Running continues to be a very popular recreational and competitive activity. Improving performance and preventing injuries are topics of importance for both researchers and participants. One performance aspect which relates to both of these areas is the mechanics of lower extremity function during the support phase. The purpose of this study was to investigate selected kinematic parameters and ground reaction forces as a function of running speed, type of runner, and type of footfall.

Procedures

The experimental setup consisted of a Kistler force platform connected to a Honeywell visicorder, two high speed super 8mm movie cameras, and a photoelectric timing system.

The cameras were operated at 200 frames per second and placed side by side, approximately 10 meters from the force platform and perpendicular to the path of motion. The cameras were used to record separate aspects of the whole body during a right foot support phase on the force platform. The force platform monitored the vertical and braking/propulsive ground reaction forces and provided information about the location of the force center. The photoelectric timing system was used to control the operation of all equipment and check running speed over an 8 meter interval.

Twelve skilled distance runners (1500 meters and longer) and twelve skilled sprinters (400 meters and shorter) participated as subjects in the study. Each subject ran at both a fast and slow pace. Performance speeds were based upon 75 percent world record pace for 100 and 10,000 meters.

The raw kinematic data were digitized from the film and together with output from the force platform, processed by a Tektronics 4051 Graphics Calculator. The data were calibrated with respect to time and adjusted for subject weight so that comparisons between the different classifications could be performed.

Data Analysis

The initial intent was to analyze the data only by runner classification and running speed. After processing the data it was decided to also evaluate the data on the basis of types of footfall. Footfalls were classified into three categories:​ (1) heel-toe, (2) toe-'neel-toe, and (3) toe. Subjects were assigned to each grouping based upon center of pressure data obtained from the force platform. The mean data curves associated with the footfall groupings revealed that each footfall classification was associated with a characteristic ground reaction force profile.

A discriminant analysis provided information concerning the differentiation in running speeds, in types of footfall, and in runner classification by kinematic parameters. A comparison between runner classification and running speed on the basis of ground reaction force profiles was not as distinctive as was the case with footfall, classification. On examining the changes in footfall patterns at different speeds, the data tended to counter the often held concept that there is an orderly shift in type of footfall from heel-toe to toe with an increase in speed. Finally, an analysis was performed on the kinematic parameters associated with changes in the horizontal velocity component of the center of gravity of the runners.