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Exercise preconditioning may offer immediate and lasting cardioprotection, according to a theory highlighted in a review calling for studies of this in humans.

The idea is to train the heart and coronary arteries to brief periods of ischemia so that infarct size and ventricular arrhythmias are minimized during prolonged occlusion.

"More specifically, the concept of exercise preconditioning indicates that, after engagement in regular exercise, cardioprotection occurs well before any changes in cardiovascular disease risk factors. This suggests that clinically relevant cardioprotection is present after one episode of exercise," wrote Dick Thijssen, PhD, of Radboud University Medical Center in the Netherlands, and colleagues in a review in JAMA Cardiology.

Animal studies have shown that one exercise session alone can protect the heart for the rest of the week. The problem with these studies is that they look mainly at infarct size and are not generalizable to humans, Thijssen's group said.

Whether acute exercise reduces infarct size in humans is still up in the air, the authors suggested. While clinical studies have shown that a period of more exercise is linked to lower mortality after coronary artery bypass grafting or an MI, no study has corrected for participants' usual patterns of physical activity. Moreover, ischemic preconditioning in the form of squeezing a patient's arm before heart surgery did not help with their outcomes, two trials showed.

"Future studies are needed to better understand the effects of exercise preconditioning in humans, preferably directly examining cardiac and coronary artery responses," Thijssen and colleagues said.

For now, it appears that "[e]xercise preconditioning represents an attractive explanation for the immediate cardioprotective effects evoked by exercise, which may be present after a single episode or a few episodes of exercise."

An episode of exercise may provide "early protection of the cardiovascular system for 2 to 3 hours and a more robust and longer period of protection that emerges after 24 hours and remains for several days," they wrote.

One way clinicians could use this to help patients is with "prehabilitation": a few sessions of exercise planned for the days preceding planned cardiac intervention. The authors expressed hope is that this may reduce in-hospital mortality and morbidity -- assuming, of course, that patients have the capacity for physical activity.

"Taken together, cardioprotection through exercise preconditioning is a facile, inexpensive, and potent therapy that deserves greater recognition and further resources to establish the optimal dose," they concluded. "Nonetheless, as is so often the case with the benefits of exercise, its prescription follows the cardinal rule: use it or lose it."

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