Alemany, J. A., Frystyk, J., Tuckow, A. P., Spiering, B. A., Hatfield, D. L., Staab, J. S., Chen, J., Flyvbjerg, A., Maresh, C. M., Kraemer, W. J., & Nindl, B. C. (2008). Effects of resistance, aerobic and combined exercise training on immunoreactive vs. bioassayable IGF-I. ACSM 55th Annual Meeting Indianapolis. Presentation number 970.

This study examined the effects of different modes of chronic exercise on IGF-I immunoreactivity vs. bioactivity. Untrained women (N = 56) were randomly assigned to one of four training groups: Control (N = 9); resistance (N = 17); aerobic (N = 13); and combined resistance and aerobic (N = 17). Training was performed on three alternating days per week for nine weeks. Resistance training was a non-linear, periodized program of three sets of seven exercises per day. Aerobic training included: 1) 20-30 minutes of continuous running (70-85% HRmax), and 2) progressive interval running (400-1,600 m). Combined resistance and aerobic training performed both the resistance and aerobic exercise programs on the same day. Resistance and aerobic training performed similar amounts of work, whereas combined training performed double the amount of work. Blood samples were taken pre-, mid- and post-training and assayed for immunoreactive and bioactive IGF-I.

IGF-I bioactivity did not change over the nine weeks of training, were not different between groups, and there was no significant group x time interaction for bioactive IGF-I. Similarly, for immunoreactive IGF-I, no changes occurred over the training period, and no group x time interactions or differences between groups were observed. Bioactive and immunoreactive IGF-I were only moderately correlated at all three time points indicating they represented largely different biological entities.

Implication. Short-term exercise training does not influence circulating immunoreactive or bioactive IGF-I in previously untrained women. The moderate correlation between immunoreactive and bioactive IGF-I suggests that these assays measure different dimensions of IGF-I biology.

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