Most age-group triathletes leave 15-30 minutes on the table in a 70.3 — not because they're undertrained, but because they make predictable execution mistakes that are entirely preventable.
We analyzed 840,000+ triathlon race results and talked to dozens of coaches to identify the patterns that separate a good race from a blow-up. Here are the seven most expensive mistakes, ranked by how many minutes they typically cost.
Mistake #1: Riding the Bike Too Hard
Typical time cost: 8-15 minutes lost on the run
This is the single most common and most expensive mistake in 70.3 racing. The pattern is unmistakable in the data: athletes who ride above 78% of FTP produce bike splits that are 3-5 minutes faster than their optimal pace — but their run splits are 12-20 minutes slower.
The math doesn't work. You save 4 minutes on the bike and lose 15 on the run. Net result: 11 minutes slower overall.
Why it happens: Fresh legs + race-day adrenaline + other athletes passing you. The bike feels easy for the first 30km, so you push harder than planned. By km 60, you've burned through glycogen reserves, your legs are loaded with metabolic waste, and you've compromised your gut's ability to process nutrition.
The fix: Set your target power and do not exceed it, period. If you don't have a power meter, set a heart rate ceiling at 80% of max and do not cross it in the first 60km. The bike should feel uncomfortably easy for the first hour.
How to pace the bike correctly →
Mistake #2: Under-Fueling on the Bike
Typical time cost: 10-20 minutes lost on the run
The second most common mistake, and it compounds with mistake #1. Athletes who eat less than 50g of carbs per hour on the bike deplete glycogen faster and bonk harder on the run.
Why it happens: Three reasons. First, you feel fine at hour 1 and don't feel the need to eat. Second, at higher intensities (see mistake #1), your gut can't absorb food, so eating feels uncomfortable. Third, you simply forget in the chaos of the race.
The fix: Set a 20-minute timer on your bike computer. Every alarm = eat something. Target 60-80g of carbs per hour. Your body needs fuel before it signals hunger — by the time you feel the need, it's too late.
Mistake #3: Starting the Run Too Fast
Typical time cost: 5-10 minutes lost in the second half
The first 2-3km off the bike feel deceptively good. You've been sitting for 2.5+ hours, the crowd is cheering, and adrenaline surges. Most age-groupers run the first kilometer 15-30 seconds per km faster than their target pace.
This early surge depletes your remaining glycogen reserves faster and pushes you into a lactate debt that you can't clear. By km 10, you're walking.
Why it happens: Adrenaline, competitive instinct, and the relief of being off the bike. Your body hasn't registered the cumulative fatigue yet.
The fix: Walk through T2 transition. Seriously, walk the first 100 meters. Then start at 5-8% slower than your target run pace. Let your legs adapt to running mechanics for the first 2-3km before settling into rhythm. The athletes who start slow finish fast.
Mistake #4: Ignoring Heat
Typical time cost: 10-25 minutes compared to a cool race
A 70.3 at 20°C and a 70.3 at 32°C are fundamentally different physiological events. But most athletes use the same power targets and pace goals regardless of temperature.
Heat increases heart rate, accelerates glycogen depletion, reduces gut absorption, and diverts blood from working muscles to skin for cooling. A 10°C increase in ambient temperature can reduce performance by 8-15%.
Why it happens: Athletes train to a plan and don't adjust. "My target is 190W" doesn't account for the fact that 190W in 32°C costs 20% more physiological "dollars" than 190W in 22°C.
The fix: Reduce bike power by 3-5% per 5°C above your typical training temperature. Slow run pace by 3-8% per 5°C above 20°C. Increase sodium by 200-300mg/hr. Increase fluid by 200-300ml/hr. Use ice at every aid station. Accept the slower finish time.
Mistake #5: Trying New Nutrition on Race Day
Typical time cost: 15-60+ minutes (including potential DNF)
GI distress is the leading cause of DNF in long-course triathlon. And the most common trigger is consuming products your gut hasn't trained with.
A gel that works fine in training at easy effort may cause cramping at race intensity. A drink mix that tastes good on a cool morning may be revolting at 30°C. A bar that's easy to eat while riding in training may be impossible to chew while racing.
Why it happens: The race expo sells exciting new products. Your friend swears by a different gel brand. The on-course nutrition is different from what you trained with.
The fix: Every product you use on race day should have been tested in at least 3-4 training sessions at race intensity. Carry your own nutrition. Don't eat anything from the aid station that you haven't practiced with — exception: water and cola, which are universally tolerable.
Mistake #6: Skipping Aid Stations on the Run
Typical time cost: 5-15 minutes in the final 8km
"I feel fine, I'll drink at the next one." This is how dehydration and calorie debt build incrementally until they become catastrophic. Each skipped aid station represents 100-200ml of fluid and potentially 100-200mg of sodium that you didn't take in.
Over 21km of running with aid stations every 2-3km, skipping 3-4 stations means you've missed 400-800ml of fluid and potentially 300-600mg of sodium. In hot conditions, this is the difference between running and walking the final 8km.
Why it happens: You feel strong early in the run and don't want to slow down to drink. The 15-second walk through an aid station feels like "wasted time."
The fix: Walk through every single aid station for the first 10km of the run. Take fluid, take electrolytes, dump water on your head. 15 seconds at 8 aid stations = 2 minutes of walking. The alternative — walking the last 6km — costs 10-15 minutes.
Mistake #7: No Race-Specific Training
Typical time cost: Varies, but affects every aspect of execution
Many athletes train hard but never rehearse race conditions. They've never eaten at race pace. Never ridden their target power for 2.5 hours followed by a run. Never practiced transitions. Never tested their nutrition in heat.
Race day becomes the experiment, and experiments have failure modes.
Why it happens: Training plans focus on building fitness (volume, intensity, threshold work) and rarely include race-specific rehearsal. Athletes assume race execution will "take care of itself."
The fix: In the 6-8 weeks before your race, include at least 3-4 "race rehearsal" sessions. A long brick (2+ hour ride at race power immediately followed by a 30-45 minute run at race pace) with race nutrition is the most valuable single workout you can do. Practice your entire nutrition plan. Wear your race kit. Simulate transitions.
The Pattern
Notice the theme: most of these mistakes come from overestimating your capacity on race day and underestimating the cumulative cost of 4-6 hours of continuous exercise. The consistent fix is to be more conservative than you think you need to be, eat more than you feel like eating, and respect the conditions.
The athletes who execute great 70.3s aren't necessarily the fittest. They're the most disciplined.
Get a Plan That Prevents These Mistakes
RaceDayAI builds your race plan around your actual fitness, your specific course, and real-time weather — with built-in guardrails to prevent every mistake on this list.
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Last updated: March 2026