I ran again the following day. It was still warm, but the conditions felt more manageable than they had during the humid easy run.
This was a quality session with several harder sections. The exact structure is no longer fully recoverable from the screenshots available to this project, so I am keeping the description deliberately broad. One of the rules of this blog is not to fill gaps with invented precision.
The data
| Metric | Result |
|---|---|
| Duration | Approximately 57 minutes |
| Average pace | 6:38/km |
| Average heart rate | 135 bpm |
| Maximum heart rate | 164 bpm |
| Average power | 235 W |
| Conditions | Warm, but better than the previous day |
Compared with the easy run, average power rose slightly while average heart rate was a little lower. The faster sections pushed my heart rate into the mid 150s and low 160s, followed by clear drops during recovery.
What the coach saw
ChatGPT interpreted the pattern as a well controlled session. The cardiovascular response looked good, and the recoveries were clear enough to show that I was not simply accumulating fatigue without recovering between efforts.
The more interesting conclusion concerned my legs. The coach believed muscular endurance was more likely to limit me than cardiovascular fitness. In simple terms, my heart and lungs appeared capable of more work than my legs could yet sustain late in a run.
That diagnosis fitted the larger goal. A faster 5K would be useful, but beating my half marathon personal best would depend more on maintaining form and pace after 15 kilometres.
What came next
The long run was moved to Saturday because I could not train on Sunday. ChatGPT recommended 17 kilometres, controlled by heart rate rather than pace. It also asked me to test taking carbohydrates and water during the run.
The decision to extend the long run after two consecutive running days was not especially conservative. Looking back, it is one of the early examples where the plan could reasonably be challenged.
I decided to follow it. The next session would show whether that confidence was justified.
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