The Half Marathon Collapse

Now I have 3 years of half marathon races.

My pace is the SAME.

I am using chatgpt to analyze my races. It is revealing stuff. Maybe things I already knew.

Diagnosis

Goal: sub-3:00 (13:44/mi)

Main issue: pacing and endurance, not raw ability

Pattern across races

• Consistent slowdown at mile 5–6
• Pace drops from ~13–14 → 16+
• After that, just holding on

Heart rate insight

• HR rises early (mile 2–4)
• Then flattens or drops later
• Indicates fatigue, not cardio limitation

What this means

• Can handle goal pace for ~3–5 miles
• Cannot sustain it over full distance
• This is a durability problem

Main mistakes

• Starting too fast
• Poor pacing discipline
• No late-race push

Core insight

• Running like a 5-mile effort, not a 13-mile effort

Simple fix

• First 5 miles at 14:45–15:00
• Then gradually build

Key rule

• Slow first 5 miles = faster overall race