This is a summary of a research study done by Dr. Christopher West and fellow ICORD researchers, to investigate the autonomic and cardiovascular consequences of spinal cord injuries.
Original Article: West, C. R., Gee, C. M., Voss, C., Hubli, M., Currie, K. D., Schmid, J. and Krassioukov, A. V. (2014), Cardiovascular control, autonomic function, and elite endurance performance in spinal cord injury. Scandinavian Journal of Medicine & Science in Sports. doi: 10.1111/sms.12308. Find the original article here.
What difficulties do individuals with spinal cord injury face when exercising?
Exercise is an important part of any healthy lifestyle and helps prevent cardiovascular disease. However, for individuals with spinal cord injuries (SCI), there are a number of complications that reduce the ability to exercise. When a SCI occurs, it can affect the individual’s autonomic nervous system (the system that controls the function of our internal organs), which controls cardiovascular functioning. Impaired cardiovascular function (the body’s ability to deliver nutrients and oxygen to tissues, and remove carbon dioxide and other waste) is a consequence of living with SCI that result in a number of complications during exercise. Often in SCI, people have lower than normal blood pressure and blood volume, which reduces their cardiac output (the total volume of blood being pumped by the heart each minute). Overall, the impaired ability to deliver blood to the working muscles negatively affects physical activity.
Dr. Christopher West and fellow researchers wanted to examine the relationship between level of injury, autonomic completeness of injury (if there is complete loss of the autonomic system functioning due to a complete cut of the spinal cord), and endurance performance in male SCI para-cycling athletes.
A sample of 23 elite male paracyclists with SCI was tested during a time-trial event at the 2013 Paracyling World Championships. Of the sample, 11 athletes were classified as having a cervical SCI, while the remaining 12 athletes had a thoracic SCI. The groups were further divided into autonomic complete and autonomic incomplete SCI.
In order to examine the relationships, researchers assessed:
- Neurological classification and questionnaires
- Cardiovascular performance at rest and exercise
- Sympathetic skin response, which is the skin’s electrical potential generated by the sweat glands (this is to assess whether autonomic functioning is intact or not to indicate a complete or incomplete classification)
- Exercises responses, including average/maximum heart rate, and average/peak speed
What did they find?
With respect to level of injury, athletes with thoracic SCI exhibited faster time-trials and faster average speeds than athletes with cervical SCI. There was no difference in maximum heart rate between the two groups, but on average heart rate was lower in cervical SCI. For athletes with cervical SCI, those with autonomic incomplete injuries produced faster time-trial performance, higher average speeds and higher heart rates during exercise than those with cervical autonomic complete SCI. There was no relationship between completeness of injury and exercise performance and cardiovascular function for those with thoracic SCI.
What does this mean for individuals living with SCI?
This is the first study to demonstrate that endurance performance in cervical SCI is dependent on both level and completeness of injury. It showed that:
- Elite athletes with autonomic incomplete injuries have an advantage during endurance competition when compared to athletes with complete injuries.
- Individuals with autonomic incomplete injuries generally produced improved physiological responses to exercise, as they are able to more effectively pump blood to the heart.
The findings from this study suggest there is a need to include an autonomic complete and incomplete category in Paralympic competitions. This classification becomes especially important in sports where there is a high cardiovascular demand, as this study found that individuals with who had more cardiovascular control performed better during endurance testing.