Wheelchair. 11:00, Room 101CD, Presentation 0843 S469

EFFECT OF WHEEL CAMBER ON MECHANICAL ENERGY AND POWER FLOW ANALYSIS OF THE UPPER

EXTREMITY IN WHEELCHAIR PROPULSION

Y.C Huang1, L.Y Guo2, C.Y Tsai1 and F.C Su1

1Institute of Biomedical Engineering, National Cheng Kung University, Tainan, Taiwan. 2Faculty of Sports Medicine, Kaohsiung Medical University, Kaohsiung, Taiwan.

email: fcsu@mail.ncku.edu.tw

INTRODUCTIONThe wheel camber is an important parameter that affects wheelchair exercise. It has been suggested that minimization of energy cost is a primary determinant for selection of rear-wheel camber. Limited studies have taken into account the mechanical energy and power flow of upper extremity during wheelchair propulsion. In this study, we investigated the rates of change of mechanical energy (mechanical power) and power flow of upper limb for 0º and 15º wheel camber to see the effects of the wheel camber. We examined the difference between these two powers estimates to find the guidelines for the configuration of wheelchairs. The results may provide more insight of the metabolic difference between the different wheelchair cambers.

METHODSSix normal subjects (mean age 23.2 yrs, mean weight 72.7 kg) participated in this study. Fourteen reflective markers were placed on selected anatomic landmarks unilaterally on each subject. An eight-camera Expert Vision™ video-tracking system was used to collect the three-dimensional trajectory data of the markers. The subjects propelled a sport wheelchair with two different cambers (0° and 15°) over level ground. The speed was controlled at 1 m/s. The test order of different cambers for each subject was randomized. The total mechanical energy (E) of a segment is the sum of the potential energy (Ep) and kinetic energy (Ek). The rate of change of total mechanical energy of a segment is mechanical power. The summation of the joint translational power (Pj) and muscle rotational power (Pm) at each end of the segment is the total power flow (Pf). The power flow of a segment was composed of the proximal (Pjp)/distal (Pjd) joint translational powers and proximal (Pmp)/distal (Pmd) muscle rotational power. The work calculated from the mechanical power and the power flow for one propulsion cycle was calculated by integrating the power curve over time during wheelchair propulsion. The nonparametric-Wilcoxon statistical test was used to estimate the effects of the wheel cambers. The p value was set as 0.05.

RESULTS AND DISCUSSION Fig. 1(a) (b) showed the mechanical power and power flow of the upper limb. They showed positive power before mid-propulsion phase and after mid-recovery phase. The maximum negative value was appeared around the end of propulsion phase.

The work done by this two power estimates and works discrepancy including upper arm, forearm and hand for a complete propulsion cycle were listed in Table 1. The work for 0 degree camber calculated from the mechanical power and power flow was 11.9 and 14.6 J, respectively. For 15 degree camber, the works from these two powers estimate was 12.0 and 16.4 J, respectively. It would be expected that power supplied to the segments is greater than the

mechanical requirement. Greater discrepancy between these two powers estimates implies inefficiency in energy expenditure during wheelchair propulsion. In this study, the camber had significant effect on total work discrepancy. The greater work discrepancy was done for 15° camber. The discrepancy work between these two powers was greater on upper arm and forearm. Because of high variation in subjects, for upper limb, only forearm discrepancy had significant effect. Work done by mechanical power had high correlation with metabolic cost in past walking study. The work for a complete propulsion cycle, using the wheel with 15°camber is larger than 0° camber. By mechanical energy and power flow analysis, we can evaluate the efficiency on work differences. Buckley et al concluded that the energy cost increased with increased camber angle during wheelchair propulsion [2]. Their result was the same with us. Propulsion with 15°camber not only greater energy cost but also greater energy lost.

REFERENCES 1. Guo LY, et al. Clin Biomech 21, 107-115, 2006. 2. Buckley SM, et al. Adapt Phys Act Quart 15, 15-24, 1998.

ACKNOWLEDGEMENTS This work was supported by National Health Research Institute grant NHRI-EX95-9318EI.

Table 1: Work values and work discrepancy for a propulsion cycle Camber (deg) Mechanical

work (J) Power flow

work (J) *Work

discrepancyUpper arm discrepancy

*Forearm discrepancy

Hand discrepancy

0º 11.9 1.3 14.6 1.5 8.8 2.1 4.3 1.0 3.5 1.1 1.0 0.2 15º 12.0 1.2 16.4 2.2 11.5 2.4 5.92 2.1 4.4 1.0 1.1 0.3 p value 0.75 0.11 0.04 0.11 0.02 0.24

Figure 1: 0° (a), 15° (b) power flow and mechanical power.

XXI ISB Congress, Podium Sessions, Thursday 5 July 2007 Journal of Biomechanics 40(S2)