title: Diurnal variations of plasma homocysteine, total antioxidant status, and biological markers of muscle injury during repeated sprint: effect on performance and muscle fatigue--a pilot study.
abstract: The aim of this study was (i) to evaluate whether homocysteine (Hcy), total antioxidant status (TAS), and biological markers of muscle injury would be affected by time of day (TOD) in football players and (ii) to establish a relationship between diurnal variation of these biomarkers and the daytime rhythm of power and muscle fatigue during repeated sprint ability (RSA) exercise. In counterbalanced order, 12 football (soccer) players performed an RSA test (5 x[6 s of maximal cycling sprint + 24 s of rest]) on two different occasions: 07:00-08:30 h and 17:00-18:30 h. Fasting blood samples were collected from a forearm vein before and 3-5 min after each RSA test. Core temperature, rating of perceived exertion, and performances (i.e., Sprint 1, Sprint 2, and power decrease) during the RSA test were significantly higher at 17:00 than 07:00 h (p < .001, p < .05, and p < .05, respectively). The results also showed significant diurnal variation of resting Hcy levels and all biological markers of muscle injury with acrophases (peak times) observed at 17:00 h. These fluctuations persisted after the RSA test. However, biomarkers of antioxidant status' resting levels (i.e., total antioxidant status, uric acid, and total bilirubin) were higher in the morning. This TOD effect was suppressed after exercise for TAS and uric acid. In conclusion, the present study confirms diurnal variation of Hcy, selected biological markers of cellular damage, and antioxidant status in young football players. Also, the higher performances and muscle fatigue showed in the evening during RSA exercise might be due to higher levels of biological markers of muscle injury and lower antioxidant status at this TOD.
authors.affiliation: Research Laboratory, Sport Performance Optimization, National Centre of Medicine and Science in Sport, Tunis, Tunisia.
authors.forename: Omar
authors.initials: O
authors.lastname: Hammouda
authors.forename: Hamdi
authors.initials: H
authors.lastname: Chtourou
authors.forename: Henda
authors.initials: H
authors.lastname: Chahed
authors.forename: Salyma
authors.initials: S
authors.lastname: Ferchichi
authors.forename: Choumous
authors.initials: C
authors.lastname: Kallel
authors.forename: Abdelhedi
authors.initials: A
authors.lastname: Miled
authors.forename: Karim
authors.initials: K
authors.lastname: Chamari
authors.forename: Nizar
authors.initials: N
authors.lastname: Souissi
mesh_terms: D000293:Adolescent; D000975:Antioxidants / Q000378:metabolism*; D015415:Biomarkers; D002940:Circadian Rhythm / Q000502:physiology*; D005080:Exercise Test; D006710:Homocysteine / Q000502:physiology*; D006801:Humans; D008297:Male; D018763:Muscle Fatigue / Q000502:physiology*; D018482:Muscle, Skeletal / Q000293:injuries* / Q000378:metabolism
chemical_list: D000975:Antioxidants; D015415:Biomarkers; D006710:Homocysteine