Heat-Proof Your Match: US Open 2025 Hydration Playbook

Why this playbook now

Record on-court heat at the 2025 US Open forced practical changes that worked in real time. The event expanded its Extreme Heat Policy with more shade, more frequent cold-towel rotations, and on-court ice slurries. Players reported pre-cooling with ice vests and sipping slushies on changeovers. Tournament med staff emphasized individualized hydration with higher sodium for afternoon sessions. Several matches saw sweat rates over 1.5 L per hour.

If you are a junior, a college player, or a coach, you can copy these tactics. You do not need a pro team. You need a plan, a cooler, and discipline.

Big idea: You do not “tough out” heat. You manage it. Cool the body. Pace the gut. Replace sodium.

I am a USPTA coach and a sport science nerd. I have paced half marathons in summer heat and sat courtside for juniors cramping in July. The fixes below are simple and repeatable. They are the same ideas pros used in New York, with gear you can carry to any tournament.

The three levers that keep performance up

• Keep core temperature down. Use ice towels and ice slurries at set intervals. Shade and airflow matter.
• Replace fluid at a rate you can absorb. Most guts handle 400 to 800 ml per hour during play. Spread sips.
• Replace sodium in line with your sweat rate. Many players need 800 to 1,500 mg sodium per liter of fluid in heat.

Think of it like holding serve on a slow court. You win by stacking small advantages, point by point, not by one heroic swing.

Build your bench: the DIY heat toolkit

Pack this for every hot match. Set it up before the coin toss.

• 2 bottles:
  • Bottle A: water or light-carb drink (2 to 4% carbs).
  • Bottle B: electrolyte mix at your sodium target. Start with 800 to 1,000 mg sodium per liter. Heavy and salty sweaters may need 1,200 to 1,500 mg per liter.
• Ice cooler with:
  • 3 to 4 ice towels in zip bags. Pre-wet with cold water. Wring lightly. Lay over ice.
  • 2 bags of loose ice for cups and sleeves.
  • 1 shaker with pre-mixed slush base (see recipe).
• Optional pre-cooling:
  • Ice vest or two gel packs for 10 to 15 minutes pre-match.
• Shade and airflow:
  • Umbrella or canopy if allowed. Small battery fan clipped to the bench when permitted.
• Small items:
  • Paper cups, spare hat, dry wristbands, face cloth, extra grip, a light towel for sweat only.

Label every bottle and bag. Keep cooling items separate from sweat towels. OffCourt players often use a simple color code in the bag to avoid mixups under stress.

Ice towel protocol that works

What pros did in New York is simple and effective.

• Before play: Place 3 to 4 wet towels over ice. Keep them sealed to reduce heat gain.
• At each changeover:
  1. Sit in shade. Fan on if available. Hat off to vent heat.
  2. Wrap one ice towel around the neck and upper back for 30 to 45 seconds.
  3. Move towel to the thighs for 20 to 30 seconds each. Quads and hamstrings carry your movement load.
  4. Lightly dab the face and forearms. Avoid saturating the hands or grip.
  5. Replace the towel in the cooler. Use a fresh one next changeover.
• Set breaks: Repeat, plus 10 to 15 seconds additional neck exposure.

Pro tip: Keep your shoes and socks dry. Pouring water down your legs can feel good but raises blister risk.

Ice slurry: recipe and timing

Research-grade slurries hit the gut cold and pull heat from the core. The US Open offered slushies, and players credited them for lower perceived effort.

• Ingredients per 600 ml serving:
  • 350 ml crushed ice
  • 250 ml 4 to 6% carbohydrate drink with 600 to 800 mg sodium per liter
  • Optional: a pinch of table salt if your mix is low in sodium
• Method:
  • Blend or shake until spoonable. You want small ice crystals, not solid ice.
• Timing:
  • Pre-match: 300 to 500 ml over the 20 minutes before walk-on.
  • During play: 100 to 150 ml at hot changeovers. Sip, do not chug.

If you cramp or run hot often, shift the in-play slush from every changeover to every other changeover to protect the gut.

The two-bottle sodium strategy

You will drink at least two different fluids:

• Bottle A: water or very light-carb drink. Use it when you feel sloshy or when your electrolyte bottle tastes too strong mid-rally.
• Bottle B: electrolyte at your sodium target. Most will sit between 800 and 1,500 mg sodium per liter in heat.

How much to drink per hour

• Start with 400 to 600 ml per hour in cool-to-warm conditions.
• In high heat, aim for 600 to 900 ml per hour if your gut allows.
• Spread sips every 2 to 3 games. Fewer big gulps, more small sips.

How to split bottle sips

• In hot sessions: 2 sips electrolyte for every 1 sip water.
• In moderate sessions: 1 to 1.

Guardrail: If your stomach feels heavy, reduce total volume for 10 minutes and take small sips of the electrolyte bottle only. Do not switch to water alone for long stretches or you risk diluting sodium.

The 10-minute sweat-rate test

Do this once in similar conditions to your match. Repeat at the start of summer, mid-summer, and before big events.

• What you need: scale accurate to 0.1 kg, timer, your usual match gear, a bottle with measured volume.
• Set up:
  1. Pee if you need to.
  2. Weigh yourself in dry shorts. Record as Pre.
  3. Warm up lightly for 5 minutes.
• Test: 4. Perform 10 minutes of realistic play or footwork at match intensity. 5. Drink from your bottle as you would in a match. Measure exactly how much you drank. 6. Towel off surface sweat quickly and weigh again in the same clothing. Record as Post.
• Calculate sweat rate:
  • Body mass loss in kg = Pre − Post
  • Add fluid consumed in liters
  • Sweat rate L per hour = [(Mass loss kg) + (Fluid drank L)] × 6

Example: Pre 70.0 kg, Post 69.7 kg, drank 150 ml. Mass loss 0.3 kg. 0.3 + 0.15 = 0.45 L in 10 minutes. ×6 = 2.7 L per hour. That is very high. Plan for 900 ml per hour intake and aggressive cooling. Most players will sit between 0.8 and 1.8 L per hour.

Estimate sodium needs

• If you see salt crust on clothes, your eyes sting, or sweat tastes very salty, start at 1,200 to 1,500 mg sodium per liter.
• If none of the above, start at 800 to 1,000 mg per liter.
• Adjust based on signs in the field: stable energy and minimal lightheadedness are green lights. Headaches or hand swelling suggest a sodium or total volume mismatch.

Log your test in your OffCourt tracker so you can build a match-day bottle plan by temperature and time of day.

Exact 60-second changeover routine

Use the first 60 seconds for cooling and fueling. Use the last 20 to 30 seconds for tactical reset and breath.

• 0 to 10 s: Sit in shade. Hat off. One deep nasal inhale, long exhale.
• 10 to 25 s: Ice towel around neck and upper back. Fan on if allowed.
• 25 to 40 s: Move towel to thighs. Quick dab to forearms and face.
• 40 to 50 s: Sip 2 to 3 mouthfuls of electrolyte. Optional 100 ml slush on hottest days.
• 50 to 60 s: One sip water if mouth feels dry. Replace towel in cooler.
• 60 to 80 s: Stand, 2 breath cycles, state 1 tactical cue. Example: “First ball deep middle.”

Set break extension

• Add 10 to 15 extra seconds of neck cooling.
• Take 120 to 200 ml slush if gut is settled and the day is extreme.

Do not overcool with ice pressed directly on the stomach. It can slow the gut.

Pre-match and between-match protocols

60 to 90 minutes before play

• 60 min: 300 to 500 ml fluid with 500 to 800 mg sodium total. Light snack if needed.
• 30 min: Put on ice vest or use two gel packs across upper back for 10 to 15 minutes.
• 20 min: Begin sipping 300 to 500 ml slush. Gentle dynamic warm-up.
• 5 min: Finish with 2 to 3 sips electrolyte. Towel dry hands.

Between matches on a hot day

• Replace 125 to 150% of body mass lost within 2 hours. If you lost 1.0 kg, drink 1.25 to 1.5 L with 800 to 1,200 mg sodium per liter.
• Eat a carb-first meal you trust. Keep fat low.
• Short nap if time allows. 20 minutes. Dark and cool room.

Drills to make it automatic

These are simple, timed, and repeatable. Use a coach or teammate to call the clock.

Drill 1: Changeover rehearsal circuit

• Goal: Execute the 60-second routine without thinking.
• Setup: Bench, cooler with two ice towels, electrolyte bottle, water bottle, slush cup, small fan.
• Work: 6 changeovers in 30 minutes.
  • Rally live ball for 4 minutes at moderate intensity.
  • 90-second changeover. Follow the routine above.
• Cues: Neck, thighs, sip electrolyte, one cue, breathe.
• Rest: None beyond changeovers.
• Progression: Add one more cooling item, like forearm dousing, without adding time.

Drill 2: Heat interval footwork plus cooling

• Goal: Train cooling under high heart rate.
• Setup: Cones on baseline corners and center mark. Cooler and towels on the bench.
• Work: 3 sets of 6 minutes on, 90 seconds off.
  • On: Shuffle-sprint pattern baseline to baseline, inside-out recovery. 20 seconds on, 10 seconds stand tall and breathe.
  • Off: Treat it as a changeover. Ice towel and small sips.
• Rest: 3 minutes between sets.
• Cues: Keep shoulders down. Light feet. Calm exhale.

Drill 3: Serve plus one with heat pacing

• Goal: Layer hydration sips into point patterns.
• Setup: Ball basket, targets past the service line.
• Work: 4 blocks of 5 minutes.
  • Serve to target, plus-one to depth gate. 6 balls per minute.
  • Every 2 minutes, jog to bench, take 2 sips electrolyte, towel neck 10 seconds, back to baseline.
• Rest: 2 minutes between blocks.
• Scoring: Count balls landing past the service line. Target 70% or better.

Simple test: 3-changeover time audit

• Run a live or scripted set of 4 games.
• Time each changeover and mark tasks completed: neck towel, thigh towel, electrolyte sip, cue.
• Score out of 12. Target 10 or better. Fix the misses next session.

Two-week heat-acclimation microcycle

Aim for 7 to 10 heat exposures across 14 days. Keep ball quality high while layering heat stress gradually. Adjust volumes for your level.

• Day 1 Mon

  • AM: Tennis 75 min cool conditions. Skills and serves.
  • PM: 25 min easy run or bike in heat zone. Hat, shade after. Post 500 ml with 800 mg sodium.

• Day 2 Tue

  • Midday: 60 min tennis live-ball. Insert 2 changeover rehearsals. 600 ml total fluid, 1,000 mg sodium per liter.

• Day 3 Wed

  • AM: Strength 40 min indoors. Mobility 10 min.
  • PM: 30 min on-court footwork heat intervals. Slush 300 ml pre, sips during.

• Day 4 Thu

  • Midday: Match play 90 min. Full bench setup. Execute all cooling steps.

• Day 5 Fri

  • AM: Recovery. 30 min easy bike or walk. Mobility 20 min.
  • PM: Short skills session 45 min in warm conditions. Practice towel swaps.

• Day 6 Sat

  • Midday: Match play 2 hours if fit. Track body mass change. Rehydrate 125 to 150% of loss.

• Day 7 Sun

  • Off or very light. 20 min mobility. Review logs in OffCourt.

• Day 8 Mon

  • AM: Tennis 60 min in shade. Technique first.
  • PM: 35 min heat run-walk. 2 sips electrolyte every 10 min.

• Day 9 Tue

  • Midday: 75 min live-ball. Add Drill 2 intervals. Test different sodium strengths.

• Day 10 Wed

  • AM: Strength 40 min. Calves and hips.
  • PM: 45 min serve patterns in heat. Slush 200 ml at midpoint.

• Day 11 Thu

  • Midday: Full match simulation 90 to 120 min. Use 3 to 4 ice towels. Record fluids.

• Day 12 Fri

  • AM: Recovery and mobility. Short nap if needed.

• Day 13 Sat

  • Midday: Tournament primer. 60 min hit. 30 min off-court bench rehearsal. Pack kit.

• Day 14 Sun

  • Match day or scrimmage. Execute the full plan. Debrief with notes.

Expect the first 3 to 5 exposures to feel harder. By day 7 to 10, heart rate at a given workload should drop and perceived effort improve in the same heat.

Safety guardrails and signs to act on

• Stop and cool aggressively if you see confusion, chills, goosebumps in heat, or a pounding headache.
• Cramping is multifactorial. It links to heat, intensity spikes, and neuromuscular fatigue. Sodium and fluid help, but pacing and cooling matter as much.
• Do not overdrink plain water. Pair volume with sodium.

Case adjustments

• Light sweater
  • Sweat rate 0.8 L per hour. Start with 800 mg sodium per liter. Drink 500 ml per hour. Slush pre-match only.
• Heavy, salty sweater
  • Sweat rate 1.6 L per hour with salt crust on kit. Start with 1,300 mg sodium per liter. Drink 800 to 900 ml per hour. Slush pre and every other changeover.

What we learned from the US Open 2025

• The expanded heat policy put ice and shade closer to the baseline. Copy that. Bring shade and ice to your bench.
• Pre-cooling and mid-changeover slush stabilized heart rate and reduced perceived exertion. Use a simple slush plan.
• Individual plans beat generic rules. Sweat rates above 1.5 L per hour were common. Your numbers drive your bottles.

Quick references you can tape in your bag

• Sweat rate formula: [(Pre kg − Post kg) + fluid L] ÷ minutes × 60
• Sodium range: 800 to 1,500 mg per liter in heat
• Intake range: 400 to 900 ml per hour, sip every 2 to 3 games
• Slush timing: 300 to 500 ml pre, 100 to 150 ml at hottest changeovers
• Ice towel order: neck, thighs, forearms, face

OffCourt coaching notes

• Track body mass change, fluid volume, sodium per liter, and symptoms in one log. Small tweaks beat big swings.
• Use the OffCourt microcycle planner to schedule heat exposures and recovery days.
• Tag drills that felt smooth and note which cooling steps you skipped under pressure. Fix the process first.

Summary

Performance in heat is a management game. The 2025 US Open showed that simple, repeatable cooling and personalized sodium keep players in the fight. Build a smart bench. Nail your 60-second routine. Run the 10-minute sweat test to set your bottles. Train it for two weeks so it holds under stress.

Next steps on-court

• Run the 10-minute sweat-rate test this week. Set your initial sodium target.
• Pack the DIY heat toolkit for your next two practices. Rehearse the changeover routine 6 times.
• Start the 2-week microcycle if your event is within a month. Log every session.
• Adjust your plan by feel and by numbers. Smooth gut, clear head, and stable power are the goal.

Fast checklist for match day

• Cooler packed with 3 to 4 ice towels, slush, two bottles labeled
• Pre-match: 300 to 500 ml slush finished 5 to 10 minutes before walk-on
• Changeovers: neck and thigh towel, 2 to 3 sips electrolyte, one tactical cue
• Set breaks: extra 10 to 15 seconds cooling, 120 to 200 ml slush if tolerated
• Post-match: drink 125 to 150% of weight lost with sodium, easy carb-first meal

You do not have to love heat to play well in it. You only have to prepare like it is coming and follow your plan. That is how pros handled New York. It will work for you too.