Introduction

Cardiovascular disease is a leading cause of death in those with spinal cord injury (SCI).1, 2, 3 Increased vascular stiffness is thought to cause an amplified pulse pressure, a reduction in pressure buffering,4 propagate increased ventricular tension and is a primary marker of cardiovascular disease risk.5, 6 Increasing vascular stiffness is related to advancing age,7, 8 poor nutrition,9, 10 smoking,11, 12 excessive alcohol consumption,2, 13, 14 other chronic conditions (such as heart disease)15 and low levels of physical activity.16 Owing to the lack of mobility and the loss of autonomic regulation, people with SCI are particularly susceptible to alterations in both central and peripheral vascular function.17, 18, 19, 20 Moreover, it has been shown recently that those with SCI have increased vascular stiffness when compared with able-bodied (AB) individuals.21, 22

Shortly after an SCI, femoral artery diameter and leg blood flow decrease significantly,23 eventually by up to 50% in comparison to AB individuals.24 It is thought that the loss of voluntary muscle contraction below the lesion level reduces blood flow to the legs: due to both a lack of oxygen demand and reduced release of metabolically stimulated vasodilatory signals (carbon dioxide, potassium, hydron, adenosine, and so on).25 Another potential mechanism is a loss of the physical lengthening and shortening of muscle tissue, which inhibits the muscle pump and reduces the arterio-venous pressure gradient across the muscle bed.26, 27, 28 Finally, in response to inactive muscular tissue and chronically reduced blood flow demand, the arterial system reacts by reducing the diameter29 and the capillary density,30 causing an increase in vascular resistance and leading to decreased venous capacitance and compliance.31

The loss of autonomic control below the lesion level appears to influence vascular stiffness as well. Although sympathetic denervation would be expected to increase vascular elasticity owing to a reduction in vascular tone, it appears that this occurs only in a transient nature,32 and with long-term autonomic denervation, affected vessels increase stiffness as compared with pre-injury levels.33 Supporting this idea is evidence showing that reduced autonomic presence in denervated limbs increases expression of endothelin-1 and reduces expression of nitric oxide, which would lead to increased arterial stiffness and resistance.34

It is well established that physical exercise generally improves cardiovascular health35, 36 and has been shown to improve arterial function in a variety of populations, disorders and disease states.7, 36, 37, 38, 39 Several papers have been published on the influence exercise has on cardiovascular function in those with SCI (see review of Warburton et al.36). The purpose of this systematic review is to present a synopsis of the scientific literature investigating the usefulness of various exercise strategies to improve vascular function in denervated limbs of those with SCI. We hypothesize that there will be strong support for the therapeutic vascular benefits of exercise training in persons living with SCI. Furthermore, we expect that exercise modalities, which employ electrical stimulation of denervated muscle, will have stronger support as compared with techniques, which allow passive motion of denervated limbs.

Methods

A keyword literature search for all scientific publications from 1950 to present investigating the influence of exercise on vascular stiffness was conducted using the following online databases: MEDLINE, EMBASE, Cochrane Library, ACP Journal Club, DARE, CCTR, CMR, HTA, NHSEED, PsycINFO, SPORTDiscus and CINAHL. Population key words—spinal cord injuries, spinal cord injury, paraplegia, tetraplegia and quadriplegia—and vascular function keywords—vascular stiffness, vascular compliance, vascular function, vascular elasticity, vascular resistance, arterial stiffness, arterial compliance, arterial resistance, arterial function, arterial elasticity, endothelial function, artery stiffness, artery compliance, artery function, artery elasticity, blood flow, arterial flow, leg blood flow, femoral artery flow and femoral blood flow—as well as exercise phrases—exertion, exercise, movement, locomotion, running, jogging, swimming, walking, dependent ambulation, motor activity, muscle contraction, isometric contraction, isotonic contraction, weight lifting, exercise therapy, physical, physical activity, body weight supported treadmill training (BWSTT) and functional electrical stimulation (FES)—were paired by permutation. A total of 283 papers were found, after which duplicates, review papers, letters to the editor, those not in English and those not evaluating arterial function outcomes were removed from the sample leaving a total of 26 articles (Figure 1). Two additional papers40, 41 were added to the sample as a result of cross-referencing, leaving a total of 28 articles.

Figure 1
figure 1

Flow of studies through systematic review.

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An evaluation of the methodological quality of each article was completed by two independent reviewers (AP, AC) and confirmed by a third reviewer with expertise in systematic reviews (DW) using either the 11-item PEDro Scale42 (randomized controlled trials; RCT) or the Down and Black Tool43 (non-RCTs). The highest and therefore most methodologically strong score attainable for a given research article is 10 for the PEDro Scale and 27 for the Down and Black Tool. Higher points indicate a superior methodological quality. Further, the level of evidence was evaluated using a five-level scale43 (simplified form of Sackett),44 where level 1 (the highest level of evidence)=RCT with a PEDro score ⩾6; level 2=an RCT with a PEDro score ⩽5, a non-randomized prospective-controlled study, or a cohort study; level 3=a case–control study; level 4=a pre- and post-test or a case series; and level 5 (the lowest level of evidence)=an observational report or case report with only a single subject.45 There was no minimum sample size owing to the low number of publications in SCI research. Librarians from the University of British Columbia and all authors approved this systematic process and methodology. Ranking scores were performed in duplicate, after which any discrepancies were solved by discussion.

Results

The articles selected for investigation were categorized into two groups: Acute Exercise and Non-Acute Exercise. Within the Acute Exercise group, the Down and Black Tool scores ranged from 10 to 19 out of 27 (limited to moderate methodological strength).46, 47, 48 The lone RCT49 categorized within the Non-Acute Exercise group received a PEDro Scale score of six out of 10 (good methodological quality),50 whereas the remaining studies ranged from 10 to 20 out of 27 on the Down and Black Scale (considered limited to moderate methodological quality).46

Acute exercise techniques

Fourteen papers investigated the vascular effects of a single acute exercise bout. Eight articles were prospective control trials31, 41, 51, 52, 53, 54, 55, 56 and six were pre–post design.40, 57, 58, 59, 60, 61 Papers investigating acute exercise included: passive leg exercise (n=3),53, 57, 60 FES (n=3),54, 55, 59 single muscle electrical stimulation (n=1),56 upper body continuous aerobic exercise (arm cycling or wheeling) (n=5),31, 40, 41, 52, 58 acute combined arm passive leg exercise (n=1)61 and stretch-induced contractions (n=1).51 Tables 1 and 2 are a summary of published investigations researching the effect of acute exercise on arterial function in SCI individuals.

Table 1 Results of the OVID (MEDLINE, EMBASE, ACP, Cochrane Library, DARE, CCTR, CMP, HTA, NHSEED) literature search
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Table 2 Effect of acute exercise interventions on arterial dynamics in SCI
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Acute passive leg exercise

Passive leg exercise, or the application of external forces on denervated limbs with the purpose of causing motion, is the simplest technique for lower body exercise in the SCI population.36 Three papers investigated the vascular effect of passive exercise on arterial function in SCI participants. One examined the influence of passive range of motion physiotherapy on leg blood flow in paraplegics (PARA) and tetraplegics (TETRA).60 This article showed that leg blood flow increases very little, if at all, in response to passive leg movement administered by a physiotherapist.60 The other two studies from this group investigated passive cycling (denervated legs are strapped to pedals and pedals are mechanically rotated) and showed disagreement in their results. Ter Woerds et al.53 measured arterial function before, during and after 10 min of passive leg movements, and 20 min of passive leg cycling for PARA and AB individuals. These authors showed no change in femoral blood flow or leg vascular resistance (calculated as mean arterial pressure divided by leg blood flow) for either group during or after (0, 1, 2, 5 or 10 min post-exercise) either of the passive exercise modalities. In contrast, Ballaz et al.57 reported that leg blood flow (measured using Doppler ultrasound) increased in PARA after 10 min of passive cycling. These authors acknowledged the discrepancy and inferred a number of methodological differences between studies to account for marked disparities (such as higher cadence, continuous exercise without 10-s rest periods for flow measurements, larger sample size and optimal force arm length to involve the maximum musculature for a given pedal rotation).57

Conclusions: There is level 4 evidence (indicating available evidence but without comparable groups) that a single bout of passive leg exercise increases leg blood flow,57 whereas there is level 253 (debatable but reliable results) and level 4 evidence60 suggesting no change in leg blood flow or leg vascular resistance in response to passive leg exercise. As only three papers have published results on leg blood flow changes in response to passive leg exercise, further research, incorporating various exercise intensities and force arm lengths with adequate sample sizes, is warranted.

Acute FES exercise

FES involves muscle stimulators placed over motor points in denervated musculature activated in a synchronized manner as to functionally manipulate an exercise device (e.g. a cycle ergometer). FES is one of the most widely studied rehabilitation techniques for the SCI population. The application of FES has shown promise for a variety of SCI-related issues including obesity62 and muscle atrophy.63 A total of three papers have investigated acute arterial function changes in response to FES.54, 55, 59 Nash et al.55 showed similar ankle/brachial index (the ratio of blood pressure in the lower legs to the blood pressure in the arms) at rest between age- and gender-matched AB and TETRA men. After an acute 30-min bout of FES, however, ankle/brachial index in AB men increased with no change in TETRA. These findings were explained by increased lower body blood pooling after exercise or decreased vascular response post-exercise in TETRA.55

The remaining two papers measuring arterial function in response to acute bouts of FES showed increased leg blood flow after exercise. In the investigation by Phillips et al.,59 pre–post exercise changes in toe photoelectric plethysmography were used to estimate changes in leg blood flow in SCI participants (C6–T12). The participants performed two different FES intensities (40 mA, 80 mA) in conjunction with arm crank exercise (hybrid), and adjusted resistance to create an intensity of 60 or 80% of VO2 peak (four trials total). These authors reported significantly elevated leg blood flow after hybrid exercise and increasing blood flow with increasing hybrid exercise intensity, suggesting that leg blood flow in SCI is intensity dependent.59 Dela et al.54 also showed increased leg blood flow with FES and no difference in leg blood flow or leg oxygen uptake between TETRA, PARA or AB after 15 min of low-intensity FES. However, for those with SCI, these variables leveled off and did not increase at the higher FES intensity as was noted in the AB group.

Conclusions: There is level 2 evidence54, 55 (reliable results but debatable) suggesting that FES exercise can improve arterial function in those with SCI. Studies examining acute bouts of FES illustrate its usefulness in identifying vascular changes in those unable to willfully contract musculature. The findings of the three studies investigating SCI arterial function in response to FES show that lower body exercise of this modality can cause an increase in leg blood flow in both TETRA and PARA. It appears that further investigations involving a variety of intensities and durations of FES are needed to clarify disagreement in the dose–response relationship between exercise and arterial dynamics in SCI. In addition, to maximize potential arterial benefits, different modalities (specifically concurrent arm cranking (hybrid) vs resting upper body) need to be compared.

Acute single muscle electrical stimulation

One article investigated the influence of single muscle electrical stimulation on arterial dynamics in those with SCI.56 This study illustrated that electrical stimulation of the quadriceps femoris leads to increased femoral artery blood flow. In addition, these authors showed that femoral blood flow increases with increasing exercise intensity in SCI participants, suggesting a dose–response relationship.

Conclusions: Currently, there is level 4 (available evidence but without comparable groups) evidence suggesting that single muscle leg electrical stimulation improves femoral artery blood flow in those with SCI. Only one study has investigated this type of intervention (n=17, 9 SCI, 8 AB); therefore, there is a great need to examine further the effect of single muscle electrical stimulation on arterial dynamics in those with SCI.

Acute arm exercise

Upper body exercise for individuals with SCI is a relatively inexpensive and simple technique to increase physical activity. The arterial changes in SCI persons induced by acute bouts of upper body exercise have been studied in five31, 40, 41, 52, 58 articles. Three papers from this group investigated blood flow changes in response to arm cranking.40, 41, 52 The common finding from this group of investigations is that the ability of the denervated vasculature to locally regulate blood volume and redistribute it to working muscles (i.e. the upper body during arm cycling) is impaired. Bidart and Maury52 showed no change in leg blood volume (plethysmography) during 1 min of arm cranking in SCI, whereas leg blood volume decreased substantially during the same exercise in AB. Kinzer and Convertino40 showed that leg blood volume increases after 10 min of arm cycling in SCI, but decreased in AB. Hopman et al.41 illustrated convincingly the impaired local regulation in denervated lower limbs by showing that both the rate of leg blood volume changes and the absolute level of leg blood volume were significantly reduced in SCI as compared with an AB control group during 25 min of arm cycling.

In addition to investigating leg blood volume changes, leg blood flow was also measured during upper body cycling exercise in four of the five papers.31, 40, 52, 58 Kinzer and Convertino40 as well as Bidart and Maury52 and Burkett et al.58 showed increases in leg blood flow during upper body arm cycling at moderate40, 52 and maximal58 intensity levels (durations of 4–15 min). The results of Kinzer and Convertino40 as well as Burkett et al.,58 however, failed to show significant changes, and work by Bidart and Maury52 did not include a statistical analysis or original data. Hopman et al.31 took this line of research a step further and illustrated that there is no statistically significant increase in femoral artery blood flow during 25 min of upper body cycling. The data from this paper, however, does show a trend of increasing mean femoral artery blood flow velocity, with no change in arterial diameter (flow=velocity × diameter).31

Conclusions: There is level 2 evidence40, 41, 52 (reliable results but debatable) showing that local blood volume regulation in denervated limbs is impaired during upper body cycling in SCI. In addition, there is level 2 evidence40, 52, 58 (reliable results but debatable) suggesting that leg blood flow increases during upper body cycling; however, these conclusions were not verified statistically. There is however level 2 evidence showing that leg blood flow does not increase to a statically significant level during upper body cycling exercise.31 More research is needed to clarify the minimum duration and intensity of arm exercise required to improve leg blood flow. Also, more research is required with regard to changes in leg blood flow during upper body cycling with larger sample sizes and relevant statistical analyses.31

Acute combined arm passive leg exercise

Only one study has examined arterial function after a single bout of active arm exercise combined with passive leg movement.61 This pre–post investigation showed that blood flow measured by double isotope disappearance rate increased in the tibialis anterior after simultaneous 30 repetition bouts of arm movement against resistance and passive leg movement performed by a physiotherapist.

Conclusions: There is currently one paper with level 461 evidence (available evidence but without comparable groups) that reported increased leg blood flow in response to combined arm exercise and passive leg movements. With such limited data, it is difficult to interpret the value of this exercise technique. Further research is required in this area.

Stretch-induced contractions

One study has investigated the changes in arterial structure and function in response to stretch-induced contractions of denervated limbs in those with SCI.51 The investigation by Bidart and Maury, which describes manually stretching the gastrocnemius to induce a spasmodic reflex contraction, found similar local blood flow responses in the gastrocnemius after stretch-induced contractions in AB and PARA. The authors also noted that because there was no quantitative comparison of the strength of spasmodic manual stretch reflex to voluntary contraction of the AB group, quantitatively comparing the blood flow response is speculative.

Conclusions: There is currently one paper with level 2 (debatable but reliable results) evidence investigating blood flow changes in response to stretch-induced contractions.51 With such limited data, it is difficult to interpret the value of this exercise technique. More research needs to be completed investigating64, 65, 66, 67, 68 the acute vascular changes in response to stretch-induced contractions.

Exercise training interventions

Fifteen papers met the systematic search criteria that examined changes in arterial function and structure resulting from exercise training (i.e. non-acute exercise) interventions. Two articles were case–control studies,69, 70 11 were of the pre–post design,24, 71, 72, 73, 74, 75 one was a case report and one was an RCT. The Non-Acute Exercise category (n=15) included passive leg exercise (n=1),49 FES (n=5),65, 70, 71, 72, 73 upper body exercise (n=2),69, 76 an electrically stimulated resistance training regimen (n=3),24, 67, 68 hybrid exercise (n=3)66, 74, 75 and BWSTT (n=1).64 Table 3 is a summary of published investigations examining the effect of non-acute exercise on arterial function in those with SCI.

Table 3 Effect of non-acute exercise interventions on arterial dynamics in SCI
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Passive leg exercise

Only one study investigated the effect of a passive, non-acute exercise program on arterial function in PARA.49 This study showed that an un-supervised 6-week home-based passive cycling intervention improves femoral artery hemodynamic response (ultra-sound derived femoral blood flow velocity) in those with SCI (n=9) after 10-min passive cycling exercise (P=0.01), but does not change resting femoral artery blood flow (P=0.08). The control group (n=8), which continued their habitual daily routine, showed no change in either measure.

Conclusions: There is currently level 1 evidence49 (highly reliable) supporting a passive leg exercise program as a technique to improve vascular function in PARA. Although only one study has investigated this intervention technique, the high level of evidence suggests that routine passive exercise improves lower body vascular function in PARA. There is a need to investigate long-term passive cycling exercise programs with larger sample sizes that include TETRA.

FES

Several investigations have examined the effect of non-acute FES training for improving arterial dynamics in SCI. All five papers investigating FES cycling showed significant improvements in vascular function in both PARA and TETRA. Overall, FES has led to increased femoral artery blood flow,70, 71, 73 improved small artery compliance,65 femoral artery compliance,72 normalized femoral flow-mediated dilatation,72 reduced leg vascular resistance73 and improved hyperemic response.70 According to work by De Groot et al.,23 a minimum of 2 weeks FES training is required for arterial dynamic improvements (femoral artery flow-mediated dilatation); however, trends start to appear after the first week. After 4 weeks of FES training, femoral arterial compliance and femoral artery blood flow showed statistically significant improvements.

Conclusions: Based on the available evidence, including a level 3 (ref. 70) (somewhat reliable) investigation, there is promising support for the use of long-term FES training in improving vascular health in SCI.

Arm exercise

Two papers have evaluated the effect of non-acute upper body (arm) exercise on arterial function in SCI participants. Jae et al.69 compared intima–media thickness, compliance and β stiffness index (a measure of arterial elasticity) of the common carotid artery between 28 PARA competitive athletes and 24 age-matched recreationally active AB controls finding no differences between groups. In addition, Tordi et al.76 published a case study examining the aortic pulse wave velocity values of a single SCI participant before and after 6 weeks of upper body endurance training (30 min, 3 times per week) showing significant improvements in central aortic stiffness post-training.

Conclusions: These studies appear to suggest that long-term upper body exercise can improve arterial structure and function in those with SCI. The study design (level 369 and level 576 evidence (somewhat reliable–to reliable)) of these investigations illustrates the need for prospective research examining the influence of non-acute upper body exercise on arterial dynamics in SCI participants with larger sample sizes and proper controls.

Electrically stimulated knee extension

Electrically stimulated knee extension, which involves electrical stimulation of the denervated musculature to increase strength, has been investigated by three studies as a potential technique for improving arterial structure and function in those with SCI.24, 67, 68 Two studies’ training regimen consisted of exercise 2 days per week, for 8 weeks. In the first study, improved quadriceps strength was found, but no improvements in femoral arterial structure or function (artery diameter, hyperemic response, exercise blood flow response).68 In the follow-up study from the same group, improved femoral artery flow-mediated dilatation was elevated after the training regimen.67 Another study performed by Taylor et al.,24 which used a progressive 3-month long knee extension exercise with the aim of allowing standing, illustrated increased muscle thickness and thigh blood flow.

Conclusions: It appears from level 4 evidence24, 67, 68 (available evidence but without comparable groups) that electrically stimulated knee extension increases quadriceps strength and improves some measures of lower body arterial function in those with SCI. More research is needed with SCI controls to verify the potential benefits of this therapy.

Hybrid exercise

A total of three studies investigated the effects of a long-term hybrid training intervention on arterial dynamics in those with SCI. Of those studies, two used FES cycling of the legs with voluntary arm cranking,74, 75 whereas the third study used a modified approach, which employed FES at the legs to assist with walking, while simultaneously supporting ones’ self using a walker to provide semi-autonomous ambulation.66 These studies reported improvements in femoral vascular function and structure for both TETRA74 and PARA participants,66, 75 including increased baseline femoral artery blood flow,74, 75 cross-sectional area,66 peak blood flow,75 diameter,74 flow-mediated dilatation74 and post-occlusion hyperemic response.66, 75 The dependency of these improvements on the exercise intervention is highlighted by Thijssen et al.,74 who showed that improvements occur after only 2 weeks of hybrid training and all vascular changes (with the exception of flow-mediated dilatation) disappear after just 1 week of de-training.

Conclusions: Hybrid exercise is a useful tool for improving vascular function in those with SCI. As of yet, no investigation has compared FES with hybrid exercise to identify whether hybrid exercise yields more vascular function gains than traditional FES training, particularly considering the increased cost of hybrid exercise equipment. The low level of evidence66, 74, 75 (level 4—limited reliability) for literature investigating the effect of long-term FES exercise interventions on arterial function and structure highlights the need for valid control groups.

Body weight-assisted treadmill training

Only one study examined the arterial function changes resulting from a non-acute program of BWSTT. Ditor et al.64 showed 4 months of training 3 days per week using BWSTT improved femoral arterial compliance, but did not increase femoral artery blood flow or carotid vascular compliance in those with TETRA or PARA.

Conclusions: It appears from this level 4 evidence64 (available evidence but without comparable groups), which showed that femoral artery compliance was increased, that BWSTT has the potential to improve vascular function in SCI participants. More studies are needed, however, with relevant (i.e. those with SCI) control subjects using varying intensities, protocols and levels of injury to clarify the maximum and minimum potential benefit, as well as timeline of functional gains for a given population.

Discussion

The purpose of this review was to compile and evaluate relevant literature examining the effect of various modes of exercise on arterial dynamics in those with SCI. We also separated articles into those investigating the effects of acute bouts of exercise and others investigating vascular changes from a multiple-session (non-acute) training intervention. As access to patients with low incidence disabilities such as SCI is very limited77 and the level of participation in physical activity within this population is lower than that of the AB population,78, 79 there is hesitation from researchers to design studies where half the willing and available participants would receive no intervention. Therefore, most research designs investigating SCI and exercise or physical activity involve poorly matched controls if present at all (level 2–5 evidence46). Testing the experimental group before and after a control phase, once the exercise intervention has been completed, may be a viable alternative, which would improve the level of evidence for studies limited in sample size.

Taking into consideration the lack of valid controls (i.e. those with SCI), the evidence still supports exercise as a viable method of improving vascular function in those with SCI. Following that, based on the available evidence, FES and hybrid exercise are the most promising types of exercise for improving arterial dynamics as they have been shown to increase femoral artery blood flow, reduce arterial stiffness and improve hyperemic response.65, 71, 72, 73, 74, 75 Finally, according to the available literature, to increase vascular health in those with SCI, hybrid or FES training with increasing levels of intensity should be performed a minimum of two times per week and continued indefinitely. Improvements in arterial structure and function begin to appear as early as 1 week into training and after 8 weeks show a range of arterial health benefits.

It should be noted that there is significant disagreement with regard to the ability of passive leg exercise to improve denervated arterial function, specifically femoral artery blood flow.49, 53, 57 In a published Letter to the editor,80 Hopman's group, which had shown no increase in femoral artery blood flow in response to passive leg exercise, questioned the results and methodology of work published by Ballaz et al.57 showing opposite results. Although no definitive conclusion resulted from this discussion, the influence of the muscle pump at increasing femoral artery flow in response to passive exercise was implicated as the potential mechanism. Research from our laboratory supports this concept and has shown the cardiac output to increase during passive exercise in patients with SCI.81 Further, others have shown the muscle pump to play a relatively small but significant role in leg blood flow during passive movement in AB individuals.82 Also, Ballaz et al.49 provided follow-up literature illustrating that long-term passive exercise interventions lead to significantly improved vascular function. This literature49, 81, 82, 83 strongly suggests that passive leg exercise increases femoral artery blood flow in people with SCI. Further research, with concurrent femoral artery flow measurements and isolated passive knee extension/flexion, is required to resolve this disagreement.

Finally, consideration must be given to the muscle groups stimulated while using FES. Three of the five papers used electrical stimulation sites at the hamstring, gluteal and quadriceps muscles,65, 71, 73 whereas De Groot et al.72 used tibialis anterior, gastrocnemius and quadriceps. Thijssen et al.75 have shown that when using FES, only the stimulated muscle tissue receives any improved arterial function or structure. Therefore, muscle groups used for electrical stimulation may be an important consideration when designing a rehabilitation program.

Conclusions

Cardiovascular disease, the primary cause of the death in those with SCI, is often overlooked in the SCI population owing to the multitude of other health issues and the focus on regenerating motor function. According to the available literature, exercise (upper body, electrically stimulated and passive modalities) improves arterial function in those with SCI. It cannot be overstated that more research should be performed investigating exercise as a means to improve arterial function in those with SCI as there is a clear shortage of published articles examining this relationship. Many exercise modalities have been explored by a single published article, and often studies lack matched or relevant control groups. Future investigations exploring exercise as a therapeutic rehabilitation technique for individuals with SCI should include the cost of, and accessibility to, equipment.