Training load calculator
Heart rate load calculator
Enter your heart rate data below to calculate the heart rate stress score (HRSS) for this session.
HRSS (Heart Rate Stress Score) uses your heart rate reserve relative to threshold to estimate training stress without a power meter.
- Calculate Heart Rate Reserve (HRR) at FTP: (FTP HR - Min HR) / (Max HR - Min HR)
- Calculate 1hr FTP TRIMP: HRR@FTP × 0.64 × e^(gender factor × HRR@FTP) × 60
- Calculate exercise TRIMP: Duration × HRR × 0.64 × e^(gender factor × HRR)
- Calculate HRSS: (Exercise TRIMP / 1hr FTP TRIMP) × 100
Gender factor: 1.92 for males, 1.67 for females.
TSS uses power data and is more precise for structured cycling. HRSS uses heart rate, which makes it useful for running, hiking, swimming, or any sport where you don't have a power meter. Both try to answer the same question: how hard was that session relative to your threshold?
Ride or run a 30-minute time trial and average your HR for the last 20 minutes. That's a solid real-world estimate. Some coaches prefer a lactate test for accuracy, but the field test gets you close enough for training purposes.
HRSS is deliberately scaled to line up with TSS, so the same ranges work:
- Under 50 - easy, you'll recover quickly
- 50 to 100 - solid session, normal training day
- 100 to 150 - hard day, you'll feel it tomorrow
- 150 to 300 - long or race-level effort, plan recovery
- Over 300 - big endurance event
Yes. HRSS works for any activity with a heart rate trace, so trail running, hiking, swimming, rowing, even Nordic skiing all count. Shape Calendar pulls them in automatically from your watch so every sport shows up on one load chart, instead of you checking three apps to piece together your week.
Most devices report their own load metric (Garmin uses "Training Load", Apple uses Move and Exercise rings), but they don't expose HRSS directly. Shape Calendar pulls in your completed activities and calculates HRSS for you, so you get a consistent score across every session regardless of which watch recorded it.
One session's score is useful, the picture gets clearer over weeks. Shape Calendar logs HRSS for every run, hike or swim and combines it with TSS from your rides into one chart, so you can see your full load across sports instead of one number per app.
Shape Calendar
One load chart for every sport.
Shape Calendar calculates HRSS for your runs, hikes and swims, blends it with TSS from your rides, and syncs everything to your watch.