Differential basal and exercise-induced IGF-I system responses to resistance vs. calisthenic-based military readiness training programs.

OBJECTIVE: The purpose of this study was to: 1) evaluate differential responses of the IGF-I system to either a calisthenic- or resistance exercise-based program and 2) determine if this chronic training altered the IGF-I system during an acute resistance exercise protocol. DESIGN: Thirty-two volunteers were randomly assigned into a resistance exercise-based training (RT) group (n=15, 27±5y, 174±6cm, 81±12kg) or a calisthenic-based training group (CT) (n=17, 29±5y, 179±8cm, 85±10kg) and all underwent 8weeks of exercise training (1.5h/d, 5d/wk). Basal blood was sampled pre- (Week 0), mid- (Week 4) and post-training (Week 8) and assayed for IGF-I system analytes. An acute resistance exercise protocol (AREP) was conducted preand post-training consisting of 6 sets of 10 repetitions in the squat with two minutes of rest in between sets and the IGF-I system analytes measured. A repeated measures ANOVA (p≤0.05) was used for statistical analysis. RESULTS: No interaction or within-subject effects were observed for basal total IGF-I, free IGF-I, or IGFBP-1. IGFBP-2 (pre; 578.6±295.7post-training; 14.3±1.9µg/mL; p=0.01). An interaction was observed for the RT group as IGFBP-3 increased from pre to mid (3462.4±216.4 vs. 3962.2±227.9ng/mL), but was not significant at the post-training time point (3770.3±228.7ng/mL). AREP caused all analytes except free IGF-I (40% decrease) to increase (17-27%; p=0.001) during exercise, returning to baseline concentration into recovery. CONCLUSION: Post-training, bioavailable IGF-I recovered more rapidly post-exercise. 8wks of chronic physical training resulted in increased basal IGFBP-2 and IGFBP-3, decreased ALS, increased pre-AREP free IGF-I and a more rapid free IGF-I recovery post-AREP. While total IGF-I was insensitive to chronic physical training, changes were observed with circulating IGFBPs and bioavailable IGF-I. To glean the most robust information on the effects of exercise training, studies must move beyond relying solely on total IGF-I measures and should consider IGFBPs and bioavailable IGF-I as these components of the circulating IGF-I system are essential determinants of IGF-I physiological action.

Reliability of military-relevant tests designed to assess soldier readiness for occupational and combat-related duties.

The purpose of this study was to determine the reliability of military-relevant tests designed to assess soldier readiness. Forty-seven soldiers (46 men, 1 woman; 22 +/- 3 years; 80.4 +/- 11.7 kg) performed each of seven soldier readiness tests on four different occasions over the course of 8 weeks. The soldier readiness tests were: (1) 3.2-km load carriage (LC) time-trial, (2) running long jump (RLJ), (3) one-repetition maximum box lift (1RMBL), (4) 10-minute repetitive box lift and carry (RBLC), (5) simulated victim rescue (VR), (6) mock grenade throw (GT) for accuracy, and (7) simulated combat rushes (CR). Repeated measures analysis of variance revealed significant learning effects for 1RMBL, RBLC, and GT; these tests required two (1RMBL and RBLC) or three (GT) trials to obtain statistically stable values. The intraclass correlation coefficient was 0.78 to 0.89 for all tests. LC, 1RMBL, RBLC, CR, and RLJ all demonstrated standard error of measurement values that were 3% to 5%, whereas VR and GT were 9% and 36%, respectively. In conclusion, the 1RMBL, RBLC, and GT tests required familiarization before a stable value was obtained. The LC, 1RMBL, RBLC, CR, and RLJ tests (and, to a lesser degree, the VR test) demonstrated reasonably acceptable levels of reliability and measurement error, whereas the GT test did not.

A systematic review of the effects of physical training on load carriage performance.

Soldiers are often required to carry heavy loads during military operations. This article reports on a systematic literature review examining the influence of physical training on load carriage performance. Several literature databases, reference lists, and other sources were explored to find studies that quantitatively examined the effects of physical training on the time taken for individuals to complete a set distance carrying an external load, with the majority of the load contained in a backpack. Effect sizes (Cohen's d statistic) were used in meta-analyses to examine the changes in load carriage performance after various modes of physical training. Effect sizes quantified training-related changes in terms of SD units. Ten original research studies met the review criteria. Meta-analysis indicated that large training effects (≥0.8SD units) were apparent when progressive resistance training was combined with aerobic training and when that training was conducted at least 3 times per week, over at least 4 weeks. When progressive load-carriage exercise was part of the training program, much larger training effects were evident (summary effect size [SES] = 1.7SD units). Field-based training that combined a wide variety of training modes and included progressive load-carriage exercise was also very effective in improving load carriage performance (SES = 1.1SD units). Aerobic training alone or resistance training alone had smaller and more variable effects, depending on the study. This review indicates that combinations of specific modes of physical training can substantially improve load carriage performance.

Combined resistance and endurance training improves physical capacity and performance on tactical occupational tasks.

The purpose of this study is to evaluate the effectiveness of aerobic endurance (E), strength (R), and combined endurance and strength (CB) training for improving performance of tactical occupational tasks and determine if combined training interferes with performance enhancements of E or R alone. A total of 56 recreationally active women were randomly placed into four groups: R (n = 18), E (n = 13), CB (n = 15), Control (n = 10). Subjects trained three non-consecutive days per week for 8 weeks. Performance was measured pre-, mid-, and post-training for bench press one-repetition maximum (1-RM), squat 1-RM, bench press throw and squat jump peak power, VO2peak, 3.2 km load carriage (LC), 3.2 km run (run), and repetitive lift and carry (RLC). R and E demonstrated improvements which were generally specific to their training. R improved squat (48.3%) and bench press 1-RM (23.8%), bench press throw (41.9%), RLC (31.3%), and LC (11.5%). E improved run (14.7%), VO2peak (6.2%), squat 1-RM (15.3%), LC (12.9%), and RLC (22.5%). CB improved squat (37.6%) and bench press 1-RM (20.9%), bench press throw (39.6%), VO2peak (7.6%), run (10.4%), LC (13.1%), and RLC (45.5%). Post-training 1-RM squat was greater in R and CB than E, while E completed the 3.2 km load carriage task faster than C. In conclusion, 8 weeks of combined training improved performance in all tactical occupational tasks measured and did not interfere with improvements in strength, power and endurance measures compared to R or E alone.

Hypohydration reduces vertical ground reaction impulse but not jump height.

This study examined vertical jump performance using a force platform and weighted vest to determine why hypohydration (approximately 4% body mass) does not improve jump height. Measures of functional performance from a force platform were determined for 15 healthy and active males when euhydrated (EUH), hypohydrated (HYP) and hypohydrated while wearing a weighted vest (HYP(v)) adjusted to precisely match water mass losses. HYP produced a significant loss of body mass [-3.2 +/- 0.5 kg (-3.8 +/- 0.6%); P < 0.05], but body mass in HYP(v) was not different from EUH. There were no differences in absolute or relative peak force or power among trials. Jump height was not different between EUH (0.380 +/- 0.048 m) and HYP (0.384 +/- 0.050 m), but was 4% lower (P < 0.05) in HYP(v) (0.365 +/- 0.52 m) than EUH due to a lower jump velocity between HYP(v) and EUH only (P < 0.05). However, vertical ground reaction impulse (VGRI) was reduced in both HYP and HYP(v) (2-3%) compared with EUH (P < 0.05). In conclusion, this study demonstrates the failure to improve jump height when HYP can be explained by offsetting reductions in both VGRI and body mass.

Effects of exercise training on the matrix metalloprotease response to acute exercise.

Matrix metalloproteases (MMPs) in the circulation are thought to modulate the activation of growth factors, cytokines, and angiogenesis, facilitating physiological adaptations to exercise training. The purpose of this work was to characterize serum MMP-1, MMP-2, MMP-3, and MMP-9 concentrations pre- and post-eight weeks of exercise training. We tested the hypothesis that exercise training would influence serum MMP concentrations in response to an acute resistance exercise test (ARET). Participants were randomized into an 8-week training program (5 days per week) that emphasized callisthenic (CT, N = 8) or resistance (RT, N = 8) exercise. Serum MMP concentrations (MMP-1, -2, -3, -9) were assessed in men (N = 16) in response to an acute bout of high-intensity resistance exercise (six sets of 10-RM squats with 2-min inter-set rest periods) both before and after 8 weeks of training. Training resulted in a temporal shift in the peak MMP-1 concentration from post-ARET to mid-ARET in both groups. Post-training, MMP-9 concentrations were increased immediately after the ARET in the CT group as compared to pre-training ARET concentrations. RT did not alter MMP-3 and -9 concentrations. These data suggest that the mode of exercise training influences the MMP response to an acute bout of exercise, revealing a possible role of MMPs in initiating training-specific adaptations.

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.

Effects of two different eight-week training programs on military physical performance.

Various physical demands are placed on soldiers, whose effectiveness and survivability depend on their combat-specific physical fitness. Because sport training programs involving weight-based training have proven effective, this study examined the value of such a program for short-term military training using combat-relevant tests. A male weight-based training (WBT) group (n = 15; mean +/- SD: 27.0 +/- 4.7 years, 173.8 +/- 5.8 cm, 80.9 +/- 12.7 kg) performed full-body weight-based training workouts, 3.2-km runs, interval training, agility training, and progressively loaded 8-km backpack hikes. A male Army Standardized Physical Training (SPT) group (n = 17; mean +/- SD: 29.0 +/- 4.6 years, 179.7 +/- 8.2 cm, 84.5 +/- 10.4 kg) followed the new Army Standardized Physical Training program of stretching, varied calisthenics, movement drills, sprint intervals, shuttle running, and distance runs. Both groups exercised for 1.5 hours a day, 5 days a week for 8 weeks. The following training-induced changes were statistically significant (P < 0.05) for both training groups: 3.2-km run or walk with 32-kg load (minutes), 24.5 +/- 3.2 to 21.0 +/- 2.8 (SPT) and 24.9 +/- 2.8 to 21.1 +/- 2.2 (WBT); 400-m run with 18-kg load (seconds), 94.5 +/- 14.2 to 84.4 +/- 11.9 (SPT) and 100.1 +/- 16.1 to 84.0 +/- 8.4 (WBT); obstacle course with 18-kg load (seconds), 73.3 +/- 10.1 to 61.6 +/- 7.7 (SPT) and 66.8 +/- 10.0 to 60.1 +/- 8.7 (WBT); 5 30-m sprints to prone (seconds), 63.5 +/- 4.8 to 59.8 +/- 4.1 (SPT) and 60.4 +/- 4.2 to 58.9 +/- 2.7 (WBT); and 80-kg casualty rescue from 50 m (seconds), 65.8 +/- 40.0 to 42.1 +/- 9.9 (SPT) and 57.6 +/- 22.0 to 44.2 +/- 8.8 (WBT). Of these tests, only the obstacle course showed significant difference in improvement between the two training groups. Thus, for short-term (i.e., 8-week) training of relatively untrained men, the Army's new Standardized Physical Training program and a weight-based training experimental program can produce similar, significant, and meaningful improvements in military physical performance. Further research would be needed to determine whether weight-based training provides an advantage over a longer training period.

Prediction of simulated battlefield physical performance from field-expedient tests.

Predictive models of battlefield physical performance can benefit the military. To develop models, 32 physically trained men (mean +/- SD: 28.0 +/- 4.7 years, 82.1 +/- 11.3 kg, 176.3 +/- 7.5 cm) underwent (1) anthropometric measures: height and body mass; (2) fitness tests: push-ups, sit-ups, 3.2-km run, vertical jump, horizontal jump; (3) simulated battlefield physical performance in fighting load: five 30-m sprints prone to prone, 400-m run, obstacle course, and casualty recovery. Although greater body mass was positively associated with better casualty recovery performance, it showed trends toward poorer performance on all the other fitness and military performance tests. Regression equations well predicted the simulated battlefield performance from the anthropometric measures and physical fitness tests (r = 0.77-0.82). The vertical jump entered all four prediction equations and the horizontal jump entered one of them. The equations, using input from easy to administer tests, effectively predict simulated battlefield physical performance.

Minimally invasive sampling of transdermal body fluid for the purpose of measuring insulin-like growth factor-I during exercise training.

Insulin-like growth factor-I (IGF-I) is a ubiquitous hormone that is secreted in both an endocrine and an autocrine/paracrine manner. IGF-I has conventionally been measured in serum; however, transdermal body fluid (TDF) remains as an unexplored biocompartment in which IGF-I also resides and may be more biologically relevant because of its proximity to tissues and cells. The purpose of this study was to compare IGF-I in serum versus IGF-I in TDF before and after 8 weeks of physical training. Twenty-eight healthy men (28 +/- 5 years old, 176 +/- 8 cm tall, weighing 83 +/- 11 kg) had TDF obtained by a novel, minimally invasive method that included the application of continuous vacuum pressure on forearm skin perforated with tiny micropores created by a focused beam from a laser system and also had blood obtained by venipuncture. An enzyme-linked immunosorbent assay measured total IGF-I concentrations. A repeated-measures analysis of variance (biocompartment x time) and Pearson Product Moment Correlation coefficients (P < or = 0.05) were used for statistical analyses. Data are presented as mean +/- SE. Total TDF IGF-I was significantly lower than serum IGF-I both before (TDF, 91 +/- 6 ng/mL; serum, 375 +/- 17 ng/mL) and after (TDF, 83 +/- 5 ng/mL; serum, 363 +/- 19 ng/mL) the exercise training. Serum and TDF IGF-I values were not significantly different pre- to post-training. Serum and TDF IGF-I levels were significantly correlated pre-training (r = 0.41), but not post-training (r = 0.34). The percent change between serum and TDF was not correlated (r = 0.09). This study has demonstrated that total IGF-I can be sampled and measured in TDF via a minimally invasive manner and is appreciably (approximately 76%) less than total IGF-I measured in serum. Additionally, the IGF-I measurements in these two biocompartments were not closely associated, possibly indicating an uncoupled, rather than a linked, regulation of IGF-I among the body's biocompartments.

The relationship between vertical jump power estimates and weightlifting ability: a field-test approach.

The purpose of this study was to assess the usefulness of the vertical jump and estimated vertical-jump power as a field test for weightlifting. Estimated PP output from the vertical jump was correlated with lifting ability among 64 USA national-level weightlifters (junior and senior men and women). Vertical jump was measured using the Kinematic Measurement System, consisting of a switch mat interfaced with a laptop computer. Vertical jumps were measured using a hands-on-hips method. A counter-movement vertical jump (CMJ) and a static vertical jump (SJ, 90 degrees knee angle) were measured. Two trials were given for each condition. Test-retest reliability for jump height was intra-class correlation (ICC) = 0.98 (CMJ) and ICC = 0.96 (SJ). Athletes warmed up on their own for 2-3 minutes, followed by 2 practice jumps at each condition. Peak power (PP) was estimated using the equations developed by Sayers et al. (24). The athletes' current lifting capabilities were assessed by a questionnaire, and USA national coaches checked the listed values. Differences between groups (i.e., men versus women, juniors versus resident lifters) were determined using t-tests (p < or = 0.05). Correlations were determined using Pearson's r. Results indicate that vertical jumping PP is strongly associated with weightlifting ability. Thus, these results indicate that PP derived from the vertical jump (CMJ or SJ) can be a valuable tool in assessing weightlifting performance.

Reliability assessment of two militarily relevant occupational physical performance tests.

To determine the number of test sessions needed to stabilize performance on two military occupational physical tests and to assess their reliability, 10 male soldiers (22 +/- 3 yrs, 183 +/- 7 cm, 87 +/- 8 kg) performed both an indoor 6-station obstacle course (OC) and a repetitive box-lifting task (RBLT). The OC consisted of 46 cm-high hurdles, zigzag sprint, low crawl, horizontal pipe shimmy, 1.4 m wall traversal, and straight sprint. The RBLT required subjects to lift 20.5 kg boxes, continuously for 10 minutes, from the ground onto 1.3 m high platforms positioned 2.4 m apart. The OC mean +/- SD times (s), for sessions 1-4 respectively, were 37.4 +/- 2.2, 35.8 +/- 2.5, 34.7 +/- 2.1, and 34.5 +/- 1.7 seconds. The number of boxes lifted was 177 +/- 31, 194 +/- 28, 189 +/- 32, and 186 +/- 37 for the RBLT. Performance stabilized on the 3rd session for the OC (7% improvement over first trial, p < 0.05) and on the 2nd session for the RBLT (9% improvement over first trial, p < 0.05). The intraclass correlation coefficients were 0.92 and 0.94 for the OC and RBLT, respectively. This study demonstrates that both are reliable tests, but they do require administration of 1 single-trial session of RBLT and 2 two-trial sessions of OC before highly reliable performance data are obtained.

Effects of a 3-month endurance event on physical performance and body composition: the G2 trans-Greenland expedition.

OBJECTIVE: Prolonged physical exertion with inadequate time for recuperation may result in an overtraining phenomenon characterized by reduced physical strength and endurance capacity. We tested the hypothesis that highly motivated men pushed to the limits of their endurance capacity for 3 months would suffer physical breakdown characterized by loss of lean mass and reduced physical performance capacity. METHODS: Two well-trained men (VO2max > 60 mL/kg/min), aged 25 years, completed an unsupported, 2928-km, south-to-north ski trek across Greenland in 86 days. The trek involved ski marching, typically for 9 h/d, pulling sleds initially containing 150 kg and a high-fat (60%) energy-dense diet of 25.1 MJ/d. Body composition and physical performance data were collected 14 days before and 4 days after the trek. RESULTS: Energy expenditure based on doubly labeled water during three 2-week periods ranged from 28.3 and 34.6 MJ/d in rugged terrain to 14.6 and 16.1 MJ/d during travel on flat terrain for subjects 1 and 2, respectively. Both men lost weight, completing the trek with low-normal fat stores (approximately 13% body fat). The lighter man gained 0.6 kg lean mass, while the heavier man lost 1.4 kg lean mass and a larger amount of fat weight (7.0 kg). Most performance measures showed trivial changes within the errors of measurement and test reproducibility, indicating no loss of endurance capacity, but anaerobic tests (Wingate and vertical jump) were markedly reduced. Markers of metabolic status, including oral glucose tolerance tests, indicated no functional impairments. CONCLUSIONS: Although the number of subjects was limited, this observational study demonstrated that well-trained and experienced long-distance ski trekkers who eat an adequate high-calorie diet can perform endurance treks in severe cold, with little or no loss of lean mass and physical capability.

Correlates of load carriage and obstacle course performance among women.

To examine correlates of the speed at which female soldiers carrying loads could cover 3.2 km on foot and traverse an obstacle course, 12 volunteers (mean +/- SD: 25.3 +/- 6 years, 166 +/- 7 cm, 61.3 +/- 7 kg) were timed over 3.2 km while carrying loads of 14, 27, and 41 kg, and while traversing an obstacle course with the two lighter loads. Pearson correlations showed that absolute VO_[2 max] and 3.2 km run time without a load were the best predictors of 3.2 km load carriage time for all loads. Also, larger subjects with greater muscle mass were able to carry the heaviest load faster than smaller, less muscular subjects, likely because the 41 kg load represented a smaller percentage of the former's bodyweight. Maximum number of sit-ups and push-ups, composite score of the Army Physical Fitness Test as well as body height were positively correlated with the speed at which some course segments were traversed.