The Swim Leg
The swim leg of an Ironman race can be looked at as an extended warm up. After swimming 2.4 miles, you may feel a little stiff, but you should definitely feel fresh, all things considered. The goal should be to draft as much as possible, avoid the washing machine (as this can strip you of much-needed energy) and conserve as much energy as you can for the bike and run. It is better to swim a few minutes slower and get out of the water thinking, “That was easy!” rather than to push yourself to a PR swim split and possible sabotage the remainder of your race.
That being said, your HR should fall well below 78% during the swim. The top Ironman performers always look nice and relaxed during the swim leg, like they are out for an easy splash in the ocean (or lake). They don't care what place they are out of the water, only about what their place is at the finish line. Keep your HR below 70% for the entire swim. If you are swimming on someone's feet and your level of effort is below 70% that is fine too. The goal is to swim reasonably well, not set the world on fire, and conserve as much energy as you can for the rest of the race. It's going to be a long day!
As you exit the swim and jog to your bike, be sure to drink some fluids on your way. You've been swimming for the better part of 1-2 hours and, aside from any seawater or lake water you inadvertently consumed – you have not taken in any fluids. You have been sweating, however, so you're on your way to dehydration if you're not careful. Drink some fluids, get changed into your bike gear and head on out to the highway.
The Bike Leg
Once on your bike, your body will take awhile to reach stasis. After being in a prone position for 1-2 hours and using primarily your arms to propel your body, you are now in a more vertical position and are using your legs to do the pumping. A lot of blood is getting shifted around in a short period of time. Give yourself time to settle down and settle into a comfortable pace. Hold off drinking and eating anything for the first 15-20 minutes.
You should settle into a pace that is between 60-78% for the ride, the majority of which should be spent below 70%. I know, I know. . .You're thinking that sounds too easy, that you'll be out for a slow, easy ride and destroy your chances to hit a PR. This is not the case. Mark Allen, whom I consider the best triathlete of all time and the most-feared Ironman athlete, normally kept his HR between 120-140 beats per minute for the entire bike leg. His aerobic zone topped out at 155 beats per minute, so the above-mentioned zone was well below 78% for him. The only time I saw him actually go above this zone was the year that Thomas Hellriegel blew the bike course record away. Mark and other athletes had a tough decision to make – go with Thomas or not. Several of them did while others tried and blew up. On the run, the rest of the athletes blew up too.
When Mark began the run, it looked truly painful! Gone was the fluid, gliding stride. He eventually loosened up, picked up his pace and won the race, but he also told me he was second-guessing his strategy to push the bike extra hard for the first half of the run. That's a long time to second-guess yourself! Best not to put yourself in that position.
So, back to strategy. You should be spinning at 90-100rpm on flat sections and 85+rpm on any climbing. The pedaling should feel “soft”, like you are not applying much pressure to turn the pedals. You can hold your HR at, say, 70% and grind it out. While your HR is where it should be, the added tension in the legs will kill you for the run. Better to hold your HR at 70% by picking an easier gear and spinning higher RPMs. Your goal should be to negative split your bike leg. If you find yourself having to back off the pace around mile 70-80, you completed the first half too strong. It is best to hit the halfway mark afraid that you have been taking it too easy rather than questioning if you've gone out too hard.
When – not if – you have to relieve yourself, you have two options. First, you can learn to pee on the fly (while still biking), or you can pull off the side of the road and dismount. There is nothing wrong with stopping to pee. Your pride will not be shattered, your race will not be blown. Always remember that the races lasts a minimum of 8 hours for the top pros and as many as 17 hours for the final finishers. There is plenty of room for patience and for getting off your bike to pee a couple of times.
In the last few miles, switch into one easier gear than normal and spin a little higher RPMs. This will help loosen the legs up a little bit and give them a quick break before the most important part of the race – the run.
The Run Leg
The bike-to-run transition should be a time for you to take inventory. How are you feeling? Take in some extra fluids and nutrition if you skimped in the latter stages of the bike leg. Stretch out stiff and tight muscles. Make a final pit stop in the Port-a-John, even if it feels like you don't have to go. Get centered and focused on the marathon before heading out on your feet.
No matter how poorly you might feel at the finish of the bike leg, chances are you will feel somewhat rejuvenated when you begin the run. It's probably equal parts the euphoria of beginning the final leg of the race among the throngs of spectators and the fact that you are using your major muscle groups in an entirely different way than you did during the past two legs of the race. Believe it or not, there still exists the danger of beginning the run too fast.
Give yourself time to find your rhythm. Your leg muscles will be somewhat tight and will take awhile to loosen up and lengthen out. Keep your HR below 70% the first couple of miles until you know you're good to go. If there are some hills in the first several miles, slow your pace down or even walk up them (depending on their length and steepness) so you don't jack your HR up too high. At this point you have to remember that you still have in excess of 3 hours to race!! And, with many hours of racing already under your belt, any push into the anaerobic arena can prove devastating to the most crucial leg of the race as well as your overall performance.
The goal should be to either even split or negative split the run leg. Your HR should fall within the 65-78% range for the first 20 miles, if not longer. Find a pace that feels almost too easy. If, during the first 13 miles, you keep asking yourself if you're going too easy, if you should speed up, don't! You have chosen the perfect pace for the first half of the run. If at around 13 miles you feel like your tank is still mostly full, then gradually pick your pace up, but keep your HR below 78%. You can bleed a full tank empty in no time this late in the race.
If after picking up the pace you are still feeling strong at around mile 20, then you can safely bump your effort above 78%. Take each mile as it comes, do a quick inventory of how you're feeling. If you're feeling the “finish line surge”, then pick it up some more. If you're wondering whether or not you can hold your pace/effort for the remainder of the race, then hold steady or slightly back off. If you're wondering if you can hold your pace/effort for another mile, then definitely back off for the next mile and reassess how you're feeling at that point.
When you cross the finish line, hopefully you've enjoyed your experience. There will be plenty of peaks and valleys in terms of how you're feeling – no matter how good your overall race goes. The goal should be to ride the peaks as long as you can and to push through the valleys. They will pass! While setting a PR is nice, time is truly inconsequential. Too many factors – temperature, choppy water, wind, flat tires, climate, etc. - affect your overall race time, and the effects are magnified greatly at an ultra-race such as an Ironman. If you've raced hard and smart, then you should be both happy and satisfied with your results.
How hard you race is dependent on the distance of the race as well as how long you will be out there on the course. If you respect your body, listen to it and take care of it, it will respond quite well to your demands. However, if you ignore its signs, and try to abuse it and push it pasts its limits, it will shut you down and sometimes take you out.
Best to race smart so you can enjoy a strong, solid performance.