Effects of exercise mode and duration on 24-h IGF-I system recovery responses.
BACKGROUND
This study hypothesized that insulin-like growth factor-binding protein (IGFBP), rather than insulin-like growth factor I (IGF-I) itself, would be more responsive to acute exercise stress in a dose-dependent fashion.


METHODS
Eight men (24 +/- 5 yr, 87 +/- 9 kg, 182 +/- 6 cm, 21 +/- 5% body fat) had blood drawn every 4 h after exercise for 24 h and assayed for IGF-I, IGFBP-1, -3, -6, the acid labile subunit (ALS), insulin, glucose, and nonesterified free fatty acids on five occasions: no exercise (control, C), moderate-duration resistance exercise (MDRE; 25, 5-10 repetition maximum (RM) sets), long-duration resistance exercise (LDRE; 50, 5-10 RM sets), moderate-duration aerobic exercise (MDAE; three 15-min cycling bouts at approximately 70% (.)VO2peak), and long-duration aerobic exercise (LDAE; six 15-min cycling bouts at approximately 70% (.)VO2peak). Energy requirements were determined from resting metabolic rate, age, and a physical activity factor. Dietary control was implemented by providing all meals during the experimental trials. A two-way ANOVA with repeated measures (P < 0.05) was used for statistical analysis.


RESULTS
Significant exercise effects were observed for IGFBP-1 (C: 14.0 +/- 2.7 < MDRE: 35.9 +/- 8.6 = LDRE: 45.2 +/- 10.6 = MDAE: 34.2 +/- 7.4 = LDAE: 47.0 +/- 11.8 ng x mL(-1) and insulin (C: 26.0 +/- 9 < LDRE: 13.2 +/- 6 ng x mL). In addition, a dose-response relationship was observed for the IGFBP-1 response (long-duration exercise (46 +/- 10 ng x mL(-1)) > moderate-duration exercise (35 +/- 7 ng x mL(-1)). There were no exercise effects for total IGF-I, IGFBP-3, and ALS. Effects of time of day were observed for all variables except ALS.


CONCLUSIONS
For the circulating IGF-I system components measured, only IGFBP-1 seems to be a sensitive biomarker capable of assessing the physiological strain of acute physical exercise.
Nindl
Bradley C
BC
Military Performance Division, U.S. Army Research Institute of Environmental Medicine, Natick, MA 01760-5007, USA. Bradley.nindl@us.army.mil
Alemany
Joseph A
JA
Tuckow
Alexander P
AP
Kellogg
Mark D
MD
Sharp
Marilyn A
MA
Patton
John F
JF
D000328:Adult; D000704:Analysis of Variance; D001823:Body Composition; D015444:Exercise; D006801:Humans; D018970:Insulin-Like Growth Factor Binding Protein 1 / Q000097:blood*; D008297:Male; D018482:Muscle, Skeletal; D010101:Oxygen Consumption; D011446:Prospective Studies; D055070:Resistance Training; D013997:Time Factors
D018970:Insulin-Like Growth Factor Binding Protein 1