Thursday, March 30, 2017

When Exercise is Toxic

Everyone should exercise. Exercise produces mental and physical health benefits, improves how we look, and enhances our physical abilities. We all know this.

Like medications, exercise requires a certain dosage: not too little yet not too much.

Exercise is like medication: a minimal amount is generally needed to attain a specific benefit (e.g. 30 minutes of walking to lower blood pressure for a day). Also, like medication, an excess could be toxic.

More isn't always better. This is certainly the case with exercise. Our bodies do not want intense exercise every day.  Research shows this in a number of areas.


When a muscle group is strength trained, it initially becomes weaker and requires roughly 72 hours to completely recover and reach a slightly stronger and larger state. If we perform another intense strength training workout before recovery is complete, there could be signs indicating a lack of recovery. For example, women were only 94% as strong when performing an intense workout just two days after their previous intense strength training session with the same muscle groups (1). Especially for those who have trained for at least a year, research reviews recommend 72 hours as the shortest possible rest periods between intense training for the same muscle group (2,3).


When our bodies experience undesired sensations, they counteract. When we're cold, we contract our muscles (shiver) to generate heat.

One study featured young men on an intense exercise program where they burned an average of 627 calories per day for 93 days (4). Expending or burning 627 calories is equivalent to me (a 180-pound male) strength training about two hours or intensely cycling for 45 minutes. While these aren't extreme for a single day, they are extreme amounts of exercise for 93 consecutive days. Did the young men's bodies resist? Yes! The researchers noticed an average metabolism decrease of eight percent. In other words, their bodies compensated for the excess of exercise by decreasing the energy needs of their organs.

A study with older women showed a similar effect: women who exercised six times per week became less active outside of their training sessions. As a result, they lost less weight than women who exercised four days per week (5). The women training four times per week actually became more active outside their workouts. Were the women who exercised six times per week exhausted due to overtraining?

Immune System

An excess of training leads to a number of immune system defects (6). In fact, extremely frequent high-intensity training leads to a suppression of the immune system. Some effects are more frequent upper respiratory tract infections and more illnesses in general. An influencing factor could be the increased risk of depression and lack of sleep that people face when performing high amounts of intense exercise.

Excessive high intensity exercise can lead to more illnesses, depression, and difficulty with sleeping.

Joint Health

Joint health is another consideration for frequent high-intensity training. While a lack of exercise increases the risk for developing osteoarthritis, being very active is also a risk factor. One study showed the people who were most active over a four-year period experienced the more joint deterioration than others who were less active or sedentary (7). Exercise should improve our bone health, not accelerate its decline.


Let's get one thing straight: I think you should exercise. I especially support you exercising intensely. Intense exercise, such as strength training, sprints, or a spin class, provides the anti-aging benefits we seek to lead long and high-quality lives. Exercising with near maximum effort also makes the largest contributions to how well we look on the beach and in the bedroom.

However, more isn't always better. Part of the exercise process is recovery. Recovery for the hours and days after intense exercise allows our bodies to rebuild and improve past our previous abilities and muscle size.

Exercise intensely...more than once per week and less than every day. Somewhere in the middle - about 3-5 days per week - should provide a balance of training and rest.


  1. Hakkinen, K. (1995). Neuromuscular fatigue and recovery in women at different ages during heavy resistance training. Electromyography and Clinical Neurophysiology, 35(7), 403-413.
  2. Kraemer, W.J. & Ratamess, N.A. (2004). Fundamentals of resistance training: Progression and exercise prescription. Physical Fitness and Performance, 36(4), 674-688.
  3. Tan, B. (1999). Manipulating resistance training program variables to optimize maximum strength in men: A review. Journal of Strength and Conditioning Research, 13(3), 298-304.
  4. Tremblay, A., Poehlman, E.T., Despr├ęs, J.P., Theriault, G., Danforth, E., & Bouchard, C. (1997). Endurance training with constant energy intake in identical twins: changes over time in energy expenditure and related hormones. Metabolism46(5), 499-503.
  5. Hunter, G. R., Bickel, C. S., Fisher, G., Neumeier, W., & McCarthy, J. (2013). Combined aerobic/strength training and energy expenditure in older women. Medicine and science in sports and exercise45(7).
  6. MacKinnon, L.T. (2000). Overtraining effects on immunity and performance in athletes. Immunology and Cell Biology, 78, 502-509.
  7. Lin, W., Alizai, H., Joseph, G. B., Srikhum, W., Nevitt, M. C., Lynch, J. A., ... & Link, T. M. (2013). Physical activity in relation to knee cartilage T2 progression measured with 3 T MRI over a period of 4 years: data from the Osteoarthritis Initiative. Osteoarthritis and Cartilage21(10), 1558-1566.


Unknown said...

Valuable information! I enjoyed reading about the two studies. Thank you!

Heidi =) said...

Great read my friend! I know that I have experienced some of this because I use teaching group exercise as a major part of my income. I'm working on more one on one client training and less group x so that my body can get the rest and recovery it needs. Thanks for posting this!

Dr. Sean Preuss said...


Thank you! I appreciate you reading.


I'm glad you're acting assertively to help your body a little more. Obviously you're in a tough spot, with part of your income being based on frequent activity...but life could be much worse than having to exercise most days, right? ;) I hope you're able to cut down soon.