Solving GI Stress & Triathlon Performance With a Bike Fit

Experiencing GI issues during triathlon? You might want to look at your bike fit… A case study of Colin Norris, ex-pro Ironman triathlete.

Let’s set the scene – you’ve invested a significant amount of time, money and effort into preparing for a peak race, only for the wheels to come off early on in the run with GI distress. 

This is up there in the list of worst case scenarios and yet is often the grim reality for a lot of triathletes, both in the age-group and pro ranks alike. Once your stomach stops playing ball so to speak, there’s very little that you can do to snatch victory from the gaping jaws of defeat. 

There are often a myriad of different reasons that can cause such GI distress; poor nutrition strategy, using sub-par nutrition products, intolerances to this, that and the other, climate conditions on race day, poor pacing strategies, boshing a fish phaal down the local curry house the night before a race… the list can be extensive!

Colin’s Situation

One of the potential causes of GI distress that can, and often does, get overlooked however is how your bike position can affect your ability to consume and process the nutrition you’re taking on. This is precisely the situation ex-pro Ironman triathlete and head coach at APB Works Colin Norris found himself in. Here’s how we went about diagnosing and fixing it.

Colin had a reputation as being one of the fastest runners on the 70.3 circuit, posting run splits of around 70 mins for the half marathon (in old school flats – no super shoes here) after a hard swim and bike, but more often than he’d like, he wasn’t able to unleash his running prowess due to crippling stomach cramps when going from a horizontal position on the bike to a vertical position to start the run. When you make your living as an athlete, this unpredictability isn’t exactly ideal.

Could Bike Fit Help?

Having undergone various rounds of testing for food intolerances, stripping his diet back to the most basic of foods to try and figure out if there were any contributing factors there (no dodgy curries on a Friday night!) and testing out almost every sports nutrition product under the sun, we were almost at a loss as to what could be the root cause of the issue as it kept happening race after race, season after season.

As with anything, there are always multiple factors that contribute to the cause of and resolution of a particular issue. There was however a bit of a light bulb moment however when at the start of the 2016 season, Colin decided that he wanted to change his bike. For context, Colin is on the taller end of the scale for a pro triathlete – around 6ft 2 in with very long legs and a shorter torso. Good for running, but not so good to fit onto a TT bike (more on that later).

Up until this point, he’d been riding an old 2013 Cervelo P2 in a 58cm frame with a 175mm crank and a 130mm / +6 degree stem to get somewhere even close to a workable front end position (see photo – credit: James Mitchell). He was perched right on the nose of the saddle and was hunched over the thing like a prawn. It was neither pretty nor effective! We decided for the new bike that we should go up a size to a 61cm P2 (the updated version first released in 2014) to give a wider range of positional adjustment.

Making Progress

It was at the same time that Colin doubled down on his S&C work; strengthening his core and increasing his mobility / flexibility though his thoracic spine in particular. Over the course of the next couple of seasons, as Colin became stronger and gained more control over his posture on the bike, we were able to make subtle modifications to his position as his functionality and strength increased,  noticing that the GI issues were starting to happen less frequently. The sports nutrition products had stayed the same, but what had changed?

The changes that we believed to have the biggest effect on getting a handle on Colin’s GI distress on the run were largely down to his bike positioning. By going up a frame size and prioritising comfort and power production over out and out aerodynamics (a more rearward seating position, longer reach and higher front end in this case), and doubling down on strengthening & mobilising certain areas of the body (core / posterior chain & back), we could lengthen his torso sufficiently to relieve pressure on the diaphragm and abdomen, allowing the stomach to function better and actually process the nutrition that Colin was consuming.

Multiple Wins

Another bonus of lengthening the torso and releasing pressure on the abdomen was better lung functionality, meaning that Colin could not only be more effective in the way his body was using the oxygen available (utilising a larger percentage of his aerobic capability), but as a result, less oxygenated blood had to be transported away from the stomach to fuel the muscles, meaning improved calorific uptake and less effort required to maintain the same output.

Fast forward to November 2022, a few different bikes and positional refinements later and the result was an 8 hrs 8 mins finish with a 2:46 marathon at Ironman Israel with no GI distress.

Colin back feeling fast and sustainable on the bike!


So, what can we learn from Colin’s experience? Here are a few key takeaways to think about;

  1. Be relentless in your approach to problem solving and leave no stone unturned, as you might just unearth something significant in a place that wasn’t immediately obvious. 
  2. Progress isn’t linear. It can take time (sometimes years!) for things to click. Focus on the process of improving rather than an obsessive outcome orientated or ”hacked” approach.
  3. You might not immediately be able to get to where you want to be with your bike position and that’s OK! Working on strengthening the body and improving overall function to be able to sustain your desired position is an essential part of the puzzle. The bike won’t do it all for you!
  4. Your bike position needs to work for YOU. Prioritising comfort and force production is often a far better bet than trying to contort yourself into a super aero position that you might not be able to maintain. There’s MUCH more to a good triathlon bike position than being aero!
  5. Find the support team (e.g. bike fitter, coach, nutritionist) that understands the demands of your event, listens to ongoing feedback and is committed to figuring out what works for you. Success is a collaborative and ongoing process, not a ”once and done” prescription.

Words by: (one ‘t’) Mat

To find out more about Colin and his coaching services visit

If you’re curious about how your bike position might be affecting your own comfort and performance, get in touch by email: or book in for a session.

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