Intervalsconfidence 0.83
4 × 2km
Colin Dismuke50 km / marathon build
Source: own Strava export
Intervals
4 × 2km
Distance
16.2 km
Moving
72:48
Rep pace
3:59/km
Avg HR
168 bpm
Reps
4
Planned vs actual · TrainingPeaksPlanned 1:13:52 · 17.0 kmRan 1:12:48 · 16.2 kmIF 1.33TSS 213
Shape of the sessionEasyWorkFastest
warm up
cool down
0:004 × work / float72:48
The decode
The session was a 4 × 2km sub-threshold set with 2-minute recoveries, bracketed by a warm-up and cooldown. It was intended to keep the reps consistent at a controlled effort below threshold.
The first two reps were 3:53/km and 3:51/km, then pace fell to 3:59/km and 4:12/km. Heart rate moved from 172 to 181, reached 182 on rep three, and was 180 on the final rep; the set did not hold its opening pace in 38 C heat.
Rep splits
| Rep | Time | Pace | HR | Float |
|---|---|---|---|---|
| 1 | 7:45 | 3:53/km | 172 | 2:00 |
| 2 | 7:42 | 3:51/km | 181 | 2:00 |
| 3 | 7:59 | 3:59/km | 182 | 2:00 |
| 4 | 8:24 | 4:12/km | 180 | 1:51 |
0.83
confidence
What the engine saw
- 4 work intervals detected from lap markers, confirmed by clear pace separation.
- Recoveries average 118s.
Calibration flags
- Running power threshold estimated from the athlete's half-marathon best efforts (60-min power 476 W, 95% of 20-min power 460 W). Treat power zones and load as ±3%.
- Zones and running threshold are one snapshot, read 2 Jul 2026 and applied to every session in the archive. An older session is scored against today's zones, not the zones the athlete trained with then.
Engine read · editorial decode by Splits
Time in zone
Heart rate
Z1
Recovery11%
Z2
Endurance12%
Z3
Tempo2%
Z4
Threshold33%
Z5
VO₂max42%
Pace
Z1
Easy59%
Z2
Endurance13%
Z3
Tempo26%
Z4
Threshold0%
Z5
VO₂max0%
Z6
Speed1%
Power
Z1
Recovery0%
Z2
Endurance30%
Z3
Tempo37%
Z4
Threshold27%
Z5
VO₂max3%
Z6
Anaerobic2%
Z7
Neuro0%
Aerobic decoupling · Pa:HR+12.6%
Effort & efficiency
0.72
Running effectiveness
speed per watt/kg, reps
5.8 w/kg
Power-to-weight
rep average
2.42
Efficiency factor
norm. power per bpm
1.03
Variability index
1.0 = perfectly even power
3.5%
Rep consistency
pace spread across reps, lower is tighter
2037 kJ
Total work
mechanical energy
1208 kcal
Energy
estimated burn
907 bpk
Cardiac cost
heartbeats per km
75%
Above threshold
≥ 164 bpm (Z4+)
+0:17/km
Split balance
positive split, slower 2nd half
Conditions-adjusted pace38°C · +83 m
Actual
3:59/km
Grade-adjusted
3:59/km
Heat-adjusted
3:38/km
−21s/km
True effort
3:38/km
−21s/km
The rep pace re-expressed for flat ground and cool air, the effort, not the clock. The gap between actual and true effort is the day's hidden work: conditions were taxing the clock.