The effect of carbon fiber insoles on knee joint loading profiles during walking in older adults: a preliminary analysis

Carbon fibre insoles (CFIs) may be a highly suitable option to augment ankle moment and improve walking performance in older adults. However, some footwear modifications have been implicated as possible contributors in detrimentally altering knee joint loading. Therefore, the purpose of the study was to determine the magnitude of differences in model-predicted knee joint loading in healthy older adults walking with three footwear conditions (i.e. standard walking shoes with and without 1.6-mm and 3.2-mm CFIs). Participants (n = 14) completed three, 2-minute walking trials (i.e. no insole, 1.6-mm CFIs, and 3.2-mm CFIs) on a dual-belt instrumented treadmill at self-selected overground walking speed. Marker trajectories and ground reaction forces were extracted from a single step occurring at the midpoint of the trial and used as inputs to a computational cost-optimisation algorithm (i.e. Concurrent Optimisation of Muscle Activation and Kinematics) to estimate medial and lateral tibiofemoral joint contact force magnitudes. A repeated-measures, functional linear model assessed within-subject differences in knee joint contact force profiles across conditions. Compared to standardised footwear alone, neither the 1.6-mm CFIs nor 3.2-mm CFIs significantly altered knee joint contact forces in the medial compartment of the tibiofemoral joint. Greater lateral compartment tibiofemoral joint contact force magnitudes were identified only for the 3.2-mm CFIs compared to the 1.6-mm CFIs in a small portion of late stance (81%–91% stance phase; maximum between-condition difference: +0.23 kN; d = 1.53). Altered knee joint forces may not be a substantial contraindication for older adults who seek to use CFIs to enhance walking performance.