Background:

Understanding the biomechanics of the medial longitudinal arch (MLA) may provide insights into injury risk and prevention, as well as function of the arch-supporting structures. Our understanding of MLA deformation is currently limited to sit-to-stand, walking, and running. Material and Methods:

Three-dimensional deformation of the MLA of the right foot was characterized in 17 healthy participants during several simulated activities of daily living. MLA deformation was quantified by both changes in arch length and navicular displacement during the stance phase of three motions: walking, stair ascent, and stair descent. Three levels of load were also evaluated: no load, a front load (13.6 kg), and a backpack load (13.6 kg). Force platforms and an eight-camera motion capture system were used to collect relevant lower extremity kinetic and kinematic data. Results:

Motion type had a significant (p < 0.05) effect on navicular displacement and arch length elongation with navicular displacement being greatest during stair descent, while the walking and stair descent conditions showed the greatest increase in arch length. External load did not significantly affect either of these two measures (p > 0.05). Conclusion:

Differences in the MLA deformation variables resulting from varied dynamic activities of daily living can be greater than those during walking and should be considered. Clinical Relevance:

Detailing the mechanics of the MLA may aid in further understanding injuries associated with the MLA, and the results of the current study indicate that these mechanics change based on activity.