Every duathlon or triathlon bike course I've ridden has turns and/or hills that require me to slow down then re-accelerate back up to speed. When you re-accelerate you're moving the mass of the bike in addition to your body weight and that's a lot of work. The effort can spike your heart rate and send you above your AT (anaerobic threshold)/LT (lactate threshold) zone which is not a good thing for an endurance event.

But on a bike there's a mechanical advantage that we don't have for the swim or run; we can take a break, pedal with less force and still maintain a fast—if not—top speed. This is becomes obvious on downhills.

So on a bike we want to maintain momentum, yet we don't want to go above our AT/LT, and we have this mechanical advantage to use.

The trick is that well-prepared riders can go above AT/LT many times during a time trial and recover. They can do this because they train this way, adapting to it over time. This is different than run pacing where if you sprinted up a short hill you would pay big time on the downhill. And when swimming you're dealing with so much resistance that varying your speed by more than just a few percent requires exponential changes on power output.

So during a time trial with rolling hills I'll increase my effort over the short hills, then ease up just enough to recover once I'm over the top. This way I maintain more momentum, a steadier pace where I don't have to re-accelerate the my combined bike and body weight to the same degree. If you can train yourself to do this it will give a net gain in speed as compared to keeping an effort level throughout. Therefore, workouts with some form of interval/speedwork on the bike are even more important than for the swim or run, but few athletes train this way.

Developing acceleration with intensity also helps you get back up to speed quickly after corners where you lose speed. It's a bit different than going fast over short hills, but your body only knows it as another near max output effort for a short time. Again, you can prepare for this with intervals in training.

The inverse principle applies for optimal pacing on long climbs. On climbs that take longer than 30-45 seconds going anaerobic is not recommended as it will take you deep into oxygen debt and you won't get a chance to recover while still climbing. Even though I'm a better than average climber, I often find myself just holding even with riders around me on long climbs. This is because my goal is not to go more than a few beats above my target heart rate.

So while many athletes will focus on attacking all the climbs, I will just attack the short ones to keep momentum; then I'll attack the whole course with equal energy—including flats and downhills. Try setting a minimum heart rate of 60 to 65% for training rides then hold it on all flats and gradual downhills. It may change your thoughts about how to pace and cover a course with an even effort on all sections.

In my 'past life' as a bike racer it was important to be ready for 'redline' intensity on all climbs as this is where most of the separation would happen, but as a triathlete all my cycling on race day are time trials so I want to be equally fast over the whole course.

Also keep in mind that for the vast majority of riders I've coached heart rate will be significantly lower on the bike than for the run at the same RPE (relative perceived effort) level. This is because we use fewer muscles on the bike than the run where the whole body gets involved in the movement. Appropriate heart rate on the bike during a race will be about 5% lower than for the run. I believe many riders' heart rate is much lower than this which means they 'give away' time during their bike split.

And one last thing—at the end of your ride you should ease up for the last minute or two. Let your heart rate drop a little and get ready for a quick transition and solid run. If you come into transition with heart rate near redline it's tougher to be smooth and efficient.