How soon do you lose fitness during an involuntary rest, and how can you minimize it? (#300)

Summer is approaching, a time when we often receive numerous inquiries about "how little training is enough to maintain fitness during vacation." Then there's the all-too-familiar "vacation cold" that tends to strike at the start of the holiday. Anyway, I thought I'd be proactive and dive into an article like this before the vacation season, exploring how quickly you lose fitness and what's required to maintain it.

Research shows you lose fitness significantly slower than many think, and it's possible to maintain a large portion of your training capacity with much less training during a period. The most crucial takeaway is to keep up intensity and training frequency as much as possible, even if you need to reduce your training volume. We'll also go through how different types of training affect the abilities you retain and how long it usually takes to get back after a break in training.

There's no clear scientific consensus on the minimal training needed to maintain your form—it becomes particularly challenging as the answer varies significantly based on your fitness level. In May 2021, a review article was published that explored existing research on generally trained individuals (VO2max around 50 ml/kg/min), and I will cover that along with supplementary studies.

First, let's talk about the elites. For elite endurance athletes, performance losses are about -2–4% per week during complete inactivity. Performance is evaluated in studies using sport-specific tests like VO2max, threshold, maximum power output, time trials, and so on. The findings are fairly consistent, with a decline of 2–4% per week over periods of 4–12 weeks, the timeframe that was studied. The data also shows that levels never drop as low as those who are untrained—you retain some training advantage once it's built up, even after taking a break for up to three months 11252068. For the well-trained, however, stroke volume is lost quickly, and an increased heart rate alone isn't sufficient for delivering oxygen to the muscles—VO2max declines rapidly. Threshold and the ability to store/use glycogen often weaken after 2–4 weeks, and recently achieved improvements in VO2max can disappear within four weeks without training.

There's also substantial research on older populations (65+ years) regarding the minimal training required to maintain muscle mass and fitness, but I won't be exploring that research here.

There's plenty of research on this since it's relatively simple to conduct: ask people to rest entirely or reduce their training and compare.

A rather extreme study titled “How to prevent the detrimental effects of two months of bed-rest on muscle, bone and cardiovascular system: an RCT” tested 23 individuals in their 30s who stayed in bed for 60 days (they could move around the area, but no training). Half were the control group (no exercises), and the other half performed a daily jump workout (6×12 jumps) once a day, 5–6 days a week. The session took about 3 minutes.

The results were clear: the control group lost 3% in bone density, 5% muscle mass, 40% in maximum strength, and 29% in oxygen uptake. The test group that did the three-minute jump session lost almost nothing in bone density, muscle mass, or strength, and decreased in oxygen uptake from 43 ml/kg/min to 40 (−7%) while the control group dropped from 50 ml/kg/min to 35 (−30%).

Conclusion: as little as 3 minutes of intense training per day is enough to maintain at least 90% of physical functions during two months of bed rest for a typical untrained to moderately trained person. Interesting for healthcare, but maybe not entirely sufficient if you're looking to maintain performance levels.

For more well-trained individuals, 3 minutes per day is not enough. In a study, researchers divided 14 elite-level kayakers (average weight ~85 kg, VO2max 69 ml/kg/min — among them World Championship and Olympic medalists) into two groups right after the World Championships. One group stopped training completely, and the other reduced their volume to 20–30% of normal but maintained intensity and frequency over 5 weeks.

Results: both groups lost in measurable variables (strength, VO2max, threshold, fat%, among others), but the group that trained 20–30% of their normal volume halved the losses compared to the group that didn't train at all (−5.6% instead of −11.3%). These figures roughly confirm the previously mentioned rate: the elite lose about 2–4% capacity per week at full rest. In this study, it was −2.3% per week for those who didn’t train at all and only −1.1% per week for those who kept 25% of their normal volume — thus losses were halved with a quarter of normal training. Not too shabby.

Here's the critical point: if you get sick or life's demands interfere, reducing your training to just 20–30% of your usual volume isn't enough to maintain your VO2 max, strength, threshold, and all sport-specific aspects. The answer is NO. The training you do primarily preserves the ability you're working on — and nothing else.

If you usually train 10 hours a week and cut back to 2–3 hours, sticking only to interval training, you'll maintain your interval capacity but lose endurance/stamina. If those 2–3 hours are long, steady sessions, you'll keep the benefits of those sessions but lose high-intensity capacity. The principle of specificity can be your friend or your foe, depending on how you choose.

This brings us back to the review article that started this discussion. They've broken down the article into sections that I'll cover now.

First up: strength training.

• Training volume reduced by 66% over 32 weeks (1 set per exercise instead of 3) but maintaining the same intensity (8–12 repetitions).

  RESULT: Muscle fiber cross-sectional area was fully maintained in younger participants (20–30 years), but decreased in older individuals (60–75 years).

• Volume reduced by about 50% from 3 sessions per week to 2, along with reducing 2 sets per exercise (instead of 3–4), but maintaining intensity (6–12 reps/set).

  RESULT: Strength was maintained throughout the entire 8-week study period for both younger and older participants.

• In one of the studies reviewed, one strength session per week was enough to maintain strength, provided the intensity was high (participants pushed themselves hard). A group training at 50% of maximal voluntary contraction (MVC) didn't maintain strength over the 8-week period. Conclusion: one heavy strength session per week may be sufficient for recreational athletes, as long as you train heavy when you do it.

Now, let's take a look at endurance training.

• A study looked at skilled runners with a VO2 max of 62 ml/kg/min, who averaged 81 km/week over 6 sessions and ran 5 km in at least 16:30. They reduced the volume by 70% to 24 km/week spread over 5 sessions for 3 weeks, keeping the same intensity distribution as before (75% of the volume below the VO2 max region and 25% at or above 95% VO2 max). Result: no significant negative changes. Maximum heart rate increased slightly — likely due to reduced plasma volume — and time to exhaustion increased, meaning they performed better with reduced volume over three weeks (think tapering).

• However, when researchers implemented similar programs and also reduced intensity, the runners performed worse on 5 km tests than if they had only cut back on volume. These studies highlight the importance of maintaining intensity when you reduce volume.

• As mentioned earlier: don't cut back on intensity. When intensity was reduced by 33% or 66% but volume stayed relatively high (6 sessions per week at 40 minutes each), it still wasn't enough to maintain capacity in recreational athletes.

“We conclude that short-term endurance and VO2 max can be fully maintained for up to 15 weeks when exercise volume is reduced by 66% (as little as 13 minutes per session), as long as exercise frequency and intensity are sustained. For exercise performances lasting 1–3 hours, it seems that volume can be reduced by 33% (as little as 26 minutes of exercise per session).”

Interesting question. Research ranging from recreational athletes to elite athletes often suggests an approximate 2:1 ratio — what you lose during two weeks of absence, you regain in about one week. This ratio seems to hold up to around 12 weeks of training absence. However, practically, the recommendation is to plan conservatively: aim for a 1:1 ratio. If you've been sick for two weeks, expect about two weeks before you're back. If it goes faster, that's just a bonus.

• Intensity is more crucial than volume for maintaining training capacity during breaks of 4–12 weeks.
• You can decrease the volume to just 25% of your normal training volume, and you'll reduce the capacity losses you'd experience with complete rest by half.
• Try to maintain your regular training frequency and type, but opt to reduce training time rather than eliminating intense elements.
• The specificity principle: you'll minimize physiological losses in areas where you train specifically. If you focus only on intervals, you'll retain more VO2max compared to only doing easy long runs — but you'll forfeit other long run benefits like fat oxidation and glycogen conservation. Sticking solely to easy long runs like a "weekend warrior" means you'll maintain endurance but lose VO2max, threshold, and speed.
• Conservatively plan for a 1:1 ratio between rest time and recovery time. If you're sick for a week, expect to need a week of normal training to fully recover. It might happen faster, but don't assume that's the norm.