yes, there are days when I feel really "speedy" and other days when I have "leggs of lead" . . most times, it makes no sense. Treadmill running is easier for me as long as I have a good CD to listen to or one of my kids to read to me or keep me company. Whenever I run on the road (which is infrequently at this time despite a history of marathon running) my ankles and shins get very sore. I recently got new shoes and this has helped somewhat (with the soreness). Overall, it's my belief that road running is far more "stressful" on the body!