The purpose of this study was to investigate the relationships between the medial longitudinal arch (MLA) index and rearfoot alignment with plantar loads in runners with plantar fasciitis (PF) in the acute and chronic phases.
Thirty-five runners of both sexes with diagnoses of unilateral PF were recruited for the study.
To evaluate the alignment of the rearfoot in the posterior view of the frontal plane, the following anatomical points were identified on the inferoposterior regions of both legs: 1) the posterior calcaneal tuberosity, 2) the second point above the centre of the calcaneus, 3) the lower third of the leg.
To classify the MLA, the Arch Index was calculated in a footprint image (obtained with a digital camera) corresponding to the foot injured by PF.
The plantar pressure distribution while running was obtained using the Pedar X system at 100 Hz; all the runners wore standard athletic shoes, which were considered to have neutral support.
The insoles were placed between the socks and the shoe, and were connected to equipment inside a backpack.
A mean value of 30 steps per subject was used for statistical purposes, and the variables calculated were – contact area (cm), maximum force (N), force-time integral (N.S), and peak pressure (kPa) over the three plantar areas of the rearfoot, midfoot, forefoot and toes.
An elevated MLA was found to predict higher plantar loads (higher force-time integral) over the forefoot while running in both PF groups and a higher maximum force over the forefoot in chronic PF.
This last finding suggests that higher loads over the forefoot, particularly during the propulsion of running, are strongly associated with elevated MLAs in runners with PF.
The rearfoot valgus alignment was determined to be a good clinical measurement for predicting increases in the maximum force, force-time integral, and loading rates over the rearfoot in runners in both acute and chronic PF.
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