Had a little problem with the treadmill today, wanted to work out 10 mins at 4 mph but got severe cramps in my left shin after about 6 min. So I quit the treadmill and worked out on the bike for 27 minutes, then returned to the t/m for another 15 min at 3.5 mph. I was disappointed but realized I need to do some stretching before such a vigorous workout.