Prevalence, Clinical Characteristics, and Self-Reported Treatment of Exercise-Associated Muscle Cramping Differ Between 21.1- and 56-Km Running Race Entrants—SAFER XXII

OBJECTIVE: To determine whether the lifetime prevalence and clinical characteristics of exercise-associated muscle cramping (EAMC) differ between runners entering a 21.1- versus 56-km road race. DESIGN: Cross-sectional study. SETTING: The 2012 to 2015 Two Oceans Marathon races (21.1 and 56 km), South Africa. PARTICIPANTS: Participants were consenting race entrants (21.1 km = 44 458; 56 km = 26 962) who completed an online prerace medical screening questionnaire. INDEPENDENT VARIABLE: A history of EAMC. MAIN OUTCOME MEASURES: The main outcome variables were lifetime prevalence (%) and clinical characteristics (muscle groups affected, timing of occurrence, severity, frequency of serious EAMC, and self-reported treatment) of a history of EAMC. Differences between 56- and 21.1-km race entrants were explored (relative risk [RR]). RESULTS: The lifetime prevalence of EAMC was 12.8%, which was higher in 56- (20.0%; 95% CI 19.5-20.6) versus 21.1-km race entrants (8.5%; 8.2-8.8) ( P = 0.0001). In all entrants, the fourth quarter was the most common onset (46.4%), calf muscles were the most commonly affected (53.1%), and most EAMCs were of mild-to-moderate severity (95%). In 56- versus 21.1-km entrants, hamstring (RR = 1.7; 1.5-1.9) and quadriceps muscle groups (RR = 1.5; 1.3-1.7) were more frequently affected ( P = 0.0001), the onset of EAMC during racing was less common in the first quarter (RR = 0.3; 0.2-0.4) ( P = 0.0001), and serious EAMC was more frequent (RR = 1.6; 1.4-1.9) ( P = 0.0001). CONCLUSIONS: In 56- versus 21.1-km runners, a history of EAMC is 2 times more frequent and muscle groups affected, onset in a race, and severity of EAMC differed. The lifetime prevalence was lower than previously reported in other events. Risk factors associated with EAMC may differ between entrants for different race distances.