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The season of short days, wet and icy roads, coughs, colds and flu is here. What happens to your fitness when unexpected circumstances force a break from training?

More importantly, how you can minimise fitness losses to be better-prepared next spring?

No matter how carefully constructed your cycling training programme, there'll be times when unexpected circumstances intervene. Even during the balmy days of summer, work pressures, family commitments and injury threaten to scupper your best-laid plans. Come winter, the hurdles are even greater.

For starters, the days are short and nights long. This means that cyclists who combine commuting and training have to ride some of their sessions in the dark - not everyone's cup of tea. Likewise, pre or post-work training sessions can't be performed in daylight because there's simply not enough of it.

Then there's the weather; unless you have a penchant for water, wet conditions are always challenging. Worse, icy or snowy roads can be downright dangerous. If that weren't enough, winter is the time of year when upper respiratory tract infections (coughs, colds, sore throats, flu) tend to peak.

If you come down with a heavy cold, the chances are you'll need to take a couple of days off or, at the very least, reduce your training intensity for a week or so. If you succumb to full-blown flu, on the other hand, you'll have no option but to abandon training completely for a couple of weeks. Even when you do resume, you can expect to feel weaker than a fluffy kitten!

Add into the mix that the activities of the festive season often result in missed sessions or reduced training, and it's easy to see why a carefully crafted winter training programme can go distinctly pear-shaped.

How much fitness loss?

The biggest worry when training sessions are lost for whatever reason is ‘detraining' - losing fitness. This happens because of a key principle in exercise physiology called ‘reversibility': gains in fitness occurring as a result of training are steadily lost once training ceases. The obvious question is: How much fitness will I lose if I'm forced to stop training and how rapidly will this occur?

To answer this, we need to understand that the term ‘fitness' actually embraces a number of aspects of performance variables, including muscular strength, endurance and power, aerobic and anaerobic capacity. In terms of exercise physiology, this involves a number of systems in the body (see boxout on next page). Of course, these systems don't all decline at the same rate. Even so, because of reversibility, when you stop training, the inevitable direction is downwards.

Half as good

In one study, Dutch scientists looked at the effects of three weeks of reduced training volume and intensity on the physical fitness of well-trained cyclists(1). These cyclists normally averaged around 16 hours per week of training. For this study, they were instructed to reduce their training volume by half and simultaneously reduce their training intensities by 20 per cent. Taken together, the combined effect of these changes resulted in a 60 per cent drop in the cyclists' training load.

Measurements of fitness were taken before and again after the three weeks of detraining. The researchers' findings surprised them. Basically, there was no drop whatsoever in either the cyclists' maximum power outputs or their oxygen uptake capacity (an excellent indicator of aerobic fitness). It didn't matter whether the reduced training load was carried out at constant or variable intensity; the fitness losses were essentially zero in either case.

For cyclists struggling to maintain fitness, especially over the winter months, these findings are encouraging because they suggest that, even if you slash your training load by nearly two-thirds for up to three weeks (for example, during a prolonged cold snap), you can expect to retain nearly all of your hard-earned gains.

One caveat, however, is that, at 16 hours per week, these cyclists' pre-layoff training loads were reasonably high. If you're training for only three hours a week to begin with, then reduce your training load by 60 per cent, the chances are that you will lose more fitness than did the cyclists in the study.

Too much detraining

In the study, the cyclists cut their training volume by 50 per cent. But what happens when you slash training volumes by much, much more - to around just one-tenth of normal? A fascinating study published recently looked at just this question.

The scientists studied the cardiovascular and body-composition changes following an ultra-distance triathlon in nine recreational triathletes over a 30-day detraining period during which training volume was reduced by 87 per cent (2). They found that after 30 days of detraining, there was a 4.7 per cent decrease in maximum aerobic capacity from 4.83 litres per min to 4.61 litres per minute (L/min).

Meanwhile, skinfold thickness totals (a measure of body-fat levels using calipers) rose a whopping 28 per cent, from an average of 43.9mm to 55.1mm.

The total blood haemoglobin (a measure of oxygen-carrying capacity of the blood) fell by 3.1 per cent, and bodyweight rose from an average of 75.1 to 77.1kg. Taken together, these physiological changes would certainly result in a performance decrease in the average cyclist.

Of particular note in this detraining study was the increase in skinfold thickness, indicating a significant rise in body fat. This phenomenon has also been observed in other sportsmen and women such as swimmers.

For example, a recent US study found that five weeks of detraining in eight swimmers resulted in an average increase in fat mass of 1.8kg and an average waist circumference increase of 1.1cm(3). Meanwhile, the swimmers' maximum aerobic capacity fell nearly 10 per cent from an average of 46.7ml/kg/min to 43.1ml/kg/min.

Good news

While these findings might make for depressing reading, it's not all bad news. For starters, we know that physically fit individuals who suffer detraining and then return to training find that their fitness returns far more rapidly than it does for those who never had the benefit of prior conditioning.

In particular, the research shows that a relatively short break (two weeks or so) is generally not considered significantly disruptive, provided the previous training adaptations have been achieved over a period of at least 12 weeks(4). Even better, for cyclists who are able to squeeze in just a little training time, there's evidence that even very small volumes of the right kind of training reduce deconditioning to a minimum.

To illustrate this, another recent study examined the effects of reducing the volume of cycle training by 60 per cent in a cyclist during the pre-season period(5).

The caveat, however, was that this cyclist had to compensate by incorporating a combination of very intense short intervals on the bike and some sessions of running (the purpose of the running training was to promote fuller recovery of the cycling muscles while still allowing the cyclist to work on his cardiovascular conditioning).

The researchers found that, compared to the pre-season period (November-February) of the previous year, amazingly, the cyclist's aerobic (VO2max) increased by 10.3 per cent and his time-trial performance improved by 14.9 per cent. Of course, this was only one case study of one cyclist, so it's impossible to draw cast iron conclusions.

However, the findings fit neatly with recent research on interval training that have suggested that lower volumes of higher-intensity work yield very significant conditioning benefits. Importantly for cyclists, this suggests that, during layoff periods of longer than two weeks, a small volume of intense work might greatly help keep detraining to a minimum.


Enforced breaks from training happen to us all at some point, and in the winter the likelihood is much greater. A short interruption of up to two weeks is unlikely to do any long-term harm, provided you start the layoff with a good fitness base.

However, for longer breaks out of the saddle, you need to think about strategies to minimise your fitness losses. Doing so will help ensure a much smoother and faster return to full fitness. The box below gives some practical advice for those facing a layoff.

Some practical advice

If you need to take a training break, consider the following: If you're a seasoned cyclist forced to take a break of two weeks or less, don't worry - your fitness losses won't be large, and you may find that the extended rest allows extra recovery, enhancing performance in the longer-term. On the other hand, those new to cycling or with a low fitness base should accept that fitness losses after any training break will be proportionately greater.

For breaks of over two weeks, try to schedule (if possible) two or three short, high-intensity interval sessions per week. Research shows that interval sessions consisting of just eight 30-second efforts two or three times a week can be very effective for cyclists seeking to retain aerobic fitness and help avoid detraining effects that would occur otherwise.

During longer breaks, even if you are able to get in the odd interval session, you will also need to curtail your calorie intake to prevent the performance-blunting effects of increased body fat. So keep your diet as nutrient-rich as possible and minimise junk calories.

Finally, remember that prevention is better than cure. If you haven't already done so, think about investing in a turbo-trainer or other training device for the long, dark winter nights and inclement weather. By keeping your diet as nutritious as possible, avoiding overtraining or becoming overtired, you'll be better able to fend off winter bugs.

What is detraining?

Detraining is what happens when you take a prolonged break from training: you lose fitness. The physiological changes your training stimulated effectively wear off - your body resets itself back to ‘sedentary mode'.

What happens during detraining?

A number of systems in the body are ‘detrained' once training ceases. These include:

Cardiovascular detraining Your blood volume falls and, as a direct result, there is a decrease in your cardiac output (amount of blood your heart can pump per minute) and stroke volume (amount of blood it can pump per beat) during exercise. The dimensions of the heart muscle also decrease with inactivity, as does respiratory (lung) function, caused by weakening of the muscles in the ribcage. All of this reduces the amount of oxygen you can transport to your working muscles, which means your maximal performance will decline.

Metabolic detraining Once you stop training, there's a comparative increase in the amount of carbohydrate used as fuel during both maximal and sub-maximal exercise, with less energy derived from your fat stores. This effectively decreases your endurance since carbohydrate stores are limited, whereas energy from fat stores is virtually unlimited. Also, something called ‘insulin sensitivity' is reduced, which means your muscles find it harder to take up glucose (muscle fuel). Moreover, less efficient oxygen metabolism means that, for a given effort level, higher levels of fatiguing blood-lactate are produced in your muscles, making it harder for you to maintain high training intensities.

Muscular detraining

In your cycling muscles, the density of capillaries (tiny blood vessels that carry oxygen to muscles) decreases and the concentration of enzymes in muscle mitochondria (the ‘energy factories' within cells) used to release energy from oxygen also decreases. Also, muscle fibres shrink in cross section and cell-signalling hormones involved with gaining/maintaining strength decline, leading to strength losses.

That's the theory

However, there's surprisingly little published research on the actual fitness losses during an extended period of detraining. This is perhaps to be expected; after all, it's very hard to recruit a group of sportsmen or women who take their training seriously and then ask them to stop training for a month or more while their hard-earned fitness ebbs away! Having said that, there has been some research carried out into the effects of reducing training volumes and intensities over an extended period of time (as opposed to ceasing training completely).


Br J Sports Med 2001;35:431-434, Int J Sports Med. 2012 Feb 8. [Epub ahead of print], J Strength Cond Res. 2011 Oct 24. [Epub ahead of print], Peak Performance 2006. 223; p4-6, J Strength Cond Res. 2011 Nov 23. [Epub ahead of print]

This article was first published in the Winter 2012 issue of Cycling Fitness. You can also read our magazines on Zinio, download from the Apple store and also through Kindle Fire.

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Founded in 1891, Cycling Weekly and its team of expert journalists brings cyclists in-depth reviews, extensive coverage of both professional and domestic racing, as well as fitness advice and 'brew a cuppa and put your feet up' features. Cycling Weekly serves its audience across a range of platforms, from good old-fashioned print to online journalism, and video.