The metabolic cost of passive walking during robotics-assisted treadmill exercise

We are investigating the potential of robotics-assisted treadmill technology as a mode of exercise in people with spinal cord injury (SCI). People with incomplete SCI can actively contribute to this form of exercise, but in the clinical setting they often walk passively in the system. It is not known whether in doing so they are meeting the recommended guidelines for increasing cardiopulmonary fitness.

The aims of this study were twofold: to characterise the intensity of passive walking during robotics-assisted treadmill exercise (RATE) in incomplete SCI; and to determine if this intensity meets the recommended guidelines for cardiopulmonary training in this population.

10 subjects with incomplete SCI twice performed an exercise test on a robotics-assisted treadmill. The test comprised a period of passive walking and a ramp phase to the limit of tolerance. Oxygen uptake VO(2) heart rate (HR) were continuously measured.

VO(2) during passive exercise was on average 1.4 times higher than resting VO(2R), but this was only 29% of peak VO(2) (VO(2 peak))(range 16-43%). Relative to rest, passive VO(2) (VO(2P) was only 12% of VO(2 peak). HR did not increase from rest to passive walking (81 ± 10 bpm to 81 ± 13 bpm respectively). The HR associated with passive walking was on average 50% of peak HR (HR(peak)) (161 ± 13 bpm). Test-retest reliability was moderate for VO(2R) (R=0.62) and resting HR (HR(R)) (R=0.68), high for VO(2P) (R=0.81), passive HR (HR(P)) (R=0.87) and HR(peak) (R=0.88), and very high (R=0.95) for VO(2 peak). Only HR(p) differed significantly between tests (p=0.029).

The intensity of passive walking during RATE is low and is insufficient to increase cardiopulmonary fitness in people with SCI. Subjects must actively contribute to the exercise in order to achieve the recommended training intensity.