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This study was designed to investigate the impact of dietary protein intake on serum concentrations of IGF-I and IGFBP-1 and relative amounts of serum IGFBP-3 during 6 d of physical activity. Ten men (23.8 ± 2.0 y of age) were assigned to 1 of 3 trials in a random crossover design. Each trial was isocaloric but with varying amounts of dietary protein: 50 g, 100 g, or 200 g. Subjects expended 500 kcal through treadmill running or weightlifting on alternate days for 6 d. Fasting blood samples were obtained for measurement of IGF-I, IGFBP-1, and IGFBP-3. Pre–post 24-h urine was measured for urea nitrogen. 50 g/d of protein resulted in a negative nitrogen balance, whereas 100 g/d and 200 g/d resulted in a positive nitrogen balance—200 g greater (P < 0.05) than 50 g and 100 g. Baseline IGF-I, BP-1, and BP-3 were not different among treatments. IGF-I decreased (P = 0.002) during the 6 d. Post intervention IGFBP-I was greater (P = 0.03) than at baseline. Post intervention IGFBP-3 values were not different from baseline or between trials. A 6-d modification of protein intake, while in energy balance, during a strength and conditioning program does not appear to modify serum concentrations of IGF-I or IGFBP-1 or relative amounts of IGFBP-3.

Eleven subjects performed a graded exercise test after 1 week of protein supplementation (PRO) or glucose polymer placebo (CON), randomly assigned in a double blind fashion. The exercise consisted of 3-min graded exercise bouts separated by 10 min of active recovery at zero pedal resistance. Subjects then performed a 30-sec Wingate test (WIN) to assess performance during supramaximal exercise. Blood samples were obtained in the last 15 sec of each exercise and recovery period. PRO resulted in a decrease in blood lactate following 120% ${\text{VO}}_2\max$ and WIN, an increase in blood alanine at all time points, and lower postexercise muscle lactate and glycogen. Resting muscle GPT activity was 47% higher during the PRO trial. Mean power output during the WIN did not differ between PRO and CON. The WIN fatigue index was not significantly different between PRO and CON. The increased alanine may reflect increased transamination of pyruvate, thereby reducing the accumulation of lactate, which in turn had a marginal effect on performance during supramaximal exercise.

We examined the effect of a protein supplement on muscular strength and body composition during 6 months of a 5 days/week concurrent strength and endurance training program. Sedentary males (n = 26) and females (n = 25), 18–25 years, were randomly assigned to receive a protein (PRO, 42 g/serving) or carbohydrate (CON) supplement twice daily. Strength and body composition (dual-energy X-ray absorptiometry) were assessed at baseline, 3 (3M), and 6 (6M) months. Protein intake was higher in PRO (PRO: 2.2 g/kg; CON: 1.1 g/kg; p < .001). Females in both groups gained similar strength at 3M and 6M in bench press and hip sled. Males in PRO gained more bench press strength at 3M (PRO: 24.6 ± 3.2 kg; CON: 14.3 ± 3.8 kg; p = .06) and 6M (PRO: 34.4 ± 4.3 kg; CON: 18.7 ± 5.1 kg; p = .03) and hip sled strength at 3M (PRO: 67.7 ± 9.2 kg; CON: 40.8 ± 10.8 kg, p = .07) and 6M (PRO: 94.0 ± 10.6 kg; CON: 65.1 ± 12.4 kg; p = .09) compared with CON. Females in PRO experienced a greater reduction in fat mass over the course of the study (6M) than CON (PRO: −1.7 ± 0.5 kg; CON: 0.1 ± 0.5 kg; p = .06). Changes in lean mass were similar for females in PRO and CON. Loss in fat mass was similar for males in PRO and CON at 3M and 6M. Males in PRO gained more lean mass at 3M compared with CON (PRO: 3.2 ± 0.3 kg; CON: 2.2 ± 0.4 kg; p = .1) but similar gains at 6M (PRO: 2.6 ± 0.4 kg; CON: 2.2 ± 0.5 kg; p = .6). The results of this study demonstrate that PRO used during a concurrent training program may augment positive changes in body composition in young sedentary males and females, and strength gains in males.

The effects of androgen precursors, combined with herbal extracts designed to enhance testosterone formation and reduce conversion of androgens to estrogens was studied in young men. Subjects performed 3 days of resistance training per week for 8 weeks. Each day during Weeks 1,2,4,5,7, and 8, subjects consumed either placebo (PL; n = 10) or a supplement (ANDRO-6; n = 10), which contained daily doses of 300 mg androstenedione, 150 mg DHEA, 750 mg Tribulus terrestris, 625 mg Chrysin, 300 mg Indole-3-carbinol, and 540 mg Saw palmetto. Serum androstenedione concentrations were higher in ANDRO-6 after 2,5, and 8 weeks (p < .05), while serum concentrations of free and total testosterone were unchanged in both groups. Serum estradiol was elevated at Weeks 2, 5, and 8 in ANDRO-6 (p < .05), and serum estrone was elevated at Weeks 5 and 8 (p < .05). Muscle strength increased (p < .05) similarly from Weeks 0 to 4, and again from Weeks 4 to 8 in both treatment groups. The acute effect of one third of the daily dose, of ANDRO-6 and PL was studied in 10 men (23±4years). Serum androstenedione concentrations were elevated (p < .05) in ANDRO-6 from 150 to 360 min after ingestion, while serum free or total testosterone concentrations were unchanged. These data provide evidence that the addition of these herbal extracts to androstenedione does not result in increased serum testosterone concentrations, reduce the estrogenic effect of androstenedione, and does not augment the adaptations to resistance training.