Growth factors can be isolated from bovine milk to form a whey growth factor extract (WGFE). This study examined whether WGFE promoted activation of the AKT/mTOR pathway enabling increased lean tissue mass and strength in resistance trained men. Forty six men with >6 months of resistance training (RT) experience performed 12 weeks of RT. Participants consumed 20 g/day of whey protein and were randomised to receive either 1.6 g WGFE/day (WGFE; n = 22) or 1.6 g cellulose/day (control, CONT; n = 24). The primary outcome was leg press one-repetition maximum (LP1-RM) which was assessed at baseline, 6 and 12 weeks. At baseline and 12 weeks body composition was assessed by dual energy x-ray absorptiometry, and muscle protein synthesis and gene expression were assessed (vastus lateralis biopsy) in a sub-sample (WGFE n = 10, CONT n = 10) pre- and 3 hr post-training. RT increased LP1-RM (+34.9%) and lean tissue mass (+2.3%; p < 0.05) with no difference between treatments (p > 0.48, treatment x time). Post-exercise P70^s6k phosphorylation increased acutely, FOXO3a phosphorylation was unaltered. There were no differences in kinase signalling or gene expression between treatments. Compared with CONT, WGFE did not result in greater increases in lean tissue mass or strength in experienced resistance trained men.

• Resistance training increased phosphorylation and activation of p70^s6k and suppressed Atrogin 1, but with no difference between treatment and control.

• Supplementation with WGFE during resistance training in resistance-trained young men did not enhance increases in muscle strength or lean tissue mass.

• Enhancement of strength increases with WGFE supplementation may occur in less well-trained individuals.