Foot kinematics and leg muscle activation patterns are altered in those with limited ankle dorsiflexion range of motion during incline walking

Background: Larger ankle dorsiflexion (DF) is required when walking on inclined surfaces. Individuals with limited DF range of motion (ROM) may experience greater tissue stress on sloped surfaces and walk in altered gait patterns compared to the those with normal DF ROM. Research question: Would the individuals with limited DF ROM walk with distinctive ankle DF patterns compared to those with normal DF ROM on the inclined surfaces? Methods: Ten Limited DF ROM (passive ROM=35.3 +/- 2.7 degrees) and nine Normal DF ROM (passive ROM=46.4 +/- 4.2 degrees) participants walked on a treadmill at five slope angles (0 degrees, 5 degrees, 10 degrees, 15 degrees, 20 degrees) for 2 min at a self-selected speed. The peak DF angles and the peak myoelectric activity levels of the tibialis anterior (TA) and soleus (SOL) muscles were quantified during the swing and stance phases of each walking trial, and they were compared between the two groups. Results: Participants with limited DF ROM walked with smaller peak DF (3.1 degrees at 0 degrees slope similar to 8.4 degrees at 20 degrees slope) and greater peak TA activity in swing than those of the Normal ROM participants (3.4 degrees similar to 12.2 degrees), with significant differences at 20 degrees slope. The peak DF angle in stance (Limited: 9.6 degrees similar to 19.0 degrees; Normal: 10.1 degrees similar to 21.0 degrees) did not differ between the two groups at all slopes, but the peak activity of the SOL muscle was significantly greater for the Limited group at slopes of 10 degrees and higher. Significance: Study results indicate that incline walking could be more challenging to the individuals with limited DF ROM as they need to approach and push-off the sloped surfaces with more efforts of the dorsiflexor and the plantar flexor muscles, respectively. Prolonged walking on inclined surfaces may produce faster development of muscle fatigue or tissue damage than those with normal DF ROM.