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  • Jenni Davies

Runner's Trots

Do you get gut problems when you run?

Research tells us that abdominal symptoms are incredibly common amongst endurance athletes, especially runners, with the incidence ranging from 30-90%.

Officially known as exercise induced gastrointestinal disturbance, symptoms include: nausea, belching, abdominal discomfort and/or cramps, vomiting, reflux, diarrhoea, blood in your stools, faecal incontinence and flatulence. Symptoms range from mild (no effect on performance) to severe (needing hospitalisation). It is a significant reason for race withdrawals.

What causes it?

This bit is still a work in progress. Research has identified a number of different factors that may present in isolation or together to cause the symptoms.

1. Ischaemic colitis – lack of blood to the guts causing inflammatory changes

At rest, the majority of our blood supply (approx. 80%) can be found in our vital organs – brain, heart, intestines, liver, stomach. However, during exercise as much as 80% of our blood supply is diverted to the working muscles to supply them with oxygen and nutrients, and the skin to enable us to cool down. This dramatic reduction in blood supply to the gut leads to the inflammatory changes that result in the symptoms of gastrointestinal disturbance. There is hot debate as to the exact mechanism of how this occurs but it is accepted that this is a primary cause of Runner’s Trots.

The longer this decreased blood supply is sustained, the more intense is the reaction of the gut. Thus, training or events involving higher intensity, longer duration and higher external temperatures lead to more severe symptoms. Whilst, in most cases, these changes are reversible, your symptoms still need to be respected and if they are worsening, something needs to change!

2. Physical jarring of the organs

Symptoms of the lower gut – diarrhoea, blood in stools, abdominal cramps, urgency and/or incontinence of the bowel – are significantly more common in runners than cyclists. This suggests that the higher impact loading of running is having an effect on the gut. There are suggestions that this jarring causes trauma to the lining of the intestines, but evidence at this point for the exact mechanism is inconclusive.

In practical terms, if you are unable to absorb the impact of running effectively, there will be an increased jarring of the organs. Factors that could cause this are: poor lower limb biomechanics, lack of lower limb/trunk strength, endurance and power, poor core stability coordination and endurance.

3. Nutrition

There is good evidence that high fibre intake, protein, sweeteners, caffeine, fat and concentrated carbohydrate gels/drinks are associated with gut disturbance during exercise. However, as ever, there is debate over the finer details. One thing that does stand out is that some people (for unidentified reason at this point in time) are more prone to the effects of what they eat than others. Interestingly, the study that looked at different carbohydrate solutions found that complex mixes of glucose and fructose were better tolerated than single fructose or glucose products.

4. Hydration

Poor fluid replacement during exercise exacerbates gut symptoms.

Research that looked at different types of carbohydrate solutions v’s water intake, found that there was no detrimental effects on performance in the water drinkers, and that their gut symptoms were significantly less.

5. Medications

Non-steroidal anti-inflammatories (NSAID’s) such as ibuprofen, nurofen, voltaren are known causers of abdominal discomfort and should be avoided during exercise.

6. Poor pelvic floor control

There is minimal research available to support or refute this claim, but it would make sense that if you have symptoms causing cramping, urgency and diarrhoea, a strong pelvic floor will definitely assist in the management of these symptoms.

We associate pelvic floor problems with women, and rightly so, as the incidence in women who have had children is incredibly high. However they are not the only ones at risk – anyone who is overweight or has had ongoing low back, pelvic or hip problems are equally at risk. This includes you blokes who have had ongoing problems with your groin or with osteitis pubis.

7. Other factors

Symptoms are more pronounced in younger less experienced runners, females, those with a higher BMI (carrying more weight) and in those with pre-existing gut issues not related to exercise. How to manage your symptoms:

  • If you have severe symptoms including blood in your stools, get checked out by a GP to ensure there is nothing more serious going on

  • Stop training until your symptoms have fully recovered

  • Keep a strict training log that includes the distance run, pace, weather, terrain, time of day, food intake day before, food intake day of, fuel intake during the run, hydration (what you’re drinking, when and how much), what symptoms you get at what point during the run and how quickly they settle after the run. It seems like a lot of attention to detail, but over time, if there is a pattern to it, it will reveal itself with this level of detail and you will be able to start manipulating the relevant factors to help you self-manage your symptoms

  • Train your gut - there is good evidence that your gut will adapt to the altered blood supply and taking on board fuel/hydration whilst running, given sufficient time. If you have built up your training too quickly, or not trained using fuel/hydration and then use it in the race, your gut won’t have learnt to accommodate it. You need to back off then build back up again, slowly, allowing time for the gut to accommodate. This means starting back with low intensity, short duration runs that are symptom-free. Using the 10% rule gradually increase your training (this is increasing your training load by no more than 10%/week). If you get no symptoms, continue to increase gradually up to a full training load. If you get symptoms and they are only mild, stay at this level until your body gets used to it and you are symptom-free, then increase again. This may take time and be frustrating if the rest of your body is feeling good, but it is by far the best approach for your long-term gut health.

  • Get checked out by a Physio with a special interest in sports, gut health and the pelvic floor to rule out a physical cause for your symptoms. They will assess your muscle function and coordination as well as lower limb biomechanics and running technique to determine how well you are absorbing impact

  • Consult a Sports Nutritionist to discuss alternate fuelling options

  • Hydrate – water and electrolytes

Enjoy your new found control over your symptoms!


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