Boston Marathon

{
  "guide": [
    "Hold back in the first 10 km. The downhill destroys quads — every second saved here costs you 30 in the Newton Hills.",
    "Run the tangents on the long straight stretches through Wellesley and Natick.",
    "Power-hike the steepest section of Heartbreak if it saves your form. The downhill to Boston Common is gentle.",
    "Pre-race: train 6+ long runs with sustained downhills to harden the quads."
  ],
  "profile": "Net downhill point-to-point. The first 25 km drop sharply — most runners blow their quads early. The Newton Hills (km 26–33) come after this damage, with Heartbreak Hill at km 33 as the final climb.",
  "terrain": "rolling",
  "keyFeatures": [
    "km 0 — Hopkinton start. Steep downhill, easy to overcook the opening 5 km.",
    "km 26–33 — Newton Hills (4 successive climbs).",
    "km 33 — Heartbreak Hill. ~27 m climb, more mental than physical.",
    "km 42 — Right on Hereford, Left on Boylston. The most famous final two turns in marathoning."
  ],
  "elevationGain": 150,
  "elevationLoss": 270
}