Broken Race Pace: 6×(100+50)m CSS Pool Session

Session Overview

This broken-format CSS session uses 6 rounds of (100+50)m with minimal rest between the two pieces — training your body to hold race pace when fatigued. Ideal for intermediate swimmers building threshold endurance ahead of open water race season.

What You’ll Need

• Pool lane — 25m or 50m
• Pace clock or swim watch
• Pull buoy (optional, for the 50m pieces)

Warm-Up (12 minutes)

400m easy continuous swim, focusing on long stroke and relaxed breathing. Then 4×50m as: 25m fingertip drag drill / 25m full stroke, 15 seconds rest between each. Finish with 4×25m build from easy to strong, 10 seconds rest.

Main Set

The “broken” format means you swim 100m at CSS pace, take only 10 seconds rest, then immediately swim 50m at slightly faster than CSS. The 10-second rest is long enough to breathe but not long enough to fully recover — so the 50m is completed in a fatigued state, exactly mimicking what happens in a race when a pack surges. Take 30 seconds rest between each complete round.

• 6× [ 100m at CSS pace — 10 sec rest — 50m at CSS pace minus 2 sec/100m ]
• 30 seconds full rest between each round
• Total main set distance: 900m
• Target CSS pace for 100m: your T-pace from a CSS 400/200 test
• Target for 50m: 1 second faster per 50m than your CSS split

Cool-Down (8 minutes)

200m very easy backstroke or mixed stroke, no intensity. Focus on opening your shoulders and slowing your breathing. Optional: 2×25m with a pull buoy, eyes on the bottom of the pool, no kick — pure recovery.

Coaching Notes

• If you don’t know your CSS pace, use 1:40–1:50/100m as a starting target for intermediate swimmers and adjust based on how you feel on round 3
• Common mistake: going too fast on the 100m pieces — you should be working but not blowing up; the 50m is where you apply pressure
• Easier version: extend rest between rounds to 45 seconds, or reduce to 4 rounds instead of 6
• Harder version: add a third piece to each round — 100+50+25m — keeping the same short rest between pieces
• RPE target: 6–7/10 on the 100m, 7–8/10 on the 50m; if you’re at 9/10 before round 4, you started too fast