Integrated biomechanical and engineering assessments were used to determine how humans responded to variations in turf during running and turning. Ground reaction force (AMTI, 960 Hz) and kinematic data (Vicon Peak Motus, 120 Hz) were collected from eight participants during running (3.83 m/s) and turning (10 trials per condition) on three natural turf surfaces in the laboratory. Surface hardness (Clegg hammer) and shear strength (cruciform shear vane) were measured before and after participant testing. Peak loading rate during running was significantly higher (p < .05) on the least hard surface (sandy; 101.48 BW/s ± 23.3) compared with clay (84.67 BW/s ± 22.9). There were no significant differences in running kinematics. Compared with the “medium” condition, fifth MTP impact velocities during turning were significantly (RM-ANOVA, p < .05) lower on clay (resultant: 2.30 m/s [± 0.68] compared with 2.64 m/s [± 0.70]), which was significantly (p < .05) harder “after” and had the greatest shear strength both “before” and “after” participant testing. This unique finding suggests that further study of foot impact velocities are important to increase understanding of overuse injury mechanisms.
Victoria H. Stiles (Corresponding Author) and Sharon J. Dixon are with Sport and Health Sciences, College of Life and Environmental Sciences, University of Exeter, Exeter, U.K. Igor N. Guisasola and Iain T. James are with the School of Applied Sciences, Cranfield University, Cranfield, U.K.