Abbreviations
SCI
spinal cord injury
PwSCI
persons with a spinal cord injury
VO 2peak
peak volume of oxygen consumption
VO 2max
maximal volume of oxygen consumption
ACE
arm crank ergometer
1-RM
one repetition maximum
WMS
WheelMill System
6-MAT
6-minute arm test
6MPT
6-minute push test
RPE
rate of perceived exertion
ASIA
The American Spinal Injury Association Impairment Scale
PO
power output
W
watts
RM
repetition maximum
ROM
range of motion
RER
respiratory exchange ratio
Introduction
Persons with a spinal cord injury (PwSCI) are at increased risk of leading less active lifestyles as compared to the general population. Spinal cord injury (SCI) results in declines in physical capacity and an increased risk of secondary health conditions. Specifically, PwSCI are three times more likely to have one or more chronic diseases such as heart disease, stroke, diabetes, cancer, or obesity compared to persons without disabilities ( ; ). SCIs often result in various physiological alterations affecting multiple body systems, including blunted hemodynamics, altered sympathetic innervation, altered glycemic control, reduced active muscle mass, deteriorated circulatory vessels below level of injury, and impaired arterial compliance and function ( ). These pathophysiological alterations amplify the risk and prevalence of cardiovascular and metabolic diseases in PwSCI. PwSCI are also at an increased risk of negative mood states including depression and anxiety ( ). An approach to managing the potential physiological and psychological implications of an SCI is engaging in physical activity or exercise.
Exercise and persons with a spinal cord injury
The typical daily routine of PwSCI does not stress the cardiorespiratory system enough to produce positive health-related changes; therefore, participation in regular exercise is needed to enhance physical capacity and to reduce the likelihood of secondary complications ( ; ). Similar to the general population, regular exercise is critical to reducing the risk of developing chronic health conditions and has positive effects on the physiological health and psychological well-being of PwSCI ( ; ). Participation in exercise is also connected to more established social networks and greater participation in life activities ( ; ). Increased cardiorespiratory fitness in PwSCI promotes not only improved functional independence, but also improved cardiovascular and metabolic health ( ).
Exercise and spinal cord injury considerations
PwSCI may experience secondary health conditions that are important to take into consideration when engaging in exercise. Bone loss and osteoporosis are complications that may occur following an SCI and can lead to an increased risk of fractures, which can have further negative consequences on health and functioning ( ). Upper extremity pain and chronic overuse injuries, particularly in the shoulder joints of PwSCI, are commonly associated with wheelchair self-propulsion and transfers ( ). Due to the direct effects of an SCI, PwSCI often lack normal protective sensation below the level of their injury. This lack of sensation combined with the reduced mobility associated with an SCI can result in the development of pressure ulcers ( ). Having an understanding of these possible secondary conditions is important when exercising. Proper biomechanical positioning when exercising, reducing the number of transfers onto exercise equipment, and implementing a regular shoulder strengthening exercise program targeted at the rotator cuff are among the actions that can be taken to prevent or delay these secondary conditions from impacting the exercise routine of a PwSCI.
Exercise recommendations for persons with spinal cord injury
Basic programming guidelines for exercise and physical activity are set forth by organizations including the American College of Sports Medicine’s Guidelines for Exercise Testing and Prescription (2020) and the Physical Activity Guidelines for Adults with Chronic Health Conditions and Adults with Disabilities from the . The U.S. Department of Health and Human Services recommends at least 150 minutes per week of moderate-intensity aerobic activity or 75 minutes per week of vigorous-intensity aerobic activity for adults with chronic conditions or disabilities, as well as muscle strengthening activities of moderate or greater intensity, 2 or more days a week. Diagnosis-specific guidelines exist for PwSCI and recommend shorter durations of weekly exercise time. For example, to gain cardiometabolic health and fitness and muscle strength benefits, the International Exercise Guidelines for PwSCI recommend that a PwSCI should engage in at least 20 to 30 min of moderate-to-vigorous-intensity aerobic exercise two to three times per week and three sets of strength exercises for each major functioning muscle group, at a moderate-to-vigorous intensity, two times per week ( ).
Barriers to exercise
Despite the widely recognized health benefits of regular exercise, PwSCI report lower levels of exercise compared to the general population ( ; ; ). Because of decreased sympathetic innervation, muscle atrophy, and decreased cardiac reserves, it is difficult for PwSCI to achieve intensity levels necessary to make health-related changes without proper support ( ; ). PwSCI face numerous challenges to participating in exercise, including personal (e.g., lack of motivation and self-efficacy) and environmental (e.g., transportation, access to proper equipment) barriers ( ). Unlike the surplus of fitness centers and equipment available for the general population, there is a considerable lack of accessible equipment, support, and professional guidance for PwSCI ( ; ). In addition, PwSCI do not always have access to the information needed to monitor their progress. Accurate and reliable measures are important so that physical activity levels of PwSCI can be assessed, recommendations can be made to better inform development of exercise programs, and PwSCI can independently track their exercise and take ownership of their health.
Importance of exercise testing
An important aspect of supporting PwSCI to successfully engage, initiate, and maintain exercise is the ability to have reliable information to inform and develop individualized programs and track change. Whether a person is an elite athlete training for the Paralympics or a newly injured PwSCI, having information to guide programs and help people achieve their goals is crucial. The following will discuss different types of testing, testing protocols, considerations for PwSCI, and equipment and adaptations.
Exercise testing for persons with a spinal cord injury
Physical fitness is the ability to perform activities of daily living, leisure activities, and other occupations without excessive fatigue. Physical fitness testing, also known as exercise testing, is important to conduct to determine a baseline fitness level, identify strengths and areas of improvement, and establish realistic goals for individuals. Comprehensive testing best informs exercise professionals to design and implement appropriate, client-centered exercise prescriptions. Follow-up testing results can also be performed and compared to baseline data to evaluate progress during and/or following a prescribed exercise program ( ). Accurate and reliable assessments are important so that exercise and fitness levels can be evaluated, recommendations can be made to better inform development of exercise programs, and PwSCI can independently track their exercise and take ownership of their health.
Exercise testing can include a number of different components; however, the two most common are cardiorespiratory endurance, also known as functional capacity, and musculoskeletal fitness testing. Musculoskeletal fitness is comprised of two components, muscle strength and muscle endurance ( ; ).
General considerations for exercise testing for people with spinal cord injury
PwSCI may experience a myriad of multi-system physiological alterations as a result of their injury ( ). For these reasons, specific considerations and precautions are recommended when conducting exercise testing with PwSCI. Exercise testing participants should obtain physician approval and signed release prior to initiation of testing. Testers should be well trained in the testing protocol, procedures, and equipment, and also familiar with potentially dangerous conditions associated with SCI, such as autonomic dysreflexia. Testing participants should be supervised and closely monitored throughout the duration of the testing session. Ambient temperature of the testing environment should be comfortable for the participant, keeping in mind persons with a cervical level injury may not be able to control their temperature by sweating and may need a fan blowing on them or cooler room temperatures. Devices such as heart rate monitors and/or other wearable sensors should be worn by testing participants for accurate monitoring of participant status. Vitals and pain level should be taken prior to initiation of testing to ensure that the session can safely proceed. The testing session should be terminated if any of the following distressful issues occur: abnormal heart rate or blood pressure, presence of a bladder infection, presence of a pressure ulcer, unusual spasticity, or autonomic dysreflexia. Testers should also determine a pain threshold at which to terminate testing; recommended thresholds may vary; however, terminating testing if reported pain is ≥ 6 out of 10 has been acceptable ( ).
Cardiorespiratory endurance testing
Cardiorespiratory testing can be categorized into laboratory or field tests. While laboratory tests provide greater accuracy and reliability, they also require advanced technology and training as well as increased cost to perform. The gold standard for assessing cardiorespiratory fitness is the measurement of peak volume of oxygen consumption (VO 2peak ) during a graded exercise test ( ). Field tests, while less sensitive thanVO 2peak , are typically more cost-effective, more readily available to administer in non-laboratory settings, and still provide a submaximal estimation of cardiorespiratory endurance. Examples of cardiorespiratory field tests that will be discussed include the 6-Minute Arm Test (6-MAT) and the 6-Minute Push Test (6MPT).
VO 2peak testing in people with spinal cord injury
While the maximal volume of oxygen consumption (VO 2max ) is widely accepted as the benchmark for measuring cardiorespiratory fitness, the VO 2 plateau and maximal heart rate criteria required to reliably establish VO 2max may be difficult for PwSCI to achieve given the various pathophysiological changes with SCI, specifically altered sympathetic innervation and reduced muscle activation. Therefore, VO 2peak is considered the gold standard to assess cardiorespiratory fitness and aerobic metabolism for this population. Breath-by-breath cardiometabolic and physiological measures can be obtained during testing using a computer-integrated metabolic measurement system; these measures include respiratory exchange ratio (RER), heart rate, pulmonary ventilation, energy expenditure, and ventilatory threshold ( ; ). VO 2peak testing is typically completed in 8 to 12 minutes, depending on the individual’s fitness level ( ). Assessing the participant’s rating of perceived exertion (RPE) throughout the graded exercise test is also highly recommended ( ). VO 2peak determination typically includes achievement of RER ≥ 1.1 and RPE ≥ 15–17 as standard indicators for test termination; however, other criteria may be incorporated, including blood lactate and heart rate ( ; ). Heart rate is only reliable for people with neurological levels of injury below T7, as autonomic dysfunction and blunted sympathetic innervation occur in individuals with higher injury levels ( ). Evidence of norm-reference values for VO 2peak in adults with SCI is sparse; however, it is accepted that VO 2peak may be impacted by sex and neurological level of injury ( ; ).
Equipment options for VO 2peak fitness testing in people with spinal cord injury
For non-wheelchair users, VO 2peak is commonly measured on treadmills or stationary bikes, both common forms of exercise for this population. For individuals with SCI using wheelchairs, the most common method of measuring VO 2peak is during a graded exercise test using an arm crank ergometer ( ), wheelchair ergometer, or a roller-based wheelchair dynamometer ( ; ).
Arm crank ergometers
An arm crank ergometer (ACE) is a low-impact exercise system for both lower and upper extremity conditioning that has hand cranks and foot pedals and a removable seat for wheelchair access. For PwSCI who use a wheelchair for functional mobility, the hand cranks are used during testing. It is recommended to use an ACE that includes adjustable arm cranks and a removable seat for wheelchair access. Arm cranks should be adjusted where the axes of rotation are positioned just below shoulder level of the participant to ensure proper alignment of the glenohumeral joint to the ACE ( Fig. 1 A ). Proper biomechanics also include ensuring that participants’ arms are slightly flexed at the elbows at the moment of furthest reach ( Fig. 1 B). Participants are able to use their personal wheelchairs (manual or power) during testing; however, if trunk stability safely allows, participants may opt to transfer to the ACE seat.
While ACEs are the most widely used and commercially available devices for cardiorespiratory testing ( ; ; ; ), have shown to be effective in testing fitness, and provide health-related changes in PwSCI, they present with limitations ( ). The operation of an ACE requires a movement pattern not typically employed during functional mobility or activities of daily living ( ). Functional impairments in hand strength and trunk control can yield further limitations of ACEs. Ace bandage wraps or specialized grip-assist gloves ( Fig. 1 C) can be used when hand grip impairments are present. Abdominal binders may be used to assist with trunk stabilization during testing.
Wheelchair-based systems
Propulsion is the primary functional movement pattern for PwSCI who use a manual wheelchair. Testing devices such as wheelchair ergometers and roller-based systems provide a simulated over-ground propulsion experience, allowing the individual to remain stationary while engaging in a functional movement pattern during testing. Each of these devices allows manual wheelchair users to use functional propulsion to complete the stepwise VO 2peak protocols. Evidence suggests that each device has strengths and weaknesses with no consensus on which type is best for exercise testing ( ).
Wheelchair ergometers, sometimes referred as dynamometers, utilize treadmill and bicycle components to allow participants to propel a manual wheelchair; however, these testing devices have limitations. Wheelchair ergometers often require participants to sit in and propel a designated laboratory wheelchair that has been pre-fit for the device. Participants report that the glide differs from typical wheelchair propulsion, potentially impacting body mechanics and performance during testing. Wheelchair ergometers typically have limited customization or fine tuning that is highly beneficial when working with a diagnosis such as SCI ( ).
Roller-based systems, also referred to as wheelchair dynamometers, consist of one or two parallel rollers and may allow for customizable manipulation of variables such as resistance ( ; ). Roller-based systems ( Fig. 2 ) further promote the functional movement pattern of propulsion by allowing for participants to use their personal wheelchairs, including sports wheelchairs, optimizing body mechanics, propulsion patterns, and performance during testing. An example of a roller-based system that has been used for VO 2peak testing for PwSCI is the WheelMill System (WMS). The WMS is a computer-controlled, motor-driven wheelchair dynamometer that has been used for VO 2peak testing ( ; ). found that despite similarities in outcomes between ACEs and the WMS during VO 2peak testing, participants consistently rated their RPE higher on the ACE compared to the WMS despite the same workload ( ). At this time, roller-based systems are not as widely available as ACE, and testers require enhanced training to operate and execute protocols using these devices. Participants should be directly supervised or spotted when transitioning their wheelchair to and from the rollers to prevent falls. Falls and wheelchair tipping should also be prevented during testing using safety straps to secure the wheelchair to the roller-based system.
Submaximal field tests
6-Minute arm test
The 6-MAT is a submaximal cardiorespiratory fitness test performed at a constant power output (PO), which is selected based on the individual’s score on the American Spinal Injury Association (ASIA) Scale, sex, mobility device (manual vs power), manual muscle testing, and current physical activity level (inactive, active, or competitive; Fig. 3 ). A standard, adjustable ACE is used for the 6-MAT. Individuals are instructed to maintain a consistent cadence of 60 rpm at the selected PO for the 6-minute duration of the test. Heart rate should be measured in 1-minute intervals, while RPE may be assessed either at 1-minute intervals and/or immediately following completion of the test ( ; ). Normative values have not been established for this submaximal field test; however, testers can use wearable sensors to gather data such as heart rate, RPE, total distance cranked, and estimated energy expenditure ( ; ) to compare pre-post for purposes of determining exercise programming effectiveness. The 6-MAT is appropriate to administer for PwSCI using either a manual or power wheelchair. Considerations for the 6-MAT are related to the aforementioned limitations and considerations of using an ACE.
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