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Too Much of a Good Thing

Submitted by Amy Sercel MS RD CD

Edited by Marcia Bristow MS RDN CSSD CD

Every health guideline seems to come with the recommendation to increase physical activity levels. It’s widely understood that getting enough activity boosts mental health, can help keep your immune system strong, and decreases your risk of chronic diseases like cancer, diabetes, osteoporosis, and heart disease. Public health officials estimate that 50-80% of the United States population falls short of the guideline to get at least 30 minutes of moderate-intensity exercise each day, for a total of at least 150-300 minutes per week.1 What about the other end of this continuum though? Is it possible to get too much exercise?

Although it is difficult to find a safe maximum amount of exercise recommended in the Physical Activity Guidelines for Americans, one study suggests that this amount may be no more than 60-90 minutes of endurance exercise per day, five days per week. At higher levels than this, the health benefits of being active actually start to decrease.2

Relative Energy Deficiency in Sport (RED-S)

Excessive exercise impacts every system in your body when you are not eating enough to fuel both physical activity and the body’s basic functions. These functions include the immune system, digestion, heart rate, and reproductive system. When RED-S occurs, the body slows down these processes in an effort to reduce overall energy expenditure. As a result, athletes who exercise excessively without eating enough to replace the calories they burn have:3

  • A higher risk of injury (such as stress fracture)
  • Difficulty concentrating due to lack of fuel for the brain
  • Feelings of depression or anxiety
  • Constipation due to slowing of the digestive system
  • Reproductive dysfunction seen as loss of menstrual cycle in females or low testosterone in males

Any athlete who engages in prolonged endurance activity on a regular basis is at risk for RED-S because they may not realize how much more they need to eat in order to make up for the energy burned during activity. Elite athletes and people training for long-distance endurance events, such as marathons or triathlons, are also at a higher risk for RED-S. Fortunately, most of the health impacts of RED-S reverse when an athlete reduces their activity level and/or begins eating enough to fuel their activity.

Cardiovascular Effects

While RED-S is one of the more immediate consequences of excessive exercise, in the long term excessive exercise can increase the risk of heart disease.

Endurance exercise causes the heart to beat more quickly. At high levels, this leads to changes in the heart’s structure that can cause heart arrhythmias, or an irregular heart beat.2,4 This in turn raises the risk of heart attack, stroke, and sudden death. For this reason, it’s suggested that lower amounts of running have the most positive impact on heart health, and researchers advise limiting vigorous endurance exercise to no more than 1 hour per day, 5-6 days per week.2

What’s the Right Amount?

While there are risks of excessive exercise, the health benefits of regular physical activity are indisputable. If you are working on increasing your activity level to promote your own health, aim for about 30 minutes of moderate-intensity activity per day. One study found that this exercise level was associated with the lowest risk of heart disease.2

If you are already highly active as an endurance athlete, make sure you are fueling your body properly by eating enough on a day-to-day basis and including good sources of energy before, during, and after workouts. If you’d like support with this, meet with a registered dietitian who can help you create a nutrition plan to complement your training. If you have a history of intense endurance exercise, it’s also important to have regular check-ups with your doctor, who can monitor your heart health over the long term.

References:

  1. Physical Activity for Everyone: Guidelines: Adults | DNPAO | CDC. http://www.cdc.gov/physicalactivity/everyone/guidelines/adults.html. Accessed June 14, 2015.
  2. Lavie CJ, O’Keefe JH, Sallis RE. Exercise and the Heart — the Harm of Too Little and Too Much. Curr Sports Med Rep. 2015;14(2):104. doi:10.1249/JSR.0000000000000134
  3. Mountjoy M, Sundgot-Borgen J, Burke L, et al. The IOC consensus statement: beyond the Female Athlete Triad—Relative Energy Deficiency in Sport (RED-S). Br J Sports Med. 2014;48(7):491-497. doi:10.1136/bjsports-2014-093502
  4. Kim Y-J, Kim C-H, Park K-M. Excessive exercise habits of runners as new signs of hypertension and arrhythmia. Int J Cardiol. 2016;217:80-84. doi:10.1016/j.ijcard.2016.05.001

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