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The use of electrical muscle stimulation to elicit a cardiovascular exercise response without joint loading: A case study

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THE USE OF ELECTRICAL MUSCLE STIMULATION TO ELICIT A CARDIOVASCULAR EXERCISE RESPONSE WITHOUT JOINT LOADING: A CASE STUDY. Brian Caulfield, Louis Crowe, Conor Minogue, Prithwish Banerjee, Andrew Clark. JEPonline 2004;7(3):84-88. To date, electrical muscle stimulation (EMS) has not been used to elicit a cardiovascular exercise effect in healthy adults without joint loading. This case study was carried out to address this issue. We have developed an EMS system capable of eliciting a cardiovascular exercise response with minimal gross movement or loading of the limbs or joints. It is modelled on shivering, the natural process for generating heat when body temperature falls. One untrained male subject (age 31 yr; weight 70 kg) completed 4 treatment sessions using this system during which the stimulus intensity was increased in increments of 10% every 3 min to reach maximum output at each session. The same subject also underwent one single EMS session of 4 hours duration at a stimulation intensity of 40-60% of maximum output. VO2 and HR responses observed during the first 4 sessions were within the zone required for cardiovascular training. At peak stimulation intensity, the subject's workload was 12 METs. VO2 ranged from 20-25 ml/kg/min during the 4-hour session. The subject expended a cumulative total of 1865 Kcal during this session. This data suggests that the benefits of vigorous exercise may now be achieved through the use of electrical stimulation. There are many potential applications for this technology.
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Case Study: Electrical Muscle Stimulation Without Joint Loading
84
JEPonline
Journal of Exercise Physiologyonline
Official Journal of The American
Society of Exercise Physiologists (ASEP)
ISSN 1097-9751
An International Electronic Journal
Volume 7 Number 3 June 2004
Clinical Exercise Physiology
THE USE OF ELECTRICAL MUSCLE STIMULATION TO ELICIT A
CARDIOVASCULAR EXERCISE RESPONSE WITHOUT JOINT LOADING: A CASE
STUDY.
BRIAN CAULFIELD1, LOUIS CROWE2, CONOR MINOGUE2, PRITHWISH BANERJEE3, ANDREW
CLARK3
1University College Dublin School of Physiotherapy, Dublin, Ireland
2Biomedical Research Ltd, Galway, Ireland
3University of Hull, Dept of Academic Cardiology, East Yorkshire, UK
ABSTRACT
THE USE OF ELECTRICAL MUSCLE STIMULATION TO ELICIT A CARDIOVASCULAR
EXERCISE RESPONSE WITHOUT JOINT LOADING: A CASE STUDY. Brian Caulfield, Louis
Crowe, Conor Minogue, Prithwish Banerjee, Andrew Clark. JEPonline 2004;7(3):84-88. To date,
electrical muscle stimulation (EMS) has not been used to elicit a cardiovascular exercise effect in healthy
adults without joint loading. This case study was carried out to address this issue. We have developed an
EMS system capable of eliciting a cardiovascular exercise response with minimal gross movement or
loading of the limbs or joints. It is modelled on shivering, the natural process for generating heat when
body temperature falls. One untrained male subject (age 31 yr; weight 70 kg) completed 4 treatment
sessions using this system during which the stimulus intensity was increased in increments of 10% every 3
min to reach maximum output at each session. The same subject also underwent one single EMS session of
4 hours duration at a stimulation intensity of 40-60% of maximum output. VO2 and HR responses observed
during the first 4 sessions were within the zone required for cardiovascular training. At peak stimulation
intensity, the subject’s workload was 12 METs. VO2 ranged from 20-25 ml/kg/min during the 4-hour
session. The subject expended a cumulative total of 1865 Kcal during this session. This data suggests that
the benefits of vigorous exercise may now be achieved through the use of electrical stimulation. There are
many potential applications for this technology.
Key Words: Electrical Stimulation, Exercise therapy, Oxygen consumption.
INTRODUCTION
The benefits of electrical muscle stimulation (EMS) in medicine and sport are well established from a wide
body of research. The use EMS to elicit contraction of skeletal muscle has been effectively employed for a
wide variety of applications including prevention of muscle atrophy (1), muscle strengthening (2), and
management of incontinence (3), spinal deformities (4) and spasticity (5). Functional electrical stimulation
(FES) of muscle has been used with some degree of success in the spinal cord injured population to facilitate
locomotion (6).
Case Study: Electrical Muscle Stimulation Without Joint Loading
85
In recent years investigators have directed attention to the use of EMS technology to elicit a cardiovascular
response. This has primarily involved the use of EMS to induce leg cycling exercise (EMS-LCE), and
therefore dissipate energy through a cycle ergometer, in spinal cord injured patients. EMS-LCE can result in
VO2 levels of the order of 0.6-0.8 L/min in SCI subjects (7,8). Training with EMS-LCE can also result in
improvements of 10-35% in aerobic capacity in SCI subjects (9,10). Conventional EMS-induced tetanic
muscle contractions have a minimal effect on energy consumption. Eijsbouts and co-workers demonstrated
that bilateral stimulation of quadriceps, hamstrings, gastrocnemius and tibialis anterior muscle groups at
maximally tolerated intensity could produce an increase in oxygen consumption (VO2) of approximately 0.1
L/min in healthy adults at rest and during arm cranking exercise (11). Such levels of VO2, in isolation, are
unlikely to result in therapeutic benefit.
To date, EMS technology has not been used successfully to elicit a vigorous cardiovascular exercise
response without loading the limbs or joints. Such an application would provide many benefits for sport and
medicine. Unloaded EMS induced cardiovascular exercise could provide an attractive alternative to
customary forms of cardiovascular exercise that involve repetitive joint loading (such as running). It could
also be used to induce a cardiovascular exercise response in people who experience barriers to participation
in voluntary weight-bearing exercise, for example those with degenerative joint disease, obesity or spinal
cord injury (12).
We have developed a novel EMS system capable of eliciting a cardiovascular exercise response with
minimal gross movement or loading of limbs or joints. The pattern of EMS used in this investigation was
modelled on shivering, which is the natural process for generating heat when body temperature falls.
Shivering generates heat with no external work through rhythmical muscle contractions, occurring at a rate
of approximately 4-8 Hz (13). We attempted to mimic this pattern of muscle activity by using EMS to elicit
cardiovascular exercise via rapid, short duration, rhythmical contractions in the large lower extremity
muscle groups. The purpose of this case study was to show that this form of EMS is capable of eliciting a
vigorous cardiovascular exercise response in a healthy adult male.
METHODS
One male subject (age 31; weight 70kg), who gave written informed consent prior to participation,
completed 4 EMS sessions using a portable muscle stimulator over a two-week period. Sessions were
performed at the same time each day with the same electrode positioning and food intake. The output
stimulus intensity of the stimulator was increased by intervals of 10% every three minutes to reach
maximum output during each 30-minute session. The same subject also underwent one single EMS session
of 4 hours duration whilst watching television in a seated position. The stimulation intensity was varied
between 40 and 60% of maximum output over the course of this session. The subject’s physiological
response to stimulation was monitored and recorded throughout each session using a Quark B2 (Cosmed,
Italy) open circuit spirometry system.
Figure 1. Location of stimulating electrodes.
A specially designed hand held muscle stimulator
(BioMedical Research Ltd, Galway, Ireland)
powered by a 9 V battery was used in this
investigation. The stimulator current waveform was
designed to produce rhythmical contractions in the
lower extremity muscle groups occurring at a
frequency of 4 Hz. The maximum peak output
pulse current used in the present study was 300 mA.
Impulses were delivered through 5 silicon rubber
electrodes on each leg (area per leg = 600 cm2) as
illustrated in Figure 1. These were applied to the
body via a pair of tight fitting shorts, which
extended to the knee. The quadriceps, hamstrings
Case Study: Electrical Muscle Stimulation Without Joint Loading
86
and gluteal muscles were stimulated while the subjects lay supine for all stimulation sessions.
RESULTS
The subject completed all stimulation sessions without difficulty. The toleration of the stimulus, both in time
and intensity, was principally limited by subject fatigue. Tachypnoea, tachycardia, sweating, and fatigue
were all present at higher stimulation intensities. Average oxygen consumption (VO2) (ml/kg/min) and
heart rate (beats/min) at each stimulation level during each of the four 30-min sessions are illustrated in
Figure 2. These results demonstrate that a repeatable linear dose response relationship exists between
stimulus intensity and physiological responses. In addition physiological responses were consistent with
responses that would be expected in voluntary exercise such as cycling or running. VO2 levels of the order
of 5 and 10 METs were consistently apparent at 40 % and 80 % of maximum stimulus intensity respectively.
This was associated with corresponding mean heart rate responses of 93 and 163 beats/min.
Heart Rate
50
70
90
110
130
150
170
190
Heart Rate (BPM)
Oxygen Uptake
0
5
10
15
20
25
30
35
40
45
10 20 30 40 50 60 70 80 90 100
Stimulation Intensity
VO2 (ml/kg/min)
Session 1 Session 2 Session 3 Session 4
Figure 2. Physiological responses to repeated electrical muscle stimulation over 4 sessions.
VO2 (ml/kg/min) and cumulative energy expenditure (Kcal) during the 4-hour session are illustrated in
Figure 3. Breaks in the VO2 graph correspond to breaks in recording due to drinking water and changing
batteries in the stimulator. The subject expended a cumulative total of 1865 Kcal during the 4-hour session.
This level of energy expenditure is equivalent to this subject running 15 miles at a 9 min/mile pace (13).
DISCUSSION
This data suggests that the benefits of vigorous exercise may now be achieved through the use of electrical
stimulation. We have demonstrated that EMS can be used to elicit a physiological response consistent with
that expected with high intensity cardiovascular exercise. In addition, he also exhibited very high
Case Study: Electrical Muscle Stimulation Without Joint Loading
87
cumulative energy expenditure during one prolonged session. Our subject experienced no adverse effects
from the stimulation and reported that his principal limiting factor was fatigue.
It is not clear whether stimulation at high intensities would prove acceptable to all as there is a great deal of
individual variability in terms of reported comfort levels with EMS (14). However, we have previously
observed good tolerance for sub-maximal stimulation (40% of maximal output) using this form of EMS in a
group of 10 healthy adults (15). This sub-maximal stimulation was associated with an average exercise
workload of approximately 4 METs.
0
5
10
15
20
25
30
35
40
00:00:10
00:30:10
01:00:10
01:30:10
02:00:10
02:35:00
03:05:20
03:35:20
04:05:30
Time (hr:min:sec)
VO2 (ml/kg/min)
0
200
400
600
800
1000
1200
1400
1600
1800
2000
Cumulative Energy Expenditure
(Kcal)
VO2 cumulative energy expenditur
e
Figure 3. Physiological response to prolonged electrical muscle stimulation.
There are many potential applications for this form of EMS. Some of the more obvious applications are in
those who possess barriers to participation in more ‘traditional’ forms of voluntary exercise such as walking,
running or cycling. This would include spinal cord injured patients, people suffering from obesity or those
with degenerative joint disease. It could also as an attractive alternative for those in sport who have a high
requirement for cardiovascular exercise training yet wish to minimize the amount of repetitive joint loading
they place upon their body. Further work needs to be done to investigate the mechanism of action of this
form of EMS and to quantify its effects in different populations.
Address for correspondence: Brian Caulfield, University College Dublin School of Physiotherapy, Mater
Hospital, Dublin 7, Ireland. Phone: 011 353 1 8034515; FAX: 011 353 1 8303550; Email:
b.caulfield@ucd.ie
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