Cardiovascular Training in Spinal Cord Injury

Original Editor - Naomi O'Reilly

Top Contributors - Naomi O'Reilly, Ewa Jaraczewska, Admin, Tarina van der Stockt, Kim Jackson, Lucinda hampton, Jess Bell, Anas Mohamed, Stacy Schiurring and Olajumoke Ogunleye  

Introduction

Aerobic activity 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 aerobic training will improve cardiovascular function. With improved cardiovascular function, individuals are more likely to be able to live independently, decrease secondary health complications, and improve muscular endurance.

Definition

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

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 individual are standardized. Precautions should also be followed when conducting cardiovascular assessments as strenuous exercise can lead to a cardiovascular event.

Peak Oxygen Consumption Tests

The Peak Oxygen Consumption (VO_{2 Peak}) test, equivalent to the VO_{2 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 v leg exercises due to both lower demand for oxygen from smaller muscle groups anand the circulatory implication of arm exercise.

In individuals with a spinal cord injury, the VO_{2 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 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 VO_{2 Peak} is the gold standard method for assessing exercise reponse 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 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 main energy system used is aerobic. While portable expired gases analysis systems can be utilised 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 estiamtion of VO_{2 Peak}, but is used as a means to monitor the response of individuals with a spinal cord injury to training, with improvements in cardiovascuar fitness indicated by decreased heart rate at at the same power output with training or improvements in individials perception of exertion with the Borg Exertion Scale.

Performed in a similar way to the VO_{2 Peak} test with a different set of protocols and terminated prior to exhaustion. A wide range of protocols are available to use, and as with VO_{2 Peak} tests, the protocol selected will depend on level of injury, level of fitness, time since injury etc. A commonly use protocl uses 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

Submaximal exercise testing appears to have greater applicability to physiotherapists in their role as clinical exercise specialists compared with maximal exercise testing, and much easier to imlement within a spinal injury unit and rehabilitation setting.

Field Exercise Tests

Response to Cardiovascular Fitness Training

Response to cardiovascular fitness training is significantly influenced by type of spinal cord injury including neurological level, level of completeness and extent of the injury. Those with a incomplete level of injury, particularly those who can ambulate and have some lower limb use doing 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 differnt reponse as a result of reliance on upper limb exercise, lower limb paralysis and most importantly loss of supraspinal sympathetic nervous control, which adversley affect cardiac output and artery-venous oxygen; the two components of VO_{2 Peak.}

Cardiac Output

Heart Rate

Heart rate is determined by the balance between sympathetic control to the heart via T1 - T4 nerve roots that increase heart rate and parasympathatic control via the vagal nerve which decrease 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 partial loss of Supraspinal Sympathetic Control to the heart, with increases in heart rate occurring primarily as a result of 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 complete loss of Supraspinal Sympathetic Control to the heart, with increases in heart rate occurring primarily as a result of 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

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 is decreased due to loss of supraspinal sympathtic control and upper limb exercise, which have a negative effect on venous return or preload; as a result of venous pooling from paralysis with loss of lower limb and intra-thoracic muscle pumps, and contractility, the primary determinants of stroke volume.

Aterio-venous Oxygen Difference

Size Exercising Muscle Mass

Ability Muscle to Extract Oxygen

Exercise Prescription

Type

Examples of Cardiovascular Exercise include;

Arm Crank Ergometers

Cycling

Nordic Ski Erg

Swimming

Wheelchair Pushing

Walking

Intensity

Guidelines

Resources

References