Yesterday was Day 1 (for the 6000th time). The plan was to run an easy 4 miles with 2-4 sprints of 50 meters. Before I started, I had to assess some muscular issues. Starting from the top, I had a slightly sore left latissimus dorsi, very sore right internal abdominal oblique, sore right piriformis, sore left sartorius and slightly sore left soleus; I'll leave out everything from ankle down. None of those are terribly unusual for runners, nor for me specifically (except the ab), but they do lead to something I can teach.
Problems start low and work their way up the body, switching sides. In my case, I have problems with my right heel. Compensating for that led to the left calf problem, which was minor, but left untreated. Later, I was feeling tightness in my left hip; one of my legs is slightly longer than the other (millimeters different) - that and babying the right heel led to a slight twist in the left leg which was straining the sartorius. Continuing to run with that untreated led to overcompensating on the right and the piriformis strain. At some point, because of that small muscle being fatigued, I strained the oblique.
One could get all of those problems at once with a basketball player straining to make a spinning jump shot.
Anyway... I felt good enough I thought I could run fast.
It was windy and 20 degrees and a few flurries had started to fall. The first mile, I felt I was struggling a bit, even though I was running with the wind. There was a slight tightness in my chest, but the legs felt fairly good. At the end of the second mile, I decided to start the first sprint. I can usually run 50m in 5.5-6.0 seconds after one or two "slow" ones in 6.5 and typically peak at 5.0 seconds. I did the first one with the Forerunner saying I hit 3:53 mile pace, a fairly standard first sprint.
And had an asthma attack. First one of the year. Too hard in cold air with too little warm-up. Ten minutes later, I felt good enough that I could jog slowly, but walked home instead.
Day 1: Fail.