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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
  1. Martin P Schwellnus1,2,
  2. Siddieq Allie1,
  3. Wayne Derman1,2,
  4. Malcolm Collins1,2,3
  1. 1UCT/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
  2. 2International Olympic Committee (IOC) Research Centre, Cape Town, South Africa
  3. 3South African Medical Research Council, Cape Town, South Africa
  1. Correspondence to Dr Martin P Schwellnus, Research Unit for Exercise Science and Sports Medicine, Department of Human Biology, Faculty of Health Sciences, University of Cape Town, 3rd Floor, Sports Science Institute of South Africa, Boundary Road, Newlands, Cape Town 7700, South Africa; martin.schwellnus{at}


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.

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  • Funding This study was supported in part by the International Olympic Committee (IOC) 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. It was also supported in part by funds from Discovery Health, the South African Medical Research Council (MRC) and the University of Cape Town Staff Research Fund.

  • Competing interests None.

  • Ethics approval This study was conducted with the approval of the Research Ethics Committee of the Faculty of Health Sciences, University of Cape Town.

  • Provenance and peer review Not commissioned; externally peer reviewed.