Adaptations to Running While Footwear Cushioning and Surface are Manipulated

Minimal footwear sales have encountered rapid growth over the last several years. Minimal footwear are often constructed with thin basic uppers and thin, flexible midsoles. It is likely that running in minimal footwear will require adaptation and adjustments as the amount of cushioning and the geometry of the foot/ground interface will be substantially different than what many are accustomed to. This research investigated the effect footwear cushioning amount and the running surface had on running patterns. Study 1 (Chapter IV) utilized two different running footwear conditions and two different cushioned treadmill conditions, as well as a barefoot condition, to investigate the effect cushioning magnitude and mode had on running patterns. Subjects ran for six minutes at 3.0 m/s for each footwear/surface condition while kinematics and acceleration data were collected. Study 2 (Chapter V) utilized three footwear conditions as well as a barefoot condition to investigate the effect of running in minimal footwear for the first time. Subjects ran for six minutes at 3.0 m/s while wearing each of the four conditions on an aluminum belt treadmill while kinematic and acceleration data were collected. The three footwear conditions were very similar except for the amount of underfoot material (foam) which varied from very little in the most minimal condition to a typical training footwear amount in the thickest condition. Study 3 (Chapter VI) utilized the same three footwear conditions worn in study 2. Subjects ran for 30 minutes at 3.0 m/s wearing each of the three footwear conditions while kinematic and acceleration data were collected in order to investigate the response to minimal footwear over the course of a sustained run. Results of Study 1 suggest that the amount of underfoot cushioning as well as how that cushioning was applied (footwear vs. surface) were both important and affected adjustments made during the run. The foot was more horizontal, the ankle joint complex more plantar flexed, and the knee more flexed in the sagittal plane at TD when running barefoot compared to all other conditions. Peak acceleration values were reduced for the most cushioned condition compared to all others. The thigh segment was more vertical at TD and peak tibial internal rotation at midstance was reduced when footwear were worn. This indicated cushioning provided through footwear altered running patterns compared to cushioning provided through the surface. More investigation is necessary to fully understand all the factors involved, but our research showed that cushioning magnitude is not the only factor affecting running patterns when footwear or running surface is altered. Some Study 2 dependent variables indicated running patterns to be significantly different for both barefoot and very minimal footwear conditions compared to footwear with thicknesses more similar to typical training footwear. Other dependent variables showed barefoot to separate from all footwear conditions implying that unique strategies were utilized for barefoot running even when compared to minimal footwear providing very little cushioning or protection. Peak accelerations implied that cushioning limited the shock transferred to the tibia and the head. Most coordination measures implied barefoot running to be significantly more variable than running in minimal running shoes. Adaptations due to running in footwear with unknown cushioning characteristics occurred quickly, in as few as six to eight steps. Kinematic adjustments were also occurring later in the six minute run. Study 3 kinematic and acceleration dependent variables indicated adjustments were made to running patterns as a result of changes in the amount of underfoot material. The foot segment was less horizontal and the AJC more dorsiflexed for the thick condition compared to both others. These changes did not completely compensate for changes in underfoot material however, as peak accelerations at the tibia and the head were increased as underfoot material was reduced. Runners were found to adjust running patterns as the thirty minute run progressed regardless of footwear condition. Several kinematic dependent variables were found to significantly increase or decrease as the 30 minute run progressed. In summary, the amount of cushioning and the mode of cushioning were found to effect running patterns. Given these findings, it is not surprising adaptations were found when comparing running in minimal footwear to running in footwear with more typical midsole thicknesses. Cushioning magnitude and the geometry of the foot/ground interface were substantially different between these footwear conditions. Although the thin condition provided almost no cushioning, differences were still shown between barefoot and this condition. Barefoot running may require a unique solution even compared to running in extremely minimal footwear. When runners wore minimal running shoes for the first time, some adaptations occurred quickly; however, adjustments were still occurring much later into the six and 30 minute runs. Runners who purchase minimal footwear can expect changes in running patterns