Effects of Camber on the Ergonomics of Propulsion in Wheelchair Athletes

MASON, B., L. VAN DER WOUDE, S. DE GROOT, and V. GOOSEY-TOLFREY. Effects of Camber on the Ergonomics of Propulsion in Wheelchair Athletes. Med. Sci. Sports Exerc., Vol. 43, No. 2, pp. 319-326, 2011. Purpose: To examine the effects of rear-wheel camber on the physiological and biomechanical responses during manual wheelchair propulsion in highly trained wheelchair athletes. Methods: Participants (N = 14) pushed on a motorized treadmill (2.2 m.s(-1), 0.7% gradient) in four standardized camber conditions (15 degrees, 18 degrees, 20 degrees, and 24 degrees). Standardization was achieved by controlling seat height, the distance between top dead center of the main wheels and "toe-in toe-out'' across all camber settings. Power output (P-O) and cardiorespiratory measures were collected for each camber setting. Three-dimensional upper body joint kinematics were also analyzed via two high-speed video cameras (100 Hz). One-way ANOVA with repeated measures was applied to all data with statistical significance accepted when P < 0.05. Results: A significantly higher P-O was observed for 24 degrees camber (24.3 W) in relation to 15 degrees (20.3 W) and 18 degrees (21.3 W), and also for 20 degrees (23.3 W) in relation to 15 degrees. This resulted in an improvement in mechanical efficiency (ME) for both 24 degrees (6.8%) and 20 degrees (6.7%) compared with 15 degrees (5.9%). However, significantly higher oxygen uptake (reduced economy) and HR responses were observed for 24 degrees (1.04 L.min(-1); 105 bpm) compared with 15 degrees (0.98 L.min(-1); 102 bpm) and 18 degrees (0.97 L.min(-1); 102 bpm). Also, significantly greater ranges of motion were established for shoulder flexion and elbow extension during the push phase for 24 degrees and were likely to have contributed toward the increased oxygen cost in this setting. Conclusions: This study revealed that 20 degrees and 24 degrees camber improved the ME of wheelchair propulsion in highly trained wheelchair athletes, yet these increased external power requirements and reduced the economy.