Urinary Creatine at Rest and After Repeated Sprints in Athletes: A Pilot Study

Abstract

Creatine plays a key role in muscle function and its evaluation is important in athletes. In this study, urinary creatine concentration was measured in order to highlight its possible significance in monitoring sprinters. The study included 51 sprinters and 25 age- and sex-matched untrained subjects as a control group. Body composition was measured and dietary intake estimated. Urine samples were collected before and after standardized physical exercise. Creatine was assessed by gas chromatography mass spectrometry. Basal urinary creatine (UC) was significantly lower in sprinters than controls (34±30 vs. 74±3 µmol/mmol creatinine, p < 0.05). UC was inversely correlated with body mass (r = −0.34, p < 0.01) and lean mass (r = −0.30, p < 0.05), and positively correlated with fat mass (r = 0.32, p < 0.05). After acute exercise, urinary creatine significantly decreased in both athletes and controls. UC is low in sprinters at rest and further decreases after exercise, most likely due to a high uptake and use of creatine by muscles, as muscle mass and physical activity are supposed to be greater in athletes than untrained subjects. Further studies are needed to test the value of urinary creatine as a non-invasive marker of physical condition and as a parameter for managing Cr supplementation in athletes.

Effect of between-set recovery durations on repeated sprint ability in young soccer players

“…This result suggests that the decline in RSS performance with reduced recovery periods was not attributable to blood lactate concentrations. In this context, many investigators considered that blood lactate is a poor indicator of fatigue in repeated sprint tests, and other metabolic factors such as Pi, pH and PCr have been suggested to play an important role in fatigue during this type of exercise [ 14 , 34 , 35 ]. Given that full regeneration of PCr stores to resting value took more than 3 minutes to achieve during repeated high-intensity exercise [ 17 ], it seems that the recovery duration between sets considerably affects RSS performance especially at the second set when the rest duration is less than 120 s. Nevertheless, the PCr alone cannot explain differences between protocols in SST and TAF, because it has been recently suggested that Pi with its inhibitory effect on release of calcium ions from sarcoplasmic reticulum could also be considered as a major factor of fatigue during repeated sprint exercises [ 36 ].…”

Development of in‐house materials for the verification of specific gravity measurements: Homogeneity, stability, and proficiency studies

“…Urine specific gravity (USG) is a dimensionless ratio and is defined as the density of urine relative to the density of distilled water, at the same temperature and pressure . This value is the most widely used and the most commonly accepted measurement of renal function in clinical medicine . USG has been extensively used as an alternative renal dilution factor to creatinine in toxicological applications, as well as in the field of doping control .…”

“…9,10 This value is the most widely used and the most commonly accepted measurement of renal function in clinical medicine. 11,12 USG has been extensively used as an alternative renal dilution factor to creatinine in toxicological applications, as well as in the field of doping control. 13 Indeed, in doping laboratories, this value is used to adjust concentrations of endogenous and exogenous substances in urine samples, [14][15][16][17][18][19][20] and critically, this value is mandatory by the World Anti-Doping Agency (WADA) in its accredited laboratories.…”