Fig. 1

Summary of trials which have independently modified T levels within the physiological range, or utilised exercise training interventions, or combined these interventions. Where a positive impact is indicated for T or exercise, there is typically evidence that the benefits are dependent on dose, and in the case of T, also on route of administration (favouring intramuscular injection). Some evidence suggests that additive effects for lean body mass may be more apparent in younger men, but that gains in strength may be less age-dependent, possibly due to neural benefits. Interpretation of this disparate literature should be compared to the results of an RCT comparing exercise and T effects, summarised in Fig. 2