Serum thyroid hormone concentrations across years of blood sampling among 498 Australian athletes including 183 females and 315 males. Serum TSH (left panel), T4 (upper middle panel), T3 (lower middle panel) and T3 to T4 ratio (right panel). Horizontal dashed lines represent the empirical reference range for that analyte. P values are shown from nondirectional 1-way analysis of variance and for downward linear trend by linear contrast.