The effects of an irregular surface on contact geometry, shock attenuation and metabolic cost during running

With the popularity of non-traditional and off-road race events on the rise, the number of runners encountering trail surfaces has undergone a marked increase in recent years. Despite the growing popularity of trail and off-road running, little research has been done to investigate the effects of running on irregular surfaces. PURPOSE: The purpose was to investigate the kinematic and metabolic effects of running on an irregular surface. We hypothesized that the irregular surface would cause runners to reduce frontal plane foot inversion and increase knee flexion at contact, increasing the metabolic cost of running and shock attenuation. We also examined how altering the frontal plane foot angle at contact using real-time feedback would affect these other variables. METHODS: Sixteen participants completed three running bouts lasting 5-7 minutes each on an irregular surface (IS) treadmill created by attaching wooden slats, on a traditional smooth surface (SS) treadmill, and on SS while receiving visual feedback of the frontal plane foot angle at contact (SSF) with a goal of matching IS foot angle on SS. Participants were outfitted with reflective markers on the pelvis and lower limb and accelerometers on the distal anteromedial tibia and frontal bone of the forehead. For a portion of each condition, participants breathed through a mouthpiece for the measurement of the rate of oxygen consumption ( VO2). Statistical analysis was completed using a one-way repeated measures ANOVA with a Sidak post hoc correction to set α=0.0127. RESULTS: Frontal plane foot angle increased by 40% from IS to SS (IS: 8.4±4.09°, SS: 11.8±4.52°, p<0.0001). Knee flexion angle decreased by 33% from IS to SS (IS: 9.23±4.88°, SS: 6.22±5.03°, p<0.0001). Rate of oxygen consumption decreased by 10% from IS to SS (IS: 37.9±5.68 ml·kg·min, SS: 34.1±5.07 ml·kg·min, p<0.0001). Frontal plane foot