Intervalsconfidence 0.83
Mona Fartlek
Colin Dismuke50 km / marathon build
Source: own Strava export
Intervals
Mona Fartlek
Distance
10.1 km
Moving
46:21
Rep pace
3:22/km
Avg HR
153 bpm
Reps
18
Planned vs actual · TrainingPeaksPlanned 48:00 · 9.8 kmRan 46:21 · 10.1 kmIF 1.30TSS 129
Shape of the sessionEasyWorkFastest
warm up
cool down
0:0018 × work / float46:21
The decode
This was an 18-rep fartlek. It was prescribed as controlled aerobic running under HR <140, but the repeated high-output changes and short recoveries made it a substantially harder session.
Work pace stayed between 3:13/km and 3:32/km as heart rate rose from 143 on the first rep to 172 on the last, with a maximum of 177. The pace held together while cardiovascular strain accumulated.
Rep splits
| Rep | Time | Pace | HR | Float |
|---|---|---|---|---|
| 1 | 0:30 | 3:14/km | 143 | 0:30 |
| 2 | 0:30 | 3:25/km | 156 | 0:30 |
| 3 | 0:30 | 3:13/km | 162 | 0:30 |
| 4 | 0:30 | 3:22/km | 163 | 0:30 |
| 5 | 0:45 | 3:32/km | 164 | 0:45 |
| 6 | 0:45 | 3:27/km | 161 | 0:45 |
| 7 | 0:45 | 3:30/km | 161 | 0:45 |
| 8 | 1:00 | 3:22/km | 164 | 1:00 |
| 9 | 1:00 | 3:29/km | 163 | 1:00 |
| 10 | 1:00 | 3:22/km | 161 | 1:00 |
| 11 | 1:00 | 3:29/km | 168 | 1:00 |
| 12 | 0:45 | 3:27/km | 165 | 0:45 |
| 13 | 0:45 | 3:21/km | 169 | 0:45 |
| 14 | 0:45 | 3:20/km | 168 | 0:45 |
| 15 | 0:30 | 3:13/km | 165 | 0:30 |
| 16 | 0:30 | 3:19/km | 170 | 0:30 |
| 17 | 0:30 | 3:13/km | 173 | 0:30 |
| 18 | 0:30 | 3:17/km | 172 | 0:30 |
0.83
confidence
What the engine saw
- 18 work intervals detected from lap markers, confirmed by clear pace separation.
- Recoveries average 42s.
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
Recovery53%
Z2
Endurance4%
Z3
Tempo14%
Z4
Threshold25%
Z5
VO₂max4%
Pace
Z1
Easy74%
Z2
Endurance4%
Z3
Tempo3%
Z4
Threshold8%
Z5
VO₂max10%
Z6
Speed2%
Power
Z1
Recovery3%
Z2
Endurance62%
Z3
Tempo12%
Z4
Threshold13%
Z5
VO₂max10%
Z6
Anaerobic0%
Z7
Neuro0%
Aerobic decoupling · Pa:HR+2%
Effort & efficiency
0.81
Running effectiveness
speed per watt/kg, reps
6.1 w/kg
Power-to-weight
rep average
2.58
Efficiency factor
norm. power per bpm
1.05
Variability index
1.0 = perfectly even power
2.9%
Rep consistency
pace spread across reps, lower is tighter
1364 kJ
Total work
mechanical energy
720 kcal
Energy
estimated burn
920 bpk
Cardiac cost
heartbeats per km
29%
Above threshold
≥ 164 bpm (Z4+)
-0:54/km
Split balance
negative split, faster 2nd half
Conditions-adjusted pace24°C · +18 m
Actual
3:22/km
Grade-adjusted
3:22/km
Heat-adjusted
3:15/km
−7s/km
True effort
3:15/km
−7s/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.