Dear Mark,

I just finished an Ironman and had a question about my marathon run. In short, it was abysmal. I felt strong on the swim and bike, but when I started the run my legs felt heavy and they never recovered. My average heart rate was around 150 for the bike (my normal training heart rate for a long ride), and I took in about 300 caloies per hour on the bike and 200 on the run, but it just didn’t seem to work. I also got bloated on the run. Any thoughts? -Disaster Struck

Dear Disaster Struck,

This is a complex problem that can surface, especially in an Ironman. It’s farily common to feel good on the swim and the bike, but almost always tough to sustain that feeling on the run. That is, unless a few things are attended to through the first two legs.

In the Ironman distance race a person can burn as many as 700 to 750 calories per hour. However, it’s tough to absorb much more than about 300 to 350 calories per hour. This poses the question, where is the remainder going to come from? The answer? Stored fat. This presents another challenge: to keep the fat burning physiology engaged, something that only happens by moderating your heart rate. If 150 beats per minute is roughly your moderate long workout effort level, then that would be a good target to avoid going over at least until you hit the run.

It’s not just a matter of drinking more sports drinks or downing a few extra gels.

If your average is 150, that means that there would have been points where you were well above as well as well below it: it’s the above part that can slow fat metabolism. This would not be an issue if you could get enough carbs in to make up the deficit caused by the reduced fat metabolism that the high heart rate brings. However, in a long and/or hot race, it’s tough to keep those carbs coming in. This is the first part of what may have caused your feeling of dead legs: simply not having enough total calories.

The solution to this is not always easy. It’s not just a matter of drinking more sports drinks or downing a few extra gels. This “solution” is often what results in the stomach backup in the first place. Once this happens, even lower amounts of hourly intake may be too much on top of what is already backed up in your stomach. However, there are a few things you may do to maximize the chances of nutritional success. The main thing is finding a source of calories that has some glucose or dextrose as one of its sources of carbohydrates. Glucose, or dextrose, absorbs passively which means that is has a very low chance of causing stomach backup. A second trick that often works is Coke. Yep, this simple drink can help reverse a queasy stomach mid-race.

The second question is regarding your total sodium intake. If your sodium levels get low (which happens very easily in an Ironman) performance starts to dip and no matter how much you desire to go fast, your body will not respond. This shows up mostly on the run because of its weight-bearing nature.

In general, a person needs at least 350 milligrams per hour of sodium, starting no later than three hours into the event. If you know you sweat a lot (i.e. you see salt caked on the outside of your riding shorts after most rides), then you will likely need even more. Most sports drinks and gels do not have enough sodium to replenish what you lose in an Ironman, so consider carrying an additional source of sodium (buffered salt tablets are the easiest solution) next time as well.

Happy Training,

Mark