Biomechanical assessment

Biomechanical assessment was performed twice (2–7 days between tests) with a subset of nine participants. A graded loading challenge (GLC) was developed to assess pain response and movement features in response to increasing step length and weight carried. The test consisted of four different difficulty levels: 1) normal walking with self-selected speed and step length, 2) walking with a 25% longer step length of participants’ original step, 3) normal walking while carrying a load of 25% of body mass (BM), and 4) walking with the 25% longer step length plus the extra 25% load, which is a combination of tasks two and three. Participants performed each level 10 times, with each repetition consisting of six (level 1 and 3) or four (level 2 and 4) steps prior to the force plate and the same number of steps after; the total walking distance of walking was approximately 11 m. Participants carried load via a double-sided weighted vest (HOMCOM, MHSTAR, England). Step length was guided by indicators of the individually-determined required step length on the ground.

Kinetic and kinematic motion capture were performed during the GLC utilising in-floor force plates (500 Hz; 9281CA, Kistler) and an infrared motion analysis system (100 Hz; CX-1, Codamotion, Charnwood Dynamics Limited, Leicestershire, UK), respectively. Thirty-four infrared markers were used, consisting of 14 individual markers on foot anatomical landmarks using Leardini protocol [41], four rigid clusters of four markers placed bilaterally on shank and thigh, and four markers located on the anterior and posterior superior iliac spine.