A forefoot strike pattern during 18° uphill walking leads to greater ankle joint and plantar flexor loading

Background: The ankle joint is one of the most involved joints in uphill walking. Furthermore, it is well known that toe walking increases the external dorsiflexion moment in the first half of stance during level walking. However, the effects of different foot-strike patterns on plantar flexor muscle forces, ankle joint forces, and other lower limb joint and muscle forces are unknown.Research question: Do foot-strike patterns during 18 degrees uphill walking affect lower limb sagittal joint angles and moments, as well as joint contact and muscle forces?Methods: This study was based on a data subset from previous publications, analysing uphill walking on an 18 degrees ramp at a preset speed of 1.1 m/s in 18 male participants (34 limbs analyzed, 27 +/- 5 years). Participants were divided into two groups based on their foot-strike pattern at initial contact: heel (HC) and forefoot (FC). Lower limb sagittal joint angles and moments as well as joint contact and muscle forces were assessed. Differences between the groups were assessed using two-sample t-tests.Results: FC showed increased soleus and gastrocnemius muscle forces as well as ankle joint forces during loading response and mid stance compared to HC. The soleus muscle force impulse was 51.1% higher in the FC group than in the HC group (p < 0.001). On the other hand, FC had a lower absolute centre of mass vertical displacement and reduced knee and hip joint, as well as iliopsoas and hamstring muscle force impulses.Significance: In terms of plantar flexor and ankle joint loading, it is advantageous to exhibit a heel strike pattern. The current results can be used to recommend foot-strike patterns for uphill walking, particularly in the presence or prevention of musculoskeletal issues.