An initial prospective exploratory investigation to identify predictors of calf cramping in rugby league players

Introduction: Exercise-Associated Muscle Cramps (EAMCs) in the calf are common in the last 10 min of a rugby league game. This period is usually when a game is won or lost, therefore it is important a player's performance is not inhibited by calf cramps. To date there are no published studies on calf cramps in team sports that fluctuate in intensity. The study's aim was to identify predictors of calf cramping in rugby league players.
Methods: Male rugby league players (n = 103; mean age 18.8 years, range 15–34) were classified as either EAMC (experienced at least one occurrence of calf cramps throughout the season) or non-EAMC (no calf cramps). The followings were considered as possible predictors of EAMC using logistic regression modelling: competition level, age, ethnicity, playing position, history of cramping, pre-cramping or low back pain, orthotic usage, foot posture and strike, muscle length and bulk, hydration, and number of games played. Players were categorised as either junior (n = 44; mean age 15.8 years, range 15–17) or senior (59; 21.1, 17–34) by the highest competition level played.
Results: Half of players, n = 52, experienced at least one incidence of calf cramping throughout the season with 21% of the EAMC group suffering four or more incidences of calf cramping. Experiencing EAMC in the previous season was found to be a strong predictor of EAMC (OR 10.85; 95% CI 2.16,54.44; p = 0.01), and playing in a senior competition level was also associated with EAMC (OR 0.21; 95% CI 0.06,0.75; p = 0.02). A novel finding was the relationship between low back pain resulting in missed field minutes and EAMC (OR 4.50, 95% CI 1.37, 14.79; p = 0.01).
Discussion: Three hypotheses are proposed for the relationship between playing in a senior competition level and EAMC: (1) senior games are 10 min longer than junior games, (2) seniors play 15 more competition rounds than juniors; and (3) senior player's mean age was six years older than junior players. For lower back pain, a hypothesis of altered neural transmission in the nerves supplying the lower limb is proposed, though potential sources of low back pain were not identified in the current study.
Conclusion: As this study suggests that there is a high incidence of calf cramping in rugby league, especially at senior competition levels it is recommended pre-season screening is undertaken in senior players to identify those at risk of calf cramping and develop possible preventative strategies.