FES Cycling is a well accepted modality with clear benefits for clients that use it. Of course, it doesn't mean that there isnt room for improvement. The fact is, FES Cycling tends to be quite in-efficient in relative terms. This becomes a difficulty, for example, when we want to take FES Cycling outdoors and make it truly practical for the type of outdoor cycling challenge proposed by Claire Lomas.
The idea of FES Cycling has been around for more than 30 years and there are a number of well - established commercial systems including the RehaMove system from Hasomed.
Over the years. FES-cycling has been most widely practiced with spinal cord injured persons but it has also been applied in people with lower-limb dysfunction in a range of other neurological populations such as adults after stroke, MS and children with cerebral palsy. A range of physiological benefits have been observed in clinical studies of subjects with SCI including improvements in cardiopulmonary fitness, muscle strength and bone density.
A recent article by Ken Hunt and colleagues in "Technology and Health Care" examines the efficiency of FES Cycling in detail. They suggest that the efficiency limitations come from what they describe as
- unfavourable biomechanics - ie crude recruitment of muscle groups
- non-physiological recruitment of muscle fibres.
Metabolic efficiency of volitional cycling in able-bodied subjects has been observed to have a metabolic efficiency of around 30% - whilst that of paralysed FES-cyclists is around two-thirds lower, lying in the region of 10%. Think of this efficiency as a measure of how easily the users ability to generate metabolic power produces useful power output at the pedals. The authors explore the meaning of efficiency and suggest possible measures for improving this.
In Binder-Macleod’s work, (see reference 1 below) during non-isometric contractions, performance was improved by switching from lower to higher frequency as muscle fatigue progressed.
In isometric tests with able-bodied subjects it was found that fatigue was most effectively countered using a strategy which first increased stimulation pulsewidth to the maximum extent possible, followed by an increase in the stimulation frequency. (reference 2)
Eser et al. [reference 3] provided further evidence that increased frequency can partially address fatigue and improve performance: in a study with nineteen paraplegic subjects, they found that substantially higher average power output was achieved at stimulation frequencies of 50 and 60 Hz in comparison to 30 Hz. Further, the power output of the last minute of the 30-minute cycling sessions was almost always higher at the higher frequencies.
The RehaMove 2 unit easily allows for automatic change and regulation of pulse width as fatigue progressed. It might be worth us exploring client training sessions that also adjust and increase frequency during a session.
1) M. B. Kebaetse, S. C. Lee, T. E. Johnston and S. A. Binder-Macleod, “Strategies that improve paralyzed human quadriceps femoris muscle performance during repetitive, nonisometric contractions,” Arch Phys Med Rehabil, vol. 86, pp. 2157-2164, Nov 2005.
2) L.-W.Chou, T. M.Kesar and S.A. Binder-Macleod, “Using customized rate-coding and recruitment strategies to maintain forces during repetitive activation of human muscles,” Phys Ther, vol. 88, pp. 363-375, Mar 2008.
3) P. C. Eser, N. de N. Donaldson, H. Knecht and E. Stussi, “Influence of different stimulation frequencies on power output and fatigue during FES-cycling in recently injured SCI people,” IEEE Trans Neural Syst Rehabil Eng, vol. 11, pp. 236-240, Sep 2003.