Dynamics of longitudinal arch support in relation to walking speed: contribution of the plantar aponeurosis

Abstract

The plantar aponeurosis (PA), in spanning the whole length of the plantar aspect of the foot, is clearly identified as one of the key structures that is likely to affect compliance and stability of the longitudinal arch. A recent study performed in our laboratory showed that tension/elongation in the PA can be predicted from the kinematics of the segments to which the PA is attached. In the present investigation, stereophotogrammetry and inverse kinematics were employed to shed light on the mechanics of the longitudinal arch and its main passive stabilizer, the PA, in relation to walking speed. When compared with a neutral unloaded position, the medial longitudinal arch underwent greater collapse during the weight-acceptance phase of stance at higher walking speed (0.1 degrees +/-1.9 degrees in slow walking; 0.9 degrees +/-2.6 degrees in fast walking; P = 0.0368). During late stance the arch was higher (3.4 degrees +/-3.1 degrees in slow walking; 2.8 degrees +/-2.7 degrees in fast walking; P = 0.0227) and the metatarsophalangeal joints more dorsiflexed (e.g. at the first metatarsophalangeal joint, 52 degrees +/-5 degrees in slow walking; 64 degrees +/-4 degrees in fast walking; P < 0.001) during fast walking. Early-stance tension in the PA increased with speed, whereas maximum tension during late stance did not seem to be significantly affected by walking speed. Although, on the one hand, these results give evidence for the existence of a pre-heel-strike, speed-dependent, arch-stiffening mechanism, on the other hand they suggest that augmentation of arch height in late stance is enhanced by higher forces exerted by the intrinsic muscles on the plantar aspect of the foot when walking at faster speeds.

Figures

Fig. 1

Left: rendering of the foot showing the location of the 12 markers employed to track the motion of the calcaneus, metatarsus and proximal phalanges of the toes in accordance with the protocol described in Caravaggi et al. (2009). Marker FMH2 is used for static calibration only. Right: the reflective markers applied on the bony landmarks of one of the subjects employed in the study. CA, upper central ridge of the calcaneus posterior surface; ST, the most medial apex of the sustentaculum tali; PT, lateral apex of the peroneal tubercle; VMB, base of the fifth metatarsal; VMH, dorso-lateral aspect of the head of the fifth metatarsal; FMB, base of the first metatarsal; FMH, dorso-medial aspect at the head of the first metatarsal; PM, the most distal and dorsal point of the head of the proximal phalanx of the hallux; SPH, TPH, FPH and VPH are the most distal and dorsal points of the proximal phalanges of toes two to five, respectively.

Fig. 2

The location of the three markers employed to measure the deformation of the medial longitudinal arch (MLA). See Fig.1 for landmarks’ description.

Fig. 3

Intersubject mean temporal profiles of the vertical (top) and anterior–posterior component (bottom) of the ground reaction force at three walking speeds over 100 walking trials for each speed during normalized stance phase. BW, body weight.

Fig. 4

Top to bottom: intersubject mean temporal profiles (±1 SD) of the rotation angles at the five metatarsophalangeal joint (MTPJ) (MTPJ1 = medial; MTPJ5 = lateral) at three walking speeds over 15 trials for each speed during normalized stance phase.

Fig. 5

Intersubject mean temporal profiles of angular deformation of the medial arch at three walking speeds over 100 walking trials per speed group during normalized stance phase. Positive angles indicate drop of the medial longitudinal arch (MLA), whereas negative angles indicate raise of the MLA relative to a neutral unloaded position (see Fig. 2).

Fig. 7

Top to bottom: intersubject mean temporal profiles of strain [l/l0] in the five slips of the plantar aponeurosis (PA) (PA1 = medial; PA5 = lateral) at three walking speeds over 15 walking trials for each speed during normalized stance phase.

Fig. 6

Intersubject mean temporal profiles of plantar aponeurosis tension at three walking speeds over 15 walking trials for each speed during normalized stance phase. BW, body weight.

Fig. 8

The main internal and external forces acting on the longitudinal arch of the foot at heel-strike. GRF, ground reaction forces; BW, body weight; PA, tension in the plantar aponeurosis; AT, tension in the Achilles’ tendon; EDL and EHL, forces exerted by the extensor digitorum longus muscle and extensor hallucis longus muscle, respectively; TA, tibialis anterior force.