If you regularly do the same thirty-minute leisurely jog or bike ride several times a week, consider adding a little HIIT to your weekly routine. (But please consult a doctor if you are thinking of trying this.) By some measures, a few minutes of HIIT provides as much benefit as, if not more benefit than, thirty minutes of conventional aerobic exercise, and it has the virtue of improving rather than just maintaining fitness. HIIT is also mercifully short-term, hence less tedious than hours of trudging. A quick HIIT session of sprinting, stair running, or whatever else you can manage is
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