I’m Mark Bowstead, an Auckland-based triathlon and Ironman coach, and a former professional triathlete. In June, 3 of my athletes raced long course on the same warm, humid weekend: two over 70.3, one over the full distance. Three very different bike legs, three very different runs. Their race files say more about pacing a long-course bike than any formula, so here’s what actually happened, with the numbers.
The short version
Athlete 1 (full distance) rode on plan at 0.74 IF, but with her heart rate 10 to 15 beats over ceiling for the first 90km. Her run came out 34 to 39 seconds per km slower than planned.
Athlete 2 (70.3) rode 0.76 IF after easing mid-ride, arrived at T2 fresh, and ran at 99% of her threshold power with a negative split.
Athlete 3 (70.3) chose 0.72 IF, his HR efficiency improved through the ride, and he held training run power with a fade only in the last 4km.
IF is intensity factor: your normalised power as a fraction of FTP. The age-group band for a 70.3 bike is roughly 0.78 to 0.85, and 0.65 to 0.75 for the full distance.
Athlete 1: the power was right and the ride was wrong
She rode the bike almost exactly to her power plan. Normalised power was inside the target range, intensity factor 0.74, right at the top of the full-distance band. On paper, a well-paced bike.
The heart rate file tells a different story. For the first 90km her HR sat 10 to 15 beats over the ceiling we’d set. Heat was part of it (a humid day lifts HR for the same watts), adrenaline was part of it, and her bike computer failed, so she rode the whole leg on feel with no numbers to govern her.
The body paid late. Back-half bike power dropped 7%, with HR falling alongside it, which is the signature of a system running out, and she reached T2 already spent. The run plan said 5:15 to 5:20 per km. She ran 5:54, and couldn’t lift her heart rate above 158 no matter what she asked of her legs. Total cost against the plan: roughly 25 to 30 minutes.
The lesson sits in the gap between the two files. A power target executed at the wrong heart rate is still an overspend. Watts are the plan. Heart rate is the day.
Athlete 2: fresh at T2 buys you the run
The second athlete went out hard, about 0.83 IF for the first 20km, then a long-standing niggle in the aero position forced her off the power. She rode the remaining 70km well under her ceiling and averaged 0.76 for the leg.
The forced conservatism became the perfect experiment. She arrived at T2 genuinely fresh, and the run showed what that’s worth: 99% of her threshold power for the entire half marathon, a negative split, decoupling of 1.2% (effectively zero), and her fastest 3km at the end of the race.
Off the bike she gave up around 18 seconds per km against her open half-marathon pace. That’s a small tax. Athletes who overcook the bike routinely give up 40 to 60.
Athlete 3: conservative on purpose
The third athlete chose the cautious ride. He’d had his build interrupted by a calf injury, he found himself solo into a headwind for almost 90km, and he made the deliberate call to ride 0.72 IF when the age-group band starts at 0.78.
His file is the cleanest of the weekend. Bike decoupling was negative (his HR efficiency actually improved as the ride went on), he held his training run power the whole way off the bike, and the only fade was a shallow 6% in the final 4km.
On the day, the call was right. And now the file is evidence for the next race: demonstrated durability plus a fresh-to-T2 ride means he can target 0.76 to 0.78 next time and take several minutes out of the bike split with little run cost. Conservative pacing done well is a rung on a ladder, and he’s ready for the next one.
What the 3 files agree on
The run scores the bike. None of these bikes was won or lost on the bike split. The full-distance athlete’s “on plan” ride cost her 25 minutes on the run. The two conservative rides bought runs at or near training power.
Power sets the plan, heart rate arbitrates the day. Heat, wind, nerves and a broken head unit all show up in HR before they show up anywhere else. Ride with both numbers visible and a hard HR ceiling for the first half.
Freshness converts. The two athletes who reached T2 fresh ran at 99% and 100% of their training run power. The one who didn’t was capped 35 seconds per km under hers.
Your taper is part of your pacing. The athlete who faded arrived at the start line over-tapered (form score of +42 when the sweet spot tops out around +25), which meant flat legs wearing a hot heart rate. The cleanest execution of the weekend came off a form score of +12.
What this means for a Taupo build
70.3 Taupo in December is cooler than a tropical race, but the rules don’t change, and the discipline is built now, in winter. Long rides want an HR ceiling attached to the power target. The first 30 minutes of race intensity should be rehearsed until riding 5W under feels normal. And the race-day kit checklist matters more than people think: one dead bike computer cost the better part of half an hour here.
Common questions
Should I pace a long-course bike by power or heart rate? Both. Power is the plan you set in training. Heart rate is the check on race day, because heat, wind and nerves move it independently of watts. When the two disagree for more than a few minutes, believe the heart rate and ease off.
What’s a sensible bike intensity for a 70.3? Around 0.78 to 0.85 IF for a well-trained age-grouper off a solid build. Off an interrupted build, or on a solo windy day, lower is smarter, and these files show the run rewards it.
How much time does overbiking actually cost? In these files, the athlete who overspent (internally, on heart rate) lost 25 to 30 minutes against her run plan. The athlete who banked freshness gave up maybe 3 or 4 minutes of bike split and ran to her ceiling. The exchange rate is brutal and it always favours the run.
If you want a race plan with both numbers on it, built around your actual training data, that’s what I do. Start with the Ironman and 70.3 coaching page (/ironman-70-3-plan), read the durability post on this blog, or get in touch (/contact).
Mark Bowstead is a former professional triathlete (2009 ITU Long Distance World Champion, 20-24) who coaches time-pressured age-group athletes through Ironman, 70.3 and marathon builds from Auckland, New Zealand.
