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A Physiological View Of What The Human Body Goes Through In An Ironman

  • By Triathlete.com
  • Published Oct 5, 2011
  • Updated Jun 19, 2012 at 12:17 PM UTC

I Think I’m Going to Puke.
Australian professional triathlete Chris Legh had emergency surgery to remove half his colon after the 1997 Hawaii Ironman. A good chunk of the organ had literally died during the event due to inadequate oxygen supply. While this type of crisis is extremely rare in Ironman racing, and in Legh’s case was probably related to a congenital heart defect, completing an Ironman is stressful to the gastrointestinal system of every competitor. Common problems include stomach discomfort and bloating, nausea, vomiting and diarrhea.

Exercise scientists do not fully understand the causes of such symptoms of GI distress during intense physical exertion. But they have identified some of the contributing factors. In a 2005 review published in the online International SportMed Journal, authors Stephen Simons, MD, and Gregory Shaskan, MD, wrote, “To date, contributing theories mainly focus on the mechanical agitation of the gut, fluid shifts, decreased splanchnic blood flow, dehydration, increased sympathetic and parasympathetic tone, endotoxaemia, changes in bowel transit time, hormone shifts and autoimmune changes. However, none of these adequately explain the full range of GI pathology.”

Triathletes also bring many of their GI troubles on themselves by trying to consume too much fluid or nutrition or foods that are too difficult to digest while competing in Ironman events. The gastrointestinal system cannot tolerate the same rates and types of nutrition intake during vigorous activity as it can at rest. Studies have shown that athletes who take in the most nutrition during endurance events are most likely to suffer gastrointestinal mishaps.

The final stretch.
If you’ve ever completed an Ironman, you know that the last few miles of the marathon are a unique experience that is only hinted at by the experience of running the last few miles of a regular marathon. Your body is so impaired from the beating it has taken over the course of the day, it’s almost funny. The simple act of lifting your foot off the ground to take the next stride feels akin to performing a heavy squat with a weighted barbell on your back. Research from the National Institute of Sport and Physical Education in Paris confirms that the energy cost of running at the end of a triathlon is significantly greater than that of running at the same speed without swimming and cycling beforehand. And that’s an Olympic-distance triathlon.

There are probably multiple causes of the “weightlifting” effect of an Ironman marathon’s closing miles. Stride form is measurably different at the end of a triathlon run than it is in the same athletes in an independent run. The stride changes that increase the energy cost of running at the end of a triathlon are themselves caused in part by local fatigue in specific muscles, which necessitates a change in form in much the same way you might start running with a locked right knee to protect a suddenly cramping right calf muscle. It’s neither efficient nor pretty, but it sure beats the alternative.

In triathlons and independent runs alike, fatigue and loss of mechanical efficiency are associated with increasing ground contact time. The closer you get to the finish line, the harder it becomes to pry your feet off the road. This bit of bodily mutiny is caused by a weakening of motor output from your brain to your working muscles. It is your brain’s way of preventing you from running faster—and perhaps even forcing you to slow down—in response to feedback from your body.

Your brain itself may become tired by the end of an Ironman—a phenomenon known as central fatigue. Like your muscles, it runs low on critical fuels and accumulates increasing levels of metabolites that interfere with its functioning, resulting in feelings of discomfort, loss of will to continue, fractured thinking, declining mood and reduced ability to fire the motor neurons that activate the muscles.

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