How Quickly Do I Lose My Swim Fitness?

As any athlete knows, progress is never linear. At some point, illness, injury, or just plain life can all cause disruptions in your training schedule. Even a period of rest and recovery is necessary once in a while, no matter how much the typical type-A endurance personality might resist it. After all, you’ve worked hard to get your swim up to par. Wouldn’t taking time off from training be a setback? How quickly do you lose your swim fitness, anyway?

If we look at swimming, some athletes may find themselves facing a long road back after months out of the water for a rotator cuff repair, while others may lament how horribly out of shape they feel after a mere week off of swimming. In one of these situations, the fitness loss is real, while the other is more imagined. Changes in various systems occur over the course of days to weeks, influenced by a variety of factors. One study showed an average 400m swim time loss of 3.8% after a four-week layoff from the water, but even this varied among subjects (and it should be noted this was conducted on teenage swimmers). So, let’s dive into the research on how quickly you actually lose swim fitness during a break – and how long it takes to get it back.

RELATED: A Complete Guide to Triathlon Swimming

How quickly do I lose my swim fitness? What the science says

Research has shown that highly trained, experienced, very fit endurance athletes can lose fitness quickly, in periods of 2-4 weeks, while those with lower starting fitness levels and shorter training histories may be able to withstand 2-3 week layoffs without a significant fitness loss. On the flip side, these losses tend to level off after about eight weeks in highly trained individuals, allowing them to maintain higher fitness levels than their sedentary counterparts, while more recently gained fitness tends to be completely lost.

This, however, is just relative to VO2 max values among a variety of endurance athletes, and it does not account for the technical nature of swimming. After all, how many of us have picked up swimming later in life and feel like all muscle memory is lost in a week’s vacation, while lifelong swimmers who can seemingly hop into the water without issue after months away? Perhaps this is an exaggeration, but in general, more years spent building neural pathways and muscle memory will help from having to start back at square one after a layoff. So, while aerobic fitness can be lost more quickly in more highly trained athletes, the multi-factorial nature of swim-specific fitness will likely withstand less of a hit in more highly experienced swimmers.

Consistently across all endurance sports, levels of other physical activity explain a large part of the variance in fitness loss with breaks from sport-specific activity.  Although swimming is unique in its technical demands, non-specific physical activity has been shown to be one the biggest moderators of swim performance decrement during a four-week hiatus. Swim speed comes from a combination of aerobic fitness, swim-specific strength, and technique, so maintaining overall aerobic fitness through a focused bike or run block, or even a two-week long backpacking trip will cause less of a detriment to swim performance than two weeks laid up on the couch with illness. Anecdotally, during the early days of the pandemic, many triathletes found themselves without a place to swim, and a good portion of those turned to increased biking or running instead. While no one (at least, presumably) was setting PRs in their first swim back, a good portion of athletes still found themselves pleasantly surprised that swim speeds didn’t take too huge of hit.

What about other factors, such as age or gender? While females are often underrepresented in sports performance literature, one study of elite swimmers did find that females maintained threshold swim speeds after a 12-week detraining period, while males did not. This, however, was a small study, and with limited wider applicability.

Not surprisingly, age plays a role in the rate of fitness loss. At one end of the spectrum, when looking at pure muscle strength, youth ages 10-13 were able to withstand a four week detraining period without any loss. At the other end, older (65–75 year old) men and women sustained greater strength losses than their younger (20-30 year old) counterparts over a longer time period. While these studies were specific to muscle strength, It’s also well-known that although VO2 max inevitably decreases with age in Masters athletes, continued endurance training can help cut the losses by about half. So, a loss of training will impact masters athletes disproportionately, as they also have to contend with normal age-related changes on top of typical detraining responses.

RELATED: Most People Get Slower with Age. But Is That Inevitable?

Where you’ll lose swim fitness first

Unfortunately, inherent with the concept of training adaptations, is the fact that they are reversible when the training stimulus is removed, leading to fitness loss.  At a cardiovascular level, VO2 max losses with detraining have been studied extensively, with losses normally first becoming noticeable around two weeks of endurance training cessation. Losses are variable (in large part related to the aforementioned outside physical activity), although in general, they occur proportionally and progressively over the first 7-8 weeks of detraining, ranging from about 5-20%.  Specifically in collegiate swimmers, a 5-6 week off-season period was shown to cause a 7.7% decrease in VO2 max. These losses can be partially attributed to a loss in blood volume, which can occur in as little as two days of stopping exercise, leading to a decrease in stroke volume (the amount of blood pumped with each heartbeat) and increase in both resting and exercise heart rates within about two to four weeks.

Metabolically, changes also occur. A decrease in insulin sensitivity among the first alterations with the cessation of endurance training, often beginning within days.  Muscle glycogen storage levels begin to decline in as little as a week after stopping swim training, and resting metabolic rate declines after a 5-6 week layoff, as well.  Additionally, blood lactate levels after swimming have been shown to increase after four week detraining periods, although training on a cycle ergometer can help combat that.

At a muscular level, a decrease in mitochondrial enzyme activity begins to occur within about two weeks of training cessation, leading to a loss of oxidative capacity-or, more simply, muscles begin to lose their ability to utilize oxygen as efficiently, leading to more fatigue.  In swimmers, the deltoid muscle has been seen to begin to lose respiratory capacity even within a week of inactivity. Twelve weeks of detraining led to losses in strength and power measures both in land and in the water in one study of highly trained swimmers, while another showed that a four week period of either reduced (1-3 days/week from 6 days/week) or no training did not result in any decrement in maximal strength loss when measured via swim bench, but all groups showed a loss in swim power. Indeed, overall muscle strength and size tends to be maintained for a bit longer than other aspects of swim-specific fitness, while changes in muscle efficiency and power occur more quickly.

How long does it take to swim fitness back?

The time it takes to regain swim fitness becomes an interplay of time away, desired fitness level, activity levels during the layoff, age, and prior swimming experience. While highly-trained competitive athletes will likely restart at higher overall VO2 maxes and fitness levels, they will also find themselves needing to climb back up to a higher ledge. Lower-level athletes may be able to return to their prior levels within about half to two thirds of the layoff time, while high level ones may need to plan about two weeks of retraining for every week of detraining to return to their prior level.

As far as speeding up the process goes, if a break from swimming training is anticipated (for example, many are at mercy of periodic pool closures), any work to maintain aerobic fitness, swim-specific strength, and technique during the layoff can help upon the return. Of course, focusing on the other disciplines of triathlon will maintain aerobic fitness. Strength, and, to some degree, technical proficiency can be partially maintained through dryland strength work and swim cords, leading to a quicker return to full speed once back in the water.

Additionally, loading shoulder muscles and tendons will help maintain their capacity to handle swimming loads, so you’ll be able to more “safely” handle swim volume upon your return to the pool.  Even if you don’t get ahead of the game or can’t anticipate a layoff, Increasing evidence has come to favor dryland resistance training as a useful adjunct for improving swim performance at any stage of the game.

RELATED: Ask a Trainer: What is Swimmer’s Shoulder?

Mistakes to avoid when rebuilding swim fitness

Although injury rates in swimming are significantly lower than in cycling and especially running, the shoulder is still a complex joint prone to overuse injuries related to repetitive overhead motion, including rotator cuff impingements and tendinopathies. All muscle tendon/units lose their ability to handle load with rest, so don’t expect to go from zero to full swim volumes off the bat, especially if you haven’t used your arms in some time! Those who have maintained overall cardiovascular fitness may be particularly vulnerable, as the engine might be able to handle more than the chassis initially-build slowly, and monitor for any pain that persists the day after a swim, or worsens from week to week.

Many athletes will be better off sticking to the pool for their return to the water, for safety reasons. Resuming swimming after a layoff always feels a little weird, so most are best off not combining that with the reactions that can sometimes come with wetsuits and cold water, as well.  If you do find yourself in open water for the first swim back, make sure to stay close to shore, and bring along a buddy!

So, will detraining-related changes happen with time away from the water? Well, yes, but some time away from the water won’t erase the benefits gained from years upon years of training, so don’t stress those few weeks away!  Although swimming might feel foreign at first, fitness will come back with a little bit of work and patience, so let life (and off season) happen, and embrace the process of rebuilding when it happens.

RELATED: Training Plan: Returning to Swimming After a Break

Jennie Hansen is a physical therapist, Ironman champion, and USAT Level 1 triathlon coach with QT2 systems. Hansen has a background as a collegiate and professional runner, as well as a number of professional triathlon podiums. She has been in the sport for over a decade.