Compared to total serum testosterone, calculated free testosterone has a stronger association with lean mass, muscle strength, power, and physical function in older men.

BACKGROUND

Low serum testosterone concentrations have been associated with low muscle mass and strength in older men. However, the existing literature is inconclusive.

AIM

To investigate the differences in the relationship between total and calculated free serum testosterone and muscle status, in young vs. old men.

METHODS

Body mass index (BMI), fat percentage, appendicular lean mass (ALM), percentage ALM (ALM%), skeletal muscle index (SMI), handgrip strength (HGS), leg extension power (LEP) and 30-s sit-to-stand performance (30-s STS) were measured in 557 healthy Danish men (326 younger (≤ 65 years) and 231 older (> 65 years)) aged 23-92 years. Total serum testosterone, sex hormone binding globulin and albumin were measured (ELISA) and subsequently, calculated free testosterone and free testosterone index (FTI) were computed. A general linear model examined the relationship between testosterone and individual muscle parameters, with age group-interaction, while a pooled effect model examined the relationship between testosterone and a compound of all muscle parameters, adjusted for age, BMI and fat percentage.

RESULTS

Total testosterone was negatively associated with 30-s STS in younger men, and positively associated with LEP in older men. Calculated free testosterone was positively associated with LEP in younger and older men, as well as SMI, ALM%, HGS and 30-s STS in older men. Calculated Free testosterone and FTI, but not total testosterone, were positively associated with the muscle compound in older men.

CONCLUSION

The present data indicates that calculated free testosterone, compared to total testosterone, is more closely linked to muscle status and physical performance in older men.