Physiological responses during hubcrank and handrim wheelchair propulsion:A pilot study

Abstract

The purpose of this pilot study was to investigate the differences in physiological responses during manual wheelchair propulsion with a hubcrank driven and a handrim driven track wheelchair. Because of the low mechanical efficiency of a handrim driven wheelchair, it is appropriate to look for a more efficient propulsion mechanism. A newly designed hubcrank mechanism (Alpha Kinetics(} which is fixed onto the hub of each rear wheel of a sports (track) wheelchair was compared with a similar radius handrim mechanism, mounted to the same sports wheelchair. Seven male wheelchair sportsmen performed two submaximal wheelchair exercise tests on a motor driven treadmill, once with the hubcrank and once with the handrim propulsion mechanism. Each test consisted of 2 protocols. In the first protocol (I), the velocity increased every third minute, ranging from .83 m.s-1 up to 4.17 m.s-1. The inclination angle of the treadmill was kept constant at 1%. Subsequently, in the second protocol (II) the velocity of the belt of the treadmill was kept constant at 3.33 m.s-1 and the inclination angle increased to 2% and 3%, respectively. Only three subjects were able to complete both protocols. Statistical evaluation was therefore performed on a limited number of subjects for both protocols, while excluding also the final slope condition of 3% in protocol II. Concerning the speed-related protocol I (N = 5 subjects) only heart rate (HR) was significantly lower under the hubcrank condition, although there were clear trends for the other physiological parameters (oxygen uptake (V̇O2), energy cost (Ėn) and mechanical efficiency (ME)), with the exception of respiratory exchange ratio (RER) and power output (Po). In the slope-related protocol II only 4 subjects were able to perform at 2% slope and thus the inclination angle of 3% was omitted from further analysis. As a result of an increasing slope V̇O2, Ėn, and HR were significantly lower and ME was significantly higher under the hubcrank condition (P < .05). The hubcrank does seem to be more efficient both at increasing speed as well as slope. A major advantage of the hubcrank may be a more natural orientation of the hand and wrist and the use of both flexors and extensor muscles during a complete cyclic motion. Some subjects had problems negotiating the hubcrank propelled wheelchair on the treadmill. Further study must substantiate possible physiological and biomechanical advantages for this propulsion mechanism. Focus should be on experiments which: (1) exclude training effects on any one of the tested propulsion mechanisms (non-wheelchair users), (2) exclude the directional and steering problems of the wheelchair-user combination (a roller-based ergometer will prevent this problem), (3) study the role of different lower arm muscles, the characteristics of force generation and the kinametics of hand and wrist. However, the practical problems in terms of braking, steering, negotiating a door opening or other obstacles, and the possible advantages of different gear ratios must be considered with respect to the technical characteristics of the hubcrank design