Association Between Euthyroidism and Muscular Parameters in Adults with an Excess of Fat Mass: A Preliminary Study

Thyroid hormones (THs) are correlated with body composition regardless of the presence of thyroid dysfunctions, whereas little is known regarding THs' influence on muscular fitness components. This cross-sectional study investigated whether THs may affect muscular parameters in adults who are overweight and affected obesity.

One hundred and five volunteers (65 females and 40 males, BMI: 33.5 (8.0) kg/m²) in an euthyroid state were enrolled. Body composition was evaluated using bioelectrical impedance analysis. Muscular parameters of interest were grip strength-evaluated using the handgrip test (HG) and muscular performance -evaluated using the 10-repetition chair-stand test (CST). Free-triiodothyronine (FT3), free-thyroxine (FT4) and their ratio (FT3/FT4) were evaluated to assess thyroid function.

In the female group, the Pearson linear regression analysis revealed a positive correlation between FT3 and HG (R = 0.261, p = 0.036) and a negative correlation between FT3/FT4 and CST (R= -0.266, p= 0.032). In the male group, a positive correlation between FT3 and skeletal muscle mass was found (R = 0.354, p = 0.025). No correlations were found between THs of interest and adiposity indexes (BMI, fat mass) in either group (p > 0.05).

FT3 and FT3/FT4 ratio levels in euthyroidism may influence muscular parameters differently in females and males affected by an excess of fat mass. More research is needed to understand the mechanisms behind this correlation and whether THs could be a potential biomarker for muscle-related parameters.