Brief high intensity sub-maximal exercise elicits acute increases in serum (total) IGF-I independent of growth hormone (GH) release and has been suggested to alter the bioavailability of IGF-I through regulation of the IGF binding proteins (IGFBPs) (Schwarz et al. 1996). The responses of total IGF-I, free IGF-I and the IGFBPs to maximal sprint exercise have not previously been characterised. Therefore, we examined whether sprint exercise alters circulating IGF-I and IGF-I binding capacity as estimated by measurement of IGFBP-1 bound IGF-I.

Following ethics committee approval, five non-obese healthy men arrived at the laboratory after an overnight fast, completed a standardised warm-up and then a maximal 30 s sprint on a cycle ergometer. Venous blood samples were drawn pre-and 5 min post-sprint. Serum levels of total IGF-I, free IGF-I, IGFBP-1 and IGFBP-1 bound IGF-I (binary complex) were determined as previously described (Frystyk et al. 2002). Data were analysed using a Student’s paired t test; significance taken at P < 0.05. Effect sizes (e.s.) were calculated for each variable; large effect when e.s.>0.8.

There were no significant changes in serum total IGF-I, free IGF-I, binary complex or IGFBP-I after sprint exercise (Table 1). IGFBP-I saturation increased following exercise (P < 0.05). Effect sizes for pre-vs. post-sprint were: total IGF-I, 0.90; free IGF-I, 0.01; binary complex, 0.37; IGFBP-I, 0.43; IGFBP-I saturation, 0.69. There was, therefore, a large effect for total IGF-I and a very small effect for free IGF-I.

This preliminary study indicates that a maximal 30 s sprint acutely increases IGFBP-I saturation, and tends to increase total IGF-I levels. However, free IGF-I remains unaltered.