Biomed Tech 2013; 58 (Suppl. 1) © 2013 by Walter de Gruyter · Berlin · Boston. DOI 10.1515/bmt-2013-4027
Cardiorespiratory and Metabolic Responses During FES Leg Exercise:
Health and Fitness Benefits Update
Davis GM
Clinical Exercise and Rehabilitation Unit, University of Sydney, Sydney, Australia
[email protected]
Abstract: This is a review of key studies that have
investigated whether FES-evoked leg exercise possesses
sufficient intensity to meet the Exercise is Medicine™
guidelines for cardiovascular health. The American
College of Sports Medicine and similar professional
organisations have aligned their recommendations about
what is sufficient physical activity or exercise to maintain
good health. These key recommendations are: (i)
moderate-intensity cardiorespiratory exercise 150
min/week, (ii) vigorous-intensity cardiorespiratory
exercise for 75 min/week, or (iii) a combination of
moderate-intensity and vigorous intensity-exercise to
achieve a total energy expenditure of at least 500-1000
Met-minutes/week. However, for FES-evoked exercise
there is uncertainty whether “moderate” or “vigorous”
intensity can be achieved. Evidence is presented
supporting or refuting the notion that FES-exercise
achieves the Exercise is Medicine™ guidelines for
aerobic fitness promotion and cardiovascular risk
reduction
Recently, The American College of Sports Medicine
and similar professional organisations have aligned
their recommendations about what is sufficient
physical activity or exercise to improve aerobic
fitness and maintain good health [1]. Those
guidelines (Fig. 1), have come to form the bases for
the Exercise is Medicine™ Global Initiative.
However, these is some mounting evidence that
terms for exercise intensity such as “moderate” and
“vigorous” may not apply well to an exercise
modality that is artificially induced, such as FES.
The purpose of this study was review key studies
that either support or refute the concept FES
exercise can improve aerobic fitness and reduce
cardiovascular risk.
Methods
Keywords: FES-evoked leg exercise, cardiovascular
health, aerobic fitness
Introduction
Exercise is beneficial not only for the able-bodied
population, but also for people affected by spinal
cord injury (SCI). The negative sequelae after SCI
can include moderate-severe muscle paralysis, loss
of lower limb functionality and usually results in
reduced levels of aerobic fitness. Since the 1960’s,
functional electrical stimulation (FES) – induced leg
exercise has been widely used in post-traumatic
rehabilitation or as exercise regimen for the
paralysed lower-limbs of people with SCI.
Fig 1. The ACSM Guidelines [1]
A systematic search of published sources was
performed in common electronic databases within
the date range 1900-February 2012. In addition,
relevant English language journal and conference
proceedings were hand searched. The collective
conclusions of the obtained RCTs and quasi-RCTs
were not sufficient to position the status of the topic
under question. The author included other nonrandomised or controlled studies, mainly clinical
trials, to encompass all available scientific evidence
pertaining to FES-induced exercise.
Results – Evidence Supporting FES exercise
Fig 2. FES-cycling increased aerobic fitness [2]
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Hooker and co-workers [2] originally observed that
sedentary paraplegics and tetraplegics increased
their peak oxygen uptake after only twice-weekly
FES-cycling over 19 weeks (Fig.2). An important
fact pertinent to the current review is that the 10%
increase of leg VO 2 peak, was above 70% of the arm
cranking peak aerobic fitness. Thus, leg cycling was
of sufficient intensity to achieve moderate-vigorous
exercise intensity meeting the ACSM guidelines.
Other studies reported in Hamzaid and Davis [3]
supported these early findings.
A recent study by Brorok and colleagues [5]
demonstrated that 8-weeks of high-intensity arm+leg
(“hybrid) interval training increased arm, leg and
hybrid peak aerobic fitness by 24-26% (Fig. 4).
However, closer examination of these findings showed
that the highest leg VO2peak after training achieved
only 32% of the peak arm+leg value – too low to be
considered even “moderate” intensity.
Hettinga and Andrews [6] undertook a thematic
review of FES studies containing 171 observations
and the authors observed that arm+leg cycling or
FES-rowing produced greater aerobic metabolism
that leg exercise alone. When this author inspected
their data, it became apparent that peak FES-leg
exercise achieved only 50-60% of whole-body
aerobic fitness – and rarely is this leg exercise
intensity deployed due to high fatigue rates (Fig.5)
Fig 3. FES-cycling improves oral glucose tolerance and
insulin responsiveness, both important factors to lower
cardiovascular risk [4].
Griffin and colleagues [4] observed that 30 minutes
of FES cycling per day, thrice weekly for 10 weeks
significantly improved lean muscle mass, cycling
power output, glucose tolerance, insulin levels, and
inflammatory biomarkers (Fig. 3). This finding
supported by a similar outcome by Chillibeck and
colleagues (1998) strongly suggests that FEScycling protects against certain “lifestyle diseases”
associated with cardiovascular disease
Results – Evidence Refuting FES exercise
Fig 5. Thematic review suggesting that leg exercise alone is
less ‘dose-potent’ to improve aerobic fitness than arm+leg
hybrid exercise
Discussion
This study reviewed key studies that either supported
or refuted the notion that FES exercise can improve
aerobic fitness and reduce cardiovascular risk. Some
key findings of this review were that randomized,
controlled, or quasi-experimental evidence of
different modes of FES-evoked exercise cautiously
support the view that FES leg exercise promotes
positive leg metabolic responses during exercise but
rarely by itself enhances peak aerobic fitness in
people with SCI.
For FES-evoked leg exercise to be clinically
effective to promote peak aerobic fitness by itself:
•
Fig. 4. Arm + FES-leg exercise increases arm and leg peak
metabolism, but leg peak is only 32% of whole body aerobic
fitness [5]
Intensive FES cycling training must achieve
sufficient ‘dose-potency’ of at least
“moderate” exercise intensity evidenced by
greater than 40% heart rate reserve for at
least 150 minutes per week.
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•
The beneficial effects of the FES cycling to
promote aerobic fitness and reduce the risk of
cardiovascular disease become more evident
with increased intensity and duration of
training.
•
The beneficial cardiovascular effects from the
adoption of exercise diminish once the FES
cycling has ceased.
However, longer durations of FES cycling than 150
min per week, may have an important role to control
weight gain, improve blood glucose tolerance and
insulin resistance and reduce obesity in the SCI
population. These are a separate cardiovascular risk
factors than low aerobic fitness. It is recommended that
when exercise intensities below “moderate” are
achieved during FES cycling, that at least 240 min of
such exercise per week be achieved.
Bibliography
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musculoskeletal, and neuromotor fitness in
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[3] Hamzaid NA and Davis GM (2009). Health and
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