How To Prevent Missed Training From Hurting Performance

Written by:

Cliff Pittman

CTS Pro Ultrarunning Coach

Updated On

November 4, 2026

CHOOSE YOUR FORMAT

►WATCH THE VIDEO

►LISTEN TO THE PODCAST

►READ THE ARTICLE

How To Prevent Missed Training From Hurting Performance

The Short Version: Fitness fades from inactivity but far more slowly than you might fear. Two weeks of missed training costs trained endurance athletes roughly 4% of their VO2 max, but that can come back quickly. Over a longer period – up to 15 weeks – you can maintain fitness even if you reduce training volume by about 50%, as long as you sustain the intensity component of your training.

A chest cold. A brutal month at work. The taper before your A-race. Every endurance athlete I’ve coached has experienced a planned or unplanned period of missed training. And most have experienced the anxiety that comes from missing training: that all your hard-earned fitness will disappear overnight.

Fitness takes time to build, and it takes time to lose. When you take a look at the science of detraining, there are good ways to minimize the negative impacts of reduced training availability, and there are also good reasons to purposely reduce training workload for a while.

What is Detraining?

Detraining is the loss of training adaptations that happens when the training stimulus drops below what your body needs to maintain them. The figure below comes from Jason Koop’s article on detraining and it is a great illustration of the curvilinear relationship between training stimulus and time. When building fitness, you see steeper improvements at first and then the rate of improvement levels off. The inverse happens with training cessation. If you do nothing, there’s a steep loss of fitness initially (first two weeks or so), and then the rate of detraining slows. If you reduce training instead of stopping altogether, the initial rate of decline slows and you can begin retraining from a higher level of fitness compared to total cessation.

Iñigo Mujika and Sabino Padilla are two of the leading researchers in the science of detraining. They wrote two highly cited research reviews, one on short term detraining (up to four weeks) and one on longer term training, which was anything beyond four weeks.

Short Term vs. Long Term Missed Training

Based on Mujika and Padilla’s reviews, the steep drop in fitness from just a few weeks of no training is largely due to reductions in blood plasma volume, which reduces VO2 max by reducing cardiac output, along with reductions in muscle glycogen storage. These are quick changes your body can make in response to reduced exercise stimulus.

It’s only after longer periods of training cessation that structural physiologic changes occur that reverse the adaptations you gained through training. After about 4 weeks you see about a 3% decrease in red blood cell mass, which reduces oxygen carrying capacity. This is natural because your body adjusts red cell mass to your demand for oxygen; lower activity levels mean you can get all the oxygen you need from fewer red blood cells. Over time, mitochondrial density will also decrease because there’s no reason to support all those cellular powerplants if you’re energy expenditure doesn’t require them.

Does training history matter?

Yes, the longer you’ve been training, the slower/less you’ll detrain, but this affects long term training cessation more than short term (note: this difference is why tapering still works). Mujika and Padilla’s 2021 review notes that VO2 max in highly trained athletes usually stays above untrained levels, even in long-term detraining studies. Newer athletes get less of that cushion, which is one more reason consistency matters early in an athlete’s development.

Avoiding Detraining from Real-World Training Disruptions

Scenario 1: Training availability declines for a few months

This is a common scenario for new parents, people who are transitioning between jobs or moving between cities, and people who get inundated with a work project. Life gets in the way for a few months and your biggest goal is to avoid losing a ton of fitness. The question becomes, what’s the minimum amount of training required to sustain the majority of your endurance fitness?

A 2021 review by Spiering, Mujika and colleagues looked at the minimum dose of exercise needed to maintain performance. Endurance held for up to 15 weeks, even with as few as two sessions per week, or when total training volume cut by about 50%. Intensity was the key variable to keep constant, meaning you can reduce the training days per week and even shorten individual training sessions, but keep the intensity.

Coaching Example: What do I cut first?

How do I prioritize an athlete’s training when they tell me their training availability will be dramatically reduced for a few months? Let’s say your plan has a long run, a couple of quality sessions, and running most days of the week. Now we must cut back. Here’s what I do:

1. Cut the easy volume first. Short recovery runs are eliminated before anything else.
2. Keep one quality session per week. That protects intensity.
3. Protect your long endurance run, if possible. This is an ultrarunning-specific recommendation aimed at preserving durability.
4. Keep as many days as you can. Consistency matters even if the sessions are short.

Frequency and consistency matter a lot here. For well-trained athletes, Mujika and Padilla recommend cutting frequency by no more than 20–30%. Cutting volume before cutting sessions fits that research.

Reduce strength training frequency

Even when training availability declines, I recommend maintaining one strength training session per week. The detraining research supports this recommendation. A 2021 review showed that one session per week with one set per exercise held strength and muscle size for up to 32 weeks, as long as the load stayed the same (Spiering et al, 2021). Older adults may need two sessions a week and two to three sets to hold muscle size.

Scenario 2: Missed Training From Acute Illness

In this scenario we’re talking about minor illnesses like a cold or the flu that last from a few days to two weeks. After 20 years of coaching, my advice is simple: rest until you’re well. Some people try to distinguish between “above the neck” and “below the neck” or suggest you can train lightly as long as you don’t have a fever. In practice, I’ve never seen anyone benefit from training while they’re sick. Pushing through illness often turns a few days off into a much longer break later. The body will take the time one way or another.

Chronic and long-term illnesses are a whole different topic. Exercise is sometimes possible and even recommended, but the goals, expectations, and modalities may be completely different and under the supervision or in collaboration with a patient’s doctors.

Scenario 3: Adapting Training for Injuries

There’s no clean study on how fast trained athletes regain fitness after a long injury layoff. One of the coaching strategies we use, when possible, is to change exercise types to maintain some cardiovascular workload as the injury heals.

For example, I coached a runner who broke his foot. His physical therapist wanted him to cease running entirely for about eight weeks. Working with the PT and the athlete, I shifted the athlete’s primary form of exercise from running to cycling.

• Bike volume and intensity were prescribed the same way his running would have been.
• He rode about six days per week, matching his usual run frequency.
• After eight weeks, he began a return-to-run protocol of walking and jogging, with the bike still carrying overall volume and intensity.
• Over the next month, run volume rose, bike volume fell, and bike intensity stayed put.
• Once fully cleared, running methodically replaced the bike. Run workouts were kept well under what he could handle, because his cardiovascular fitness was well ahead of his musculoskeletal system.

The result: once he was back to full volume with intensity, his lactate threshold pace hadn’t dropped at all. He ran the same threshold pace as before the injury, possibly a touch faster.

My example is purely anecdotal, but notice what stayed in place the whole time: frequency, intensity, and roughly the same total volume. That lines up with Mujika and Padilla’s guidance for adapting training when availability declines: protect intensity, keep frequency reductions small, and let volume come down. Their 2021 review also supports similar-mode shift for well-trained athletes. Return to your sport as soon as it’s safe, and until then, train in the closest way your injury allows.

Scenario 4: Reducing training for a pre-race taper

A pre-race taper is a planned reduction in training load meant to reduce stress and improve performance.

A 2007 meta-analysis by Bosquet and colleagues covered 27 studies in competitive athletes. The best results came from a two-week taper that cut volume by 41–60%, with no change in intensity or frequency.

For single-day ultra events, I recommend a two week taper that cuts total volume by about 50% in the first week and roughly half again in race week, keeping frequency the same with some intensity.

Read more on tapering for ultramarathons here: “Tapering for Ultrarunning: Boost Race Performance and Prevent Taper Tantrums”

Scenario 5: Missed training for a purposeful break

After an A-race or at season’s end, a planned break lets your body and head recover. Again, Mujika and Padilla’s review suggests a partial reduction in training may help limit losses between seasons.

What does this look like in practical terms? For most athletes, a complete cessation of training shouldn’t extend past four weeks. Athletes who are newer to training and time-crunched athletes with lower training loads are better off with about two weeks completely off.

A hybrid offseason can last longer, where you reduce training workload in line with the recommendations for Scenario 1 for a month or two. When it’s a purposeful break, switching up activities and exercise types can be helpful, too.

Four things to remember

1. When training time shrinks, shorten sessions but keep the pattern. Protect some intensity, keep as many days as you can, and keep one longer session. If the plan says 60 minutes and you have 30, take the 30. Thirty beats zero.
2. Keep one strength session a week at your normal loads, even if it’s one set per exercise.
3. Match your response to the reason for the break. Sick: rest until you’re well. Injured: keep the training stimulus going however the injury allows, while letting it heal. Control what you can and make the next best decision available.
4. After a long break, ramp back gradually. Don’t jump straight back into your old volume.

References

• Bosquet, L., Montpetit, J., Arvisais, D., & Mujika, I. (2007). Effects of tapering on performance: a meta-analysis. Medicine and science in sports and exercise, 39(8), 1358–1365.
• Mujika, I., & Padilla, S. (2000). Detraining: loss of training-induced physiological and performance adaptations. Part I: short term insufficient training stimulus. Sports medicine (Auckland, N.Z.), 30(2), 79–87.
• Mujika, Inigo, and Sabino Padilla. “Detraining: Loss of Training-Induced Physiological and Performance Adaptations. Part II.” Sports Medicine, vol. 30, no. 3, 2000, pp. 145–154., doi:10.2165/00007256-200030030-00001.
• Spiering, B. A., Mujika, I., Sharp, M. A., & Foulis, S. A. (2021). Maintaining Physical Performance: The Minimal Dose of Exercise Needed to Preserve Endurance and Strength Over Time. Journal of strength and conditioning research, 35(5), 1449–1458.