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Marathon pacing

Marathon Race Plan Calculator: Hills, Weather, and HR Caps in Google Sheets

Build a marathon pacing calculator that adapts to hills, weather, and heart-rate caps—powered by your Strava history synced with StrideSync. Ship a printable race card and a dynamic sheet in one afternoon.

Updated Feb 2026
14 min read
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Baseline fitness inputs

Auto-pull long runs, tempo, and race-pace workouts from Strava via StrideSync.

Course difficulty

Import GPX, compute grade-adjusted pace (GAP), and hill fatigue per segment.

Weather load

Heat/humidity (WBGT or temp+dew point) to set HR caps and adjust target pace.

Race card output

5K/10K splits, hill notes, gels, water stops, and printable PDF/phone view.

Template setup

Duplicate the race plan template

The template ingests your StrideSync sheet, imports a GPX course profile, applies heat adjustments, and outputs segment targets with HR caps and gel timing.

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Data inputs

  • Recent block runs: long runs, tempo, race-pace workouts (auto-synced via StrideSync).
  • Threshold pace and HR (from your best recent tempo/threshold session).
  • Planned marathon base pace target (recent 10K/HM result or calculator output).
  • Course GPX (elevation, mile/km markers) and forecast (temp + dew point or WBGT).

Sheet layout

  • Inputs: Marathon goal, recent race results, LT pace/HR, forecast temp/dew point.
  • Course: Imported GPX with distance, elevation, grade; add aid stations.
  • Adjustments: Heat penalty (sec/mile or sec/km) and hill penalty per segment.
  • Output: Segment table (5K/10K splits), HR caps, gels, notes.

Key formulas

Heat adjustment (sec/mile)

=IF(WBGT>72,(WBGT-72)*3,0)

Segment GAP pace

=ACTUAL_PACE - (GRADE * 12)

Adjusted target pace

=BASE_PACE + HeatAdj + HillAdj

HR cap by segment

=MIN(LT_HR, EASY_HR + SegmentFatigue)

Tip: Use MAP or LAMBDA to keep calculations clean as you import GPX rows.

Course & weather

Course profile

Convert GPX to a table: distance, elevation, grade. Add “segment” column for 5K/10K splits.

Heat/humidity

Use temp + dew point → WBGT estimate. Apply penalties: ~2–3 sec/mi per WBGT point over 72°F (adjust if you’re heat-adapted).

HR caps

Set a base cap (e.g., LT-5 bpm) and lower it on hot segments; raise slightly on cool/shaded segments.

Gels & aid plan

Insert gels every 25–35 minutes; align with aid stations. Add a “reminder” column for each segment.

Forecast aware

Adjust pace to conditions before race week

The sheet recalculates pace and HR caps when you update forecast and GPX. Run a cool and hot scenario to de-risk pacing.

  • Heat penalty slider: mild, moderate, aggressive to match your fitness/heat training.
  • Segment-specific HR caps: tougher hills drop pace but control drift.
  • Auto-updates after every long run or race-pace session (via StrideSync syncs).
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Checklist

  • Load your GPX and forecast.

    Paste distance/elevation, add temp/dew point, and pick heat penalty.

  • Set progression strategy.

    Negative/steady/positive split options apply to segment paces.

  • Print/export race card.

    Use a compact view for phone/watch cheatsheet.

Troubleshooting

  • Too aggressive pace? Increase heat penalty, use steady split, or lower LT pace by recent training signal.
  • GPX mismatch? Ensure distance markers align; resample GPX to 200–400 points.
  • HR caps feel low? Raise by 2–3 bpm if you’re heat-adapted; drop for un-seasoned runners.
  • Hilly course? Add a hill fatigue term that lowers HR cap on back-to-back hills.

Ship your race plan

Connect StrideSync, drop in your GPX and forecast, and export a race card you can trust.

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