Critical Swim Speed (CSS)

For many triathletes, swimming can be the most challenging discipline to get faster. These same athletes have a tendency to swim nearly the same pace for all training. Despite hours in the pool, they only see small gains in speed. CSS training is a simple way to help an endurance athlete understand pacing, while also improving swim fitness and muscular endurance.  This also serves as a method to test our swim fitness throughout the season.

Swim Session Intensity

ZonesDescriptionRPERest IntervalPace
1– Easy  Easy 1-2 as needed Technique or recovery 
2– Light Aerobic Steady 3-4 10-30 sec CSS + 10 sec - 140.6 pace  
3– Moderate Aerobic Mod Hard 5-6 10-30 sec CSS + 5 sec. - 70.3 pace 
4– Threshold Hard 7-8 30-60 sec CSS or Threshold - sprint tri pace 
5– Above Threshold Very Hard 9-10 30-60 sec Fast as possible