Increased running speed and pre-race muscle damage as risk factors for exercise-associated muscle cramps in a 56 km ultra-marathon: a prospective cohort study.

BACKGROUND: Despite the high prevalence of exercise-associated muscle cramping (EAMC) in endurance runners, the aetiology and risk factors for this condition are not fully understood.
PURPOSE: The purpose of this prospective cohort study was to identify risk factors associated with the development of EAMC in ultra-distance runners.
METHODS: 49 runners participating in a 56 km race completed a validated pre-race questionnaire. Pre-race muscle pain in the calves, hamstrings and quadriceps muscles was recorded (visual analogue scale) and pre-race serum creatine kinase (CK) activity was measured. 20 runners reported EAMC (EAMC group) during or within 6 h after the event, while 29 runners reported no cramping (CON group).
RESULTS: EAMC was not associated with age, body mass index, sex, recent and past personal best running times, pre-race muscle pain and pre-race training (duration and frequency). Runners in the EAMC group tended to report on average longer training sessions during the 3 days before the race (EAMC 1.2 (1.1), CON 0.6 (1.0); p=0.077). Significant risk factors for EAMC were a past history of EAMC (EAMC 100%, CON 48%; p<0.001) and a faster running time (min) for the first 28 km split time of the race (EAMC 144 (20), CON 157 (14); p=0.029) despite being matched for recent (<15 weeks before race) personal best times in the 42.2 km race. Pre-race CK activity tended to be higher in the EAMC group (EAMC 89 (80), CON 58 (35); p=0.066).
CONCLUSIONS: Novel risk factors for EAMC in distance runners are a past history of EAMC, faster running pace at the early stage of a race and possibly pre-race muscle damage.