Overview: This study is a side-kick to a previous manuscript (Free fulltext) which discussed the kinematic and kinetic outcomes of the experimental data from various shoe conditions. This study added the PF model estimates for two conditions (neutral shoes vs. barefoot). Runners who habitually run with shoes were recruited, and ran on a track in four shoe conditions (barefoot, minimalist shoe, flats, and neutral shoe). Kinematics and reaction forces were collected. For two conditions, PF stress were estimated using a model based on several equations estimating contact area, knee moment, quadriceps force, etc...
Findings: 1) From the first study: Peak knee flexion and knee extensor moments were LESS in the barefoot condition, but the SAME across all 3 shoes. 2) From the second study: Peak PF stress was less in barefoot condition vs. neutral shoes Here's a plot of moments from the first study:
Why?: A big part of why barefoot running alters running mechanics is due to the fact that we don't like pounding the fat pads under our feet very hard. Even wearing a minimalist shoe aids in comforting our fat pads, which allows us to pound them harder to reach the same pain threshold than when barefoot.
The biggest - these runners were habitual shod (shoe) runners. What happens when they are fully adapted to barefoot running? Do fat pads stiffen up and allow runners to pound harder on their feet? Or do the differences increase more through increased comfort using the ankle joint as a shock absorber?
Another - The running velocities need to be kept constant across conditions or else the results don't mean much. The authors claim that the velocities ended up (on average) being EXACTLY the same across all 4 conditions, seemingly without feedback to the runners on their speed. This seems dubious to me. In addition, how different would the results be if moments and PF stresses were calculated for each trial and THEN averaged, vs. the other way around?