Is it possible to train so hard that you become nauseous? Experience and observation indicate a definite yes. Certain factors, however, may predispose you to exercise-induced nausea. Some research even shows that exercise-induced higher levels of growth hormone are associated with the onset of nausea in some people. Common gastrointestinal symptoms experienced during exercise include heartburn, abdominal cramps, a strong urge to defecate (hopefully, not during an exercise), diarrhea and nausea.
Studies show that 60 percent of marathon runners have such symptoms. Among triathletes, the gastrointestinal distress usually occurs during the running phase rather than the swimming or cycling phases of the race. Duration and intensity of exercise are thought to play a role in exercise-related nausea symptoms. Women experience gut attacks more often than men, while experienced athletes tend to get less nauseous than beginners.
One obvious cause of such problems is eating too close to a workout. I regularly observe people at Gold’s Gym, Venice, where I train, eating a full meal immediately before their workouts. I’ve often wondered about the rationale behind that. Surely those people don’t think that the meal will provide any source of immediate energy. Could they be so clueless as to not be aware that food needs to be digested and absorbed? Others say they like to eat right before training for ‘psychological reasons,’ as if having something in their gut makes them train harder. In fact, any food eaten right before training will just sit there, since blood is diverted to muscles during exercise.
A new study confirms that eating too close to training is associated with a higher level of exercise-induced nausea.1 The subjects were six men and six women, whose ages ranged from 20 to 37. Three of the men were competitive triathletes, while three of the women competed in boat racing. The subjects were studied on seven different occasions, including during high- and low-intensity exercise under three circumstances: when they didn’t eat before training, when they trained immediately after eating a beef patty and when they trained an hour after eating. They were even studied for 180 minutes after eating without engaging in exercise.
The exercise involved pedaling on a stationary bike, using both a high and low level of intensity as determined by maximal heart rate during exercise. The results showed that both high- and low-intensity exercise can induce nausea. The highest levels of nausea occurred during exercise after fasting and immediately following a meal. Higher-intensity exercise promoted a greater degree of nausea than lower-intensity exercise. The experienced athletes in the group showed the same levels of nausea as the untrained subjects.
The researchers point out that exercise-induced nausea may result from an interaction of gastrointestinal receptors and the brain, as well as nerve receptors in the joints, muscles, inner ears and eyes and postural sensors in the spine and legs. The digestion slowdown’which results from eating right before training’has a close relationship to nausea onset.
Exercise also stimulates the sympathetic nervous system, which releases such hormones as epinephrine and norepinephrine. Heightened sympathetic activity not only inhibits digestive processes (by diverting blood to muscles) but also increases gut sensitivity. The researchers say that in that sense exercise is a stressor and nausea is part of a generalized stress response. Hypoglycemia, or low blood glucose, is also a stressor and is also linked to exercise-induced nausea. Dehydration can cause nausea during training as well.
Since the study showed that the incidence of exercise-related nausea greatly decreased one hour after eating, the obvious message is to wait at least an hour after eating before commencing training and two hours or more if you eat a larger meal. IM
1 Kondo, T., et al. (2001). Exercise-induced nausea is exaggerated by eating. Appetite. 36:119-125.