Abstract
Complete lower-limb paralysis resulting from spinal cord injury precludes volitional leg exercise, leading to muscle atrophy and physiological de-conditioning. Cycling can be achieved using phased stimulation of the leg muscles. With training there are positive physiological adaptations and health improvement. Prior to training, however, power output may not be sufficient to overcome losses involved in rotating the legs and little is known about the energetics of untrained paralysed muscles. Here we propose efficiency measures appropriate to subjects with severe physical impairment performing cycle ergometry. These account for useful internal work (i.e. muscular work done in moving leg mass) and are applicable even for very low work rates. Experimentally, we estimated total work efficiency of ten untrained subjects with paraplegia to be 7.6 ± 2.1% (mean ± SD). This is close to values previously reported for anaesthetised able-bodied individuals performing stimulated cycling exercise, but is less than 1/3 of that of able-bodied subjects cycling volitionally. Correspondingly, oxygen cost of the work (38.8 ± 13.9 ml min−1 W−1) was found to be ∼3.5 times higher. This indicates the need, for increased power output from paralysed subjects, to maximise muscle strength through training, and to improve efficiency by determining better methods of stimulating the individual muscles involved in the exercise.
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Notes
Even then, it may not be. Consider a subject running downhill: external work is negative, and if internal work is neglected a physically-impossible efficiency of less than zero will result (Margaria 1963).
The terms “work” and “energy” are synonymous. They have the units of Joules (J). “Power” is the rate of doing work (it is synonymous with “work rate”). Power is expressed in Watts (W ≡ J s−1).
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Acknowledgments
Supported by the UK Engineering and Physical Sciences Research Council and the Swiss Paraplegic Foundation. We thank Lynsey Duffell (Division of Applied Biomedical Research, King’s College London), Pius Hofer and Helga Lechner (Swiss Paraplegic Research, Nottwil), and Stan Grant (formerly of the Faculty of Biomedical and Life Sciences, University of Glasgow) for their contributions to this study.
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Hunt, K.J., Saunders, B.A., Perret, C. et al. Energetics of paraplegic cycling: a new theoretical framework and efficiency characterisation for untrained subjects. Eur J Appl Physiol 101, 277–285 (2007). https://doi.org/10.1007/s00421-007-0497-5
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DOI: https://doi.org/10.1007/s00421-007-0497-5