Competitor overcome when glycogen stored in body is exhausted.

Medical research studies suggest that an upset tummy (gastrointestinal disorders) can arise because of intense physical activity such as many hours of hiking and walking.   Over-exercise can make you feel sick.   This is not news to most humans who move around and play hard.

During my long march across France through the Pyrenees and other mountain walks on La Gomera,  in Kamchatka, and  Central Asia, I’ve felt that gut-seizing signal that twists knickers and sweats the brow.  Sometimes, it’s been caused by a too-tight pack support band and too much food.  Other times, the weak-in-the-knees reaction occurred after eating dense starchy food such as potato soup, gnocchi, pasta and energy bars.  At least once, I drank contaminated water and suffered full blown gastroenteritis. Better hope there are rehydration salts in your first aid kit.  Usually, it’s just a case of eating the wrong fuel.  So take care of yourself, rest as long as it takes, and carry on, resolving to avoid carb-loaded food that’s hard to digest while the rest of the body is working hard.

Connections between intense exercise for extended periods of time and gastrointestinal symptoms are well known.  Marathoners and IronMan competitors do collapse or vomit at the finish line — we’ve seen the photos.   However, research also indicates that upset stomachs and symptoms in the lower GI tract may occur even with lower intensity exercise such as long-distance walking.

Eating and drinking  before, during and after sustained exercise, should be planned  carefully by the person doing the physical activity or a sports nutrition expert.  Those involved in competitive events know their body’s response after months of training.

All outdoors trekkers and travelers need to factor circadian rhythms and whether jet-lag fatigue still applies while setting off on a long-distance trek.  Altitude adds yet another stress variable.  Shifting weather — rain, wind, sleet, intense hot or cold temperatures — always affects people exercising outdoors. Planning for long distance walks involves lots of complicated details.

High intensity competitors aren’t the only ones who suffer GI issues  related to exercise.  Even moderate exercisers embarking on a long distance walk or multi-day trek or hundred mile cycling trip may experience upset stomach response.  It may be caused by undigested food as the body is busy supplying blood to toiling muscles.  It may arise from ingesting too much water or not enough. Could be caused by insufficient glucose when muscles are starving for simple sugars rather than complex carbs that the body has to work to break down into fuel.

Some people simply react adversely to certain foods during sustained exercise.  For example, if you don’t usually consume  dense high-carb “fitness” snacks, energy boosting drinks and electrolyte replacement beverages, perhaps there will be an unwelcome physical reaction.

Know your body and don’t inflict sustenance surprises when your body is working hard. If you plan to use energy boosting beverages and snacks, try them out gradually in small amounts, depending on your body size and type.  Plan ahead to have fast-delivery glucose nutrients that your gut can process rapidly.

No correlation of symptoms were linked to a subject’s gender, physical fitness, age
or walking speed.

References:

Brouns, F. (1991) Etiology of gastrointestinal disturbances during endurance events. Scandinavian Journal of Medicine & Science in Sports, 1: 66–77. doi: 10.1111/j.1600-0838.1991.tb00274.x .  Wiley Online Library http://onlinelibrary.wiley.com/doi/10.1111/j.1600-0838.1991.tb00274.x/abstract

Peters, Harry P.F.,  et al. (1999) Gastrointestinal symptoms during long-distance walking. Medicine and Science in Sports and Exercise, June 1999 v31 i6 p. 767(7).

Shi, Xiaocai, et al. (2004) Gastrointestinal discomfort during intermittent high-intensity exercise: effect of carbohydrate-electrolyte beverage. Int J Sport Nutr Exerc Metab, 14.6 : 673-83.

Ironman Nutrition: Pro Secrets. Triader.com

Is Vomiting a good sign after a race or hard effort? The Running Institute, San Diego.