Don’t Waste Energy on Speed Work
Pure runners typically perform two fast runs each week. Pure cyclists typically perform two fast rides each week. Many triathletes try to do two fast rides and two fast runs each week. I don’t think this is a good idea for anyone, except perhaps World Cup racers, but it’s definitely not a good idea for those training for Ironman events. The problem is that fatigue from cycling transfers all too well to running, and vice versa, such that doing two hard rides and two hard runs weekly is almost tantamount to a pure runner doing four hard runs every week. Fatigue will accumulate, and performance in all of those hard workouts will be compromised.
Even for those few athletes who hold it together, the Ironman marathon is run at a relatively low intensity—about 60 percent of VO2max. While faster runs could theoretically stimulate improvements in aerobic capacity and efficiency that would enhance performance in the low-intensity Ironman marathon, these theoretical benefits are outweighed by the fatigue cost that would come with trying to combine high-intensity run training with high-intensity bike work.
I believe that Ironman triathletes are better off committing themselves to either one or the other, and specifically to high-intensity bike training. Doing two hard rides per week in addition to a long ride will make you that much stronger on the bike and that much more likely to have enough legs left at the start of the marathon to hold goal pace—which, again, is not a particularly fast pace for any triathlete—all the way to the finish. And keep in mind that, just as fatigue crosses over between cycling and running, so does fitness, albeit to a lesser degree. So you can count on those hard rides to also elevate your running a bit.
I am not suggesting that you avoid fast running altogether, but I am suggesting that you strictly limit it. In addition to the threshold-pace transition runs I described above, you may also do some fartlek runs with 30- to 60-second spurts of 5K to 3K race pace running scattered throughout an otherwise steady, moderate-pace run, some very short (eight to 10-second) hill sprints after you’ve completed one of your weekly easy runs, and progressions, consisting of one to three miles of running at marathon to 10K pace at the end of a base run or long run. That should do it.
As I suggested above, doing frequent, short transition runs off the bike will prepare you to start your Ironman marathon strong, and when you start the marathon strong, you have a good chance of finishing it strong. However, a one- or two-mile transition run does not fully prepare the body for the stress of running an entire marathon after a long, hard ride. Nothing does, actually, but a long bike-run brick workout will help.
Four to five weeks before you race an Ironman, do what I call a metric Ironman. As you know, an Ironman features a 112-mile bike leg and a 26.2-mile run. A metric Ironman workout consists of a 112K (69.6-mile) bike leg and a 26K (16.1-mile) run. That’s about two-thirds of what you will have to do on race day, which is about perfect in terms of simulating the Ironman challenge without overtaxing your body. Perform both the bike and the run at close to Ironman race intensity. (You can even start with a 2.4K [1.5-mile] swim if you like.)
Running a marathon off the bike will neither seem nor be quite as hard once you’ve gotten this metric Ironman workout under your belt.