Reference values for the creatine kinase response to professional Australian football match-play.

OBJECTIVES: Due to the importance of monitoring markers of muscle damage in high-level sport from a medical and athlete recovery perspective, this study aimed to determine the upper limits of normal (ULN) for post-match plasma creatine kinase (CK) in professional Australian footballers. Raw CK values were considered, along with intra-individual deviations from the season-mean. DESIGN: Case series. METHODS: CK was collected between 36-48h following professional Australian football match-play. A total of 1565 samples from 62 players were assessed over three consecutive seasons. The ULN were determined for raw scores and as a percentage of each player's season-mean response. RESULTS: The ULN for raw CK, as determined by the 97.5th, 95th and 90th percentiles were 1715 (90%CI: 1605-1890), 1380 (90%CI: 1325-1475) and 1110 (90%CI: 1050-1170) UL-1 respectively. The ULN intra-individual response (97.5th percentile) was defined as a player's score being greater than 94% (90%CI: 84-102%) above their season-mean. CONCLUSIONS: Professional Australian football elicits a profound effect on the CK response. The values provide a reference tool for athletes competing at this level of competition. The novel method of representing the CK response as a percentage difference from an individuals' season-mean enables a superior comparative ability between CK responses and reduces the high CK responder bias that occurs when using raw scores alone. The data will assist medical and conditioning staff in excluding medical emergencies and also aid in individualising the prescription of training loads and recovery to optimise athlete performance and minimise further muscle damage.

Central activation, metabolites, and calcium handling during fatigue with repeated maximal isometric contractions in human muscle.

PURPOSE: To determine the roles of calcium (Ca2+) handling by sarcoplasmic reticulum (SR) and central activation impairment (i.e., central fatigue) during fatigue with repeated maximal voluntary isometric contractions (MVC) in human muscles. METHODS: Contractile performance was assessed during 3 min of repeated MVCs (7-s contraction, 3-s rest, n = 17). In ten participants, in vitro SR Ca2+-handling, metabolites, and fibre-type composition were quantified in biopsy samples from quadriceps muscle, along with plasma venous [K+]. In 11 participants, central fatigue was compared using tetanic stimulation superimposed on MVC in quadriceps and adductor pollicis muscles. RESULTS: The decline of peak MVC force with fatigue was similar for both muscles. Fatigue resistance correlated directly with % type I fibre area in quadriceps (r = 0.77, P = 0.009). The maximal rate of ryanodine-induced Ca2+-release and Ca2+-uptake fell by 31 ± 26 and 28 ± 13%, respectively. The tetanic force depression was correlated with the combined reduction of ATP and PCr, and increase of lactate (r = 0.77, P = 0.009). Plasma venous [K+] increased from 4.0 ± 0.3 to 5.4 ± 0.8 mM over 1-3-min exercise. Central fatigue occurred during the early contractions in the quadriceps in 7 out of 17 participants (central activation ratio fell from 0.98 ± 0.05 to 0.86 ± 0.11 at 1 min), but dwindled at exercise cessation. Central fatigue was seldom apparent in adductor pollicis. CONCLUSIONS: Fatigue with repeated MVC in human limb muscles mainly involves peripheral aspects which include impaired SR Ca2+-handling and we speculate that anaerobic metabolite changes are involved. A faster early force loss in quadriceps muscle with some participants is attributed to central fatigue.