Cardiovascular Training in Spinal Cord Injury

Introduction[edit | edit source]

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.

Definition[edit | edit source]

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".[1]

Assessment of Cardiovascular Fitness[edit | edit source]

A cardiovascular fitness assessment is essential to directly determine training or conditioning intensities required to elicit improvements in cardiovascular and cardiometabolic health of a trained individual. Gold standard laboratory-based assessment (i.e. with an ergometer, arm crank, wheelchair treadmill) is becoming more commonplace, particularly in competitive sport. However, the results of these tests alone do not provide a complete picture. It is paramount to assess cardiovascular fitness first under reproducible test situations, including equipment standardisation, constraints used, and position for testing. Because strenuous exercise can lead to a cardiovascular event, physiotherapists should consider precautions when conducting an assessment.

Before completing any maximal exercise testing, a physiotherapist should obtain a detailed medical and surgical history to identify indications for an exercise test and determine any underlying conditions. These include: cardiovascular, pulmonary, musculoskeletal, or neurological dysfunction, the presence of diabetes, hypertension, heart block requiring a pacemaker, anaemia, thyroid dysfunction, obesity, deformity, vertigo, or impaired cognitive function. It is also essential to be aware of any medications that can influence test procedures and the response to the exercise.[2][3]

Peak Oxygen Consumption Tests[edit | edit source]

The Peak Oxygen Consumption (VO2 Peak) test, equivalent to the VO2 Max test in non-disabled individuals, measures the maximal capacity of the body to deliver oxygen from the lungs to the mitochondria of exercising muscles by expired gas collection. It is the most accurate way to assess cardiovascular fitness in spinal cord injury. [4] This definition reflects the lower maximal rate of oxygen consumption during arm exercises compared to leg exercises. It is due to the lower demand for oxygen from smaller muscle groups and the circulatory implication of arm exercise.[5]

VO2 Peak Test Testing conditions for individuals with spinal cord injury:

  • Performed using an arm cycle ergometer, manual wheelchair propulsion,  handcycle on an ergometer or treadmill.  
  • Exercise intensities are increased gradually until exhaustion.  
  • 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

Example of VO2 Peak Test Testing: [5]

  • Individual with 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.

  • Individual with 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[edit | edit source]

Submaximal exercise tests are frequently used to measure the responses to standardised everyday physical activities in individuals with a spinal cord injury. They evaluate the adaptation of the oxygen transport system to exercise below maximal intensity, so that the primary energy system used is aerobic.[1]

Examples of submaximal exercise tests are:

  • Portable expired gas analysis systems utilised in high-performance Paralympic sport
  • Heart rate measurement used in spinal injury rehabilitation units

The use of heart rate measurements does not, however, allow the assessor to estimate VO2 Peak. It helps to monitor the response of individuals with a spinal cord injury to training. Improvements in cardiovascular fitness are indicated by decreased heart rate at the same power output with training or improvements in an individual's perception of exertion with the Borg Exertion Scale.[5][3]

There are numerous submaximal protocols to choose from, many of which 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.[5]The fitness is measured by conducting a continuous, graded arm crank protocol. The suggested protocols for individuals with paraplegia and tetraplegia with a high level of fitness are as follows:

  • Individuals with Paraplegia with High Level of Fitness; 7 minutes at 40 Watts, 7 minutes at 60 Watts and 7 minutes at 80 Watts.

  • Individuals with Tetraplegia; 7 minutes at 20 Watts, 7 minutes at 30 Watts and 7 minutes at 40 Watts.

The goal of submaximal testing is to establish a level of exercise activity that does not provide physiological or biomechanical strain for a trained individual. Factors considered when selecting the appropriate test include the person's:

  • Primary and secondary pathologies and how they physically affect the person's daily life
  • Cognitive status
  • Age
  • Weight
  • Nutritional Status
  • Mobility
  • Use of walking aids
  • Use of orthotic or prosthetic devices
  • Level of Independence
  • Work Situation
  • Home Situation
  • Needs and Wants

Submaximal exercise testing overcomes many of the limitations of maximal exercise testing. They appear to have greater applicability to physiotherapists in their role as clinical exercise specialists and are much easier to implement within a spinal injury unit and rehabilitation setting.[3]

New evidence also suggests that in individuals with a high level of spinal cord injury, peak heart rate and blood lactate concentration attained during maximal incremental laboratory-based wheelchair exercise on a treadmill were below those obtained during maximal field-based exercise testing in highly trained wheelchair rugby athletes. It suggests that incremental exercise testing in the laboratory does not elicit true peak cardiometabolic responses in highly-trained wheelchair rugby athletes with a high level of spinal cord injury. Field exercise tests may give a better indication of maximal performance.[7]

Field Exercise Tests[edit | edit source]

Field exercise tests measure physiological function produced while an athlete is performing in a simulated sport situation. It is often thought not to be as reliable as lab-based tests, but they have more validity due to greater specificity. The following are the range of options for field testing:

Time Based; Measurements of distance travelled over a set period of time, eg., 12 minute push standardised test

Distance Based; Measurements of time taken to complete a certain distance, eg., time for 1km

Implications for Rehab[edit | edit source]

  • The use of regular cardiovascular capacity testing during spinal cord injury rehabilitation allows the physiotherapist to monitor the impact of rehabilitation interventions on an individual level.
  • Incremental arm ergometry with small increments per stage is the best means of assessment for peak cardiovascular capacity for individuals with a spinal cord injury.
  • A submaximal wheelchair ergometer test is preferable for the assessment of daily life functioning.
  • Systematic reporting on test termination, peak outcomes criteria, and adverse events is key to enhancing the comparability of results.[2]

Response to Cardiovascular Fitness Training[edit | edit source]

Response to cardiovascular fitness training is influenced by the level of spinal cord injury, its completeness, and the extent of the injury. Individuals with an incomplete injury, particularly those who can ambulate and have some lower limb use during exercise, respond to exercise in a similar way to individuals without injury. Persons with a complete cervical level injury or upper thoracic level injury have a significantly different response due to reliance on upper limb activity, lower limb paralysis, and loss of supraspinal sympathetic nervous control. The latter adversely affects cardiac output and arterio-venous oxygen that are the two components of VO2 Peak.[5][8]

The following is the Fick Principle summarising the relationship between cardiac output, arteriovenous oxygen difference, and VO2 Peak;

VO2 Peak = Cardiac Output (Q) x (a-vO2 Difference) [5]

Key determinants of Heart Rate, Stroke Volume, and Arterio-Venous Oxygen Difference
Heart Rate Stroke Volume Arterio-Venous Oxygen Difference
Sympathetic Nervous System

Parasympathtetic Nervous System

Circulating Noradrenalin

Intrinsic Heart Rhythm

Venous Return



Blood Volume

Size of Exercising Muscle Mass

The ability of Muscles to Extract Oxygen

  • Capillarisation
  • Number Mitochondria
  • Blood Flow through Exercising Muscle
  • Oxidative Enzyme Activity

Cardiac Output[edit | edit source]

Cardiac Output (Q) is defined as the amount of blood pumped per minute by the left ventricle of the heart. It is expressed as litres/minute.

Cardiac Output (Q) = Heart Rate (HR) x Stroke Volume (SV)

Heart Rate[edit | edit source]

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 minute. This is the intrinsic firing rate of the sinoatrial node in the heart, without input from either the sympathetic or parasympathetic systems.

Normally during exercise in non-disabled 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.[5]

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. This results in lower maximal heart rates of between 110 - 130.[5][8]

In spinal cord injury lesions T1 and above, there is complete loss of supraspinal sympathetic control to the heart. This results in increases in heart rate due to the withdrawal of excitatory input from the vagal nerve. In individuals with tetraplegia, the heart rate cannot increase beyond the natural rhythm of the heart. As a result, the heart rate may not be considered the best indicator of the effect of training in persons with tetraplegia.[8]

Stroke Volume[edit | edit source]

Stroke volume is the volume of blood ejected at each stroke of the heart during systole. A typical stroke volume in non-disabled individuals is 70ml at rest, which increases to a maximum of 120 ml during strenuous exercise as an adaption to cardiovascular training.

In individuals with spinal cord injury, maximal stroke volume and cardiac output decrease due to a loss of supraspinal sympathetic control below the level of the injury and the use of only the upper limbs during exercise. These factors harm venous return: venous pooling with the reduced return of oxygen from the lower limbs and reduced intra-thoracic muscle pumps, and contractility, meaning less blood returns to the heart with each beat.[5]

Arteriovenous Oxygen Difference[edit | edit source]

The arteriovenous oxygen difference measures 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; haemoglobin dissociates quicker, and a higher arteriovenous oxygen difference occurs. In trained athletes, the arteriovenous oxygen difference increases as a result of the tissues becoming more efficient in oxygen uptake with aerobic training.[9]

Size Exercising Muscle Mass[edit | edit source]

The size of the exercising muscle mass is the most important determinant of the arteriovenous oxygen difference. This can be seen in non-disabled athletes where the VO2 Max with upper limb exercise is approximately 70% of their VO2 Max when exercising with the lower limbs. This occurs because of reduced opportunity, need, and ability to extract and utilise oxygen with upper limb exercise. [5]

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. Similarly, 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.[5]

Muscle's Ability to Extract Oxygen[edit | edit source]

Oxygen extraction from the exercising muscle is the other key determinant of arteriovenous oxygen difference. Oxygen extraction is determined by factors including type of muscle fibers, the density of capillaries, regulation of blood flow, the size and number of mitochondria and the type of metabolism. These factors 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 non-disabled individuals, increasing blood flow to the exercising muscles. When this does not adequately occur in individuals with a spinal cord injury, it can result in exercise-induced hypotension.[5][8]

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 of cardiovascular training in individuals with a spinal cord injury (both tetraplegia, and paraplegia), as it delays the onset of muscle fatigue and increases maximal exercise capacity.[5]

Exercise Prescription[edit | edit source]

Several national and international organisations (e.g. the 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. These should be considered when prescribing cardiovascular exercise for individuals with a spinal cord injury. You can read more about these guidelines here.

Safe and effective exercise prescription requires careful consideration for the individual's target health status, baseline fitness, goals, and exercise preferences. When considering exercise prescription in an individual with a spinal cord injury, physiotherapists should take the level of neurological injury into consideration due to its implications on the type of exercise available and any modifications required for successful therapy participation. Such modifications can include: trunk stability and balance, use of strapping and gripping aids, and assistive devices.[8] The FITT Principle (Frequency, Intensity, Time and Type) should be used to develop, guide, and monitor cardiovascular training to ensure an effective exercise programme. For those just beginning to participate in cardiovascular training, start with smaller doses of exercise and gradually increase the duration, frequency, and intensity.

FITT Principle [8]
F Frequency How Often to Train 3 - 5 Days per Week
I Intensity How Hard to Train 50 - 80% Peak Heart 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

Interval Training

Frequency[edit | edit source]

In line with the new 2017 International Spinal Cord Injury Exercise Guidelines to improve cardiorespiratory fitness, adults with a spinal cord injury should engage in at least;

2 x sessions of aerobic exercise per week for Cardiorespiratory Fitness

3 x sessions of aerobic exercise per week for Cardiometabolic Health

Those who are not already exercising should start with a lower frequency and gradually increase the frequency as a progression towards meeting the guidelines while recognising that exercise below the recommended levels may or may not bring small changes in cardiorespiratory fitness.[10]

Intensity[edit | edit source]

This is an extremely important aspect of the FITT Principle and it is probably the hardest factor to monitor, particularly in individuals with a spinal cord injury. In non-disabled 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.[5][8][11]

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. While there is currently a lack of moderate or high-quality evidence for a strong clinical recommendation for their use, there is some emerging evidence to suggest the use of the overall RPE 6-20 Scale. Thus, 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".[11]

In line with the new Spinal Cord Injury Exercise Guidelines to improve cardiorespiratory fitness, adults with a spinal cord injury should engage in:

Moderate to vigorous intensity aerobic exercise for Cardiorespiratory Fitness and Cardiometabolic Health

For those not already exercising, start with a lower intensity and gradually increase the intensity as a progression towards meeting the guidelines, recognising that exercise below the recommended levels may or may not bring small changes in cardiorespiratory fitness.[10]

Time[edit | edit source]

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;

20 minutes of aerobic exercise for Cardiorespiratory Fitness

30 minutes of aerobic exercise for Cardiometabolic Health

For those not already exercising, start with smaller amounts of time and gradually increase the time as a progression towards meeting the guidelines, recognising that exercise below the recommended levels may or may not bring small changes in cardiorespiratory fitness.[10]

Type[edit | edit source]

While it may seem restrictive initially, there are many different 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 and wheelchair tennis.[5][8] The appropriate type of exercise will depend 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. However, 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 programme is key, and variety in the training program can be useful to improve adherence. Cardiovascular training programmes should balance frequency, intensity, and duration for maximum effectiveness and safety.

Upper Limb Training[edit | edit source]

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 Spinal Cord Injury Research Evidence (SCIRE) Project 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.[12] This page on the Grades and Levels of Evidence describes what each of these levels mean.

  • Vigorous-intensity (70% - 80% HR Reserve) exercise leads to greater improvements in aerobic capacity than moderate intensity (50 - 60% HR Reserve) exercise (Level 1b evidence).[13] 
  • 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 1b and Level 2 evidence).[14] 
  • Hand cranking against a workload corresponding to 60% of workload achievable (WMax), performed 3-5 hours/day for one year, increases WMax and VO2 Max (Level 2 evidence).[15] 
  • Hand cycling exercise increases the power output, oxygen consumption, and muscle strength in individuals with paraplegia, but not tetraplegia during active rehabilitation (Level 2 evidence).[16]
  • Hand cycling increases power output and oxygen consumption in individuals with tetraplegia, although further research is warranted (Level 4 evidence).[17]
  • Hand cycling interval training program increases peak power output and peak VO2 in individuals with paraplegia and tetraplegia (Level 4 evidence).[18]
  • Aortic pulse wave velocity is significantly lower in hand cyclists with a spinal cord injury compared to sedentary individuals with a spinal cord injury (Level 5 evidence).[19]

Treadmill Training[edit | edit source]

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.[20] 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. [12]

  • Level 1a evidence that cardiac autonomic balance improves in persons with tetraplegia and paraplegia with BWSTT.[21] 
  • Level 2 evidence that standing and stepping exercises with BWSTT can increase VO2 and heart rate levels in individuals with spinal cord injury.[22]
  • Level 2 evidence that gait training with neuromuscular electrical stimulation can increase metabolic and cardiorespiratory responses in individuals with complete tetraplegia.[23]
  • Level 4 evidence that arterial compliance is improved with BWSTT in individuals with motor complete spinal cord injury.[24]
  • Level 4 evidence of decreased walking exercise heart rate following 8 weeks of underwater treadmill training.[25] 
  • 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.[26][27] 

Functional Electrical Stimulation[edit | edit source]

There is evidence that the use of Functional Electrical Stimulation (FES) training may improve muscular endurance, oxidative metabolism, exercise tolerance, and cardiovascular fitness.[12][28]

  • Level 1b evidence handcycling has beneficial effects on metabolic syndrome components, inflammatory status, and visceral adiposity.[29]
  • Level 4 evidence that FES assisted arm-crank exercise increases peak power output and may increase oxygen uptake.[30]
  • Level 4 evidence that decreased platelet aggregation and blood coagulation occurs following FES leg cycle ergometry in individuals with a spinal cord injury.[31] 
  • Multiple Level 4 evidence that exercise cardiac function is improved with FES training in individuals with a spinal cord injury. [32][33][34]
  • 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.[35][36][37][38][39][40][41][42]
  • Level 5 evidence that metabolic rate, heart rate, and ventilation levels are higher during hybrid cycling than during hand cycling.[43]

Resources[edit | edit source]

Physical Activity Recall Assessment for People with Spinal Cord Injury (PARA-SCI)[edit | edit source]

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.

ProACTIVE SCI Toolkit[edit | edit source]

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 is 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[edit | edit source]

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 for Individuals with Spinal Cord Injury[edit | edit source]

SCI-U Physical Activity Course is a collection of modularised training sessions.  It includes Modules on Living an Active Life, Ways to Get Fit, Overcoming Barriers, and Reaching Your Goal.

SCI Action Canada Knowledge Mobilization Training Series[edit | edit source]

SCI Action Canada's Knowledge Mobilization Training Series (KMTS) is a collection of modularised 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.

References[edit | edit source]

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