Cardiovascular Training in Spinal Cord Injury
- 1 Introduction
- 2 Definition
- 3 Assessment of Cardiovascular Fitness
- 4 Response to Cardiovascular Fitness Training
- 5 Exercise Prescription
- 6 Resources
- 7 References
Cardiovascular training involves the use of oxygen to meet the energy demands of the body’s muscles during exercise. It is associated with longer duration exercise during a given session of training, often at a consistent pace. Regular cardiovascular training has been shown to improve cardiovascular function, aerobic capacity, and exercise tolerance in individuals with a spinal cord injury, often resulting in improved independence in activities of daily living.
According to the Oxford Dictionary of Sport Science and Medicine, cardiovascular fitness is the "ability of the heart and blood vessels to supply nutrients and oxygen to tissues, including muscle, during sustained exercise".
Assessment of Cardiovascular Fitness
Assessment of cardiovascular fitness is essential for physiotherapists to directly determine training or conditioning intensities required to elicit improvements in cardiovascular and cardiometabolic health. Gold standard laboratory-based assessment with ergometer i.e. arm crank, wheelchair treadmill is becoming more commonplace, particularly within the competitive sport, although these results alone do not represent the full picture. Pushing proficiency, sport-specific skills, wheelchair propulsion technique, and individual adaptations to their wheelchair in order to develop appropriate exercise programs and monitor the response to training it is important to first assess cardiovascular fitness under reproducible test situations, ensuring factors such as the type of ergometer, constraints used, position of the individual are standardized. Precautions should also be followed when conducting cardiovascular assessments as strenuous exercise can lead to a cardiovascular event.
Prior to completing any maximal exercise testing a detailed medical and surgical history is required to identify indications for an exercise test and determine any underlying conditions, For example, cardiovascular, pulmonary, musculoskeletal, or neurological dysfunction or the presence of diabetes, hypertension, or heart block requiring a pacemaker, anemia, thyroid dysfunction, obesity, deformity, vertigo, or impaired cognitive function. It is also important to be aware of any medications that can influence the test procedures and the response to the exercise.
Peak Oxygen Consumption Tests
The Peak Oxygen Consumption (VO2 Peak) test, equivalent to the VO2 Max test in able-bodied individuals, measures the maximal capacity of the body to deliver oxygen from the lungs to the mitochondria of exercising muscles by expired gas collection and is the most accurate way to assess cardiovascular fitness in spinal cord injury. The terminology is used to reflect the lower maximal rate of oxygen consumption with arm exercises vs leg exercises due to both lower demand for oxygen from smaller muscle groups and the circulatory implication of arm exercise.
In individuals with a spinal cord injury, the VO2 Peak Test is typically performed using an arm cycle ergometer, but can also be completed with manual wheelchair propulsion or handcycle on an ergometer or treadmill with gradually increasing exercise intensities until exhaustion. Rest periods of 20 - 30 seconds are at times provided for between each increment. Starting points for arm ergometry vary depending on the level of spinal cord injury and level of fitness. Power output can be adjusted by changing the cranking velocity and/or externally applied resistance. For example; 
Paraplegia; Start at 30 Watts and increase by 10 - 15 Watts every 2 minutes. Maximal power output is likely to be between 50 - 100 Watts.
Tetraplegia; Start at 5 Watts and increase by 2.5 - 10 Watts every 2 minutes. Maximal power output is likely to be between 10 - 50 Watts.
While the VO2 Peak is the gold standard method for assessing exercise response for an individual with a spinal cord injury, it is rarely used in spinal cord injury units due to the complex nature of the test.
Submaximal Exercise Tests
Submaximal exercise tests, typically involve measuring the responses to standardized physical activities that are typically encountered in everyday life and are more commonly used in individuals with a spinal cord injury to evaluate the adaptation of the oxygen transport system to exercise below maximal intensity, so that the main energy system used is aerobic. While portable expired gas analysis systems can be utilized and are often used in high-performance Paralympic sport, heart rate measurement is more commonly used in spinal injury rehabilitation units. Use of heart rate measurements does not allow estimation of VO2 Peak but is used as a means to monitor the response of individuals with a spinal cord injury to training, with improvements in cardiovascular fitness indicated by decreased heart rate at the same power output with training or improvements in individual's perception of exertion with the Borg Exertion Scale.
Performed in a similar way to the VO2 Peak test with a different set of protocols and terminated prior to exhaustion. There are numerous submaximal protocols from which to choose, many of which have been developed to meet the needs of individuals with various functional limitations and impairments, including spinal cord injury. A commonly used protocol for individuals with a spinal cord injury includes 3 x 7 Minute Exercise Bouts of exercise at 40%, 60%, and 80% of predicted maximal exercise capacity.
Paraplegia with High Level of Fitness; 7 mins each at 40 Watts, 60 Watts and 80 Watts
Tetraplegia; 7 mins each at 20 Watts, 30 Watts and 40 Watts
Production of a sufficient level of exercise stress without physiologic or biomechanical strain is the key goal of submaximal testing. Factors that we believe should be considered in selecting the appropriate test include the person's primary and secondary pathologies and how these pathologies physically affect the person's daily life. Other factors include cognitive status, age, weight, nutritional status, mobility, use of walking aids or orthotic or prosthetic devices, independence, work situation, home situation, and the person's needs and wants.
Submaximal exercise testing overcomes many of the limitations of maximal exercise testing, appears to have greater applicability to physiotherapists in their role as clinical exercise specialists compared with maximal exercise testing, and are much easier to implement within a spinal injury unit and rehabilitation setting. There is new evidence to suggest that in cervical level spinal cord injury peak heart rate and blood lactate concentration attained during maximal incremental laboratory-based wheelchair exercise on a treadmill were below those attained during maximal field-based exercise testing in highly trained wheelchair rugby athletes, suggesting that incremental exercise testing in the laboratory does not elicit true peak cardiometabolic responses in highly-trained wheelchair rugby athletes with a cervical spinal cord injury and field exercise tests may give a better indication of maximal performance.
Field Exercise TestsA field exercise test is usually a measurement of a physiological function produced, while an athlete is performing in a simulated sport situation. While often thought not to be as reliable as lab-based tests, they are considered to have more validity as a result of greater specificity. A range of options can be used for field testing including;
Time Based; Measurements of distance travelled over a set period of time, e.g. 12 min push standardised test
Distance Based; Measurements of time taken to complete certain distance, e.g. Time for 1km
Implications for Rehab
- The use of regular cardiovascular capacity testing during spinal cord injury rehabilitation allows us to monitor the impact of rehabilitation interventions on an individual level.
- Incremental arm ergometry with small increments per stage is the most relevant means of assessment for peak cardiovascular capacity for individuals with a spinal cord injury.
- Use of the submaximal wheelchair ergometer test is preferable to use for the assessment of daily life functioning.
- Systematic reporting on test termination, peak outcomes criteria, and adverse events is key to enhance the comparability of results. 
Response to Cardiovascular Fitness Training
Response to cardiovascular fitness training is significantly influenced by the type of spinal cord injury including neurological level, level of completeness, and extent of the injury. Those with an incomplete level of injury, particularly those who can ambulate and have some lower limb use during exercise, respond to exercise in a similar way to able-bodied individuals. While those with a complete cervical level injury or upper thoracic level injury have a significantly different response as a result of reliance on upper limb exercise, lower limb paralysis, and most importantly loss of supraspinal sympathetic nervous control, which adversely affect cardiac output and arterio-venous oxygen; the two components of VO2 Peak.The Fick Principle summarises the relationship between cardiac output, arteriovenous oxygen difference, and VO2 Peak;
VO2 Peak = Cardiac Output (Q) x (a-vO2 Difference) 
|Heart Rate||Stroke Volume||Arterio-Venous Oxygen Difference|
|Sympathetic Nervous System
Parasympathtetic Nervous System
Intrinsic Heart Rhythm
|Size of Exercising Muscle Mass
The ability of Muscles to Extract Oxygen
Cardiac OutputCardiac Output (Q) is defined as the amount of blood pumped by the left ventricle of the heart per minute. It is expressed as liters/minute.
Cardiac Output (Q) = Heart Rate (HR) x Stroke Volume (SV)
Heart rate is determined by the balance between sympathetic control to the heart via T1 - T4 nerve roots that increase heart rate and parasympathetic control via the vagal nerve which decreases heart rate. The heart will beat at between 70 - 80 beats per min, the intrinsic firing rate of the sinoatrial node in the heart, without input from either the sympathetic or parasympathetic systems.
Normally during exercise in able-bodied individuals heart rate increases as a result of reduced vagal nerve activity and increased activity of the sympathetic nervous system, with maximal heart rates between 200 - 220bpm possible. 
In spinal cord injury lesions between T1 - T4 there is a partial loss of Supraspinal Sympathetic Control to the heart, with increases in heart rate occurring primarily as a result of the withdrawal of excitatory input from the vagal nerve, resulting in lower maximal heart rates of between 110 - 130. 
In spinal cord injury lesions T1 and above there is a complete loss of Supraspinal Sympathetic Control to the heart, with increases in heart rate occurring primarily as a result of the withdrawal of excitatory input from the vagal nerve. As a result in many individuals with tetraplegia they are unable to increase their heart rate beyond the natural rhythm of the heart, and as such, heart rate may not be considered the best indicator of training in tetraplegia.
Stroke volume is the volume of blood ejected at each stroke of the heart during systole, with typical stroke volume in able-bodied individuals 70ml at rest increasing to a maximum of 120 ml during strenuous exercise. Typically stroke volume increases during exercise in able-bodied individuals as an adaption to cardiovascular training.
In spinal cord injury maximal stroke volume, and as a result, cardiac output is decreased due to loss of supraspinal sympathetic control below the level of the injury and use of the upper limb alone during exercise. Both these factors have a negative effect on venous return as a result of venous pooling with the reduced return of oxygen from the lower limbs and reduced intra-thoracic muscle pumps, and contractility, meaning less blood returning to the heart with each beat.
Arterio-Venous Oxygen Difference
The arteriovenous oxygen difference is a measure of the amount of oxygen taken up from the blood by the tissues. Cardiac output and arteriovenous oxygen difference are the determinants of overall oxygen uptake. During exercise blood flow increases to the tissues; hemoglobin dissociates quicker and easier. This results in a greater arteriovenous oxygen difference during exercise. In trained athletes, the arteriovenous oxygen difference is greater as a result of the tissues becoming more efficient in oxygen uptake with aerobic training.
Size Exercising Muscle Mass
The size of the exercising muscle mass is the most important determinant of the arteriovenous oxygen difference. This can be seen in able-bodied athletes where the VO2 Max with upper limb exercise is approximately 70% of their VO2 Max when exercising with the lower limbs, which occurs as a result of reduced opportunity, need, and ability to extract and utilize the oxygen with upper limb exercise. 
In spinal cord injury, individuals with tetraplegia and partial paralysis in the upper limb have a smaller active muscle mass than those individuals with paraplegia, similarily those with an incomplete injury have a larger active muscle mass than those with a complete injury at the same neurological level. Cardiovascular training has the ability to increase the arteriovenous oxygen difference through muscle hypertrophy, resulting in increased muscle mass.
Ability Muscle to Extract Oxygen
Oxygen extraction from the exercising muscle is the other key determinant of arteriovenous oxygen difference, which is determined by factors including some and type of muscle fibers, the density of capillaries, regulation of blood flow, the size and number of mitochondria and type of metabolism, which tend to be relatively unaffected by spinal cord injury, although the loss of supraspinal sympathetic control can impact the ability of the body to redirect blood from non-essential organs to exercising muscles. Vasoconstriction in the non-essential organs occurs as a result of sympathetic activity during exercise in able-bodied individuals, increasing blood flow to the exercising muscles and when this does not adequately occur in individuals with a spinal cord injury it can result in exercise-induced hypotension.
Increased ability of the exercising muscles to extract oxygen, and therefore play a key role in increased VO2 Peak, is one of the key benefits from cardiovascular training in individuals with a spinal cord injury, both tetraplegia, and paraplegia, which delays the onset of muscle fatigue and increases maximal exercise capacity.
Several national and international organizations, e.g. American College of Sports Medicine provide clinicians and allied health professionals with guidelines on how to screen, assess, and, when appropriate, prescribe exercise for different population groups. A group led by Dr. Kathleen Martin Ginis at the University of British Columbia and Dr. Victoria Goosey-Tolfrey at Loughborough University, UK have recently developed international guidelines on exercise after spinal cord injury which provide minimum thresholds for improving cardiorespiratory fitness and muscle strength and for improving cardiometabolic health, which should be considered when prescribing cardiovascular exercise for individuals with a spinal cord injury, which you can read more about here.
Safe and effective exercise prescription requires careful consideration for the target individual's health status, baseline fitness, goals, and exercise preferences. When considering exercise prescription in an individual with a spinal cord injury you should also consider their neurological level of injury, and the implications it may have the type of exercise available and the modifications required to support their participation including trunk stability and balance, and use of strapping, gripping aids and assistive devices. The FITT Principle (Frequency, Intensity, Time and Type) should be used to develop, guide, and monitor cardiovascular training to ensure an effective exercise program, and the initials F, I, T, T, stand for Frequency, Intensity, Time and Type.] For those only starting to participate in cardiovascular training, start with smaller amounts of exercise and gradually increase the duration, frequency, and intensity.
|F||Frequency||How Often to Train||3 - 5 Days per Week|
|I||Intensity||How Hard to Train||50 - 80% Peak Herat Rate
Can use Borg Scale to monitor
|T||Time of Exercise||How Long to Train||20 - 60 minutes|
|T||Type of Exercise||What Exercise||Continuous Training
Varied Pace Training
FrequencyIn line with the new Spinal Cord Injury Exercise Guidelines to improve cardiorespiratory fitness, adults with a spinal cord injury should engage in at least;
Aerobic Exercise 2 times per week for Cardiorespiratory Fitness
Aerobic Exercise 3 times per week for Cardiometabolic HealthFor those not already exercising, start with a lower frequency and gradually increase the frequency as a progression towards meeting the guidelines, recognizing that exercise below the recommended levels may or may not bring small changes in cardiorespiratory fitness.
This is an extremely important aspect of the FITT Principle and is probably the hardest factor to monitor, particularly in individuals with a spinal cord injury. In able-bodied individuals, heart rate is the most commonly used method to gauge the intensity of cardiorespiratory exercise, but this is less reliable for individuals with a spinal cord injury who have a loss of supraspinal sympathetic control.
Subjective measures of aerobic intensity such as Rating of Perceived Exertion Scales are suggested to be the most appropriate method to use in a clinical setting to monitor training intensity, although currently there is a lack of moderate or high-quality evidence for a strong clinical recommendation for their use. However there is some emerging evidence to suggest the use of the overall RPE 6-20 Scale and current recommendations state that “Overall RPE 6-20 can tentatively be used to assess and form the basis for regulating upper-body exercise at a moderate to vigorous intensity in adults with chronic spinal cord injury who have high fitness levels, have been familiarized with the measure and are prompted with the scale during exercise" In line with the new Spinal Cord Injury Exercise Guidelines to improve cardiorespiratory fitness, adults with a spinal cord injury should engage in at least;
Moderate to Vigorous Intensity Aerobic Exercise for Cardiorespiratory Fitness and Cardiometabolic HealthFor those not already exercising, start with a lower intensity and gradually increase the intensity as a progression towards meeting the guidelines, recognizing that exercise below the recommended levels may or may not bring small changes in cardiorespiratory fitness.
TimeIn line with the new Spinal Cord Injury Exercise Guidelines to improve cardiorespiratory fitness, adults with a spinal cord injury should engage in at least;
20 Mins of Aerobic Exercise for Cardiorespiratory Fitness
30 Min of Aerobic Exercise for Cardiometabolic HealthFor those not already exercising, start with smaller amounts of time and gradually increase the time as a progression towards meeting the guidelines, recognizing that exercise below the recommended levels may or may not bring small changes in cardiorespiratory fitness.
While it may seem restrictive initially, there is a wide range of exercise types available to individuals with a spinal cord injury including wheelchair propulsion (daily wheelchair or racing wheelchair), handcycling / handcycle ergometer, nordic skier, rowing, swimming, seated aerobics, and wheelchair sports including wheelchair basketball, wheelchair rugby, wheelchair tennis.  The appropriate type of exercise will be dependant on the needs of the individual and whether power output needs to be monitored. Ergometers provide the means to monitor exercise, improve overall cardiovascular fitness and exercise capacity but the benefits may not be transferrable to wheelchair propulsion, particularly during early rehabilitation post-injury where the individual may be significantly deconditioned. Individual motivation and adherence to a cardiovascular training program is key, and variety in the training program can be useful to improve adherence. Cardiovascular training programs should balance frequency, intensity, and duration for maximum effectiveness and safety.
Upper Limb Training
Upper limb training can incorporate a wide choice of exercise activities including hand crank ergometry, handcycling, nordic ski, rowing, swimming, etc., and can be adapted to the needs of the individual. A SCIRE Review outlined the following significant evidence that individuals with a spinal cord injury can improve their cardiovascular fitness and physical work capacity through aerobic upper limb exercise training. 
- Level 1b evidence that vigorous-intensity (70% - 80% HR Reserve) exercise leads to greater improvements in aerobic capacity than moderate intensity (50 - 60% HR Reserve) exercise.
- Level 1b and Level 2 evidence that moderate-intensity aerobic arm training, performed 20-60 min/day, three days/week for at least 6-8 weeks, is effective in improving aerobic capacity and exercise tolerance of individuals with a spinal cord injury. 
- Level 2 evidence that hand cranking against a workload corresponding to 60% of WMax, performed 3-5 hours/day for one year, increases WMax and VO2 Max.
- Level 2 evidence that hand cycling exercise increases the power output, oxygen consumption, and muscle strength in individuals with paraplegia, but not tetraplegia during active rehabilitation.
- Level 4 evidence that hand cycling increases power output and oxygen consumption in individuals with tetraplegia, although further research is warranted.
- Level 4 evidence that hand cycling interval training program increases peak power output and peak VO2 in individuals with paraplegia and tetraplegia.
- Level 5 evidence that aortic pulse wave velocity is significantly lower in hand cyclists with a spinal cord injury compared to sedentary individuals with a spinal cord injury.
Treadmill training is often used more commonly during the rehabilitation phase following a spinal cord injury and in individuals with an incomplete spinal cord injury. In the SCIRE Review, they show the following growing list of evidence for body weight supported treadmill training (BWSTT) to improve indicators of cardiovascular health in individuals with complete and incomplete spinal cord injury. 
- Level 1a evidence that cardiac autonomic balance improves in persons with tetraplegia and paraplegia with BWSTT. 
- Level 2 evidence that standing and stepping exercises with BWSTT can increase VO2 and heart rate levels in individuals with spinal cord injury.
- Level 2 evidence that gait training with neuromuscular electrical stimulation can increase metabolic and cardiorespiratory responses in individuals with complete tetraplegia.
- Level 4 evidence that arterial compliance is improved with BWSTT in individuals with motor complete spinal cord injury.
- Level 4 evidence of decreased walking exercise heart rate following 8 weeks of underwater treadmill training.
- Multiple Level 4 evidence that BWSTT increases peak oxygen uptake and heart rate, and decreases the dynamic oxygen cost for individuals with spinal cord injury.
Functional Electrical Stimulation
There is evidence that the use of Functional Electrical Stimulation training may improve muscular endurance, oxidative metabolism, exercise tolerance, and cardiovascular fitness. 
- Level 1b evidence handcycling has beneficial effects on metabolic syndrome components, inflammatory status, and visceral adiposity. 
- Level 4 evidence that FES assisted arm-crank exercise increases peak power output and may increase oxygen uptake. 
- Level 4 evidence that decreased platelet aggregation and blood coagulation occurs following FES leg cycle ergometry in individuals with a spinal cord injury. 
- Multiple Level 4 evidence that exercise cardiac function is improved with FES training in individuals with a spinal cord injury. 
- Multiple Level 4 evidence that a minimum of three days per week FES training for two months may be effective for improving musculoskeletal fitness, the oxidative potential of muscle, exercise tolerance, and cardiovascular fitness. 
- Level 5 evidence that metabolic rate, heart rate, and ventilation levels are higher during hybrid cycling than during hand cycling.
Physical Activity Recall Assessment for People with Spinal Cord Injury (PARA-SCI) is a self-report physical activity measure for individuals with spinal cord injury. It aims to measure the type, frequency, duration, and intensity of physical activity performed by individuals with a spinal cord injury who use a wheelchair as their primary mode of mobility.
The ProACTIVE SCI Toolkit, from SCI Action Canada, is designed to help physiotherapists work with individuals with a spinal cord injury to be physically active outside of the clinic. It's a step-by-step resource that uses three overarching strategies including education, referral, and prescription to develop tailored strategies that work for both the physiotherapist and the individual with a spinal cord injury.
Active Living Leaders is comprised of a series of peer-mentor training videos with the goal of helping people who would like to use the latest physical activity knowledge, sports resources, and transformational leadership principles to inform and motivate adults living with a spinal cord injury to lead more active lives.
SCI-U Physical Activity Course is a collection of modularized training sessions. It includes Modules on Living an Active Life, Ways to Get Fit, Overcoming Barriers, and Reaching Your Goal.
SCI Action Canada's Knowledge Mobilization Training Series (KMTS) is a collection of modularized training sessions, with the goal of advancing physical activity knowledge and participation among individuals living with spinal cord injury. It includes Modules on the Physical Activity Guidelines and Physical Activity Planning.
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