With every workout, the goal is to challenge the body in some way. When we work out, we disrupt the body’s normal state, forcing it to adapt to the stressors it experiences. These adaptations result in the body building stronger muscles, improving cardiovascular fitness and becoming more efficient at producing energy. These adaptations occur over time and essentially make the body more resilient to exercise. But what happens to these adaptations when you stop training?
After prolonged periods of inactivity, your body gradually begins to lose some of the adaptations that it worked to build. This is known as detraining. While detraining does not occur overnight, extended breaks from your regular exercise routine can lead to noticeable declines in performance and overall fitness. The good news here is that this is a gradual process, and the fitter you are, the easier it is to regain those adaptations once you are training consistently again.
The first system affected by inactivity is the cardiovascular system. Within the first two to four weeks of inactivity, our V02max declines. V02max is often referred to as our aerobic engine, and it’s our body’s ability to deliver and use oxygen during exercise. This makes it a key factor in endurance performance. V02max declines due to reduced blood volume, decreased amounts of red blood cells and a reduction in cardiac output. Our cardiac output refers to the amount of blood pumped by the heart and typically begins to decline around 4-8 weeks of detraining.
In other words, our heart becomes weaker and less efficient over periods of detraining. As these changes occur, our heart has to compensate in other ways. To compensate, our heart rate will spike in order to deliver sufficient oxygen to the working muscles. This means that workouts that used to feel comfortable suddenly feel much more challenging and require more effort to maintain the same levels of intensity.
When our aerobic capacity declines with detraining, we have less oxygen available to the muscles. These declines typically start to become significant within 2-4 weeks of detraining. With prolonged periods of reduced oxygen availability to the muscles, mitochondrial density within the muscles begins to decline. This is important because the mitochondria in muscles produce the energy (ATP) required for muscle contractions. With fewer mitochondria, the muscles become less efficient at producing energy. This leads to earlier-onset fatigue and makes sustained exercise feel harder than it did before your training break.
With periods of inactivity, not all fitness adaptations disappear at the same rate. Strength and power tend to be more resilient than cardiovascular fitness to detraining losses. With strength training, declines in strength are minimal within the first two weeks of inactivity, especially in individuals with a longer, more consistent history of strength training. This means you will feel reductions in endurance before you notice a meaningful decrease in the amount of weight you can lift.
On a more encouraging note, those with a longer history of regular exercise have an easier time getting back to previous levels of fitness after periods of prolonged inactivity. With years of consistent training, our bodies build up “muscle memory,” and they can rebuild lost adaptations much faster than it took to initially develop them. The biggest takeaway here is that it doesn’t take much effort to maintain your fitness levels to avoid having to build back up from scratch. When life gets busy and you cannot maintain your full weekly training volume, most people can get by with 1-2 quality workouts per week to minimize detraining adaptations.
As shown here, the loss of fitness adaptations does not occur overnight; however, with multiple weeks of reduced training volume, individuals may begin to see losses in fitness. With the summer months ahead of us, our schedules tend to get more chaotic, making it harder to follow our typical routines. This is not to discourage you; rather, it’s meant to demonstrate that consistency over perfection will win every time, rather than taking an all-or-nothing approach to fitness. It’s important to remember that fitness is built over months of consistent training, not days. Missing a workout here and there won’t erase your progress, but maintaining some level of movement during the summer months will make it much easier to return to your normal routine. Even in small doses, consistency will outperform perfection.
