Reduced activity of the potent anabolic effectors: insulin-like growth factor-I (IGF-I) and fibroblast growth factor-2 (FGF-2), play a role in aging associated muscle loss. The effect of fitness level on IGF-I and FGF-2 responses to all-out anaerobic exercise in older men was studied. Twenty four healthy older males: 12 higher fit (58 ± 1y) and 12 lower fit (59 ± 1y) underwent the Wingate anaerobic test. Serum levels of IGF-I and FGF-2 were measured before, immediately after exercise, and 50 min into recovery. Immediately post exercise, the average peak power output and serum lactate were higher (p < 0.05) in the higher fit (446.0 ± 14. 9 kgm·min^-1 for mean (± SD) peak power and 12.6 ± 1.1 mml·l^-1 for lactate) compared with the lower fit individuals (284.0 ± 6.5 kgm·min^-1 and 8.5 ± 0.7 mml·l^-1, respectively). Pre-exercise IGF-I was lower and FGF-2 was higher in the higher fit (335.0 ± 54.0 ng·ml^-1 and 1.6 ± 0.1 ng·ml^-1, respectively) compared with lower fit individuals (402.0 ± 50.0 ng·ml^-1 and 1.4 ± 0.2 ng·ml^-1, respectively). Following the anaerobic exercise, in both groups, FGF-2 decreased dramatically (p < 0.05); in the higher fit individuals FGF-2 level was 0.4 ± 0.1 pg·ml^-1 compared to 0.1 ± 0.02 pg·ml^-1 in the lower fit individuals. In contrast to FGF-2, IGF-I increased transiently to levels of 405.0 ± 62.0 ng·ml^-1 in the higher fit individuals and to levels of 436 ± 57.0 ng·ml^-1 in the lower fit individuals. However, the IGF-I elevation was significant (p < 0. 05) only in the higher fit individuals. In conclusion, the present study demonstrates that during aging, fitness level can alter circulating levels of IGF-I and FGF-2. Furthermore, fitness level can affect the response of both mediators to all-out anaerobic exercise.

• The present study suggests that during aging, fitness level can alter circulating levels of IGF-I and FGF-2.

• Furthermore, fitness level can affect the response of both mediators to all-out anaerobic exercise.

• Anaerobic muscle activity is represented in many daily life activities of elderly individuals.

• This may have clinical implications during aging, where the declined activity of growth factors is a major determinant of the loss of muscle strength and function.