Academic journal article Research Quarterly for Exercise and Sport

Stride Adjustments during a Running Approach toward a Force Plate

Academic journal article Research Quarterly for Exercise and Sport

Stride Adjustments during a Running Approach toward a Force Plate

Article excerpt

Gait analyses depend extensively on evaluating ground reaction forces. These forces are commonly measured using force plates, with a normal or typical stride assumed as a runner approaches and hits the plate (cf. Hay, 1993; Miller, 1990). However, force plates "must be designed to accommodate foot contact with a minimum necessity of targeting the platform" (Dainty & Norman, 1987, p. 88). Related research has indicated that stride adjustments occur when approaching a target (Hay, 1988; Hay & Koh, 1988; Lee, Lishman, & Thomson, 1982; McGinnis & Abendroth-Smith, 1989; Warren, Young, & Lee, 1986).

The importance of targeting a specific location is readily apparent for athletes such as long and triple jumpers and pole vaulters who must aim for a toe board or plant box, respectively. Visual control strategies (targeting) are used by athletes more often than motor programming strategies (nontargeting) when foot placement is important (Hay, 1988; Hay & Koh, 1988; Lee et al., 1982; McGinnis & Abendroth-Smith, 1989; Warren et al., 1986). If a targeting strategy is used in approaching a force plate, the resulting stride adjustments may affect force measurements. For example, Warren et al. (1986) examined the use of visual control of step length during running over irregular terrain, such as cross-country runners might experience. They concluded that an efficient way to produce varying step lengths was through the use of a visual control strategy that changed the magnitude of force exerted on the ground during contact. Studies that have intentionally manipulated stride lengths have noted differences in the resulting ground reaction forces, including such variables as support time, first maximum vertical force, average vertical force, and anterior/posterior maximum braking and propelling force (Holt, Hamill, & Greer, 1987; Martin & Marsh, 1992). Martin and Marsh (1992) recommended against constraining stride length and stride frequency for evaluating representative gait kinematics and kinetics.

Because of the potential problems that may exist in adjusting strides when approaching a force plate, it would be interesting to note whether a targeting strategy is used by runners and, if so, where adjustments to step lengths occur in order to contact the force plate. Therefore, the purpose of this study was to investigate control characteristics of locomotion when approaching a force platform. More specifically, this study attempted to determine if the use of a force platform resulted in an artificially induced stride pattern that is not reflective of a stride pattern during normal gait and if a targeting strategy was responsible for possible alterations in stride lengths.

Method

Participants

Twelve experienced midrange distance runners (4 males, 8 females) participating in a U.S.A. Olympic Training Camp served as participants in the study. Midrange distances include 1,500 meters to 3,000 meters. Training paces averaged 2.46-3.38 min/km during data collection. Informed consent was obtained from all participants prior to data collection.

Design

Two 50-m tapes marked with alternating black-and-white meter lengths placed along the sides of the running lane served as background markers. This enabled measurement of step length using a single-camera panning videographic technique (Chow, 1987). Runners were videotaped using a sampling rate of 60 fields/s and a shutter speed set at .0001 s. The force plate was flush with and centered in the running lane, approximately 40 m from the runners' starting point. During the approach, when either foot was in contact with the ground, the toe and four points surrounding the foot (background markers) were then digitized from the videotape. Plane geometry was used to locate toe position, and simple proportions were used to compute the distance from the start (Chow, 1987).

Measurement error was examined using a sample trial. …

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