort.