Impact loads are widely believed to be associated with some injuries in runners, though the evidence for that is not overly compelling, but it does make sense that reducing impacts may help prevent overuse injuries in runners. A number of different strategies can be used for this and one that is commonly advocated is the use of minimalist running shoes to change the running technique or form. This new study compared running in a Nike Pegasus (standard cushioned shoe) and a Nike Free 3.0 (minimalist shoe). The results of this study is going to get a lot of commentary in the blogosphere:
Kinematic and Kinetic Comparison of Running in Standard and Minimalist Shoes
Willy, Richard W.; Davis, Irene S.
Medicine & Science in Sports & Exercise: 19 July 2013
Purpose: The purpose of this study was to determine if running in a minimalist shoe results in a reduction in ground reaction forces and alters kinematics over standard shoe running. The secondary purpose of this study was to determine if within-session accommodation to a novel minimalist shoe occurs.
Methods: Subjects were 14 male, rearfoot striking runners who had never run in a minimalist shoe. Subjects were tested while running 3.35 m/s for 10 minutes on an instrumented treadmill in a minimalist and a standard shoe as 3-D lower extremity kinematics and kinetics were evaluated. Data were collected at minute 1 and then again after 10 minutes of running in both shoe conditions to evaluate accommodation to the shoe conditions.
Results: Shoe x time interactions were not found for any of the variables of interest. Minimalist shoe running resulted in no changes in step length (p=0.967) nor step rate (p=0.230). At footstrike, greater knee flexion (p=0.001) and greater dorsiflexion angle (p=0.025) were noted in the minimalist shoe. Vertical impact peak (p=0.017) and average vertical loading rate (p<0.000) were greater during minimalist shoe running. There were main effects of time as dorsiflexion angle decreased (p=0.035), foot inclination at footstrike decreased (p=0.048) and knee flexion at footstrike increased (p=0.002), yet the vertical impact peak (p=0.002) and average vertical loading rate (p<0.000) increased. Conclusions: Running in a minimalist shoe appears to, at least in the short-term, increase loading of the lower extremity over standard shoe running. The accommodation period resulted in less favorable landing mechanics in both shoes. These findings bring into question whether minimal shoes will provide enough feedback to induce an alteration that is similar to barefoot running.
The authors found…
we found that running in the minimalist shoe failed to result in changes in temporospatial parameters, increased average vertical loading rates and vertical impact peaks when compared with running in a standard running shoe
…which is the opposite of what would have been expected and certainly counter-intuitive.
Also of interest was the finding of a more dorsiflexed angle of the foot at touchdown in the minimalist condition which is also the opposite of a couple of previous studies, though one did use a more minimalist shoe (Vibrams) than used in this study and the other used habituated barefoot runners rather than the acute intervention of the above study.
The higher dorsiflexion angle could possibly be indicative that a forefoot/midfoot strike pattern was not automatically adopted when using minimalist shoes. The Nike Free 3.0 does have some minimal cushioning in the heel, but much less that the Pegasus. The results show that transitioning to minimalist shoes will theoretically increase the risk for injury (if you believe that impacts are a significant risk factor for injury) unless other factors to do with the running technique are addressed. However, as shown in this study, that does not mean that strains on the tibia are actually reduced.
As always, I go where the evidence takes me until convinced otherwise, and this study shows that when first using minimalist shoes, impact forces increase. It probably also says that the running form must also be addressed at the same time as going to minimalist running shoes.
Willy, Richard W., & Davis, Irene S. (2013). Kinematic and Kinetic Comparison of Running in Standard and Minimalist Shoes Medicine & Science in Sports & Exercise DOI: 10.1249/MSS.0b013e3182a595d2