My running coach told me to take a break from running after I finished my winter 5K training block. A week later, I am anxious about losing running fitness.
The benefits of a running break are apparent to most. Physically, your body gets a chance to recover from the goal race and the weeks of training leading up to the rest. Your mind also gets a break from the intense focus and pressure of training. Your friends, family, and social life gets a break from the early bedtimes, long runs, and time away necessitated by training. Your diet gets a break, perhaps with a few more sweets. But how long should a break last?
You are striking a balance in a running break between recovery and not losing running fitness. From my research, here is what I have distilled. Most runners start feeling their fitness decline after 5 to 7 days without running. In reality, very little fitness is lost as measured by VO2 max and cardiac performance.
For most runners, your aerobic fitness takes 7 to 21 days to decline[1]. Your blood plasma begins to decrease up to 12%, lowering the volume of oxygenated blood to muscles. VO2 max drops 4 to 6%. Your body begins less efficient at firing muscle fibers, producing the feeling of “rustiness” in your legs. Since your heart has not worked as hard, the heart’s size will decrease along with the stroke volume, the amount of blood pumped per stroke. Your body also gets less efficient at processing glycogen.
Fortunately, the fitness you lose first is the gains you have made over the last several months of training[2]. Once you return to exercise, many of these losses will be regained. Most importantly, your base aerobic fitness developed through the years is much harder to lose.
A several months break from running does begin to change your body in ways that will require a slower buildup back to running form. Your body will have gotten less efficient at burning fat for energy. The capillary beds flooding your muscles with oxygen-rich blood will have shrunk. Mitochondria, the powerhouse of cells, will have become less efficient at creating ATP, the body's energy currency. Your muscles will have atrophied. However, with time and patience, runners can return to their prior fitness level and do so safely, minimizing injury.
Do not be afraid to take a break from running. The gains you have made are not as easily lost. After a short break, you will return energized and refreshed.
Best wishes on chasing your running goals!
[1] https://pubmed.ncbi.nlm.nih.gov/3944049/
[2] https://pubmed.ncbi.nlm.nih.gov/10966148/