In the December 2009 issue of Thorax, a group of researchers conducted a “meta-analysis” (defined below) of studies that examined whether there were differences in COPD patient physical conditioning when exercising at a constant, moderate level of intensity versus a shorter, but more intense level of aerobic exercise. Their conclusion – there is no meaningful difference in conditioning benefits between the two exercise approaches for COPD patients. (Beauchamp EK, et al. Interval versus continuous training in individuals with COPD - a systematic review. Thorax published online December 8, 2009. doi: 10.1136/thx.2009.123000).
What’s odd about this conclusion is that in both healthy adults and those who have been diagnosed with heart disease, interval training has been shown to deliver notably higher conditioning benefits. This conclusion was recently reaffirmed by a review article that appeared in the January/February 2010 issue of the Journal of Cardiopulmonary Rehabilitation and Prevention (Kemi OJ, Wisloff U. High-Intensity Aerobic Exercise Training Improves the Heart in Health and Disease. JCRP. 2010; 30:2-11).
Despite their differing conclusions about whether one form of aerobic exercise is better than the other, both sets of researchers are clear in their statements that both constant, moderate level exercise and high-intensity interval exercise delivers powerful conditioning benefits (for COPD patients, heart disease patients, and healthy adults).
Before diving into the details, let us first explain the term meta-analysis. At times, researchers will compile and analyze data from a range of studies that examine a similar subject matter in order to determine whether there are broader conclusions to draw from collective body of work on the subject matter. This analysis is referred to as a meta-analysis. In conducting a meta-analysis, the researchers first cull through the various published studies to eliminate those that in their opinion do not pass muster in terms of sample size, study construction, study duration and other influencing factors. The data from the remaining studies after this weeding out process are then evaluated for broad similarities. In the Thorax article, 8 studies made it into the meta-analysis.
As mentioned above, the basic issue examined in both articles is whether or not people benefit more from participating in aerobic activity at a constant, moderate level or from high intensity interval aerobic activity. Typically, in constant-moderate aerobic exercise regimens, subjects work out at a level that is between 50-70% of their maximum peak exertion (different researchers use different measures to determine this level , one common measurement method is called VO2 max – the maximum amount of oxygen a person uses during one minute of intense aerobic exercise). In constant-moderate aerobic exercise studies, the researchers first establish the maximum peak exertion threshold for each patient. With this information in hand, the researchers do subsequent testing where they reduce the exercise intensity (typically done by lowering resistance/incline/speed of various cardiovascular exercise equipment) until the subject can maintain 50-70% of their maximum peak threshold for an extended period of time (typically 30-40 minutes).
By contrast, high-intensity interval aerobic exercise typically involves repeated short segments of exercise at 90-95% of the subject’s maximum peak exertion level (anywhere from 30 seconds to 4 minutes) intermixed with lower intensity aerobic exercise segments (at 30%-50% of maximum exertion) in between for similar amounts of time. So in a 20-30 minute interval session, a patient will perform multiple segments of 1-3 minutes high-intensity aerobic activity alternating with multiple segments of 2-4 minute low-intensity aerobic activity.
Some researchers believe that the interval approach tends to build higher levels of conditioning because the subjects are pushing their heart, lungs, circulation system and muscles to handle higher loads of activity in comparison to constant-moderate aerobic exercise. Even the Thorax researchers noted, “In healthy subjects and in those with CHF (congestive heart failure), high-intensity interval training has been shown to be as effective or superior to continuous training with respect to effects on physiological markers of exercise capacity.”
We think this point of view makes intuitive sense but for some reason this phenomenon is not demonstrated consistently in COPD patients. One suggestion by the researchers in the Thorax article is that COPD patients (who in general are not regular exercisers) see such huge gains in physical conditioning in pulmonary rehabilitation from any form of aerobic exercise that the relative performance of one type of aerobic exercise versus another is minimized.
But the Thorax researchers also suggest that interval training might be a valuable option in pulmonary rehab for COPD patients in that some patients adhere to their exercise schedule better when they can mix up the time/duration/intensity of exercise (the variety makes it more interesting, and interval training takes less time).
In noting the potential value of both forms of aerobic training, the researchers conclude, “…evidence from the eight trials included in this review suggests that there are no differences between the effect of interval and continuous training on improving exercise capacity and health-related quality of life in individuals with COPD. Interval training may therefore be considered as a training option or complement to continuous exercise in patients unable to tolerate high-intensity continuous exercise.”
In our opinion, if you are interested in mixing up your aerobic exercise routine, it is worth considering high intensity interval training. The research is clear that it at least provides the same conditioning benefits as constant-moderate level training. For moderate to severe COPD patients, you should consult your physician first to determine if interval training is appropriate in your situation. We also highly recommend that you consult a personal trainer at a fitness center or a respiratory therapist in your pulmonologist’s office or pulmonary rehab clinic to help create an "starter" interval program that is right for your level of current conditioning.
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