Was supposed to run 20 miles, so decided on 200 minutes of cardio. 40 minutes on the spin bike, followed by 10 minutes running, repeated 4x. Ended up feeling good ... no pain or tightness ... so went 140 minutes on the spin bike and 60 minutes running.
It has been almost 5 weeks since my hamstring went ballistic. Two weeks reduced to 24 miles each, and then 2 weeks with virtually no running. I'm hopeful I can get back to 24 miles next week and then build quickly from there. With the biking, I should not have lost too much fitness, so it's just a matter of not crossing over that line where I push my body too hard from running.