JRRD

Volume 45, Number 2, 2008
Pages 241–248

Journal of Rehabilitation Research & Development

Treadmill training after spinal cord injury: It’s not just about the walking
Audrey L. Hicks, PhD;* Kathleen A. Martin Ginis, PhD
Department of Kinesiology, McMaster University, Hamilton, ON, Canada

The SCI population is considered one of the mostinactive of all segments of society. This inactivity is aserious health issue given that it can lead to a variety of
secondary health complications and a decline in physicalcapacity over and above that caused by the SCI [6]. People who are wheelchair-dependent invariably rely on
upper-body exercise as a means to optimal fitness. While
good evidence exists that various upper-body exercises
can improve both strength and cardiovascular endurance[7–9], exercise of a larger muscle mass (i.e., the legs) is agreater physiological challenge and likely results ingreater increases in fitness, cardiovascular function, andmetabolic control. We also cannot disregard the potential
psychological benefits associated with upright walking
exercise in wheelchair-dependent individuals. Therefore,
before BWSTT is dismissed as an expensive, but perhaps
not superior, alternative to conventional rehabilitation
after SCI, we need to consider the potential effect of thistherapy on a variety of health-related outcomes.

Abstract—Body weight-supported treadmill training (BWSTT)
is being used throughout the world as a method for improving
functional ambulation after spinal cord injury (SCI). This therapy, however, is very labor-intensive, and recent evidence suggests that it may not be superior to other more conventional
forms of rehabilitation for improving locomotor ability. Recognizing that the value of BWSTT may extend well beyond its
potential to improve functional ambulation is important, and thephysiological and psychological benefits associated with thiswhole-body upright exercise may justify its use in both the acuteand chronic SCI populations.

Key words: body weight-supported treadmill training, cardiovascular disease, exercise, health benefits, health risks, muscle
composition, psychological benefit, rehabilitation, spinal cord
injury, walking.

INTRODUCTION
Over the past decade, body weight-supported treadmill training (BWSTT) has emerged as a promising
method for improving functional ambulation after spinal
cord injury (SCI). Early reports of this therapy were very
promising [1–4], yet a recent multicenter randomized
clinical trial suggested that even though BWSTT may
improve locomotor ability in the acute SCI population, it
may not be superior to more conventional forms of rehabilitation in which the same amount of time is devoted towalking [5]. What most of these studies have neglectedto address, however, is the efficacy of BWSTT as an
exercise intervention for the SCI population.

Abbreviations: ASIA = American Spinal Injury Association,
BMD = bone mineral density, BWSTT = body weight-supported
treadmill training, CVD = cardiovascular disease, FES = functional electrical stimulation, HDL = high-density lipoprotein,
HRQOL = health-related quality of life, LDL = low-density
lipoprotein, PWB = psychological well-being, SCI = spinal cord
injury.
*Address all correspondence to Audrey L. Hicks, PhD;
Department of Kinesiology, McMaster University, 1280 Main
St West, Hamilton, ON L8S 4K1, Canada; 905-525-9140, ext
24643; fax: 905-525-7629. Email: hicksal@mcmaster.ca
DOI: 10.1682/JRRD.2007.02.0022
241

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Advances in acute medical management following
SCI have greatly improved survival rates. Given that the
majority of SCIs occur in young adulthood, people with
SCI live many years with their disability and the associated morbidity. Although life expectancy for people withSCI has steadily increased over the last few decades, it isstill somewhat lower than for the nondisabled population[10–11]. Recently, investigators have reported that muchof the excess (and early) morbidity and mortality in people with chronic SCI relates to potentially treatable factors, such as cardiovascular disease (CVD), diabetes, andsmoking-related illnesses [12]. This fact certainly highlights the importance of promoting interventions that can
improve health, fitness, and overall quality of life in thispopulation. In this article, we will discuss BWSTT as one
such intervention that we believe shows tremendous
promise for improving both physical and psychologicalhealth in people with SCI.

SECONDARY HEALTH COMPLICATIONS AFTERSCI AND ROLE OF BWSTT[19,22–23], and both increase the risks for type 2 diabetes
and CVD in this population.
Finally, cardiovascular function very much depends
on a healthy vascular endothelium, in which the arteries
readily expand and recoil with changes in pressure. This
vascular characteristic is controlled by the autonomic nervous system and, therefore, can be significantly affected
by SCI [24]. An increase in arterial stiffness (i.e., reduced
compliance) has been indicated as the number one factor
associated with CVD progression [25], and increased femoral artery stiffness and associated endothelial dysfunction
have been observed in the SCI population [26–27].
Based on these observations, we are not surprised that
the SCI population appears to be significantly more vulnerable to CVD than the nondisabled population, but anothertroubling statistic is that people with SCI tend to develop
CVD at younger ages [12–13,28]. Since physical inactivity
and low fitness are also recognized as primary risk factors
for CVD [29], initiatives that focus on increasing exercise
could have important implications for decreasing CVD
incidence and progression (through modification of otherrisk factors) in the SCI population.

Changes in Cardiovascular Fitness and Function
After SCI
CVD is the leading cause of death in both the nondisabled and SCI populations [13–14], but evidence suggests that people with SCI may have an earlier onset andan increased prevalence of CVD compared with the general population [15–16]. Physical inactivity may be oneof the key mechanisms behind this increased risk since itis recognized both as a major independent risk factor for
CVD and an important modifier for a number of otherrisk factors for this disease.
For example, elevated serum lipid concentrations, specifically triglycerides, total cholesterol, and low-density
lipoprotein (LDL) cholesterol are associated with the development of atherosclerotic plaques and progression of CVD.
Cross-sectional investigations have shown that people withSCI have elevated LDL cholesterol, total cholesterol, andtriglycerides and reduced high-density lipoprotein (HDL)
cholesterol compared with nondisabled controls [17–19],
all of which increase the risk of CVD.
Another factor contributing to atherogenesis is persistent hyperglycemia, a condition resulting from progressive insulin resistance and associated with type 2 diabetes[20–21]. Reduced glucose tolerance (due to increased
insulin resistance) and abnormal glucose homeostasis arealso commonly observed in people with chronic SCI

Effects of BWSTT on Cardiovascular Fitness andFunction
To date, no published reports demonstrate the efficacy
of BWSTT in reducing CVD in the SCI population, but
we have promising evidence that several of the risk factors
for CVD can be significantly reduced with regular
BWSTT. We have been able to demonstrate that 6 monthsof regular BWSTT (three times a week) improves the
blood lipid profile of people with incomplete SCI (American Spinal Injury Association [ASIA] classification C) by
decreasing LDL cholesterol and the ratio between totalcholesterol and HDL cholesterol [30]. Similarly, this same
training load improved glucose tolerance and insulin sensitivity in participants with SCI [31].
We also have evidence that BWSTT improves boththe autonomic regulation of heart rate and blood pressure
and causes positive changes in vascular dynamics in thefemoral and carotid arteries [32–34] in people with motorcomplete (ASIA B) and motor-incomplete (ASIA C) SCI,
all of which may have important implications with respect
to CVD risk. We hypothesize that BWSTT, through its
involvement of a larger muscle mass and the postural
challenge of being upright, may provide a greater stimulus
for inducing positive cardiovascular changes than more
traditional exercise protocols such as arm exercise andfunctional electrical stimulation (FES).

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CHANGES IN BODY COMPOSITION AFTER SCI
Muscle Composition-Metabolism
The first 6 to 12 months after traumatic SCI are characterized by severe muscle atrophy and changes in the distribution of muscle fiber types. Significant atrophy of type I,
IIa, and IIx fibers (up to 68 percent) has been reported
within the first 6 months postinjury, together with a conversion among type II fiber subtypes [35–36]. The typical fiber
type transformation that occurs soon after SCI is anincreased proportion of the highly fatigable type IIxfiber, with a corresponding reduction in the type IIa andpossibly type I fiber types [35–36]. The observed changes
in muscle fiber type distribution during the first year after
SCI are presumably accompanied by changes in the regulation of muscle energy metabolism; however, relatively little
work has been conducted to confirm this hypothesis. The
available evidence from both human [35] and animal [37]studies suggests that SCI leads to a marked decrease inmitochondrial oxidative metabolism and an increase innonoxidative energy provision.
One of the negative consequences of a significantly
reduced skeletal muscle mass is a reduction in glucose tolerance and a corresponding increase in risk of developing
type 2 diabetes. The incidence of reduced glucose tolerance
among persons with SCI has been shown to be significantly
higher than in the nondisabled population [16,38], likely
resulting from both reduced skeletal muscle mass [16] andreduced neural input to paralyzed muscles [22,29].
Effects of BWSTT on Muscle Composition-Metabolism
Activity-based interventions show tremendous promise for improving muscle mass after SCI. We have shownthat after 6 months of BWSTT (three times a week) inpeople with chronic SCI (average 7 years postinjury),
mean fiber area increased 25 percent, percentage area
occupied by type IIax/IIx fibers decreased, and percentage area occupied by type IIa fibers increased [30]. Thesechanges were accompanied by a 39 percent increase incitrate synthase activity, providing evidence for improved
oxidative capacity. We also have evidence that by implementing BWSTT in the first 6 months postinjury at a frequency of only two times a week, the predicted muscle
atrophy and fiber type redistribution can be prevented[39–40]. We should note that the majority of participantsin the latter study were classified as motor-complete(ASIA B). Thus, BWSTT is effective in both the prevention and treatment of SCI-induced muscle atrophy.

An improvement in muscle mass and muscle composition is important not only for improving strength andfunction for potential reattainment of ambulation but also
for other significant health benefits associated with anincrease in muscle mass, specifically glucose tolerance
and type 2 diabetes risk (see previous section). BWSTT
has been shown to improve glucose tolerance, glucose
transporter content, and insulin sensitivity in people withchronic SCI [31]. Participants in Phillips et al.’s study
underwent a modified oral glucose tolerance test before
and after 6 months of BWSTT. Following training, a significant decrease in both the insulin and glucose response
to a standard glucose load was present, along with a morethan two-fold increase in the content of GLUT-4 (glucose
transport protein, isoenzyme 4) [31]. These results are inagreement with previously published reports of theeffects of FES cycle ergometry on these same outcomes[22,41–42].
Fat Mass
While skeletal muscle mass decreases post-SCI, fat
mass (absolute and percentage of body weight) increases.
Fat mass of persons with chronic SCI ranges from 23 to
35 percent of body weight [43–45], consistent with thedefinitions of overweight and obese [46]. Obesity, specifically visceral abdominal fat, is strongly and independently
associated with numerous CVD risk factors in nondisabled persons, including dyslipidemia, hyperinsulinemia,
glucose intolerance, and hypertension [47]. Despite theprevalence of many of these same risk factors in the SCI
population, few studies have determined the relationshipbetween measured fat mass (and none between visceralabdominal fat) and CVD risk factors in persons with SCI.
Effects of Exercise on Fat Mass
The ability of exercise to decrease total fat mass andattenuate fat mass accretion in nondisabled adults is
widely recognized [48]. Even in the absence of weight
loss, exercise reduces visceral abdominal fat and insulin
resistance [49]. Few prospective studies in the SCI literature have measured the relationship between exercise andbody fat, but a recent article from Japan suggests thatexercise is associated with reduced percentage body fat,waist circumference, and waist:hip ratio in athletes withSCI [50]. To date, BWSTT has not been shown to reduce
total fat mass in people with SCI; based on whole-bodydual-energy X-ray absorptiometry scans, fat mass remained
unchanged after 12 months of BWSTT in the chronic SCI244
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population [31] and slightly elevated after 6 months of
BWSTT in those with acute SCI [41]. Exercise regimes
need to be fairly intense and of sufficient frequency toresult in a decrease in total fat mass, and a BWSTT frequency of two to three times a week likely does not result inenough energy expenditure for the energy balance equation
to change. However, future studies should focus on theeffects of BWSTT on visceral fat stores since the exercise
stimulus associated with BWSTT may improve fat distribution in the SCI population, even in the absence of changes
in total fat mass.
Bone Mass
Bone loss after SCI is rapid, likely beginning within
2–4 days of injury [51]. The highest rate of bone mineralloss occurs in the first 1–2 years postinjury, is most evident in appendicular areas below the level of the lesion(i.e., leg bones), and is more prominent in trabecular versus cortical bone [52]. The decrease in mechanical loading together with neural, vascular, and hormonal changes
associated with the injury all contribute to the substantial
loss in bone mineral density (BMD). The skeletal fragility resulting from this progressive loss in BMD is associated with an increased incidence of osteoporosis andlower-limb fractures in the SCI population [52]. Age andtime since injury are positively correlated with fracture
risk, and as in the nondisabled population, women are
more prone to fragility fractures than men [53].
Effects of BWSTT on Bone Mass
Although the study numbers are low, no evidence
exists that activity-based therapies can prevent the boneloss associated with SCI. In the only BWSTT study thatinvestigated BMD in the acute SCI population, the twice
weekly training frequency could not prevent losses in
BMD in the study participants [40], although no nonexercising control group was included for comparison.
Researchers have also studied whether activity-based
interventions can attenuate the rate of loss or possibly
improve BMD in the chronic SCI population. In contrast
to the several studies that have shown FES to improve
BMD [54–57], BWSTT has not been shown to increase
BMD in people with chronic SCI [58]. Differences intraining frequency and/or duration likely account for theapparent superiority of FES; frequencies of two to threetimes a week of BWSTT or FES do not appear to be a
sufficient stimulus for bone formation [54,57], yet fivetimes a week may be more effective [55–56].

CHANGES IN PSYCHOLOGICAL WELL-BEING
AND HEALTH-RELATED QUALITY OF LIFE
AFTER SCISCI is typically accompanied by a loss of independence, increased family and caregiver load, and reduced
vocational and social participation by the injured person.
These consequences can have a profound impact on psychological well-being (PWB) and health-related quality oflife (HRQOL) [59–61] and are further exacerbated by physical inactivity [62]. Inactivity can compromise the ability tolive independently and maintain a sense of personal autonomy and control over one’s life. Indeed, some investigators
estimate that as a result of inactivity-related decrements,
only 25 percent of healthy young persons with paraplegia,
and even fewer with tetraplegia, have the minimum level offitness needed to perform the activities of daily living necessary to maintain independent living [62–63]. Similarly,
only 26 to 32 percent of Canadians with SCI are employed
and able to fulfill social roles such as “provider” or “caregiver” [11]. The majority are unable to return to work
because they can no longer fulfill the physical demands oftheir jobs. Although partly attributable to the SCI itself, a
reduction in work capacity is also a function of physicalinactivity [63]. Of additional concern, depression and anxiety are far more prevalent in the SCI population than thegeneral population [64–65], and people with SCI who areinactive are more likely to experience these psychopathologies than their active counterparts [66–67].

EFFECTS OF BWSTT ON PSYCHOLOGICAL
WELL-BEING AND HEALTH-RELATEDQUALITY OF LIFE
The few studies that have examined the effects of
BWSTT on HRQOL and PWB have produced encouraging results. With regard to changes in HRQOL, two studies
have shown that BWSTT is associated with improvementsin overall life satisfaction [68–69] and in specific dimensions of HRQOL, including satisfaction with health andfunctioning and social and economic well-being [69].
These studies also showed improvements in aspects of
PWB. Specifically, BWSTT was associated with improvements in overall PWB [69] and body image [68–69].
In contrast, the limited research to date has not shown
any effects of BWSTT on depression [69–70]. These null
effects must be interpreted with caution, however, given

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the relatively small study sample sizes and the very low
levels of depressive symptoms reported by participants at
study baseline. Given that single acute bouts of BWSTT
have small- to medium-sized positive effects on mood[71], the cumulative effects of multiple bouts of BWSTT
could improve PWB among people with higher levels ofdepressive symptomatology.
How might BWSTT improve HRQOL and PWB? Certainly any intervention that improves functioning andindependence can have concomitant effects on these endpoints. For example, if BWSTT improves participants’ability to stand or transfer into a car, it can profoundly affectindependence which, in turn, can influence how people feel
about themselves and their quality of life [69]. Another possibility is that like other forms of exercise training [72],
BWSTT improves PWB and HRQOL vis-á-vis reductions
in pain. Indeed, the mood improvements observed in
Martin Ginis and Latimer’s study of BWSTT were significantly correlated with decreases in pain [71]. In addition,
BWSTT may improve one’s sense of self; for individuals
who are wheelchair-reliant, BWSTT provides an opportunity to stand upright, look people directly in the eye, andengage in the “normative and desirable” activity of walking[69]. Many BWSTT participants also report a positive emotional thrill associated with engaging in “the inspirational
activity of seeing themselves walk again” [69, p. 101].
Taken together, these reports suggest that even if people do
not regain their ability to walk after training, BWSTT is apotentially powerful stimulus for improving aspects of their
HRQOL and PWB.

equipment costs associated with BWSTT are significant,however, and further studies are needed to provide definitive evidence of the cost:benefit ratio. In this regard, thepotential efficacy of robotic devices to assist with locomotor training should also be explored, since these devices
may be less costly in the long run than traditional manual
training.
In summary, compelling evidence exists that BWSTT
has the potential to produce important physical and psychological improvements in people with SCI. Furthermore, these training-induced adaptations do not appear to
be dependent on the degree of functional walking
improvement; in fact, they even occur in individuals who
would not normally be expected to improve their locomotor ability (e.g., ASIA B). Clearly, important healthrelated gains are being achieved through BWSTT, andfuture research should now focus on potential long-term
health benefits. The important next step for community
translation will be to establish a clear link between participation in locomotor training and reduced morbidity fromsecondary health complications in the SCI population.
This evidence will be crucial in informing the scope andnature of the rehabilitation process after SCI.

ACKNOWLEDGMENTS
This material is the result of work supported by a
Canadian Institute of Health New Investigator Award to
K. Martin Ginis.
The authors have declared that no competing interests
exist.

CONCLUSIONS AND FUTURE DIRECTIONS
While BWSTT has received most of its research attention on the basis of its potential to improve functional
ambulation in people with SCI, we must also recognize thevalue of this intervention as a whole-body exercise therapy.
Not only do wheelchair-dependent individuals enjoy andvalue the normalizing experience of seeing themselves
upright and participating in the walking motion, regular
exposure to BWSTT results in some very significant
health-related benefits that may decrease the risk of secondary health complications. Given that people with SCI are(1) living longer and (2) at increased and earlier risk forsecondary health complications associated with physicalinactivity, the importance of providing opportunities forfull-body exercise cannot be overemphasized. The labor/

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Submitted for publication February 1, 2007. Accepted inrevised form May 31, 2007.