legs of lead

The workout today was to be 5 miles tempo (9:35 to 9:40 ppm) followed by an easy mile.  I began the run at 6:20 a.m.  Temp was 71 degrees and high humidity.  One of the rare June days when a person could run that time of morning at Silver Lake without a shirt.  First mile 9:38 and second mile was 9:32.  During the 3rd mile my legs turned to lead, and I took my shirt off.  Third mile was 9:53, fourth mile 10:11, fifth mile 11:13, and sixth mile a blistering 11:05.  Just could not breath right and legs very tired, even with yesterday off.  Total time was 1:02:08 (10:22 ppm). Does not bode well for the Seaway Run this Saturday where it is usually warm and humid near the big lake.