6533b7d7fe1ef96bd12679e9

RESEARCH PRODUCT

Circulating IGF-I is associated with fitness and health outcomes in a population of 846 young healthy men

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Abstract Context Insulin-like growth factor-I (IGF-I) is thought to mediate many of the beneficial outcomes of physical activity. While IGF-I has previously been shown to be positively related with aerobic fitness, few studies have examined IGF-I relationships with other fitness and health parameters. The robustness of IGF-I as a biomarker of fitness and health has yet to be fully determined. Objective To determine the association of circulating IGF-I with fitness, body composition and health parameters in young, healthy men. Design and subjects A cross-section of 846 young, healthy Finnish men (25 ± 5 yr, 180 ± 6 cm, 81 ± 13 kg). Subjects were divided into quintiles of IGF-I concentrations (Q1: lowest; Q5: highest) for statistical evaluation. Main outcome measures Circulating IGF-I, physical fitness: peak aerobic capacity (VO 2 peak), maximal strength of leg and arm extensors, muscle endurance (sit-ups, push-ups, and repetitive squats) and health outcome parameters (total blood cholesterol, triglyceride, high-density lipoproteins (HDL), low-density lipoproteins (LDL), systolic and diastolic blood pressure, waist circumference, % body fat, and drinking, smoking and physical activity behavior). Results Higher IGF-I was associated with higher VO 2 peak (Q1: 39 ± 7 vs. Q5: 44 ± 9 mL/kg/min), sit-ups (Q1: 35 ± 10 vs. Q5: 41 ± 10 repetitions), push-ups (Q1: 27 ± 13 vs. Q5: 31 ± 14 repetitions), repetitive squats (Q2: 42 ± 10 vs. Q5: 45 ± 8 repetitions), HDL (Q1: 1.5 ± 0.4 vs. Q5: 1.53 ± 0.3 mmol/L), and lower age (Q1: 28 ± 6 vs. Q5: 23 ± 2 yr), %BF (Q1: 20 ± 7 vs. Q5: 16 ± 6%BF), waist circumference (Q1: 89 ± 11 vs. Q5: 84 ± 9 cm), BMI (Q1: 25.6 ± 4 vs. Q5: 24.3 m 2 /kg), diastolic blood pressure (Q1: 78.5 ± 9 vs. Q5: 75.4 ± 8 mm Hg), cholesterol (Q1: 4.72 ± 0.9 vs. Q5: 4.44 ± 0.8 mmol/L) and smoking (Q1: 44% vs. Q5: 32%). No association was observed for IGF-I and maximal leg extension (Q1: 2982 ± 927 vs. Q5: 2932 ± 853 N) and bench press (Q1: 895 ± 197 vs. Q5: 919 ± 203 N) strength, fat-free mass (Q1: 64.6 ± 8 vs. Q5: 66.6 ± 7 KG), LDL (2.54 ± 0.7 vs. Q5: 2.35 ± 0.6 mmol/L), or triglycerides (Q1: 1.05 ± 0.6 vs. Q5: 0.99 ± 0.5 mmol/L). Conclusion IGF-I is positively associated with aerobic fitness and muscular endurance, but not with measures of muscle strength or FFM. IGF-I is positively associated with improved health and fitness outcomes in young, healthy men.