Improved efficiency with a wheelchair propelled by the legs using voluntary activity or electric stimulation  Richard B. Stein, DPhil, Su Ling Chong, PT, Kelvin B. James, BSc, Gordon J. Bell, PhD  Archives of Physical Medicine and Rehabilitation  Volume 82, Issue 9, Pages 1198-1203 (September 2001) DOI: 10.1053/apmr.2001.24014 Copyright © 2001 American Congress of Rehabilitation Medicine and the American Academy of Physical Medicine and Rehabilitation Terms and Conditions

Fig. 1 Schematic of the new wheelchair. Modified footrests allow rotation around the knee center. This rotation is coupled to movement of the wheels by a sprocket, a chain, and a 1-way clutch that converts bidirectional to unidirectional movement to produce forward movement of the wheelchair. A lever (not shown) connected to the front wheel enables the wheelchair to be steered. Archives of Physical Medicine and Rehabilitation 2001 82, 1198-1203DOI: (10.1053/apmr.2001.24014) Copyright © 2001 American Congress of Rehabilitation Medicine and the American Academy of Physical Medicine and Rehabilitation Terms and Conditions

Fig. 2 Example of a subject propelling the wheelchair with her legs at a velocity of 67m/min for 4 minutes after a 2-minute rest. (A) Heart rate increased by 16 beats/min, so her PCI was 16/67 = .24. (B) V̇O2 increased 270mL/min, so the oxygen index was 270/67 = 4.0. Resting values returned after a few minutes rest. Mean values were calculated from the time segment indicated by the horizontal line. Archives of Physical Medicine and Rehabilitation 2001 82, 1198-1203DOI: (10.1053/apmr.2001.24014) Copyright © 2001 American Congress of Rehabilitation Medicine and the American Academy of Physical Medicine and Rehabilitation Terms and Conditions

Fig. 3 (A) Mean PCI, by group. Leg wheeling (left bars in each set) had the lowest cost in all 3 groups. (B) The change in heart rate and (C) exercise velocity are shown, because they are the components of PCI. Error bars show the SE. Archives of Physical Medicine and Rehabilitation 2001 82, 1198-1203DOI: (10.1053/apmr.2001.24014) Copyright © 2001 American Congress of Rehabilitation Medicine and the American Academy of Physical Medicine and Rehabilitation Terms and Conditions

Fig. 4 Effect of exercise velocity and age on PCI (A) for 1 control subject and (B) for all control subjects. Because no significant trends existed, the horizontal lines show mean values. (A) Upper line shows arm wheeling and walking (these were not significantly different for this subject); lower line shows leg wheeling. (B) Upper line shows arm wheeling; middle line, walking; bottom line, leg wheeling. Archives of Physical Medicine and Rehabilitation 2001 82, 1198-1203DOI: (10.1053/apmr.2001.24014) Copyright © 2001 American Congress of Rehabilitation Medicine and the American Academy of Physical Medicine and Rehabilitation Terms and Conditions

Fig. 5 PCI for group 3, by subject. A logarithmic scale was used because of the wide range of values. The heavy lines and the associated means are also shown for the Mn6 (n = 6) and Mn7 (n = 7) subgroups whose PCI during walking was below or above 1.3, respectively. Archives of Physical Medicine and Rehabilitation 2001 82, 1198-1203DOI: (10.1053/apmr.2001.24014) Copyright © 2001 American Congress of Rehabilitation Medicine and the American Academy of Physical Medicine and Rehabilitation Terms and Conditions

Fig. 6 Oxygen index (mL/m) calculated from changes in oxygen consumption. (A) Data correlated with PCI calculated from heart rate changes (best-fitting lines are shown; the outlier is discussed in fig 7). (B) Comparison of the oxygen indexes for leg wheeling and arm wheeling. All subjects with values below the solid (unity) line required less energy to wheel with the legs than with the arms. Archives of Physical Medicine and Rehabilitation 2001 82, 1198-1203DOI: (10.1053/apmr.2001.24014) Copyright © 2001 American Congress of Rehabilitation Medicine and the American Academy of Physical Medicine and Rehabilitation Terms and Conditions

Fig. 7 Anomolous findings from 1 outlier. (A) Heart rate decreased (PCI = −0.6 beats/m); (B) V̇O2 increased (oxygen index = 2 mL/m); presumed cause, autonomic dysreflexia. Subject had complete SCI and used FES to stimulate the quadriceps and hamstring muscles to move the legs. Data were smoothed with a 3-point running mean. Archives of Physical Medicine and Rehabilitation 2001 82, 1198-1203DOI: (10.1053/apmr.2001.24014) Copyright © 2001 American Congress of Rehabilitation Medicine and the American Academy of Physical Medicine and Rehabilitation Terms and Conditions