An attempt to assess the effect of oral creatine monohydrate supplementation on prolonged high-intensity intermittent exercise that simulates team sport play

Two studies were conducted to examine the effect of oral creatine monohydrate supplementation on prolonged high-intensity intermittent exercise that simulated team sport play. Study 1 aimed at developing and validating a team sport play simulation. An activity profile representative of team sport play was developed. The activity profile was based on a number of time and motion studies of various sports including soccer, rugby union, basketball and Australian rules football. The activity profile was based around a 15 min protocol comprised of standing still, walking, jogging, running, fast running and sprinting. Each movement category speed was based on a percentage of the participant's peak sprinting speed. There were 94 changes in speed with a mean change in speed every 9.6 s during the 15 min activity profile. These changes in speed included three 3 s sprints and three 6 s sprints throughout the 15 min activity profile. The 15 min activity profile was repeated three times (45 min), followed by a 15 min break, followed by another three 15 min periods (45 min) for a total work duration of 90 min. The team sport play simulation was conducted on a non-motorised treadmill to allow participants to sprint more effectively than on a motorized treadmill and also allow changes in sprint speed to be measured. A Woodway non-motorised treadmill was instrumented to allow the measurement of force, power, speed and distance. Measures of oxygen uptake, heart rate, blood lactate and RPE were also collected. Five participants covered a mean distance of 10196 ± 403 m over the 90 min protocol, which is within the values typically observed during team sport play (Reilly, 1994). Heart rate and oxygen uptake throughout the protocol averaged 170 b·min⁻¹and 74% Vo₂max respectively, which compare favourably to actual match-play (Bangsbo, 1994). Blood lactate concentration averaged 8.7 mmol·L⁻¹over the course of the simulation, which is somewhat higher than previously reported during actual match play (Reilly and Doran, 2001). Peak sprint speed declined significantly from 24.9 ± 0.9 km·h⁻¹in the first half to 23.6 ± 0.7 km·h⁻¹in the second half. While no previous studies have reported the changes in peak sprint speed during team sport play, Bangsbo (1994) reported that mean 20 m sprint speed declined by 2.3% in soccer players following a match. The team sport play simulation was found to have acceptable reliability (coefficient of variation) for the total distance covered (2.2%) and peak sprint speed (4.1% and 3.5% for the 3 s and 6 s sprints, respectively). However, peak sprint power was found to be an unreliable measure with a coefficient of variation of 8.8% for the 3 s sprints and 10.2% for the 6 s sprints. The results of Study 1 strongly suggest that the treadmill protocol effectively recreated the movement patterns and physiological responses to team sport play and therefore demonstrated both logical and criterion validity. Study 2 extended the validated treadmill protocol to the examination of the effect of oral creatine monohydrate supplementation for team sport play. Twelve participants completed the protocol following either five days of oral creatine monohydrate supplementation or placebo supplementation. Participants allocated to the creatine group were required to supplement their normal diet with creatine monohydrate (Creatine Plus, Sport-Test, Australia) at a rate of 20 g·day⁻¹. Participants were required to consume 5 g of creatine monohydrate plus 1 g of glucose four times per day. Muscle biopsies were performed prior to and following each simulation. Muscle samples were analysed for glycogen, phosphocreatine, ATP, free creatine, total adenine nucleotides and lactate. There were no significant differences between the creatine and placebo groups for the performance measures of total distance covered, mean peak sprint speed or sprint distance. There were also no significant differences between the groups for any of the physiological measures including heart rate, oxygen uptake, plasma lactate, RPE, body mass and plasma uric acid. While the results suggest that creatine-loading does not enhance team sport play performance, there was no significant difference in total muscle creatine concentration between the treatment and placebo groups prior to the team sport play simulation. There were a number of limitations in the design of the present study, such as the lack of a presupplementation muscle biopsy and a small sample size that have reduced the value of the present study. Consequently, no conclusions regarding the efficacy of creatine supplementation for team sport players can be drawn from the current study. Further detailed experiments are required before the practice of oral creatine monohydrate supplementation can be recommended for team sport players.