My sprint workout today was 75% (effort) 50 free, followed by a 95% 100 free. Repeat 10 times (1500 yd total). I do the 50s on 45 sec and the 100s on the 1:30.
The time intervals for the 50s give little rest, but I think it builds endurance on top of the strength that the 100s produce.
Have fun.
