This study investigated the effects of resistance training (RT) on the metabolism of testosterone (T) in younger (n = 5, 28 +/- 3 yrs.) and older (n = 8,70 +/- 2 yrs.) men. Experimental heavy resistance exercises (5 x 10RM leg presses) were performed before and after a 12-month of RT. No age differences were found in the production or metabolic clearance rate of T (determined by stable isotope dilution method), skeletal muscle androgen receptor content or serum LH concentrations clue to acute or chronic RT. The T production capacity response to gonadotropin stimulation and the concentrations of the urinary T metabolites (androsterone and etiocholanolone) were lower in the older compared to younger men (p < 0.05-0.01). This study further showed that RT may have acute effect on T production and clearance rates, while the exercise-induced increases in serum T appeared to be induced by decreased metabolic clearance rate of T. Attenuated T production capacity and urinary excretion of T metabolites in older men may reflect the known reduction in testicular steroidogenesis upon aging. No changes were observed in T metabolism clue to RI indicating a homeostatic stability for this hormone in men of different ages. (C) 2015 Elsevier Inc. All rights reserved.