Alexander P. Tuckow

Reliability assessment of ballistic jump squats and bench throws.

The purpose of this investigation was to determine the test-retest reliability and coefficient of variation of 2 novel physical performance tests. Ten healthy men (22.0 ± 3.0 years, 87.0 ± 8.0 kg, 20.0 ± 5.0% body fat) performed 30 continuous and dynamic jump squats (JS) and bench throws (BT) on 4 separate occasions. The movements were performed under loaded conditions utilizing 30% of subjects predetermined 1 repetition maximum in the back squat and bench press. Mean power (MP; W), peak power (PP; W), mean velocity (MV; m·s-1), peak velocity (PV; m·s-1), and total work (TW; J) were assessed using a ballistic measurement system (Innervations Inc., Muncie, IN). Data were analyzed using repeated measures analysis of variance with Duncans post hoc test when mean differences were p ≤ 0.05. Intraclass correlation coefficient (ICC) and within-subject coefficient of variation (CV%) were also calculated. All values are presented as mean 6 SE. BT variables were statistically similar across the 4 sessions: MP (350.0 ± 13.9 W), PP (431.4 ± 18.5 W) MV (1.6 6 0.03 m·s-1), PV (2.0 ± 0.03 m·s-1), and TW (199.1 ± 7.2 J). For JS, session 3 PP (1,669.8 ± 111.2 W) was significantly greater vs. sessions 1, 2, and 4 (1,601.2 ± 58.4 W). Session 4 MP (1,403.2 ± 88.6 W) and MV (1.9 6 0.1 m·s-1) for JS were significantly lower during sessions 1, 2, and 3 (MP: 1,479.4.5 ± 44.8 W, MV: 2.0 ± 0.05 m·s-1). TW (834.7 ± 24.3 J) and PV (2.2 ± 0.04 m·s-1) were staistically similar during all sessions for JS. The CVs ranged from 3.0 to 7.6% for the BT and 3.2 to 5.7% for the JS. ICCs for MP, PP, MV, PV, and TW were 0.92, 0.95, 0.94, 0.91, and 0.95, respectively, during BT. ICCs during JS for MP, PP, MV, PV, and TW were 0.96, 0.98, 0.94, 0.94, and 0.89, respectively. The results of the current study support the use of a 30 continuous and dynamic BT protocol as a reliable upper-body physical performance test, which can be administered with minimal practice. Slightly greater variability for JS was observed, although the test had high reliability.

Growth hormone molecular heterogeneity and exercise

NINDL, B. C., W. J. KRAEMER, J. O. MARX, A. P. TUCKOW, and W. C. HYMER. Growth hormone molecular heterogeneity and exercise. Exerc. Sport Sci. Rev., Vol. 31, No. 4, pp. 161–166, 2003. There are more than 100 molecular isoforms of circulating growth hormone (GH), but the traditional measurement approach in the exercise literature has only focused on the main isoform ( i.e., 22 kDa). New assay methodologies now can assess various GH isoforms. The current data suggest that exercise results in the preferential release of GH isoforms with extended half-lives, thereby sustaining biological actions.

Exercise-induced insulin-like growth factor I system concentrations after training in women.

INTRODUCTION This study examined the effects of short-term physical training on the acute hormonal response (i.e., growth hormone, total and free insulin-like growth factor I [IGF-I], and IGF binding proteins [IGFBP]-1, IGFBP-2, and IGFBP-3) to resistance exercise (RE) in women. METHODS Forty-six women (20.3 ± 0.3 yr, mass = 64.1 ± 7.3 kg, height = 165.7 ± 1.0 cm) were randomly assigned to an endurance training (E), resistance training (R), combined training (R + E), or control (C) group for 8wk. Subjects completed a standardized bout of RE (six sets of back squats at 10 repetition maximum) before and after training. Blood samples were obtained at rest (PRE), after the third set, immediately postexercise (POST), and at 15 min and 30 min after exercise. RESULTS Acute RE significantly increased (P < 0.05) serum growth hormone (mean ± SD; change from PRE to POST = +10.9 ± 7.5 μg·L-1), total IGF-I (+66.1 ± 25.4 μg·L-1), IGFBP-1 (+2.5 ± 3.1 μg·L-1), IGFBP-2 (+86.0 ± 86.8 μg·L-1), and IGFBP-3 (+0.69 ± 0.25 mg·L-1) concentrations and decreased free IGF-I concentrations (-0.14 ± 0.21 μg·L-1). After 8 wk of training, total IGF-I concentrations were significantly increased (change in POST concentrations from week 0 to week 8 = +82.5 ± 120.8 μg·L-1), and IGFBP-1 concentrations were significantly decreased (-6.7 ± 13.6 μg·L-1) during exercise in groups that participated in resistance training (R and R + E); no significant changes were seen after E or C. CONCLUSIONS Participation in resistance training increased total IGF-I and reduced IGFBP-1 concentrations during acute RE, indicating exercise mode-specific adaptations in the circulating IGF-I system.

Effects of Exercise Mode and Duration on 24-h IGF-I System Recovery Responses

INTRODUCTION 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.

Circulating bioactive and immunoreactive IGF-I remain stable in women, despite physical fitness improvements after 8 weeks of resistance, aerobic, and combined exercise training

Insulin-like growth factor-I (IGF-I) is regulated by a number of IGF-binding proteins (IGFBPs) and proteases that influence IGF-I bioactivity. A specific IGF-I kinase receptor activation assay (KIRA) has been developed that determines the ability of IGF-I to activate the IGF-I receptor by quantification of intracellular receptor autophosphorylation on IGF-I binding. KIRA-assessed IGF-I bioactivity has not been utilized within the context of chronic exercise training paradigms. This study measured total and free immunoreactive IGF-I, bioactive IGF-I, and IGFBP-1, -2, and -3 before (Pre), during (Mid), and after (Post) 8 wk of exercise training in young, healthy women, who were randomized into one of four groups: control (n = 10), resistance (n = 18), aerobic (n = 13), and combined (n = 15) exercise training. The training programs were effective in improving physical fitness specific to the exercise mode engaged in: increases were observed for lean mass ( approximately 2%), aerobic fitness (6-7%), and upper (20-24%) and lower (15-48%) body strength (all P values < 0.05). By contrast, no time, group, or interaction effects were observed for the circulating IGF-I system, as immunoreactive total (Pre = 264 +/- 16 microg/l; Mid = 268 +/- 17 microg/l; Post = 271 +/- 17 microg/l), free (Pre = 0.70 +/- 0.1 microg/l; Mid = 0.63 +/- 0.1 microg/l; Post = 0.63 +/- 0.2 microg/l) and bioactive (Pre = 2.35 +/- 0.3 microg/l; Mid = 2.25 +/- 0.3 microg/l; Post = 2.33 +/- 0.3 microg/l) IGF-I were unchanged throughout the study. All IGFBP measures were also unchanged. We conclude that increased lean mass, aerobic fitness, and upper and lower body strength resulting from an 8-wk exercise training programs can occur without concomitant increases in either circulating bioactive or immunoreactive IGF-I, as well as associated IGFBPs. In terms of reflecting positive anabolic neuromuscular outcomes, these data do not support a role for endocrine-derived IGF-I.

Relationship between growth hormone in vivo bioactivity, the insulin-like growth factor-I system and bone mineral density in young, physically fit men and women

CONTEXT Bone mineral density (BMD) is influenced by growth factors, such as growth hormone (GH) and insulin-like growth factor-I (IGF-I). The in vivo bioassay for GH (bioGH) provides a more physiologically relevant measurement than an in vitro immunoassay, since bioGH is quantified on a biological outcome. OBJECTIVE To determine if bioGH and components of the IGF-I system were associated with BMD in age-matched men (M; n=41, 19.1+/-0.2 year, 70+/-3 kg, 163+/-25 cm) and women (W; n=39, 18.6+/-0.3 year, 66+/-3 kg, 141+/-15 cm). DESIGN Blood was analyzed for growth-related hormones [bioGH, immunoreactive growth hormone (iGH), IGF-I and associated binding proteins], and BMD was measured by pDXA, pQCT, and central DXA (spine, hip). For the bioGH assay, hypophysectomizied female Sprague-Dawley rats were injected with a s.c. bolus of either a GH standard or unknown (each subjects plasma) in four daily injections. The tibia was then examined for epiphyseal growth plate width from which bioGH concentrations were extrapolated. RESULTS M had greater (P<0.05) calcaneal BMD when measured by pDXA (M: 1.27+/-0.02; W: 1.14+/-0.02 g/cm2), while pQCT-assessed BMD at the tibia was not different (M: 777+/-16; W: 799+/-16 g/cm2). bioGH was similar between M (5388+/-800 microg/L) and W (4282+/-643 microg/L) and was not correlated with BMD. The only BMD-related biomarkers in women were acid-labile subunit (ALS; r=0.40) and IGFBP-3 (r=0.42) with DXA-measured spine and femoral neck BMD, and ALS (r=0.47) with pQCT-assessed tibial BMD and cortical thickness, respectively. CONCLUSION Although bioGH was not associated with BMD, IGF-I and associated binding proteins (IGFBP-3 and ALS) emerged as correlates in W only.

Effects of Acute and Chronic Exercise on Disulfide-Linked Growth Hormone Variants

PURPOSE To test the hypothesis that the appearance of disulfide-linked growth hormone (GH) aggregates during and after an acute resistance exercise test (ARET) in men could be influenced by chronic physical training. METHODS Fourteen men (28 +/- 1 yr) underwent two different 8-wk physical training programs designed to improve military performance. Before and after chronic training, subjects performed an ARET (six sets of 10 repetition-maximum squat) and had venous blood drawn pre-, mid-, and post-ARET (0, 15, and 30 min postexercise). To determine whether GH molecules were disulfide-linked, serum samples were chemically reduced via glutathione (GSH). Serum immunoreactive GH (IRGH) and immunofunctional GH (IFGH) concentrations were determined using two specific immunoassays, in nonreduced (-GSH) and reduced (+GSH) states. Data were analyzed using repeated-measures ANOVA. RESULTS No differences were observed in the GH responses of the two training programs; therefore, training group data were combined for analysis. GSH reduction increased the mean GH signal (-GSH: 1.4 +/- 0.3 microg x L(-1) vs +GSH: 1.7 +/- 0.3 microg x L(-1); P < 0.01) only when quantifying IRGH. Post hoc testing indicated that serum contained IRGH disulfide-linked GH aggregates at the mid, 0-, 15-, and 30-min posttime points of the ARET (P < 0.01), whereas GSH reduction did not affect IFGH concentrations. Chronic physical training had no effect on the ARET-induced GH response. CONCLUSION Acute resistance exercise leads to the appearance of disulfide-linked IRGH aggregates, and this response does not appear to be affected by 8 wk of chronic physical training. The physiological significance of increased proportions of disulfide-linked GH aggregates postexercise remains uncertain; however, structural alterations in GH moieties after acute exercise may represent important regulatory steps in mediating GH biological activity at selected target tissues.

Twenty-hour growth hormone secretory profiles after aerobic and resistance exercise.

INTRODUCTION The pulsatile secretion pattern of growth hormone (GH) is an important parameter of GH action at peripheral tissues, and more information is needed on how exercise impacts GH secretion. This study hypothesized that both aerobic and resistance exercise would exhibit dose-response relationships with respect to exercise duration and 20-h postexercise GH secretion. METHODS Eight healthy men randomly completed five separate conditions: 1) control (no exercise; CON), 2) a moderate-duration (1-h) aerobic exercise session (MA), 3) a long-duration (2-h) aerobic exercise session (LA), 4) a moderate-duration (1-h) resistance exercise session (MR), and 5) a long-duration (2-h) resistance exercise session (LR). Exercise intensity, diet, sleep, and physical activity were strictly controlled during each condition, and blood was sampled postexercise every 20 min for 20 h, and GH secretion parameters were analyzed via cluster and deconvolution analyses. RESULTS Only the 2-h aerobic exercise bout resulted in a significant amplification of GH secretion as evidenced by increases in GH burst peak amplitude (∼100%), basal GH secretion rate (∼127%), total GH basal secretion (∼120%), total pulsatile secretion (∼88%), and total GH secretion (∼89%) over the control (i.e., no exercise) condition. GH secretions for the resistance exercise conditions were not different from control. CONCLUSIONS The fact that the 2-h aerobic exercise condition resulted in higher energy expenditure than the other exercise conditions could offer a partial explanation for the greater GH amplification because of the metabolic effects that GH exerts in stimulating postexercise lipolysis. We conclude that extending the duration of aerobic exercise, but not resistance exercise, from 1- to 2-h significantly amplifies GH secretion during a 20-h period.

IGF-I System Responses During 12 Weeks of Resistance Training in End-Stage Renal Disease Patients

OBJECTIVE To examine the hypothesis that 12 weeks of resistance training would alter circulating concentrations of IGF-I system components in end-stage renal disease (ESRD) patients. DESIGN Ten ESRD patients underwent 12 weeks of resistance training after a 6 week control period and had morning fasted blood drawn on four occasions (weeks - 6, 0, 6, 12). Immunoassays were performed for serum total and free IGF-I, IGF binding proteins (IGFBPs) 2 and 3, and the acid labile subunit (ALS). Immunoaffinity depletion of ALS-based complexes allowed measurement of non-ternary (i.e., binary) IGF-I and IGFBP-3. RESULTS Significant improvements in strength and functional performance were observed. All IGF-I measures were stable during the control period and no changes were observed for the first 6 weeks of resistance training. At week 12, total IGF-I (-15.4+/-28.9%), ternary IGF-I (-16.4+/-36.7%), and the IGF-I/IGFBP-3 ratio had significantly (p < or = 0.05) declined from week 0 values. No changes were observed for free IGF-I, IGFBPs 2 and 3, or the acid labile subunit. The proportion of IGF-I in ternary ( approximately 76.3+/-6.8%), non-ternary ( approximately 22.5+/-6.6%), and free ( approximately 1.2+/-0.5%) forms remained constant throughout the training. CONCLUSIONS 12 weeks of resistance training in ESRD patients induced a decline in total IGF-I, but did not alter the proportion of IGF-I circulating in free, ternary or non-ternary molecular complexes. The decline in IGF-I occurs in the presence of positive training adaptations on physical performance and we conclude that this response pattern appears to be reflective of favorable neuromuscular anabolic adaptations.