Swim PDC (pace-duration curve)

What the PDC is

The swim pace-duration curve (PDC) is the swim equivalent of the power-duration curve in cycling: your best swim pace at each duration plotted on log-scale. It tells you whether you are sprint-biased or endurance-biased in the water, and where your CSS sits on that curve.

URL (API): GET /api/athlete/<public_id>/analytics/swim/?days=180. The dashboard pulls from this same endpoint.

What goes into the curve

The swim PDC pulls from three sources, in priority order:

1. CSS test results (your structured 200 + 400 m time trials) for the canonical threshold anchor.
2. EO SwimBETTER session data for whatever distances you tested.
3. Pool training intervals: the parser extracts best pace at each standard distance from set-based pool swims.

The curve combines them into a single best-pace-at-each- duration trace.

What you see on the page

The swim section of the analytics page renders:

• The PDC curve with current data and (when available) a prior-window overlay so you can see trend.
• A best paces table at standard pool distances (100, 200, 400, 800, 1500 m).
• Lap distribution histograms for stroke rate, pace at stroke rate, and pace at distance per stroke (useful for technique work).
• EO history if EO sessions are uploaded.
• Tech assessments if Technical Swim Assessments are filed.

Reading the curve

• The point where the curve crosses 30 minutes worth of swimming is approximately your CSS (sustainable threshold).
• The steepness above CSS (between 1 and 5 minutes) is your anaerobic capacity.
• The values below CSS (15+ minutes) are your race-pace ceiling for long-course swims.

How CSS aligns with the curve

The dashboard pins a CSS marker on the curve. If your CSS test result and your training-data-derived curve disagree materially, that gap is interesting:

• If training-derived pace is faster than CSS pace at the same duration, you may have tested CSS in a fatigued state or undercooked the time trial.
• If training-derived pace is slower, your CSS may be stale or your training is not pushing the threshold.

See also: CSS calculator, CSS Test assessment, Yousuli swim zones.