How much is too much aerobic activity?

There are many benefits to incorporating aerobic activity into one’s life. Aerobic activity has been shown to improve common metabolic and cardiovascular conditions, including obesity, type 2 diabetes, metabolic syndrome, hypertension, coronary heart disease, stroke and peripheral vascular disease.(Vuori 2007) These conditions are major health burdens, especially in industrialized countries, but have a global impact as well with over a billion adults being overweight and 300 million fitting into the classification of obese.(Vuori 2007) Aerobic activity, with all its benefits, is obviously something that everyone should include in their daily practice. The question is can there be too much of a good thing?
Healthy People 2010 has made the recommendation of 30 minutes of moderate aerobic activity 5 or more days a week or 20 minutes of vigorous activity 3 or more days per week; “moderate activity causes a noticeable increase in heart rate while vigorous activity is associated with rapid breathing and a greater increase in heart rate.”(Oberg 2007) These recommendations are minimums, but Healthy People 2010 say nothing about recommended maximum amounts of aerobic activity.
“The American College of Sports Medicine (ACSM) recommends 20-60 minutes of aerobic exercise 3-5 days per week at an intensity of 64/70-94% of heart rate maximum, and 40/50-85% of heart rate reserve (HRR) or oxygen uptake reserve (VO² R).” (DALLECK, DALLECK 2008) Training at a sub minimal level will lead to a decrease in desired results, but exceeding the maximal recommended intensity can lead to negative consequences such as overtraining, immunosuppression, and possible injury. In both Healthy People 2010 and ACSM’s recommendations, age and gender are not variables.
Gleeson reports “while engaging in moderate activity may enhance immune function above sedentary levels, excessive amounts of prolonged high-intensity exercise induce detrimental effects on immune function.”(Gleeson 2004) This means that exceeding the high ranges of recommended aerobic activity for excessive periods of time puts you at risk for infection and illness such as upper respiratory infection. Gleeson reports that “there is a 100-500% increase in picking up an infection in the weeks following a competitive ultra-endurance event.”(Gleeson 2004) Age seems to be a factor in the degree of immunosuppression related to excessive aerobic exercise. Timmons states that “children tend to be resistant to major exercise-induced perturbations to the immune system, and children’s immune systems tend to recover more quickly than those of adults.”(Timmons 2006)
Another risk of exceeding the upper recommended levels of aerobic activity is the possible risk of overuse injuries. Avoidance of injury requires a balance of training and recovery. Cosca et al. states that “an imbalance caused by overly intensive training and inadequate recovery leads to a breakdown in tissue reparative mechanisms and eventually to overuse injuries.”(Cosca, Navazio 2007) Possible injuries could include patellofemoral pain syndrome, iliotibial band friction syndrome, medial tibial stress syndrome (shin splints), Achilles tendinopathy, plantar fasciitis, stress fractures, and overuse syndrome. Although not completely understood, the symptoms of overuse syndrome occur because the intensity of the training program overwhelms the body’s ability to recover. These symptoms include mood disturbances, decreased performance, generalized fatigue, poor sleep, “heavy legs”, increased basal heart rate and increased rates of illness.(Cosca, Navazio 2007, Halson, Jeukendrup 2004)

As one can see, there are many potential negative effects of excessive aerobic training. Where that line of “excessive” is drawn is at the point where one’s body begins to be negatively impacted by the activity.
In addition to the physical impacts of excessive aerobic activity, there are potential psychological ramifications as well. Hausenblaus and Symons describe exercise dependence as “a condition in which moderate to vigorous physical activity becomes a compulsive behavior.”(Hausenblas, Downs 2002) Exercise dependence is also referred to as obligatory, compulsive, fanatic or addictive exercise. Excessive behavior has been shown to negatively affect social interactions, interpersonal relationships, and work performance among other things. Exercise dependence, like drug dependence, has similar components such as tolerance, withdrawal effects, intention effects (doing more than you intended to do), lack of control, interference with other activities, and continuation despite knowledge of having a problem.(Hausenblas, Downs 2002)
Although clear guidelines have been given, determination of excessiveness of aerobic activity is dependent on the individual. Understanding one’s starting point, what the specific goal is, and what is being done to promote recovery is all going to affect how much is “too much”. Guidelines are given for the average person residing under the bell curve, but there are always outliers who, as long as they listen to their bodies, may fit outside of the stated recommendations.

Cosca, D.D. & Navazio, F. 2007, “Common problems in endurance athletes”, American Family Physician, vol. 76, no. 2, pp. 237-244.
DALLECK, L. & DALLECK, A. 2008, “The Acsm Exercise Intensity Guidelines for Cardiorespiratory Fitness: Why the Misuse?”, Journal of Exercise Physiology Online, vol. 11, no. 4, pp. 1-11.
Gleeson, M. 2004, “Immune Function and Exercise”, European Journal of Sport Science, vol. 4, no. 3, pp. 52-66.
Halson, S.L. & Jeukendrup, A.E. 2004, “Does Overtraining Exist?: An Analysis of Overreaching and Overtraining Research”, Sports Medicine, vol. 34, no. 14, pp. 967-981.
Hausenblas, H.A. & Downs, D.S. 2002, “How Much is Too Much? the Development and Validation of the Exercise Dependence Scale.”, Psychology & Health, vol. 17, no. 4, pp. 387.
Oberg, E. 2007, “Physical activity prescription: our best medicine”, Integrative Medicine: A Clinician’s Journal, vol. 6, no. 5, pp. 18-22.
Timmons, B. 2006, “Immune Responses to Exercise in Children: A Brief Review”, Pediatric Exercise Science, vol. 18, no. 3, pp. 290-299.
Vuori, I. 2007, “Physical activity and health: metabolic and cardiovascular issues”, Advances in Physiotherapy, vol. 9, no. 2, pp. 50-64.

Tags: ACSM, aerobic activity, aerobic guidelines, exercise addiction, Healthy People 2010, overuse injury

This entry was posted on Saturday, October 24th, 2009 at 4:09 pm and is filed under Fitness, Fitness Educational Information, Matt's Blog Spot. You can follow any responses to this entry through the RSS 2.0 feed. You can leave a response, or trackback from your own site.