Scand J Med Sci Sports 1997: 7: 206-213 Printed in Denmark zyxwvutsrqponm ’ AN rights reserved Copyright zyxw 0 Munksgaard 1997 Scandinavian Journal zy of zyx MEDICINE & SCIENCE IN SPORTS zyx ISSN 0905-7188 zyx Muscle phosphocreatine repletion following single and repeated short sprint efforts Dawson zyxwvutsrq B, Goodman C, Lawrence S, Preen D, Polglaze T, Fitzsimons M, Fournier zyxwvuts l? Muscle phosphocreatine repletion following single and repeated short sprint efforts. Scand J Med Sci Sports 1997: 7: 206-213. 0 Munksgaard, 1997 Phosphocreatine (PCr) repletion following either single (1 X 6 s, n= 7) or repeated (5x6 s, departing every 30 s, n=8) maximal short sprint cycling efforts was measured in separate groups of trained subjects. Muscle biop- sies (vastus lateralis) were taken pre-exercise before warming up, and then at 10 s, 30 s and 3 min post-exercise. After the 1 x 6 s sprint PCr concentration was respectively, 55% (10 s; P<0.01), 69% (30 s; P<0.01) and 90% (3 min; NS) of the pre-exercise value (meankSD) (81.127.4 mmol . kg-’ DM), whereas after the 5x6 s sprints, PCr concentration was, respectively, 27% (10 s; P<0.01), 45% (30 s; P<0.01) and 84% (3 min; P<0.01) of the pre-exercise value (77.1?4.9 mmol . kg-’ DM). PCr con- centration was correlated with muscle lactate at 30 s (Y= -0.82; P<0.05) and 3 min of recovery (Y= -0.94; P<0.01) for the 1 X6 s sprint, but not for the 5x6 s sprints. The extent of PCr repletion was significantly greater after the 5 x 6 s sprints than the 1x6 s sprint between both 10 s and 30 s and 30 s and 3 min, despite lower PCr levels at 10 s, 30 s and 3 min following the 5 x 6 s sprints. Full repletion of PCr is likely to take longer after repeated sprints than single short sprints because of a greater degree of PCr depletion, such that replenishment must commence ftom lower PCr levels rather than because of slower rates of repletion. 6. Dawson’, C. Goodman’, S. Lawrence2, D. Preen’, T. Polglaze2, M. Fitzsimons2, P. Fournier‘ ’Department of Human Movement, The University of Western Australia, Nedlands, 2Western Australian Institute of Sport, Perth Superdrome, Mt Claremont, Western Australia, Australia Key words: phosphocreatine; ATP; lactate; recovery post-exercise Dr B. Dawson, Department of Human Movement, The University of Western Australia, Nedlands WA 6907, Australia Tel.: 61-9-380 2361; fax: 61-9-380 1039 Accepted for publication 9 December 1996 Many team and individual sports require short sprint efforts to be repeated regularly over the course of a game. Hirvonen et al. (1) have highlighted the im- portance of the phosphocreatine (PCr) stores to short-term maximal exercise performance. They dem- onstrated that in a series of maximal sprints (40-100 m) skeletal muscle PCr stores are severely depleted after 5-7 s, and at this point maximal running speed starts to decline, as glycolysis must then provide the bulk of the ATP to complete the sprint. Further, it was found that better sprinters utilized more of their available PCr stores over the first 5-7 s than did sprinters of slightly lesser ability. When short sprints must be repeated before PCr resynthesis is complete (as is likely, given the unpre- dictable nature of such games), then glycolytic energy supply becomes increasingly important (2). Indeed, studies of repeated short sprint ( 5 6 s) exercise proto- cols have regularly reported blood lactate levels of 12 mmol- 1-I or more (3-5). These levels are very similar to those commonly associated with sustained sprint efforts of 30 s or more. Consequently, repeated short 206 sprint efforts will also result in the accumulation of H+ ions and a fall in muscle pH. Both Spriet et al. (6) and Tesch et al. (7) have suggested that these cellular changes are likely to inhibit the rate of PCr resyn- thesis post-exercise, since the initial fast phase of PCr resynthesis is an oxygen-dependent process, while the subsequent slow phase may be limited by intramus- ‘cular pH changes (8). These observations suggest that PCr repletion following repeated short sprints is likely to be slower than after a single short sprint ef- fort. To the best of the authors’ knowledge, there are no research reports that have studied PCr replenish- ment following either single or repeated maximal short-term (<lo s) sprint exercise. The first paper to investigate PCr replenishment post-exercise was that of Hultman et al. (9). In a series of experiments where continuous, aerobic workloads lasting several minutes (i.e. not sprint ef- forts) were used, it was concluded that ‘the resyn- thesis of PCr after work is complete within a few min- utes’. DiPrampero & Margaria (10) later calculated a half-time of 3040s for PCr resynthesis based on the