Hot Weather Adjusted CSS: 8×100m Pool Session

Session Overview

This 45-minute pool session applies CSS (Critical Swim Speed) threshold training with pace targets adjusted for warm summer water temperatures. When pool temperatures rise above 28°C, your heart rate will run 5–8 beats higher than normal for a given pace — this session teaches you to work to feel and adjusted pacing rather than chasing your standard CSS splits.

What You’ll Need

• Swimming pool (lane session preferred)
• Pace clock or waterproof watch
• Pull buoy (optional — for the warm-up drills)
• Water bottle on the poolside — hydration is more critical in warm conditions

Warm-Up (10 minutes)

Swim 400m easy at Zone 1–2 effort, alternating 50m freestyle / 50m backstroke to activate different muscle groups. In warm conditions, do not rush the warm-up — your heart rate needs time to stabilise before you hit the main set. Finish with 4×25m pull-buoy drill: focus on high elbow catch and driving your hands past your hips before the exit.

Main Set

Calculate your hot-weather adjusted CSS target: take your standard CSS pace (typically from a 400m + 200m time trial) and add 3 seconds per 100m. This accounts for the thermoregulatory effort at elevated water temperatures. The goal is to hold exactly this adjusted pace throughout all 8 reps — not faster, not slower.

• 8×100m at adjusted CSS pace (CSS + 3 sec/100m), with 15 seconds rest between reps
• After rep 4, take 60 seconds extra rest and check your perceived exertion — it should feel like a 7/10 effort. If it feels like a 9/10, add another 2 sec/100m to your target for the back half.
• Total main set: 800m

Cool-Down (8 minutes)

Swim 200m easy backstroke followed by 100m very easy freestyle with deliberate long glides. The cool-down serves a dual purpose in warm conditions: lowering core temperature and flushing lactic acid from working muscles. Don’t skip it in summer — it’s more important than in cooler water.

Coaching Notes

• Your stroke rate should remain consistent through all 8 reps — if your rate drops noticeably, you’ve gone out too fast. CSS work is about consistency, not heroics.
• Drink water between sets. Dehydration in a warm pool affects coordination and slows your time even at a given effort level.
• Easier variation: reduce to 6×100m and extend rest to 20 seconds. Harder variation: 10×100m with 10 seconds rest, holding standard CSS (not adjusted) if the pool is below 27°C.
• RPE target for all reps: 7–7.5/10. You should be able to maintain technique throughout but not feel comfortable.