What happens to your endurance fitness if you take an extended break from training? I’m going to explain the timeline showing what changes in fitness you can expect when you stop training for six months.
According to the fitness mantra, you either have to ‘use it or lose it’! It might be a bit of a cliché, but it turns out that this saying perfectly sums up one of the key principles of fitness – reversibility. So long as you train, you can maintain and (hopefully) build your fitness levels. However, stop training, and your fitness levels will steadily decline. The obvious question that you might ask therefore is: ‘how much fitness will I lose if I decide to take a break or I’m forced to stop training because of injury, illness or other circumstances? And how rapidly will this fitness loss occur?’
Components of fitness
So let’s take an imaginary well-trained athlete 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 September 16th- after Redman Triathlon in Oklahoma City.
This is your last training day/Race for six months. After today, you store your bike away, hang up your shoes and join the bulk of folk who do no regular vigorous exercise whatsoever!
Sept 20: 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 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 off, muscle fibers damaged during hard training have been fully repaired and favorable 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.
Sept 23: After a week of 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 hard exercise. The consequence is that you won’t be able to sustain quite the same exercise intensity!
Oct 3: 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!
Oct 16: All of the detraining changes outlined above continue to progress but fundamental muscle changes are now becoming prominent. By now, your muscle capillarization will have returned to your pre-training baseline (however 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, your ability to maintain a full-out effort (for example, a sprint to the finish line) diminishes dramatically.
Dec 1: 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.
Feb 19: By six months, your fitness declines have mostly stabilized. 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 utilize 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’, with all the health risks that involves.
Look for our next blog post for Part II: Ways to maintain your fitness in the off season.