Broken 1650m CSS Time Trial: Pool Benchmark Session

Session Overview

A broken time trial swaps one continuous 1650m effort for the same total distance split into chunks with brief rest — giving you a genuine benchmark of your CSS (Critical Swim Speed) pace without the pacing risk of blowing up 300m from the wall on a solo time trial.

What You’ll Need

• Pool access (25m or 50m pool both work — adjust interval counts accordingly)
• Stopwatch or pace clock
• Pull buoy (optional, for the warm-up only)

Warm-Up (10 minutes)

400m easy freestyle, building the last 100m to near race pace. Follow with 4 x 50m at a strong but controlled effort, 15 seconds rest, to prime your feel for pace before the main set.

Main Set

Swim 1650m broken into three blocks with 30 seconds rest between each. Hold the same pace across all three — the goal isn’t to hammer the first block and fade, it’s an honest, even-paced benchmark. Note your total time (including the two 30-second rests) for a true CSS reference.

• Block 1: 600m at your best sustainable pace, 30 seconds rest
• Block 2: 600m holding the same pace, 30 seconds rest
• Block 3: 450m holding the same pace to the finish

Cool-Down (10 minutes)

300m easy mixed stroke, followed by 4 x 50m loosening drill (catch-up or fingertip drag) to flush out before you get out.

Coaching Notes

• 1650m is the classic pool-mile benchmark distance — use your total time (minus the 60 seconds of rest) to estimate your CSS pace per 100m for future threshold sets
• Common mistake: going out too hard in Block 1. If your split for Block 1 is faster than Block 3, you paced it wrong — retest in 4-6 weeks with a more even effort
• Scaling down: beginners can extend the rest to 45-60 seconds between blocks, or reduce total distance to 1200m (3 x ~400m)
• Scaling up: advanced swimmers can shorten rest to 15 seconds or attempt the full 1650m unbroken as a true time trial once this benchmark feels comfortable