I wish I could run. When I run my calves end up hurting (almost like a cramp) so I've stopped running entirely. At the same time, I've been able to walk at a very brisk pace (5.5 mph on the treadmill) and that gets my heart rate up to about 85% (according to my heart rate monitor). That gives me a good workout for sure.
Tomorrow I go to the dreaded Fat Loss II B workout from The New Rules of Lifting and I dread the Bulgarian Split Squats as usual. That entire workout makes me (literally) sick to my stomach when I do it!