How much will taking a few days off running running hurt my fitness? It's one of the most common questions I get from runners struggling with an injury, fighting the flu, or hesitant to take a much needed rest from training. As runners, we are all paranoid about taking a few days off, generally thinking it will ruin our months of meticulous training.
As a coach, I am not immune to being frightened by this irrational fear. While I was training for the NCAA championships while in college, I had a swimming accident that left my left shoulder separated and required a visit to the hospital to get it back in place. The doctors told me I needed to take a few days off to let the shoulder heal. Not wanting lose any precious training time, I strapped my left arm tight across my body using a combination of saran wrap and duct tape and went on a 12-mile run the next morning. Luckily, I did not suffer any lingering effects from the imbalances I created by running with one arm. However, I wanted to share this story with you to demonstrate that I write this article with the deepest understanding of how hard it can be to listen to science and understand that a day off is not going to end your hopes of running as fast as you've dreamed.
When we look at the effects of taking time off from running, we have to analyze the de-training from two perspectives: (1) your metabolic systems such as aerobic fitness, threshold and VO2 max; and (2) your structural systems such as your muscles and neuromuscular coordination (how fast and efficiently your brain can tell your body to perform and execute a specific movement).
Effect of de-training on the aerobic system Because VO2 max is one of the best measurements of a runners physical fitness, I will use it as the baseline to compare the effects of de-training on your aerobic system. To be brief, VO2 max is an individual's maximum ability to transport and use oxygen during exercise.
Recent studies show that there is little reduction in VO2max for the first 10 days following inactivity in well-trained athletes. It is prudent here to mention that all of these guidelines assume you are a decently trained runner, having trained consistently for a 4-6 month period. Beginner runners will lose fitness at a slightly faster rate since they have a smaller base of fitness.
After two weeks of not running, studies show that VO2 max decreases by 6%. After 9 weeks VO2 max drops by 19% (sorry, I could not find any data on 3-8 weeks postactivity). After 11 weeks of no running, Studies demonstrate that VO2 max falls by 25.7% from peak physical fitness. So, as you can see, from an aerobic standpoint, you have very little to worry about if you have to take a break from running for two weeks or less. This is very important for those runners that need to take a hiatus because of a small injury or are nervous about taking downtime after a long training segment. A 6% decline in VO2 max can be made up with one or two weeks of solid training.
While percentages are fantastic, what do those numbers really mean for runners? Let's use an example of a 20 minute 5k runner. A 20 minute 5k runner has a VO2max of roughly 49.81 ml / kg / min (estimated using a formula). After 2 weeks of no running, the 5k runner would lose 6% of his VO2 max, which would be 46.83 and would now be in 21:05 shape, according to most estimates. After 9 weeks of no running, the same 20-minute 5k runner would now be in 24:00 minute 5k shape. After 11 weeks of no running, our poor running friend would be in 25:30 shape.
Effect of de-training on the structural system While the reduction in aerobic fitness has been tolerably studied in an applicable manner, the effect of de-training on specific running muscles has been harder to find. However, the little research that does exist about de-training in general proposals that the most dramatic reduction in fitness occurs within a 10-28 day window. Before and after this window, de-training from a structural perspective is not severe. What does this mean? After 7-10 days of not running, you will lose some muscle power and coordination, but not enough to totally derail your goals. With a few specific workouts such as hill sprints, you'll be back to your pre-de-training levels before you know it. If your break from training is longer than two weeks, than you'll have a little bit to make up before you can get back to personal best shape.
What does it all mean? Basically, you should not be too worried about losing significant fitness if your break from running is less than two weeks. You'll lose some condition in your aerobic system and muscles, but pre -activity fitness will return quickly. Again, this assures that you have built a healthy and consistent base of training of 4-6 months prior to taking time off. It's not the end of your career if you have not been training for this long; it simply means that the reduction in fitness will be slightly more pronounced. After two weeks of not training, significant reductions in fitness begin to occur and you'll have about 2-8 weeks of training (depending on the length of activity) ahead of you to get back to your previous level of fitness. Basically, here is an easy to follow form chart:
By no means am I suggesting that taking time off from running is an enjoyable experience. However, sometimes it's inevitable or for the best in the long-term. I hope this article answers all your questions in a practical yet scientifically supported way.