ORIGINAL RESEARCH Factors Associated With a Self-Reported History of Exercise-Associated Muscle Cramps in Ironman Triathletes: A Case–Control Study Gavin Shang, MBBCh, MPhil,* Malcolm Collins, PhD,*†‡ and Martin P. Schwellnus, MBBCh, MSc(Med), MD*‡ Objective: Exercise-associated muscle cramping (EAMC) is a common medical condition in endurance athletes. The exact cause of and risk factors for EAMC are still being investigated. The main objective of this study was to investigate factors that are associated with a self-reported history of EAMC in Ironman triathletes. Design: Case–control study. Setting: Field study at an international Ironman Triathlon. Participants: Triathletes participating in an Ironman Triathlon were recruited as subjects. Assessment of Risk Factors: A previously validated prerace questionnaire was completed by 433 subjects who were divided into subjects who reported a history of EAMC (EAMC group = 216) and those who no reported history of EAMC (CON group = 217). Main Outcome Measures: Training, anthropometric, injury and performance, and other variables that were related to the history of EAMC. Results: Compared with the CON group, triathletes in the EAMC group were significantly taller and heavier, had faster Ironman race times despite being of similar caliber (past personal best times), and predicted and achieved a faster overall time during the Ironman Triathlon. There was an association among a positive family history for EAMC, a history of tendon and/or ligament injuries, and a self- reported history of EAMC. Conclusions: There is evidence from this study that a history of EAMC is associated with (1) exercising at a higher intensity during a race that may result in premature muscle fatigue, (2) an inherited risk (positive family history), and (3) a history of tendon and/or ligament injury. Key Words: exercise-associated muscle cramping, risk factors, muscular fatigue, altered neuromuscular control, Ironman Triathlon (Clin J Sport Med 2011;21:204–210) INTRODUCTION The Ironman Triathlon consists of a 3.8 km swim, a 180 km cycle, and a 42.2 km run. Medical conditions commonly occur during training or competition in the Ironman Triathlon. 1 One of the most common medical conditions that Ironman triathletes suffer from is ‘‘exercise-associated muscle cramps’’ (EAMC), 1,2 which can be defined as ‘‘painful, spasmodic, involuntary contraction of skeletal muscle that occurs during or immediately after exercise.’’ 3 Clinically, EAMC presents as painful spasmodic muscle cramps, localized to exercising muscle groups. 4 Intrinsic and extrinsic risk factors associated with EAMC have been the topic of scientific debate over the years, and these have recently been reviewed. 4,5 Traditional risk factors for the development of EAMC are a combination of extreme environmental heat and humidity, dehydration and electrolyte disturbances, in particular sodium depletion. It is still assumed that dehydration and sodium depletion are the main etiological factors in the development of EAMC, 5–9 despite the fact that evidence for these risk factors is weak. 10 The ‘‘altered neuromuscular control’’ hypothesis is an alternative hypothesis for the development of EAMC 3,4,10–12 and is based on evidence from clinical observations and experimental studies (animal and human), which suggest that the development of muscular fatigue, and other factors, can lead to abnormal neuromuscular control in the skeletal muscle. 10 It is, however, clear that further research is required to determine the risk factors for EAMC in athletes. One model to Submitted for publication August 17, 2010; accepted December 15, 2010. From the *UCT/MRC Research Unit for Exercise Science and Sports Medicine, Department of Human Biology, Faculty of Health Sciences, University of Cape Town, Cape Town, South Africa; †South African Medical Research Council, Parow, Cape Town, South Africa; and ‡International Olympic Committee Research Centre, Clinical Sport and Exercise Medicine Research Group, Department of Human Biology, Faculty of Health Sciences, Universityof Cape Town, Cape Town, South Africa. Funding for this study was provided in part by funds from the Discovery Health, the South African Medical Research Council and the University of Cape Town Staff Research Fund, and the International Olympic Committee Research grant to the Clinical Sports Medicine Group of the UCT/MRC Research Unit for Exercise Science and Sports Medicine of the University of Cape Town. The authors report no conflict of interest. Corresponding Author: Martin P. Schwellnus, MBBCh, MSc(Med), MD, UCT/MRC Research Unit for Exercise Science and Sports Medicine, Department of Human Biology, Faculty of Health Sciences, University of Cape Town, South Africa, 3rd Floor, Sports Science Institute of South Africa, Boundary Rd, Newlands, Cape Town 7700, South Africa (martin. schwellnus@uct.ac.za). Copyright Ó 2011 by Lippincott Williams & Wilkins 204 | www.cjsportmed.com Clin J Sport Med  Volume 21, Number 3, May 2011