5 times 400m, then 5 times more approx 5 seconds faster... with ~150m jog in between. Good workout, felt pretty fluid.
1:33 400m
2:00 rest
1:27 I
1:53 R
1:30 I
1:55 R
1:29 I
2:03 R
1:29 I
3:00 R
1:22 I
2:05 R
1:23 I
2:06 R
1:23 I
2:23 R
1:22 I
2:31 R
1:22 I