Swim Pacing Guidance
CSS: 'Critical Swim Speed' - this pace (for swimming) is analogous to 'threshold' speed on the bike or run. It's a good marker for a pace to aim for during your repeats. This pace will be worked out after undertaking a 'CSS test'.
It is expressed as pace per 100m, so a CSS pace might be 1.50 (1 minute 50 seconds per 100m)
Sometimes pace guidance will be given like this, in terms of ‘how the swim pace feels’ :
Easy: CSS +12s
Steady: CSS + 8s
Moderate: CSS + 4s
Hard: CSS pace
Very Hard: CSS - 4s
'CSS+4' means 'CSS pace plus 4 seconds per 100m.'
If your CSS pace was 1.50, CSS+4 would be 1.54 per 100m