Critical Swim Speed (CSS) refers to the theoretical swimming speed that can be maintained for 1500m. It is a crucial metric for swimmers, particularly triathletes, as it provides a benchmark for their aerobic fitness in the water.

How to measure your CSS pace:

To prepare for swimming at a fast pace, make sure to warm up properly in the pool. 

1. Begin with a 400m time trial, starting from a push (not a dive), and note down your time.

Take sufficient rest or recovery after the 400m trial to fully recover and be prepared for a maximum effort in a 200m time trial.

2. Swim a 200m time trial, starting from a push (not a dive), and record your time.