The Reversibility Principle – Use it or Lose it!

By nisus 0

People who have taken time off from training will have experienced the reversibility principle or detraining. Detraining can be described as the partial or complete loss of training adaptions, in response to insufficient training. When a person stops training for an extended period of time (> 1 week), they can rapidly lose significant physiological and performance adaptions. Performance levels that were once easily achievable are now out of reach. Muscle soreness which used to be a distant memory, now returns with a vengeance. Very noticeable conditioning can be lost after about 2-6 weeks of inadequate training and even quicker if no physical activity is performed at all. Within a few months of inactivity, any fitness gains made previously can completely disappear.

When you train hard, your body adjusts to meet this higher demand, but unfortunately when you don’t train your body will quickly adjust to this lower demand as well. E.g. Loss of muscle mass or loss of aerobic fitness.

Studies have shown that VO2max can decline by 4%-20% with just two weeks of inactivity. Other studies have proven that total inactivity can lead to rapid losses of muscle mass which will have a negative impact of a person’s strength and power performance. Again this can happen in as little as two weeks.


You should always try to maintain some form of moderate activity year round to slow or stop the consequences of detraining. The training philosophy ‘3×52’ is a good starting point, meaning you should train at a minimum of 3 times per week for 52 weeks of the year to see progress and maintain it.

Where a prolonged break from training is desired or needed, the training program should incorporate enough activity to help maintain general fitness. The minimum frequency of stimulus needed to maintain fitness levels for a short period of reduced activity is x2 per week. It’s important to note that the intensity of these two training sessions must remain high, in order to hold on to that high fitness level. This is especially relevant if you decide to taper or rest before an important competition.

Athletes are just as vulnerable to the reversibility principle as non-athletes. Field sports players should be aware that repeat sprint ability performance can decline by 24% during the off season (5 weeks) if no off season training takes place.

If a person does lose strength, power or endurance due to the reversibility principle, obviously it can be achieved again through retraining. Initially improvements are rapid once training begins again, but this does slow, and it may take a minimum of 20 weeks to recapture previous fitness levels.

In conclusion, everyone can expect a large and rapid decline in fitness levels if training is stopped for an extended period of time. Although fitness levels can be regained, it can take almost twice the time (of the break) to recapture. Everyone should avoid being inactive at any time of the year but where a break is unavoidable (due to fatigue, illness, injury, holiday) some sort of maintaining program should be incorporated.


At Nisus we encourage our Training Club and Online Clients to strive for consistency to avoid falling victim to the reversibility principle. We encourage time off, rest days like anybody else but we encourage an active lifestyle to maintain gains. This is why systems such as Precision Nutrition and MyZone Heart Rate monitoring play such a significant role in supporting our clients no matter where they are based around the world. Through the help of our partners, we encourage our clients to view fitness as a lifestyle choice and with that comes good nutritional habits, routines and accountability.


Anthony O Leary is a full time personal trainer working with Online PT Clients and leading sessions at the Nisus Fitness Training Club. He holds a BSc. in Health & Leisure and is currently completing a Masters Degree in Strength & Conditioning from the Limerick Institute of Technology.

Join the Nisus Fitness Newsletter mail list here





  • Vigelsø, A., Gram, M., Wiuff, C., Andersen, J.L., Helge, J.W. and Dela, F., 2015. Six Weeks’ Aerobic Retraining After Two Weeks’ Immobilization Restores Leg Lean Mass and Aerobic Capacity But Does Not Fully Rehabilitate Leg Strength in Young and Older Men. Journal of rehabilitation medicine, 47(6), pp.552-560.
  • Staron, R.S., Leonardi, M.J., Karapondo, D.L., Malicky, E.S., Falkel, J.E., Hagerman, F.C. and Hikida, R.S., 1991. Strength and skeletal muscle adaptations in heavy-resistance-trained women after detraining and retraining. Journal of Applied Physiology, 70(2), pp.631-640.
  • Taaffe, D.R., Henwood, T.R., Nalls, M.A., Walker, D.G., Lang, T.F. and Harris, T.B., 2008. Alterations in muscle attenuation following detraining and retraining in resistance-trained older adults. Gerontology, 55(2), pp.217-223.
  • Godfrey, R.J., Ingham, S.A., Pedlar, C.R. and Whyte, G.P., 2005. The detraining and retraining of an elite rower: a case study. Journal of Science and Medicine in Sport, 8(3), pp.314-320.