Accentuated IGF-I and Attenuated IGFBP-1 Exercise-Induced Responses After 9 Weeks of Combined Resistance and Aerobic Training in Women

Abstract

The bio availability of IGF-I is governed by it's family of binding proteins (BPs) with IGFBP-3 considered stimulatory and IGFBP-1 considered inhibitory. The confounding influences of nutritional intake, initial fitness level, seasonal variation, and exercise mode make it difficult to interpret the equivocal results observed in the literature for the circulating IGF-I system responses to exercise training. PURPOSE: To test the hypothesis that chronic training would alter the circulating IGF-I system response to an acute exercise stress through changes in IGF-I binding proteins. METHODS: 17 untrained women (20.1 ± 1.6 yr, 65.1 ± 2.5 kg, 165.1 ±26.7 cm) were randomly assigned to either a training group (n=9; TRN) or a non-exercising control group (n=8; CON). The TRN group exercised on three alternating days per week for 9 weeks: training consisted of a periodized, multi-set total-body resistance training program as well as 20–30 min. of aerobic and interval training. Both groups performed an acute resistance exercise test (ARET) consisting of 6 sets of 10 repetitions of back squat at 75% of their 1-RM before (week 0) and after training (week 9). Blood was sampled during the ARET (pre-exercise, mid-exercise, post-exercise, +15 min, +30 min). Blood was assayed for total IGF-I and the IGFBPs 1, and 3. Data were analyzed using ANOVA with Tukey's post-hoc to determine significance at p<0.05. Data are presented as mean ± standard error as ng/ml. RESULTS: ARET (week 0 and week 9) induced significant changes in the IGF-I system which returned to baseline by +30 min into recovery. IGF-I was higher at week 9 compared to week 0 in TRN at all time points during the ARET (pre-exercise 472±30 vs 536±31; mid-exercise 532±31 vs 605±35; post-exercise 539±34 vs 612±37; +15 min 479±29 vs 536±29; +30 min 456±27 vs 541±31). IGFBP-1 was significantly decreased in TRN by week 9 at the pre-exercise (26.1±5.0 vs 16.5±3.7), mid-exercise (26.9±5.2 vs 19.4±4.0), and post-exercise (26.6±5.4 vs 19.0±3.8) time points. IGF-I and IGFBP-1 were not changed in CON week 0 to week 9. CONCLUSION: In untrained women, 9 weeks of combined resistance and aerobic training results in higher IGF-I and lower IGFBP-1 concentrations after acute exercise stress. These chronic exercise-associated IGF-I system changes are reflective of potentiated IGF-I bioactivity.