Cramps caused by effort, not dehydration and electrolyte shortage
Eight articles on PainSci cite Schwellnus 2011: 1. The Complete Guide to Trigger Points & Myofascial Pain 2. The Complete Guide to Muscle Strains 3. Water Fever and the Fear of Chronic Dehydration 4. A Deep Dive into Delayed-Onset Muscle Soreness 5. Does Epsom Salt Work? 6. Heat for Pain and Rehab 7. Vitamins, Minerals & Supplements for Pain & Healing 8. Cramps, Spasms, Tremors & Twitches
PainSci notes on Schwellnus 2011:
Blood samples from 210 Ironman triathletes were checked for electrolytes and other signs of hydration status. 43 had suffered cramps. There were no significant differences between the crampers and the non-crampers in any of the pre-testing or post-testing. Dehydration and electrolyte shortage don’t cause cramps — intense effort does. “The results from this study add to the evidence that dehydration and altered serum electrolyte balance are not causes for exercise-associated muscle cramps.” This is a nice myth-mangler of a paper.
original abstract †Abstracts here may not perfectly match originals, for a variety of technical and practical reasons. Some abstacts are truncated for my purposes here, if they are particularly long-winded and unhelpful. I occasionally add clarifying notes. And I make some minor corrections.
BACKGROUND: Despite the high prevalence of exercise-associated muscle cramping (EAMC) in endurance athletes, the aetiology and risk factors for this condition are not fully understood.
AIM: The aim of this prospective cohort study was to identify risk factors associated with EAMC in endurance triathletes.
METHODS: 210 triathletes competing in an Ironman triathlon were recruited. Prior to the race, subjects completed a detailed validated questionnaire and blood samples were taken for serum electrolytes. Immediately before the race, pre-race body weight was obtained. Body weight and blood samples for serum electrolyte concentrations were obtained immediately after the race. Clinical data on EAMC experienced during or immediately after the race were also collected.
RESULTS: 43 triathletes reported EAMC (cramping group) and were compared with the 166 who did not report EAMC (non-cramping group). There were no significant differences between groups in any pre-race-post-race serum electrolyte concentrations and body weight changes. The development of EAMC was associated with faster predicted race times and faster actual race times, despite similarly matched preparation and performance histories in subjects from both groups. A regression analysis identified faster overall race time (and cycling time) and a history of cramping (in the last 10 races) as the only two independent risk factors for EAMC.
CONCLUSION: The results from this study add to the evidence that dehydration and altered serum electrolyte balance are not causes for EAMC. Rather, endurance runners competing at a fast pace, which suggests that they exercise at a high intensity, are at risk for EAMC.
- “Magnesium for skeletal muscle cramps,” Garrison et al, Cochrane Database of Systematic Reviews, 2020.
- “Origin and Development of Muscle Cramps,” Minetto et al, Exercise & Sport Sciences Reviews, 2013.
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