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Too much of a good thing? How cycling can harm or hurt your immunity

James Witts
16 Oct 2020

Fit people are less likely to get ill. So training must boost your immunity, right? True… unless you overdo it. Photos: Rob Milton

Unless you’re a committed hypochondriac, never has there been a period in our lifetime where we have been so aware of illness and immunity. Locking down and keeping out of other people’s shadows hopefully prevents infection and keeps you healthy.

We’re also told that keeping fit helps to protect against viruses, so as cyclists we should be fine. Maybe, maybe not. It’s time to talk J-curves, open windows and 80:20 rules…

The pros and cons of exercise

Numerous studies into exercise and immunity show that regular, modest cycling boosts immunity. In general, the fitter you are, the stronger your immune system. Doctors John Campbell and James Turner of Bath University have conducted studies into this area. They have pinpointed three strands to immunity and all three are strengthened through exercise.

The first is healing wounds – for example, road rash – which is accelerated in fitter folk. The second is more efficient ‘natural’ immunity, which comprises cells like neutrophils and natural killer cells (the kind that fight and kill aberrant cells such as viruses). The third is ‘adaptive’ immunity that is made of lymphocytes called T and B cells.

‘Research has shown that regular exercise helps maintain a healthy number of young T cells as we age,’ Campbell explains. ‘This might better identify pathogens and cancer as we grow older.’

The problems occur when we overdo either or both cycling intensity and volume. This is where the J-curve comes in. Sedentary people have an average chance of getting colds and coughs. Moderate exercise on the bike reduces this chance, however regular and demanding exercise turns the corner on the J, sending your chance of infection sky high. That J curve builds over sessions and time.

‘There’s also the open window theory that states that after a single, hard exercise session the immune system drops,’ says UAE Team Emirates’ physician Adriano Rotunno. ‘We notice it in professionals but their immune systems are pretty robust.

‘Then again, as per the J curve, 10 days into a Grand Tour they can struggle. They might have a virus and need rest to fight it. Instead, their body is fighting something else: 200km a day at 150-160bpm.’

The rest of us might not be riding Grand Tours but the reality is, if you’re pushing 85% of your maximum heart rate on Zwift for hours on end, there’s a three-hour to three-day window where there’s an increased susceptibility to illnesses such as upper-respiratory infection. So how do you safely balance training load and progression without falling ill? 

Models of success

There are numerous training models designed to achieve this. For starters, there’s traditional periodisation, where riders build aerobic strength in the off-season with long, moderate-intensity rides before speed work in the race season.

Then there’s reverse periodisation, made famous by Team Sky many moons ago, where that traditional template is reversed. Or block periodisation, where riders work on specific parameters of fitness for short, intense periods of time.

Many recreational riders favour the former, although studies show that it’s arguably the longer rides that damage the immune system, specifically in suppressing natural killer cells.

We know that many WorldTour teams favour block periodisation, designed for advanced cyclists. It’s something we posed to NTT ProCycling sports scientist Elliot Lipski.

‘It depends on the rider and the coach as well as the individual’s main goals for the season,’ says Lipski in lockdown in Lucca, Italy. ‘With the impact of the global pandemic, we’ve opted for a higher-intensity period to work on strengths and weaknesses.

‘But riders have different challenges, with half of the team confined to the indoor trainer and the other half able to ride outside. In this instance it’s difficult – and not always advisable – to increase load through volume on the indoor trainer.’

Lipski stresses that there are periods of the season that stretch immunity more than others. As an example, the Classics guys have a heavy schedule in the spring, as well as a lot of travel, beginning with February’s UAE events and then flying back to Europe.

He also says that key to monitoring health in and out of lockdown is the team’s wellness app. Most teams use off-the-peg offerings, although some develop bespoke versions. Not surprisingly, NTT, whose main sponsor is a technology company, chose the latter option.

‘We worked closely with NTT and Lumin Sports to build a custom portal for our riders to input daily subjective wellness measures. Every morning and evening the riders report via an app and that is available to the performance team, to track and intervene where required.’

For those without a tech sponsor, apps from respected outfits such as Training Peaks and Today’s Plan can help you to identify the spectre of illness before it derails you.

As will adhering to the work of noted exercise physiologist Dr Stephen Seiler from the University of Agder, Norway.

80:20 training

‘From our research, it’s clear that elite athletes train around 80% of the time at what we’d call low intensity,’ he says. ‘They then spend 20% training hard. Whether the elite athlete is training 20 or 40 hours a week, cycling or running, their training broadly follows this 80:20 split.’

Lipski says his riders broadly follow an 80:20 approach. Which is all well and good but what about recreational cyclists, who have much less time in which to to train?

‘That’s the real win,’ says Seiler. ‘We undertook further research and showed that the 80:20 model is equally relevant if you’re training four sessions a week or 14.’

And, he adds, that’s arguably more important than prescribing sessions for the elite, as amateur cyclists often fall into intensity no-man’s land, which can lead to illness.

‘Many recreational cyclists feel they must red-line every time, so they do a lot of training in this threshold area. That’s at around 80-87% of maximum heart rate. The problem is, they’re too tired to do high-intensity sessions.’

Seiler says the 80:20 split is a guideline rather than a rule, so he ‘can live with training 85:15 or 75:25’. But don’t veer too far away from these. And don’t overcomplicate things.

‘The 80:20 rule is based on categories,’ he says. ‘I base a session as either hard or easy. If I do an interval session, even though effort and heart rate fluctuates, it’s hard. If you cycle four times a week, no matter the length, if one’s hard that’s a 75:25 split.’

Seiler also stresses, ‘People doing intervals think they have to reach a point where they throw up. We don’t see that with the elites. It’s OK to work at a slightly lower intensity – 90% instead of 95%, for example.’

With interval sessions of mixed low and high-intensity efforts, one a week should be enough for most cyclists. That’s especially true for athletes aged 50 or above, who require longer recovery periods. ‘Just remember that under 80% of maximum is low,’ Seiler says. ‘And over 90% is high.’

This form of overload-and-recover training is effective at boosting immunity, but it should be combined with sage advice from experts (now back in favour in this post-Brexit environment) on protecting yourself from infection at all times.

According to medical journal Acta Medica in a 2013 review into immune-suppression in athletes, the advice is strangely familiar: wash hands frequently throughout the day; don’t share drinks or towels; protect airways from very cold or dry air when performing strenuous exercise; maintain adequate carbohydrate intake of at least 60% of daily calories; and try to get a minimum seven hours of sleep a night.

Follow these guidelines, manage your training intensity and volume, take government advice and you’ll ride out of lockdown in peak condition ready to face whatever the revised race climate looks like.

Road to health

Feeling ill? Here’s the lowdown on recovery and exercise

According to a group of leading exercise immunologists, cited in a study by Anthony Hackney, professor of exercise physiology at the University of North Carolina, the following course of action is advised if you’re showing overt signs of having an infection:

  • Day 1 of illness – no strenuous exercise or competition. The ill athlete should drink plenty of fluids; keep from getting wet or cold; minimise life-stress. If feverish, use a decongestant
  • Day 2 of illness – if symptoms worsen, no exercise; rest. If no fever or worsening of symptoms, then light exercise of 30-45min is allowed
  • Day 3 of illness – if fever and symptoms persist, see a doctor. If no fever or worsening of symptoms, then light exercise of 45-60min is allowed
  • Day 4 of illness – if no symptom relief, no exercise and continued rest. If relief (first day of improved symptoms) and no fever, then light exercise of 30-45min. Use the same number of days off as the number it’ll take you to return and step up to normal training. Gradually increase exercise intensity. Take further days off if starting to feel ill.

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