The Overtraining Syndrome: A Meta-Analytic Review.

The overtraining (OT) syndrome has been studied extensively with little agreement as to reliable markers for detection. The purpose of this meta-analysis was to provide summary quantitative findings of markers (e.g., blood, physiological, and psychological) associated with the OT syndrome. A meta-analytic research design was utilized to investigate selected studies allowing for a coding process to record data. Thirteen studies met the inclusion/exclusion criteria. Markers included samples taken with the subjects in the normal (N) condition and during the OT. The biomarkers consisted of glutamine (um), glutamate (um), cortisol (nmo·L^-1), IL-6 (nm), testosterone (mg·dL^-1), total cholesterol (mg·dL^-1), glucose (mg·dL^-1), leptin (ng·mL^-1), hematocrit (%), hemoglobin (g·L^-1), norepinephrine (pg·mL^-1), epinephrine (pg·mL^-1), and creatine kinase (u·L^-1). Cardiovascular variables included resting heart rate (RHR, beats·min.^-1), and resting diastolic and systolic blood pressure (DBP and SBP, mmHg). Psychological measures included tension, anger, fatigue, confusion, depression, vigor, sleep, stress, and self-perceptions of physical status. Selected variables (i.e., anger, depression, etc.) were noted in terms of direction (+, -) of change in the OT state compared to the N state. To determine magnitude of difference between N and OT, the effect size calculation of M₂-M₁/SD₁ was used where M₂ is the mean of the OT sample, M₁ was the mean of the N sample and SD₁ is the standard deviation of the N sample. Combined sample size (N) was 238 subjects with the mean time in OT of 6.6 wks. The following are mean (SD) of the combined subject demographics: height (cm) 175.4 (2.4); weight (kg) 71.7 (2.6); body fat (%) 11.8 (0.9); age (yrs) 23.5 (2.03); VO₂ max (mL·kg^-1·min^-1) 55.4 (0.8). Mean (SD) biomarker changes from the N state to the OT state were glutamine -56.3 (-2); glutamate 49.7 (2); cortisol -89.7 (-12.2); IL 6 -0.52 (0.12); testosterone -88.9 (-30); cholesterol 4.6 (-1.6); glucose -13.3 (1.9); leptin 0.15 (-0.11); hematocrit -0.83 (-0.4); hemoglobin -20; norepinephrine 36 (-4.1); epinephrine -2.2 (-3.5); creatine kinase 29.2 (8.5). Effect size calculations for the above biomarkers were considered large for the following: glutamine (-4.02), glutamate (8), cortisol, (-1.4), IL 6 ( -5.2), glucose (-1.1). Mean (SD) cardiovascular changes and direction of change (+, -) were the following: RHR, -1.9 (-0.22); resting SBP, -2 (-2); resting DBP, 0 (1). Effect size calculations for the above measures were -0.95, -0.33 and 0, respectively. Three articles reported decreases in tension at OT, and one noted increases at MW. Fatigue increased at OT in 6 studies and showed n o change in a separate study. Confusion did not change in two studies, increased at OT in another, and increased at MW and, then, declined at OT in a final article. Vigor reportedly remained stable in two studies and decreased in two other studies. Anger did not change in 2 articles, decreased in another, and increased in a different study with its peak at MW. There was no change in depression in three studies, but a decrease was reported in a separate article at OT with an increase at MW. Studies reported impaired sleep patterns, increased wakefulness, and decrements and stability in sleep quality. Two studies indicated increased levels of stress with one specifying stress related to training, sleep, and health. Findings showed a decreased perception of strength, decreased perception of recovery, and no change in perception of muscle soreness. From this analysis, the noted biomarker changes and direction of change (+, -) indicates considerable immune-suppression and increased stress with athletes experiencing the OT syndrome. A negative effect size for HR and SBP indicates questionable alterations from N to OT in subjects. Increased sympathetic and/or decreased sympathetic influence may be affected in the OT state. However, low effect size calculations allow for non-determinant conclusions related to cardiovascular indicators of the OT syndrome. Lastly, athletes in the OT state are likely to experience disturbances in sleep, self-perception, and mood factors. [ABSTRACT FROM AUTHOR]