We all know we need to train consistently, train hard and “recover hard” in order to achieve optimal performance, but how much down time is enough, and how much is too much? Triathletes have the reputation of training more and training harder.
With work and life obligations on top of training demands, getting adequate recovery from day to day can be a real challenge. But what happens when we take an extended break from training, either voluntarily or involuntarily? How much down time is enough, and how much is too much? When and why does detraining start to occur? Let’s explore the concepts of detraining and residuals to help you better understand and balance training stress and extended recovery needs.
Training Reversibility: “Use it or Lose it”
The principle of training reversibility states that while regular physical training results in enhanced athletic performance, stopping or substantially reducing training causes a partial or complete reversal of physical adaptations, thus compromising athletic performance. In the simplest of terms: use it or lose it. When triathletes stop training for an extended period of time, their hard-won fitness gains deteriorate and eventually completely disappear, often faster than they were gained. Sufficient training stimulus must be maintained in order to retain training-induced adaptations. In one study, an Olympic rower hit peak fitness during the Games, then took an 8-week hiatus from training. It took him 20 weeks to return to his previous fitness level! (12)
Aerobic development and maintenance is an ongoing process. VO2 max, the body’s ability to taken in and utilize oxygen, begins to decline at about day 10 of no training, but will continues to decrease over time. Significant reductions in VO2 max begin to occur within 2 to 4 weeks of detraining. This immediate decline is related to a decreased cardiac output and decreased blood volume (1). Studies of runners show VO2 max drops about 6% after 4 weeks (2), 19% after 9 weeks (3) and by 11 weeks of no running, it drops by 20-25%. However, any deficit caused by taking a couple of weeks off at the end of the season or for an injury, any deficit can be made up with a few weeks of consistent training.
From a cardiorespiratory perspective, within 4-8 weeks of suspended training, blood volume, stroke volume and cardiac output decrease. (1,2,3,4) The body loses its ability to move large volumes of blood. This occurs partly because heart muscle size can actually decrease over time. Less muscle mass impairs the heart’s ability to contract forcefully. Maximal heart rate increases, and at submaximal intensities, heart rate response is higher. Recovery heart rate also steadily increases as time off increases. Ventilatory efficiency will diminish after short layoffs from training. (5,6)
In terms of metabolism and muscle function, detraining also has a significant impact on the trained body. The body’s respiratory exchange ratio goes up, meaning fat metabolism becomes impaired, resulting in increased fat storage. Adrenaline drops, altering your “readiness” to train. The ability to train at higher intensities becomes more difficult because lactate accumulates quicker and at a lower intensity (loss of buffering capacity). Muscle glycogen levels also drop, leaving less in the tank to draw from.
When capillary density and oxidative enzyme activity decrease, oxygen delivery to working muscles is impaired. As well, muscle mass, EMG activity (nerve innervation of muscle fibers) and the number of fast twitch or Type 1 muscle fibers decrease. There is a marked reduction of mitochondrial ATP production.(6,7,8) With all of the above declines in cardiorespiratory, metabolism and muscle function, endurance performance declines.