How much fitness do you really lose over 2-3 months of no trainingUnfortunately, 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 athletes who take training seriously and then ask them to stop training for a month or more! However, a fascinating study on detraining in triathletes looked at the cardiovascular and body composition changes in nine recreational triathletes over a 30day detraining period (during which training volume was reduced by 87%) following an ultra-distance triathlon. The researchers found that after 30 days of detraining there was a 4.7% decrease in maximum aerobic capacity from 4.83L/min to 4.61 litres per minute. Meanwhile, skinfold thickness totals (a measure of body fat levels using callipers) rose 28%, from an average of 43.9mm to 55.1mm. Of particular note in the detraining study was the increase in skinfold thickness, indicating a significant rise in body fat – something that has been observed in swimmers. One 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. Meanwhile, maximum aerobic capacity fell nearly 10% from 46.7mls/kg/min to 43.1mls/kg/min. Components of fitness To properly understand how detraining affects fitness, it’s important to understand that there are several different components of fitness including muscular strength, muscular endurance and cardiovascular (heart, lung and circulatory) endurance. Stop training and the performance decline in each of these components will take place at a different rate. So let’s take an imaginary well-trained cyclist and observe what happens to his or her body over a period of six months following the complete cessation of training. Let’s assume that all training stops on May 1st 2017 and track the changes that would occur This is your last training day for six months. After today’s ride, you store your bike away, hang up your cycling shoes and join the bulk of folk who do no regular vigorous exercise whatsoever! After three days of inactivity, you might expect that your fitness has already begun to decline. In reality however, the losses at this stage are very minimal. In fact, if you had been training hard prior to day zero, after three days of rest, your cycling fitness is now probably enhanced! That’s because in those three days, your muscles have had time to fully recover; muscle carbohydrate stores (glycogen) have been topped up, muscle fibres damaged during hard training have been fully repaired and favourable metabolic changes in the muscles have had time to occur. Indeed, this peak in performance after a few days of rest is exactly the reason why tapering works and why you shouldn’t train right up to the day of a big event. After a week’s complete inactivity, changes begin to occur in the body that result in fitness losses. For example, after three days, your blood volume can be reduced by 5-12%. This means a decrease in amount of blood your heart can pump – both in terms of amount of blood pumped per beat and total blood volume per minute. The result is that your heart has to work slightly harder to maintain a given workload on the bike. There are some metabolic changes too; after six days or so, muscles begin to become less efficient at ‘soaking up’ glucose (the body’s premium fuel for exercise) from the bloodstream. This means that during exercise, you need to place more reliance on your (limited) muscle glycogen stores and also that you become less efficient at building up those glycogen stores after exercise. A third change is that your muscles start to become less efficient at coping with lactate accumulation during sustained efforts of hard cycling. The upshot is that you won’t be able to sustain quite the same exercise intensity before having to back off because of the burning sensation in the legs and laboured breathing! At this point, your maximal oxygen uptake (VO2max – the prime measure of your aerobic fitness) will have declined by anything from 4-20%. Part of this stems from reduced cardiac output – not helped by the fact that the muscle mass in the pumping chambers of the heart can decrease by almost 20% after three weeks of inactivity! It also arises because of changes in muscle physiology and biochemistry that are beginning to take place. For example, the fine network of muscle capillaries built up with endurance training begins to decline. As a result, oxygen uptake in the muscles can decline by up to 8% All of the detraining changes outlined above continue to progress but fundamental muscle changes are now becoming prominent. By now, your muscle capillarisation will have returned to your pre-training baseline (however is that it’s still likely to be higher than that in people who have never trained. In addition, alterations are taking place in your muscle biochemistry. In particular, the biochemical pathways that help your muscles burn fat for energy start to become less efficient, making it harder to burn fat while you ride, which in turn reduces your endurance capacity. On top of that, not only is your overall muscle mass declining (reducing your maximum power and strength), muscle fibres known as Type IIa (used during high-intensity sustained efforts) start to revert to Type IIx fibres, with greatly reduced endurance capacity. In short, your ability to maintain a full-out effort (for example, a sprint to the finish line) diminishes dramatically. After two months of inactivity, your heart is noticeably less muscular, with the thickness of the muscle walls that comprise the pumping chambers reduced by as much as 25%. The muscle mitochondria are also becoming less efficient at using oxygen to produce energy in your muscles. This efficiency can decline by 25-45% up to twelve weeks after training cessation. After three months, you also begin to undergo ‘hormonal detraining’. Hormones are chemical messengers that regulate the body’s biochemistry; as you become detrained, more stress hormones are released during exercise, which basically means that the same exercise intensity becomes more stressful for the body, which in turn increases recovery times. All of the detraining changes outlined above continue to progress but fundamental muscle changes are now becoming prominent. By now, your muscle capillarisation will have returned to your pre-training baseline (however is that it’s still likely to be higher than that in people who have never trained. In addition, alterations are taking place in your muscle biochemistry. In particular, the biochemical pathways that help your muscles burn fat for energy start to become less efficient, making it harder to burn fat while you ride, which in turn reduces your endurance capacity. On top of that, not only is your overall muscle mass declining (reducing your maximum power and strength), muscle fibres known as Type IIa (used during high-intensity sustained efforts) start to revert to Type IIx fibres, with greatly reduced endurance capacity. In short, your ability to maintain a full-out effort (for example, a sprint to the finish line) diminishes dramatically. By six months, your fitness declines have mostly stabilised. However, there are still undesirable changes taking place. For example, the actual volume of mitochondria per unit volume of muscle is declining, further reducing your ability to utilise oxygen during exercise. In addition, while you’ve lost muscle mass, you’ve almost certainly gained body fat due to a lower daily calorie burn and reduced muscle mass. So while you may not have gained weight on the scales, you will have almost certainly become ‘fatter’, A CASE STUDY ON MIGUEL INDURAIN Hailed as one of the greatest cyclists ever, Spain’s Miguel Indurain was the dominant Tour rider in the 1990’s with five consecutive wins (1991 through 1995) in the Tour de France, and two wins in the Giro d’Italia (1992 and 1993). Indurain was also the first to win the time trial when it was introduced in the Olympics in 1996, having already bagged the World Championship Time Trial in 1995. During his racing years, Indurain’s stats made mightily impressive reading: His heart/lung system enabled him to transport around 7 litres of oxygen around his body per minute, compared to 3–4 litres for an ordinary person and 5–6 litres for his fellow riders. His maximum cardiac output was measured at 50 litres a minute (a fit amateur cyclist’s is about 25 litres per minute) while his maximum oxygen uptake capacity was reputed to be around 88ml/kg/min - in comparison, Lance Armstrong’s was ‘only’ 83.8 ml/kg/min! When Indurain retired, he gave up cycling completely. Fourteen years of inactivity later, Indurain’s body mass had increased from around 80kg in his competitive years to 92.2kgs and his maximum oxygen transport capacity had fallen to 5.3 litres per minute. Meanwhile his maximum oxygen uptake capacity had also declined to 57.4 ml/kg/ min. The magnitude of Indurain’s decline (over 20% per decade) in one of the most genetically gifted cyclists ever is far greater than that typically observed in studies on ordinary cyclists who continue to train as they get older (under 5% per decade), and points to his inactivity rather than simple ageing per se as the main factor. While Indurain is undoubtedly blessed with superior cycling genetics (and perhaps maintained more fitness than would be expected in lesser cyclists), the results suggested that the bulk of his fitness loss was due to detraining, which was exacerbated by his significant weight gain. KEY POINTS IN THE DECLINE OF FITNESS COMPONENTS DURING DETRAINING There are a number of components of fitness that become ‘detrained’ when you cease training. These include:
- The dimensions of the heart muscle decrease with inactivity as does respiratory function, caused by weakening of the muscles in the ribcage.
- Cardiovascular Stop training and your blood volume falls, which means there is a decrease in the total amount of blood your heart can pump 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 Over time, your muscles will find it harder to produce energy from your fat stores. This effectively decreases your endurance since carbohydrate stores – the other major fuel source during exercise - are quite 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, a 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 ‘aerobic 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 Article from Peak Performance. May 2017 number 364, available on subscription only