How to get back into training after illness (and covid)

Can getting back into training too soon after illness hinder your recovery and performance in the long term? Dr Hamed Kamali explains all.

Training isn’t just about how you look; it's about your strength, fitness, and even the sport you play. To most of us, training is as essential as getting enough sleep, water, and food.  

I had covid in November 2021, and given my training background and fitness level, I thought it would be a walk in the park. However, it is becoming clear that long-term problems associated with even a mild covid infection are evident in people regardless of age, race, sex, or previous cardiovascular disease [1]. To put it into context, a 2020 study of 199 Swiss armed forces recruits found a reduction in exercise tolerance in a significant number of the recruits who experienced symptomatic covid infection [2].  

So why does covid affect how we feel and perform beyond the initial infection? And what can we do to move forward with our training and sports performance? 

1. How can covid affect training and performance?

We can glean insight into how covid affects training and performance by looking at what happens in covid infection and potential mechanisms leading to long covid.  

Having worked as a senior registrar in intensive care through the first and second waves of covid, it’s clear that this is a multi-system disease. The initial infection can lead to a cascade of events that cause further organ damage [3].  

In training, this can lead to: 

  • Arrhythmias 
  • Shortness of breath 
  • Autonomic nervous system damage (the fight or flight system) 

Practically, we may see a reduction in exercise tolerance, increased resting heart rate, decreased heart rate variability (HRV) and VO2 Max. 

2. “If you can’t measure it, you can’t improve it”

Marrying up how you feel with objective data is helpful. Weeks after I had covid, my exercise tolerance and strength both noticeably reduced. I would contact friends who had recently also had covid to check if I was alone, but I wasn’t.  

My resting heart rate was raised, and my heart rate variability (HRV) was reduced. The HRV is a measure of neurocardiac function, a combination of heart-brain interaction and autonomic function [4]. It can be thought of as a measure of physical and psychological stress. The greater the stress, the lower the normal pattern of biological heart rate variability (reduced HRV). 

Additionally to how you are feeling and your vitals, blood markers can see if there is any persistent inflammation and provide insight into your overall health. Biomarkers included in our Ultimate Performance Blood Test can provide useful data over time.

3. Testing the testosterone to cortisol ratio

Testosterone isn’t just for muscles. Although an important anabolic hormone, testosterone has multi-system effects and plays a role in our energy levels, motivation, sexual function, mood and body composition.  

Cortisol is also an important hormone that helps mobilise energy stores during stress (including exercise) and suppresses the immune system's inflammatory response.  

However, there is an inverse relationship between cortisol and testosterone, which is why strenuous exercise can increase cortisol and decrease testosterone. When recovering from covid, several factors can affect the things that usually help maintain your healthy hormones. Sleep, nutrition, and stress levels can all be affected - often in a multifactorial fashion.  

When you have covid, you're told to rest. This is because covid can start a chain of events that cause changes to your body and mood.  

  1. Covid affects your routine and way of coping with stress. 
  2. Your routine and stress management affect your testosterone levels and resilience. 
  3. Testosterone and resilience affect your motivation, diet and mood.  

However, exercising at 60% or more of your VO2 Max can be enough physical stress to increase cortisol and decrease testosterone [5]. So maybe training whilst also experiencing the stress of recovering from covid isn’t the answer either? 

The truth is that it is difficult to strike a balance. Your testosterone-to-cortisol ratio trend over time can be helpful to monitor. A reduction of 30%, alongside other features of overtraining, could indicate that you need to reduce your training load and increase your recovery. Our blog on overtraining covers this in much more depth if you'd like to know more. 

sports performance collection banner

4. The British Journal of Sports Medicine protocol 

The British Journal of Sports Medicine published the Graduated Return To Play (GRTP) portal in its June 2020 issue [6]. 

For people who showed no signs of frailty and were previously active, they advise an initial rest period of ten days following symptoms (walking and normal daily activities only). There must then be a seven-day period, free of symptoms and any medication, before starting the GRTP protocol.  

The subsequent days involve a gradual increase in intensity and volume with monitoring objective and subjective measures, such as resting heart rate (RHR) and rate of perceived exertion (RPE). Rest and steady increase in activity levels are important as they can help reduce the risk of developing the risk of heart, kidney, lung, or blood problems in the future.  

This protocol provides a good basis for the first few weeks after infection. However, what do you do afterwards? The authors recognise that some athletes take over three weeks to recover. In the young (median age 21) Swiss Army Recruits, there was a persistent decrease in VO2 Max at the end of the study, two months after symptom onset.  

In medicine, if things aren’t going as planned, we resort to going back to the beginning. Starting at the basics, the fundamentals and then working up. With regards to persistent symptoms, we need to check in with ourselves. Are we achieving adequate; hydration, sleep, and nutrients in our diet? Our Sports Performance Guide can give a better insight into what to aim for in these realms. If you are getting the basics right, and your symptoms are persisting, you should talk with your doctor to make sure there are no underlying issues. Alongside this, checking blood markers can help identify factors that are either causing or making your symptoms worse. Examples could be nutrient deficiency and hormonal imbalance.  

If your results show no evidence of any underlying issues, then you know that it is okay to start pushing yourself. The measure of this should be your perceived exertion rather than an endpoint (like a 5k time or weight lift). It may be that recovery may take longer, so only train if you feel recovered and your resting heart rate/HRV values are within the normal limits for you. If like me, the thought of taking it easy is daunting, you can add in light exercise / additional walking on your recovery days to keep yourself active.   

Don’t be tempted to power through, it may only hinder your recovery. 

5. Summary of training post-illness and covid

  • Exerting yourself too early on can hinder your recovery and performance in the long term
  • Focus on objective and subjective measures of how you are performing and recovering to guide you  
  • Use the GRTP protocol as a guide through the first three to four weeks
  • Keep checking in with yourself to ensure you are focusing on the foundations - sleep, nutrition, hydration, and mindset/stress management

You know what is best for you. The only study that matters here is the N=1 / single subject trial. Make adjustments and see how you feel. Stay positive and patient because you will feel better. Don’t use earlier measures of fitness and strength - start again but know that you could be even better.  

It may also be helpful to pursue new goals or methods of training. Going to a gym with a strong community is also a great way to maintain social interaction, meet new supportive people and move the focus away from the numbers.


  1. Xie Y, Xu E, Bowe B, Al-Aly Z. Long-term cardiovascular outcomes of COVID-19. Nat Med. 2022 Mar;28(3):583-590. doi: 10.1038/s41591-022-01689-3. Epub 2022 Feb 7. PMID: 35132265; PMCID: PMC8938267. 
  2. Crameri Giovanni Andrea GerardoBielecki MichelZüst RolandBuehrer Thomas WernerStanga ZenoDeuel Jeremy Werner. Reduced maximal aerobic capacity after COVID-19 in young adult recruits, Switzerland, May 2020. Euro Surveill. 2020;25(36):pii=2001542. 
  3. Castanares-Zapatero D, Chalon P, Kohn L, Dauvrin M, Detollenaere J, Maertens de Noordhout C, Primus-de Jong C, Cleemput I, Van den Heede K. Pathophysiology and mechanism of long COVID: a comprehensive review. Ann Med. 2022 Dec;54(1):1473-1487. doi: 10.1080/07853890.2022.2076901. PMID: 35594336; PMCID: PMC9132392. 
  4. Shaffer F, Ginsberg JP. An Overview of Heart Rate Variability Metrics and Norms. Front Public Health. 2017 Sep 28;5:258. doi: 10.3389/fpubh.2017.00258. PMID: 29034226; PMCID: PMC5624990. 
  5. Brownlee KK, Moore AW, Hackney AC. Relationship between circulating cortisol and testosterone: influence of physical exercise. J Sports Sci Med. 2005 Mar 1;4(1):76-83. PMID: 24431964; PMCID: PMC3880087. 

Related tests

Ultimate Performance Blood Test

Our ultimate blood test for men and women gives you our most comprehensive health check, including advanced profiles for your hormone health, thyroid function, and sports nutrition

  • Results estimated in 3 working days
  • 56 biomarkers
Testosterone and Cortisol Blood Test

Measure your testosterone to cortisol ratio (T:C) - a sensitive test to identify possible overreaching and overtraining syndromes

  • Results estimated in 3 working days
  • 3 biomarkers