As a result of the increasing temperature, the jostling of the run gait, and the relative inefficiency of running, you'll be able to tolerate significantly fewer calories while running than you did while cycling—typically 50 to 150 calories per hour fewer.
Plan for this, and try to keep gel or liquid as your only fuel sources during the run, as solid foods can be difficult to digest on a hilly and hot run course. Similar to the bike, drink water whenever you're thirsty, which by this point in the day will mean taking small sips of water at nearly every aid station. I personally use the same fueling mixture on the run as I do on the bike, but simply carry the run fuel in a 10-ounce running flask.
On the three loops of the run, you'll experience six significant uphill climbs. If you "blow yourself up" on any of these climbs, it could turn your race into a struggle to the finish line. So run conservatively on these uphills, with steady, focused form—leaning forward, driving your knees, and using your arms. If you feel yourself getting very hot, go into a brisk 30- to 60-second walk on any of the aid stations that occur on the uphill portions, and during this brief walk, douse yourself with ice and cold water.
On the downhills, make up time by increasing your stride rate, letting gravity do its work on your body, and running slightly faster than you think you should. This will feel like "uneven" pacing, but will ultimately result in a much lower chance of you experiencing a significant rise in body temperature and being forced to slow to a crawl on the run leg.
The final downhill stretch to the finish line is an amazing feeling. Stride out, put a smile on your face and get ready for the cheering as you finish the 70.3 World Championships.
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