Exercise Intensity: Does It Really Matter?

Everyday, we implore our patients to become (more) physically active.  Most recommendations are for 150 minutes/week of moderate intensity exercise or 75 minutes of high intensity exercise.  If you're (chronically) short on time, then high intensity exercise seems to be the way to go.  But it takes a lot of discipline to engage in physical activity at this level on a regular basis.  

What if we had more incentive to exercise at high intensity?  Wouldn't it be nice to know that there's a result from high intensity that can't be achieved w/moderate intensity exercise?  In fact, as Dr. Michael M pointed out to me, a re-analysis of the Northern Manhattan Study was published in Neurology two weeks ago in which the authors concluded that high intensity exercise was associated w/less silent brain infarcts or subclinical cerebrovascular disease.

They arrived at their conclusion after performing brain MRIs on 1,238 clinically stroke-free individuals average age 70yo and found 197 w/silent brain infarcts.  After adjusting for the usual variables and going  thru the typical statistical machinations, the authors concluded that those individuals who engaged in physical activity in the highest quartile of intensity as measured by metabolic equivalents (METs) were almost half as likely to have subclinical cerebrovascular disease as those in the lowest quartile of intensity.

What are the implications for you & me?  Well, let's first remember that this is/was an observational study.  Therefore, it's good for generating hypotheses but it does not prove cause & effect.  Second, it's intriguing to note that it's not the only study to support a greater threshold for exercise than we currently recommend.  So while any exercise is better than none at all, this study begs the question whether protecting our brain might require greater intensity than preventing heart disease.  Third, as for applicability, the Northern Manhattan Study includes women & Hispanics, which broadens our ability to generalize beyond our typical Caucasian male.

Lastly, let's not forget that this study looked at silent brain infarcts.  While subclinical cerebrovascular disease has been linked to impaired mobility & falls, cognitive dysfunction & dementia, and initial stroke & death, this study makes no statement as to these clinical manifestations, unlike the headlines in recent news publication.  So stay tuned for more to come!