Shifts. Your strap recorded heart rate only, so shifts are inferred from it. A shift starts where heart rate begins a sustained climb and ends at the peak before it falls. To count, a climb must last at least 40 seconds, rise at least 15 bpm and peak above 75% of your max heart rate. Short dips under 30 seconds, like a whistle, stay inside the shift. Heart rate lags the play by roughly 10–20 seconds, so each shift's start and end can be off by about that much.
Time on Ice is the sum of detected shift lengths. Drill-heavy practices without clear bench breaks are detected less reliably than games.
Calories are the number your workout device reported (Polar today; Apple Watch or Garmin later), so they match what you see in that app and on Strava. If a device gives none, Line Change estimates them from heart rate with the Keytel equation, your age on the day and your 98 kg profile weight, using a resting rate below 90 bpm.
60-Sec HR Recovery is a heart-rate number, not a time. It is how far your heart rate falls in the 60 seconds after a shift ends. For example, a peak of 180 bpm that is down to 150 a minute later is a 30 bpm recovery. A faster drop usually means better aerobic fitness. It's the closest thing to a fitness trend this data allows.
Games and Drop-Ins. A session that starts between 9 AM and 3 PM and runs 115 minutes or longer is treated as a drop-in; everything else is a game. Averages, trends and the arrows use games only. Put "(Drop-in)" or "(Game)" in the Strava title to correct one.
Effort and Load score each session out of 10 against your previous 10 games, where 5.0 is a normal night, with the % difference from your norm. Effort is how hard you pushed regardless of ice time: heart-rate intensity per minute, share of ice time above 90% of max, and how high your shift peaks got. Load is the total work (time in each heart-rate zone, weighted by how hard the zone is). Heart rate also moves with sleep, illness, heat and caffeine, so treat a low score as a prompt, not a verdict.
Arrows in the session summary compare that session with your game average: ▲ more than 2% above, ▼ more than 2% below, – within 2%. Shifts, time on ice and calories are compared per minute played, so a short session isn't automatically marked down.
Not Here Yet: distance needs accelerometer data, which these recordings don't have. VO2max can't be measured from game heart rate. Your last Polar Fitness Test (April 2020) gave 50.