When it comes to fitness, nothing is permanent. Your body is always in a state of flux, and with sufficient training it adapts to become faster and more capable. But when that training stimulus is removed, the opposite happens, and fitness declines. This is called detraining, and every athlete can benefit from a better understanding of what it is, why it happens, and the rate at which it occurs.
For more information on detraining check out Ask A Cycling Coach Ep 293.
Your body is extraordinarily skilled at allocating resources. At the simplest level, this is why training makes you faster. The stress of repeated workouts disrupts the internal state of balance, otherwise known as homeostasis. Resources are automatically allocated to adjust in response, and adaptation occurs. A new state of balance is reached, with a higher level of physical capabilities- in other words, fitness increases.
Homeostasis is fragile, and any change disrupts the balance, including a reduction or removal of training. Since the physical adaptations of fitness take energy and resources to maintain, the body moves these resources elsewhere if they aren’t needed. Stop training, and eventually your body settles at a new state of balance, with a lower level of physical capability. This is known as detraining, and the end result is you get slower.
Detraining is a natural part of the training process. Minor detraining occurs during rest weeks or when tapering for an event, but it’s outpaced by the performance improvements that come with recovery. More significant detraining occurs during the offseason, when a full recovery facilitates greater fitness improvements in the coming months. In these cases, detraining is temporary, intentional, and productive.
The detraining that comes with longer-term breaks from training, on the other hand, can be unproductive. Complete detraining can dramatically decrease your fitness with no real benefit, potentially erasing improvements you’ve worked long and hard to obtain. Luckily, it usually doesn’t take much to stave off these effects, and the fitter you’ve been in the past, the easier it is to bounce back.
Detraining is quite literally the opposite of training, as all of the performance-benefitting adaptations that occur to make you faster gradually undo themselves. And just like the benefits of training, the various effects of detraining occur at different rates and to different degrees.
Aerobic capacity is the first thing to be affected, as VO2 max decreases significantly in the first month of inactivity. This is caused by declines in blood volume, a drop in red blood cell count, and an overall reduction in cardiac output. With less oxygen available to reach your muscles, your heart rate increases to compensate, raising RPE (rate of perceived exertion) across the board.
These aerobic declines effectively shift some burden to your anaerobic system, and blood lactate levels increase as a result. Muscle glycogen stores plummet, as do the levels of enzymes responsible for synthesizing them, making your body less efficient at fueling muscles during exercise. The practical result is a significant decline in your FTP.
After a few weeks, peripheral cardiovascular systems also experience accelerating effects. Capillary density drops, as does mitochondrial density and the levels of oxidative enzymes. Muscular losses cause a drop in peak power output, and the size of the heart and pliability of the left ventricle decreases. Improvements in blood pressure resulting from exercise reverse by the 12th week of inactivity, and ventilatory function falls up to 14% from its trained maximum after a few months.
Finally, some muscle fibers convert from type 2a to type 2b, becoming more reliant on anaerobic metabolism. This can ironically make anaerobic efforts feel easier as you detrain, but don’t mistake this paradoxical effect for an improvement in fitness. Eventually, with a sufficient decrease in training stimulus, your body almost completely reverts to its untrained state.
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As a general rule of thumb, it takes about as long to lose fitness as it takes to gain it. Deep-seated base fitness developed over months declines gradually, while sprinting ability is more fleeting and decreases after just a few days. The upside is that maintaining fitness takes much less work than building from scratch, and it’s relatively easy to prevent significant declines with just a few workouts each week.
The chart below shows approximately how long different types of fitness take to significantly decline with a complete cessation of training. It also shows the minimum amount and frequency of exercise to temporarily prevent these declines for most athletes.
|Fitness Type||Detraining Timetable||Maintenance Workout|
|Aerobic Endurance||30 days or more||One multi-hour aerobic ride per week|
|Anaerobic Capacity||About 18 days||One hour-long 30 second repeat workout per week (example: Taylor-2)|
|Muscular Endurance||~ 15 days||One sustained power Sweet Spot or Threshold workout per week (example: Eichorn)|
|Sprint Power||~ 5 days||One sprint workout per week (example: Berryessa)|
These maintenance workouts could potentially be combined into two weekend rides: a long ride targeting aerobic and muscular endurance on Saturday, and a workout with sprints and longer anaerobic efforts on Sunday.
Detraining seems to affect athletes differently depending on their training history. Long-term endurance athletes detrain to a higher baseline VO2 max than athletes who are new to training, for whom time off can lead to a complete reversal of fitness. Experienced athletes can also regain previous fitness more quickly.
Some evidence suggests this may be partly related to an increase in muscle fibers that comes from long-term training. When previously-conditioned muscles waste away during detraining, their nuclei persist intact, ready to reactivate quickly if training resumes. These nuclei have a half-life of about 15 years and are easier to produce at young ages, potentially explaining a reason why athletes who reach high fitness early in life can more easily regain and maintain exceptional capabilities.
Maintaining a baseline of fitness probably takes less work than you think. Just one or two workouts a week can be enough to minimize losses in VO2 max, maximal heart rate, and time to exhaustion, while still facilitating recovery from a hard season. The type of workout required for maintenance depends on your experience level and how much fitness you want to maintain; relatively new cyclists can successfully use aerobic cross-training to maintain most of their capabilities during the offseason, while elite cyclists will need to ride their bikes to stay fit.
Some studies have suggested that partial detraining can increase subsequent sensitivity to training stress, making time off a potentially useful tool to help break through plateaus in the coming year. And whatever your experience level, an offseason period of reduced activity is an important part of training, allowing your body to recover and repair itself. But complete and sustained cessation of training might do you more harm than good, especially if you’re relatively new to the sport.
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