I definitely see a correlation between exercise and INR over the 7 years I've been self-managing. Specifically, with moderate or higher intensity exercise; brisk walks and being generally active doesn't have the same effect. My theory has been that exercising turns up my metabolism, and that increases the rate at which my body processes and eliminates the warfarin. The metabolic theory also seems to hold in that I have had to adjust my dosage down incrementally over time as I age, and as my overall stress and activity levels have declined (i.e with retirement). I started out with 8 mg/day, and currently I take 6, or less when the various factors that affect me are in play (alcohol, exercise, illness, acetaminophen). But for me, exercise is definitely a significant factor.