II. Historical overview
Time-motion analysis has permitted the quantification of external demands in field-based sport, which have in turn been characterised as acylical and intermittent in nature (1). Specifically, repeated sprints in team sport have been shown to last anywhere between 3-6s interspersed by < 21 seconds (1). Additionally, one of the earlier studies investigating metabolic demands on a cycle ergometer reported phosphocreatine (PCr) decrement as a function of repeated sprints (2). Misinterpretation of blood lactate findings within this repeated sprint protocol may have inadvertently influenced the misconception of its apparent contribution to fatigue, since an inverse relationship was found between power output decrement and blood lactate increase. A more plausible explanation of fatigue mechanisms has since been presented; the inhibiting effects of metabolic by-products (e.g. hydrogen irons, inorganic phosphate) have been shown to allosterically inhibit the configuration of rate limiting enzymes such as phosphofructokinase, a catalyst in glycolytic energy production (3). More recently, impairments in oxidative energy supply (central), excitation-contraction coupling and metabolic by-product accumulation (peripheral) have been cited as factors contributing to fatigue during repeated high-intensity efforts that characterise team sport (4).
In an effort to improve ecological validity, subsequent research turned its attention to field-based sport. Quantification of energy demands in soccer players during match play corresponded to ~70% of maximal oxygen uptake (VO2max), with aerobic metabolism accounting for >90% of total energy expenditure (5). Later, seminal work in Danish soccer players utilised muscle biopsies and blood samples in and around soccer match play, enhancing our understanding on the aetiology of peripheral fatigue in intermittent field-based sport (6). Specifically, limitations of using blood lactate as a surrogate for muscle lactate and thereby inferring anaerobic energy contribution were highlighted. Additional findings elucidated the stress invoked on the glycolytic (non-oxidative) pathways, in particular depletion of PCr and the liberation of hydrogen ions following intense efforts, consequently facilitating decreases in muscle pH. Taking into account the delay between cessation of exercise and biopsy sampling (~30s), it would be prudent to interpret these measures as an underrepresentation of perturbations in intracellular acidosis immediately following intense exercise. This further accentuates appreciation for the stress invoked upon non-oxidative pathways at the peripheral level during repeated sprints, such as those encountered in team sport.
Anaerobic glycolysis during initial sprint has been shown to contribute up to 40% of total energy supply (2). However, greater glycolytic contribution during initial sprint has also been correlated with greater performance decrement (7). In contrast, it can also be argued that greater glycolytic energy supply has the potential to increase initial sprint performance, with initial sprint performance in turn being correlated with repeated sprint performance (7). In support of a centrally (cardiovascular) limited hypothesis, ATP supply from aerobic metabolism has been shown to progressively increase to as much as 40% of total energy supply as sprints are repeated (8). Moreover, a relationship between relative V̇O2max and repeated sprint performance (9) as well as faster oxygen uptake kinetics and performance decrement during a repeated sprint test (10) have been found. Given the importance of the aforementioned aerobic and anaerobic contributions underpinning repeated high-intensity efforts, the attention of the reader is now directed towards more recent studies on training methods.
Aerobic interval training methods have been defined as intensities near or up to V̇O2max with durations ranging anywhere from 1-7 mins (11). Differentiation in adaptations were observed between recreationally-trained and well-trained subjects, with the former demonstrating increases in PCr resynthesis and glycolytic rates alongside typical V̇O2max increases, suggesting carry over in adaptation to non-oxidative pathways. Notably, in well-trained subjects, increases in buffering capacity and aerobic performance (tlim) were also observed. However, others have brought into question that the absence of supramaximal intensities is insufficient to tax non-oxidative pathways and promote longitudinal adaptations that will adequately prepare team sport players for the demands of competition (12). The same group argued to the contrary - a repeat sprint protocol used in this study was superior to an aerobic high-intensity interval training (HIT) protocol at addressing the demands of competition (Yo-Yo IR1) and inducing aerobic adaptations (relative V̇O2max). Since these approaches sit at either end of the extensive-intensive HIT continuum, it would be prudent to analyse supramaximal interventions that don’t quite involve maximal intensities of repeated sprints. The neuromuscular load of such sessions would arguably be less and time spent at intensities >90% V̇O2max (red zone) would maximally stress the oxygen transport and utilisation systems whilst minimising the interference phenomenon across technical and tactical training (13).
In summary, this synopsis can be taken to suggest that the aerobic-alactic nature of team sport necessitates a highly developed aerobic system, which in turn underpins the ability of the athlete to repeat and sustain high intensity efforts as well as recover effectively between bouts.
(1) Spencer, M., Bishop, D., Dawson, B., & Goodman, C. (2005). Physiological and metabolic responses of repeated-sprint activities: Specific to field-based team sports. Sports Medicine, 35, 1025-1044.
(2) Gaitanos, G. C., Williams, C., Boobis, L. H., & Brooks, S. (1993). Human muscle metabolism during intermittent maximal exercise. Journal of Applied Physiology, 75, 712-719.
(3) Ross, A., & Leveritt, M. (2001). Long-term metabolic and skeletal muscle adaptations to short-sprint training: Implications for sprint training and tapering. Sports Medicine, 31, 1063-1082.
(4) Girard, O., Mendez-Villaneuva, A., & Bishop, D. (2011). Repeated-sprint ability – Part I: Factors contributing to fatigue. Sports Medicine, 41, 673-694.
(5) Bangsbo, J. (1994). Energy demands in competitive soccer. Journal of Sports Sciences, 12, 5-12.
(6) Krustrup, P., Mohr, M., Steensberg, A., Bencke, J., Kjaer, M., & Bangsbo, J. (2006). Muscle and blood metabolites during a soccer game: Implications for sprint performance. Medicine and Science in Sports and Exercise, 38, 1165-1174.
(7) Mendez-Villaneuva, A., Hamer, P., & Bishop, D. (2008). Fatigue in repeated-sprint exercise is related to muscle power factors and reduced neuromuscular activity. European Journal of Applied Physiology, 103, 411-419.
(8) Bogdanis, G. C., Nevill, M. E., Boobis, L. H., & Lakomy, H. K. (1996). Contribution of phosphocreatine and aerobic metabolism to energy supply during repeated sprint exercise. Journal of Applied Physiology, 80, 876-884.
(9) Jones, R. M., Cook, C. C., Kilduff, L. P., Milanović, Z., James, N., Sporiš, G., Fiorentini, B., Fiorentini, F., Turner, A., & Vučković, G. (2013). Relationship between repeated sprint ability and aerobic capacity in professional soccer players. The Scientific World Journal, 2013, 1-5.
(10) Dupont, G., McCall, A., Prieur, F., Millet, G. P., & Berthoin, S. (2010). Faster oxygen uptake kinetics during recovery is related to better repeated sprinting ability. European Journal of Applied Physiology, 110, 627-634.
(11) Laursen, P. B., & Jenkins, D. G. (2002). The scientific basis for high-intensity interval training: optimising training programmes and maximising performance in highly trained endurance athletes. Sports Medicine, 32, 53-73.
(12) Ferrari Bravo, D., Impellizzeri, F. M., Rampinini, E., Castagna, C., Bishop, D., & Wisloff, U. (2008). Sprint vs. interval training in football. International Journal of Sports Medicine, 29, 668-674.
(13) Buchheit, M., & Laursen, P. B. (2013). High-Intensity interval training, solutions to the programming puzzle. Part I: Cardiopulmonary emphasis. Sports Medicine, 43, 313-338.