Why is cardio-respiratory training in stroke so necessary?

By Marlou Tacugue, Exercise Physiologist (EP)

The facts

One Australian every 19 minutes experienced a stroke for the first time in their lives in 2020.

Alarmingly, the Stroke Foundation states that more than 80% of all strokes could have been prevented with lifestyle intervention and increased physical activity levels. This is a very powerful fact to really spread awareness to those with stroke risk factors and to those at risk of having another stroke. With the right guidance and support, there is so much you can do to reduce your risk of having a stroke or having a further stroke.

In 2020, 24% of total first-ever strokes occurred in people aged 54 years and under. Sadly, the rates of stroke in young people are increasing largely due to poor control of lifestyle factors, and its impact will continue to grow unless action is taken. Without action by 2050, it is predicted that the number of first-ever strokes experienced by Australians annually will increase to one stroke every 10 minutes. There will be over 819,000 survivors of stroke living in the community (Stroke Foundation, 2020).

What is cardio-respiratory fitness?

Cardio-respiratory fitness is the ability of the circulatory and respiratory systems to supply oxygen to skeletal muscles during sustained physical activity. The keyword is ‘sustained’! This means continuous physical activity or exercise for more than 3 minutes to achieve a steady-state heart rate response. To put it simply, this means that you need to be working for at least 3 minutes for your cardiorespiratory system to give you the green light of how hard you’re working for that level of physical activity through a heart rate response.

The primary measure of someone’s level of cardio-respiratory fitness is what we call VO₂max. It refers to the maximum rate of oxygen consumption during incremental exercise. The more oxygen your body can consume during exercise, the more effectively your body can use that oxygen to generate the maximum energy to sustain that level of exercise or physical activity for longer periods.

Aerobic exercise has the ability to improve a person’s VO₂max, meaning that their heart and lungs are more trained to pump blood more efficiently, allowing more oxygen to be delivered to the muscles and organs around the body, including the brain. A stroke is caused by a lack of blood supply to the brain, so this is important to know and make sure that our brain is regularly getting enough oxygen and nutrients. And we know that regular aerobic exercise will make these systems more efficient!

Why is VO₂max important?

VO₂max is actually one of the best predictors for survival following a stroke. There is a direct association between life expectancy and the risk of developing cardiovascular disease or, worse, a recurrent stroke.

Somebody who has suffered a stroke has an accumulated risk of a subsequent stroke of 43% over ten years, which shows the importance of addressing the loss of cardiorespiratory fitness sooner rather than later!

What happens to someone’s VO₂max after a stroke?

Following a stroke, physical inactivity or just ten days of bed rest causes rapid loss of muscle strength (−13.2%), muscle power (−14%), and cardiorespiratory fitness (−12%) (Kortebein, 2008). We also know that in observational studies looking at the level of physical activity of stroke survivors during inpatient stay between 8 am to 5 pm, they found that they were in bed or sitting 76% of the time and only standing or walking 23% of the time!

In stroke, VO₂max is reduced to 45% lower than the average normative values in their age category. To put that in perspective, fitness levels in these ranges are associated with loss of independence (Shepard, 2009). They will lack the fitness and endurance to complete everyday tasks at home, such as washing the laundry, ironing and vacuuming.

Why should you start aerobic exercise?

The consensus-based recommendations from the Australian Clinical Guidelines for Stroke Management state that:

• All stroke survivors should commence cardiorespiratory training during their inpatient stay
• Stroke survivors should be encouraged to participate in ongoing regular physical activity regardless of their level of disability.

So, diving deeper into this, to produce an aerobic training effect, you need to be exercising through a heart rate range of 60-90% of your maximum heart rate. Previous studies have suggested that traditional inpatient stroke rehab reports of less than 3 mins of physical therapy and OT were under 1 min working inside these heart training zones. So, only 1-2 weeks of not training in these zones decrease VO₂max by 8% for stroke survivors.

This becomes a huge problem because poor aerobic capacity after stroke is likely to limit participation in physiotherapy and occupational therapy such as relearning to walk, stand or other motor relearning activities due to the higher energy demand required.

The benefits of starting sooner rather than later!

Establishing an individualised aerobic exercise training program in the earlier stages will give you the best shot of recovery in relation to achieving your functional goals. An accredited exercise physiologist (EP) will be able to assess your baseline fitness levels and monitor the intensity of your program closely to ensure you receive the correct dosage and amount needed to maximise your aerobic capacity and improve your fitness levels.

Not only that, but your EP will also be able to identify any modifiable risk factors and give you the coaching and advice on the necessary lifestyle changes that you can start making today to get you back on the path of living a more physically active lifestyle. We know that stroke survivors do not meet the minimum physical activity guidelines from the World Health Organisation, predisposing them to sedentary lifestyles and increasing their risk of developing secondary metabolic conditions such as obesity, diabetes or worse, a recurrent stroke. Your EP will address this with you on an ongoing basis and will regularly review your body mass index, waist to hip ratio and blood pressure to ensure that we are doing our best to get you back within the normal ranges so we can minimise your risks of developing any of these conditions.

If you had a stroke a while ago, it’s never too late to start. Introducing aerobic exercise at any point can have enormous benefits both for your health and your function.

What about the science behind aerobic exercise?

There are many physiological adaptions in response to aerobic exercise that you may not be completely familiar with. We see an increase in total cerebral blood flow by 25-30% during aerobic exercise, which is the blood supply to the brain. This is important to bring vital nutrients and removal of harmful waste. Aerobic exercise has been shown to decrease inflammation in the central nervous system and can have a neuroprotective effect on the brain following a stroke.

We see improvements in cardiac output, allowing for greater blood volume being pumped out from the heart and supplying more oxygen and energy more efficiently to our resting and working muscles. This means there will be less mechanical stress of our arteries and therefore helps to reduce your resting blood pressure.

We also see improvements in insulin sensitivity and body composition – this helps control the amount of sugar in the blood and helps reduce the risk of developing metabolic conditions such as Type 2 diabetes. In fact, structured interventions combining physical activity and modest weight loss have been shown to lower Type 2 diabetes by up to 58% in high-risk populations.

Finally, we can’t forget the effects it has on our mental health and well-being. Aerobic exercise has been shown to reduce stress, anxiety, and depression to the same degree as medications like anti-depressants in mild to moderate cases. Therefore, improving one’s self-esteem, confidence and quality of life.

How much aerobic exercise should we be doing? How much is enough?

We can use the FIIT principle (frequency, intensity, time, type) to help determine the exercise dose or quantity needed to improve health outcomes similar to pharmacological intervention.

• Frequency: 3-5 days per week
• Intensity: 55-80% heart rate max
• Time: 20-60 mins per session or several 10 min bouts per day
• Type: large muscle activities such as walking, arm, leg or arm-leg ergometry, functional activities

Starting an aerobic exercise program for the first time can be challenging, but your EP will be able to guide you through this throughout an 8-week program where we start to see improvements to your fitness levels or VO₂max scores. Your EP will get you started at a very light intensity and will be guided by your own self-selected pace initially until you build your exercise tolerance. This should help motivate you and increase your adherence to the program as you start gaining more confidence. The first 2-4 weeks of your program is considered the “conditioning phase”, and your EP will educate you on how to monitor your intensity using the RPE (rate of perceived exertion – how hard you think you are working from a score out of 10 being the maximal effort) scale and talk test to get you started and comfortable with light intensity exercise. Using the RPE scale, this intensity should be less than 64% of your heart rate max, which is a 1-2 effort out of 10. In addition, you should be able to comfortably hold a conversation with your EP and still breathe quite normally, and the goal would be to gradually hold this intensity of up to 10 minutes.

Once you can tolerate up to 10 minutes of continuous low-intensity aerobic exercise and have increased your exercise tolerance, your EP will begin to increase the intensity of your program, where you will start to reach moderate intensities. This will be between 64-76% of your heart rate max at RPE 3-4, which is considered your aerobic training zone. This is where you are starting to work just outside your comfort zone. You will find that you are beginning to breathe more heavily, but you should still be able to speak in brief sentences. This will start to form the basis of incorporating more periods of higher intensity exercise as you begin to condition and adapt to increased physical activity levels. This is what we call the “adaptation phase”, in which it could take up to 4-8 weeks of building aerobic capacity and fitness at moderate intensities. Once you start to reach these levels, this is where the fun begins with more HIIT (high-intensity interval training) style workouts which your EP will design specifically for you to challenge your cardio-respiratory system further.

How do I get started?

An accredited Exercise Physiologist at ARC can help address the loss of cardiorespiratory fitness following a stroke event. An EP will understand that there will be different approaches to your exercise program, and your program will be tailored and individualised based on your goals and needs. This includes the severity of your disability, stage of recovery, exercise tolerance, available social support, physical activity preferences, and limitations will all need to be considered by an EP when setting up an exercise program for each stroke survivor.

At Advance Rehab Centre, we provide one to one exercise sessions and group programs such as NeuroFit and NeuroGym classes that aim to deliver adaptive and innovative training to a range of neurological conditions such as a stroke. Our EP’s in the clinic conduct these programs to improve your aerobic capacity in a fun and social group setting while subsequently decreasing the morbidity of risk factors associated with a stroke event. We also run programs ‘At Your Gym’, so people can access an EP where they live, in a gym convenient to them.

We also have a dedicated team of clinicians interested in supporting people to try inclusive sport and recreation activities. So starting to get fit is a positive step in the right direction.

What to do next?

If you or someone you know is affected by a stroke event, then come and see the Exercise Physiology team at ARC for an individualised cardio-respiratory fitness training program working towards building your aerobic capacity and fitness levels.