Swim-Run Brick: 4 Rounds of 400m Swim + 2km Run

Session Overview

This advanced 90-minute+ brick session alternates between 400m pool swims and 2km runs for four complete rounds, training your body to rapidly switch between energy systems. It builds the race-specific fitness needed for aquathlons and multisport events, and sharpens the mental discipline of managing effort across repeated sport transitions.

What You’ll Need

• Pool access with a running route immediately adjacent (or a treadmill for bad weather)
• Trisuit or tight swimwear you can run in without changing
• Running shoes positioned poolside in advance for fast transitions
• Watch for tracking swim splits and run pace separately
• Optional: socks can be skipped for faster transitions

Warm-Up (10 minutes)

400m easy swim: 200m freestyle, 100m catch-up drill, 100m easy backstroke. Then 5 minutes easy jog at Zone 1 to activate the running muscles before the main set begins. Do not skip this — jumping straight into the first swim from cold is an injury risk.

Main Set

Complete 4 rounds of the following with no additional rest beyond the transition time. Keep transitions under 2 minutes.

• 400m pool swim at CSS pace or moderate-hard effort (RPE 7/10)
• Transition: shoes on, start running within 2 minutes of finishing the swim
• 2km run at 70.3 run pace — RPE 7/10, sustainable but not comfortable
• Transition: return to pool, shoes off, into the water for the next round

Cool-Down (5 minutes)

200m gentle freestyle after the final run, then stand in the shallow end for shoulder and calf stretches. Hydrate immediately — four transitions in warm conditions depletes more fluid than it feels.

Coaching Notes

• The first 200–300m of each run will feel heavy and uncoordinated from the swim — this is normal. Focus on cadence, not pace, for the opening 400m of each run and let your legs find their rhythm.
• Practise open-water sighting technique in your final pool swim rep — sighting slows your stroke and costs energy, so it’s worth practising under fatigue.
• Scale down: reduce to 3 rounds, or shorten runs to 1.5km per round
• Scale up: increase swim distance to 600m per round for a stronger swim-to-run transition stimulus