coach: okay guys, we've only got 8 sets of 55 x 4's today, 14 sets of gpp, and 15 100 yd
55 yards sprinted 80%-100% 4 times through per set
"coach: okay guys, we've only got 8 sets of 55 x 4's today, 14 sets of gpp, and 15 100 yd" What is the definition of "55 x 4's"?