Proactive balance strategy while maintaining a stationary wheelie.

OBJECTIVE

To test the hypothesis that a reactive balance strategy is used while maintaining a stationary wheelie, specifically that a forward pitch from the wheelie equilibrium position is associated with a forward displacement of the wheelchair and a rear pitch with rear displacement, with the displacement slightly after the change in pitch.

DESIGN

Descriptive and quantitative kinematic analysis.

SETTING

Kinesiologic laboratory.

PARTICIPANTS

A convenience sample of 10 able-bodied adults.

INTERVENTION

Subjects taught to pop and maintain a stationary wheelie for 15 seconds while remaining within a .75 x .75 m2. Three trials of 5 seconds; digitized targets videotaped for analysis.

MAIN OUTCOME MEASURES

Pitch angle and rear-wheel position of the wheelchair, derived from digitized videotape and time-series analysis of phase lag.

RESULTS

There was an inverse relationship between the direction of pitch and linear displacement-rear pitch was associated with forward wheel displacement and forward pitch was associated with rearward wheel displacement. The mean pitch angle +/- standard deviation was 13.6 degrees +/- 2.3 degrees and the mean horizontal position of the wheelchair was 0.0 +/- 4.9cm. There was little or no phase lag between pitch and displacement.

CONCLUSIONS

Wheelie performers maintaining a stationary wheelie appeared to use a proactive balance strategy, in which they used a functional base of support that was larger than the geometric one. These findings may have significance for those who are learning and teaching wheelies and provide broader insights into the nature of dynamic balance.