Effect of Acute Alterations in Foot Strike Patterns during Running on Sagittal Plane Lower Limb Kinematics and Kinetics

The purpose of this study was to determine the effect of foot strike patterns and converted foot strike patterns on lower limb kinematics and kinetics at the hip, knee, and ankle during a shod condition. Subjects were videotaped with a high speed camera while running a 5km at self-selected pace on a treadmill to determine natural foot strike pattern on day one. Preferred forefoot group (PFFG, n = 10) and preferred rear foot group (PRFG, n = 11) subjects were identified through slow motion video playback (n = 21, age = 22.8 +/- 2.2 years, mass = 73.1 +/- 14.5 kg, height 1.75 +/- 0.10 m). On day two, subjects performed five overground run trials in both their natural and unnatural strike patterns while motion and force data were collected. Data were collected over two days so that foot strike videos could be analyzed for group placement purposes. Several 2 (Foot Strike Pattern -forefoot strike [FFS], rearfoot strike [RFS]) x 2 (Group -PFFG, PRFG) mixed model ANOVAs (p < 0.05) were run on speed, active peak vertical ground reaction force (VGRF), peak early stance and mid stance sagittal ankle moments, sagittal plane hip and knee moments, ankle dorsiflexion ROM, and sagittal plane hip and knee ROM. There were no significant interactions or between group differences for any of the measured variables. Within subject effects demonstrated that the RFS condition had significantly lower (VGRF) (RFS = 2.58 +/- .21 BW, FFS = 2.71 +/- 0.23 BW), dorsiflexion moment (RFS = -2.6 1 +/- 0.61 Nm.kg(-1), FFS = -3.09 +/- 0.32 Nm.kg(-1)), and dorsiflexion range of motion (RFS = 17.63 +/- 3.76 degrees, FFS = 22.10 +/- 5.08 degrees). There was also a significantly higher peak plantarflexion moment (RFS = 0.23 +/- 0.11 Nm.kg(-1), FFS = 0.01 +/- 0.01 Nm.kg(-1)), peak knee moment (RFS = 2.61 +/- 0.54 Nm.kg(-1), FFS = 2.39 +/- 0.61 Nm.kg(-1)), knee ROM (RFS = 31.72 +/- 2.79 degrees, FFS = 29.58 +/- 2.97 degrees), and hip ROM (RFS = 42.72 +/- 4.03 degrees, FFS = 41.38 +/- 3.32 degrees) as compared with the FFS condition. This research suggests that acute changes in foot strike patterns during shod running can create alterations in certain lower limb kinematic and kinetic measures that are not dependent on the preferred foot strike pattern of the individual. This research also challenges the contention that the impact transient spike in the vertical ground reaction force curve is only present during a rear foot strike type of running gait.