When you sign up for a race one of the best things is that the concrete date gives you focus, helping you train, inspiring you to pull on your trainers and head out the door even when you don’t want to.

The downside is that if you lose any of your valuable time your carefully compiled training schedule goes out of the window.

This time of year (winter at the time of writing) seems to be the riskiest when it comes to illness; there are many nasty viruses floating around, and at the moment, a lot of people seem to have been battling the same cold/virus/cough for many weeks (with one person I know clocking in at two months. Their doc had the following helpful advice: “It’s a virus, there’s nothing you can do.”)

So when is it ok to run when you feel ill, and how quickly do you lose fitness?

The funny thing with many runners is that it almost takes more discipline to have rest days than to train, and it can be hard to make an executive decision. But there are different levels of cold/illness, and according to experts, it’s important to evaluate where yours falls before you decide.

Often a cold won’t stop you from going to work – in that case, it might be ok to go out for a gentle trot. The exercise and following hot steam shower sometimes help people feel a bit invigorated as well as providing a small psychological boost. Some sports scientists believe in the ‘above the neck’ rule – meaning a head cold is fine if you want to workout, but if you have chesty symptoms or anything below the neck, it’s probably better to rest. Medics seem to agree almost universally that you shouldn’t run if you have a temperature.

While opinions vary, an exception to this rule is if you are suffering from a sinus infection (or sinusitis), which is an inflammation of the sinus cavity. Symptoms include facial pressure, a headache, runny nose, and cough. Running can make this condition worse. According to the Marshfield Clinic: “Although sinus infections are common, for some activities, it is best to reduce playtime or sit out when you have one. Clogged nasal passages may cause dizziness that can weaken coordination, muscle control and balance. For these reasons, it is recommended you do not weight lift with a sinus infection. You also should not exercise or participate in sports if you have chest pressure with a sinus infection. This can make breathing difficult, which makes the heart work faster, possibly leading to a heart attack or stroke.”

It’s worth bearing in mind that cold, dry winter air can increase the chances of developing sinusitis, or make it worse. One option is to shift some workouts inside onto the treadmill. If you decide to push through your cold, remember to take it easier, or you could end up making it linger.

But what if you’ve decided not to run – how quickly will your fitness drop?

There is an official name for this kind of hiatus – it’s called ‘detraining’, and there are a number of things to take into account, with age, your exercise programme and fitness levels all playing a part. Because this post is about running (rather than strength training) that’s what I focussed my research on – turns out most sources believe cardio fitness starts to dip before strength – and it starts to happen relatively quickly.

After a single week of inactivity, changes happen to your heart which broadly speaking, mean the heart has to work harder to maintain the same output. In addition, the body starts to become slightly less efficient at mobilising glucose (its key energy source) from the bloodstream, making you more reliant on limited muscular glucose stores. One study is often quoted when discussing detraining, conducted by Elizabeth Ready and Arthur Quinney,they studied two groups of men – one group of 12 cyclists rode hard for 30 minutes, four times a week for nine weeks. Another (control) group did nothing.

The scientists measured Vo2 max, which is the body’s uptake of maximum oxygen. This affects muscle function, with the more oxygen getting to muscles, the better. They also measured anaerobic threshold before the experiment and then every three weeks, discovering that after training stopped the cyclists’ fitness quickly declined. After just three weeks anaerobic threshold and V02 max dropped by almost 20 per cent. This is not the only study which showed both a steep initial drop in Vo2 max – a study conducted by Edward Coyle et al showed Vo2 max dropped by seven per cent after 12 inactive days.

By the time you get to a month of inactivity, these changes continue, but there’s more too: when you’re doing endurance training you start to build a fine network of muscle capillaries. These help oxygen uptake in the muscles. By the time you hit a month of no exercise, this network starts to decline – this means oxygen uptake can start to decline.

That’s some of the bad news. Is there any good?

Well – sort of. These losses do start to level off. Both the Elizabeth Ready and Arthur Quinney study and the study by Edward Coyle showed the Vo2 max drop off started to taper after a few weeks.

It’s also worth noting a number of sources believe greater drops take place in higher performing athletes than in your average hobby runner – possibly because the standard is higher to begin with.

So what does this all mean for your race training plan?

It can be really difficult to restart a training plan after some time off, whether that be due to illness, injury, or something else. From my own experience, the first run back can be tough. But the time off is unlikely to have undone all the hard work put in before. Only you know whether your hiatus has taken you too far off plan to still compete. It’s important not to lose focus, but it’s also important not to push through if it’s only going to derail you further down the line. The attitude often taken during events is to ‘MTFU’ but ultimately there’s no point in making an injury or illness last longer for the sake of a short term accomplishment.



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