Long run · Friday, 21 August 2026

Long run, 17.5 miles

32 weeks to MDS

My write-up for this run isn't up yet. Everything the watch recorded is below.

Distance: 17.5 mi; 28.2 km
Moving time: 4h 04m; started 17:27
Average pace: 13:57; per mile
Heart rate: 124; average · max 145
Climb: 1230 ft; 375 m
Conditions: –; 68% humidity

How well the running held up

I compare how efficiently I was running early in the run (speed for each heartbeat, corrected for hills) with the late part. The drop was 6.5%. Over 5% is what I call a late fade. That band is a coaching convention, not a validated threshold.

A sustained drop began around 3h 11m into the run.

Late on, pace slowed 4% and heart rate rose 2.6%.

Efficiency across the run against the early baseline (100%). The dashed line is 95%.

First half against second half

Comparing pace against heart rate in the first half with the second, the gap was 5.5%. Under 5% is the convention I coach to: it suggests the aerobic side coped with the length of the run. It says nothing about why.

Mile by mile

Mile	Pace	Avg HR	Climb
1	12:43	122	92 ft
2	13:18	122	13 ft
3	14:51	125	135 ft
4	14:23	123	82 ft
5	13:41	122	46 ft
6	12:53	121	13 ft
7	14:40	123	121 ft
8	13:31	120	59 ft
9	13:15	122	52 ft
10	15:02	123	125 ft
11	14:53	120	89 ft
12	13:43	123	20 ft
13	13:30	124	33 ft
14	13:49	126	79 ft
15	13:31	125	26 ft
16	15:06	126	102 ft
17	14:55	127	115 ft
0.52	12:58	123	0 ft

Figures from my watch via Intervals.icu, read by the Ultra Event Training app. Heart rate from a watch is a proxy for effort, not a lab measure. The efficiency figures compare speed per heartbeat early and late in a run with a hill correction; they show what changed, not the cause.