Open one split and see what happened in it

The splits table shows you which kilometre was slow. This screen is for why. Tap a row — in Splits, in 5K Splits, or under Segments if your watch recorded laps — and that one stretch gets a page of its own.

The lines at the top

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The rows read top to bottom in the order you’d ask about them:

• Starts and Ends are minutes into the run, not the time of day — 18:29 to 24:21 means this was the stretch just before the twenty-five-minute mark. Handy when you’re matching a split to the heart rate trace on the run page.
• Total Distance is where in the run you were when this split ended, so you don’t have to count rows.
• Avg. Pace and Maximum Pace — the average is the row you tapped; the maximum is the fastest moment inside it. A big gap between the two means the kilometre wasn’t run at one speed.
• Avg. Grade Adjusted Pace is the same kilometre as if it were flat. When it’s faster than the pace above it, the hill is the reason. There’s a whole page on reading that difference.
• Heart rate and intensity — average and maximum for the split, then the same two as a percentage of your Max HR. 76% is the number to compare across splits, because it means the same thing whether your maximum is 175 or 195.
• Elevation Ascend and Descend, separately. The run page gives you the whole climb; this is the climb inside one kilometre, and it’s the most common answer to “why was this one slow”. Twenty seconds off your average with 30 m of ascent in it wasn’t a bad kilometre.
• Steps, Cadence and Stride Length for that stretch alone. Cadence holding while stride shortens on a climb is the normal picture. Both dropping is the one to notice.

Two more rows appear with Pro: Pace Stability Index and Efficiency Factor, worked out for this split rather than the run. They’re the ones to open when a run scored low on stability and you want to know which kilometre did it.

The zone bar and the charts

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• Heart Rate Zones is the run’s zone bar, cut down to this split. If the watch lost your pulse for part of it, a grey Missing Data line says how long, the same way it does on the run page.
• Pace, Heart Rate and Elevation each get a chart zoomed to the split, which is where the detail actually shows. On the run page a kilometre is a sliver of the trace; here it’s the whole width.
• Touch a chart and a marker follows your finger with the value and the time, so you can put a number on the exact moment the pace dropped.

The elevation profile is drawn faintly behind the pace and heart rate lines too. Most of the time that’s all you need: the pace line dips exactly where the grey rises, and the question answers itself.

Worth knowing

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• Everything on this screen is free except the two Pro rows. It works on every run already in Apple Health, however old.
• A treadmill split has no elevation rows, no GAP and no elevation chart — there’s no route to take them from. Pace, heart rate, cadence and stride are all still there.
• A very short split has no charts. Anything under a minute — usually the last few hundred metres of a run — shows the rows only; there isn’t enough of a line to draw.
• Intensity uses the Max HR in your settings. If it looks wrong on every split, the fix is in your zones, not the run.
• Don’t read the first split too hard. GPS settles over the first few hundred metres, so kilometre one has the least trustworthy pace and elevation in the run.