Bioavailable IGF-I Is Associated with Fat-Free Mass Gains after Physical Training in Women

Sex Does Not Affect Changes in Body Composition and Insulin-Like Growth Factor-I During US Army Basic Combat Training

ABSTRACT

Roberts, BM, Staab, JS, Caldwell, AR, Sczuroski, CE, Staab, JE, Lutz, LJ, Reynoso, M, Geddis, AV, Taylor, KM, Guerriere, KI, Walker, LA, Hughes, JM, and Foulis, SA. Sex does not affect changes in body composition and insulin-like growth factor-I during US Army basic combat training. J Strength Cond Res 38(6): e304-e309, 2024-Insulin-like growth factor 1 (IGF-I) has been implicated as a biomarker of health and body composition. However, whether changes in body composition are associated with changes in IGF-I is unclear. Therefore, we examined the relationship between body composition changes (i.e., fat mass and lean mass) and total serum IGF-I levels in a large cohort of young men ( n = 809) and women ( n = 397) attending US Army basic combat training (BCT). We measured body composition using dual energy x-ray absorptiometry and total serum IGF-I levels during week 1 and week 9 of BCT. We found that pre-BCT lean mass ( r = 0.0504, p = 0.082) and fat mass ( r = 0.0458, p = 0.082) were not associated with pre-BCT IGF-I. Body mass, body mass index, body fat percentage, and fat mass decreased, and lean mass increased during BCT (all p < 0.001). Mean (± SD ) IGF-I increased from pre-BCT (176 ± 50 ng·ml -1 ) to post-BCT (200 ± 50 ng·ml -1 , p < 0.001). Inspection of the partial correlations indicated that even when considering the unique contributions of other variables, increases in IGF-I during BCT were associated with both increased lean mass ( r = 0.0769, p = 0.023) and increased fat mass ( r = 0.1055, p < 0.001) with no sex differences. Taken together, our data suggest that although changes in IGF-I weakly correlated with changes in body composition, IGF-I, in isolation, is not an adequate biomarker for predicting changes in body composition during BCT in US Army trainees.

Physiological biomarker monitoring during arduous military training: Maintaining readiness and performance

OBJECTIVES

Physiological and psychological stressors can degrade soldiers' readiness and performance during military training and operational environments. Integrative and holistic assessments of biomarkers across diverse human performance optimization domains during multistressor training can be leveraged to provide actionable insight to military leadership regarding service member health and readiness.

DESIGN/METHOD

A broad categorization of biomarkers, to include biochemical measures, bone and body composition, psychometric assessments, movement screening, and physiological load can be incorporated into robust analytical pipelines for understanding the complex factors that impact military human performance.

RESULTS

In this perspective commentary we overview the rationale, selection, and methodologies for monitoring biomarker domains that are relevant to military research and specifically highlight methods that have been incorporated in a research program funded by the Office of Naval Research, Code 34 Biological and Physiological Monitoring and Modeling of Warfighter Performance.

CONCLUSIONS

The integration of screening and continuous monitoring methodologies via robust analytical approaches will provide novel insight for military leaders regarding health, performance, and readiness outcomes during multistressor military training.

Initial military training modulates serum fatty acid and amino acid metabolites

Initial military training (IMT) results in increased fat-free mass (FFM) and decreased fat mass (FM). The underlying metabolic adaptations facilitating changes in body composition during IMT are unknown. The objective of this study was to assess changes in body composition and the serum metabolome during 22-week US Army IMT. Fifty-four volunteers (mean ± SD; 22 ± 3 year; 24.6 ± 3.7 kg/m2 ) completed this longitudinal study. Body composition measurements (InBody 770) and blood samples were collected under fasting, rested conditions PRE and POST IMT. Global metabolite profiling was performed to identify metabolites involved in energy, carbohydrate, lipid, and protein metabolism (Metabolon, Inc.). There was no change in body mass (POST-PRE; 0.4 ± 5.1 kg, p = 0.59), while FM decreased (-1.7 ± 3.5 kg, p < 0.01), and FFM increased (2.1 ± 2.8 kg, p < 0.01) POST compared to PRE IMT. Of 677 identified metabolites, 340 differed at POST compared to PRE (p < 0.05, Q < 0.10). The majority of these metabolites were related to fatty acid (73%) and amino acid (26%) metabolism. Increases were detected in 41% of branched-chain amino acid metabolites, 53% of histidine metabolites, and 35% of urea cycle metabolites. Decreases were detected in 93% of long-chain fatty acid metabolites, while 58% of primary bile acid metabolites increased. Increases in amino acid metabolites suggest higher rates of protein turnover, while changes in fatty acid metabolites indicate increased fat oxidation, which likely contribute changes in body composition during IMT. Overall, changes in metabolomics profiles provide insight into metabolic adaptions underlying changes in body composition during IMT.

Mendelian Randomization Analysis Reveals Causal Effects of Plasma Proteome on Body Composition Traits

CONTEXT

Observational studies have demonstrated associations between plasma proteins and obesity, but evidence of causal relationship remains to be studied.

OBJECTIVE

We aimed to evaluate the causal relationship between plasma proteins and body composition.

METHODS

We conducted a 2-sample Mendelian randomization (MR) analysis based on the genome-wide association study (GWAS) summary statistics of 23 body composition traits and 2656 plasma proteins. We then performed hierarchical cluster analysis to evaluate the structure and pattern of the identified causal associations, and we performed gene ontology enrichment analysis to explore the functional relevance of the identified proteins.

RESULTS

We identified 430 putatively causal effects of 96 plasma proteins on 22 body composition traits (except obesity status) with strong MR evidence (P < 2.53 × 10 - 6, at a Bonferroni-corrected threshold). The top 3 causal associations are follistatin (FST) on trunk fat-free mass (Beta = -0.63, SE = 0.04, P = 2.00 × 10-63), insulin-like growth factor-binding protein 1 (IGFBP1) on trunk fat-free mass (Beta = -0.54, SE = 0.03, P = 1.79 × 10-57) and r-spondin-3 (RSPO3) on WHR (waist circumference/hip circumference) (Beta = 0.01, SE = 4.47 × 10-4, P = 5.45 × 10-60), respectively. Further clustering analysis and pathway analysis demonstrated that the pattern of causal effect to fat mass and fat-free mass may be different.

CONCLUSION

Our findings may provide evidence for causal relationships from plasma proteins to various body composition traits and provide basis for further targeted functional studies.

Effects of resistance training on muscle strength, insulin-like growth factor-1, and insulin-like growth factor-binding protein-3 in healthy elderly subjects: a systematic review and meta-analysis of randomized controlled trials

BACKGROUND

Findings regarding the effects of resistance training (RT) on muscle strength, serum level of IGF-1, and its binding proteins are contradictory. To resolve this contradiction, we performed a systematic review and meta-analysis to investigate the effects of RT on muscle strength, the levels of serum IGF-1, and IGF-binding protein-3 in the elderly and aged.

MATERIALS AND METHODS

The PubMed, CINAHL, Medline, Google Scholar, and Scopus databases and reference lists of included studies were systematically searched to identify randomized controlled trials (RCTs) comparing subjects who underwent RT and control individuals up to May 15, 2020. This study was performed following the Preferred Items for Reporting of Systematic Reviews and Meta-Analyses guidelines. We identified and analyzed 11 eligible trials in this meta-analysis.

RESULTS

Pooled data displayed an overall significant elevation in IGF-1 (mean difference (MD): 17.34 ng/ml; 95% confidence interval (CI): 7.23, 27.46) and in muscle strength in leg press (SMD: 0.82; 95% CI: 0.30, 1.34) and bench press (SMD: 0.82; 95% CI: 0.42, 1.23) following RT. By contrast, the pooled estimate showed a non-significant elevation in IGFBP-3 (MD: 0.13 ng/ml; 95% CI: - 39.39, 39.65). Subgroup analysis revealed that the elevation in serum IGF-1 levels after RT was significant only in women (MD: 19.30 ng/ml); moreover, it increased after intervention durations of both > 12 weeks (MD: 21.98 ng/ml) and of ≤ 12 weeks (MD: 15.31 ng/ml).

CONCLUSION

RT was associated with elevated muscle strength. Moreover, RT was correlated with increased serum levels of IGF-1 among women and among those who received the training for ≤ 12 weeks or > 12 weeks. Further studies are required to elucidate the mechanisms underlying the impact of RT on IGF-1, IGFBP-3, and muscle strength.

Hormonal response patterns are differentially influenced by physical conditioning programs during basic military training

OBJECTIVES

Compare traditional military physical training and more contemporary physical training on catabolic and anabolic hormones and body composition in recruits undertaking basic military training (BMT).

DESIGN

A prospective cross-sectional study design.

METHODS

Two recruit intakes were assessed over the 12-week Australian Army BMT course. The control group (CON) comprised 40 recruits (26M/14F) and the experimental group (EXP) comprised 35 recruits (25M/10F). Hormone concentrations (IGF-I, testosterone, cortisol, SHBG) and body composition were assessed at weeks 1 and 12. The EXP group undertook a higher-load/intensity physical training regimen, while CON undertook the extant physical training program which focused on cardiovascular and muscular endurance. Total physical activity within physical training sessions was assessed during weeks 2, 6 and 9.

RESULTS

There was a significant group×time interaction (p<0.01) for IGF-I and cortisol, and main effects over time (p<0.01) for IGF-I, cortisol and SHBG. There were main effects for time (p<0.05) for lean and fat mass, and these changes were associated (p<0.05) with altered hormone concentrations. Physical activity levels were approximately 50% lower in EXP than CON during physical training sessions.

CONCLUSIONS

This is the first study to report a differential hormone response to contrasting physical conditioning regimen during BMT. The results indicate that the recruits who completed the EXP physical training regimen had an attenuated stress profile. This is an important observation, as any enhancement of recruit training outcomes are critical for Army noting that fundamentally, organisational capability is reliant upon the physical capability of its personnel.

Preparatory training attenuates drastic response of the insulin-like growth factor binding protein 1 at the point of maximal oxygen consumption in handball players

BACKGROUND

Intensive exercise changes physiological need for glucose and several biochemical pathways responsible for its metabolism response. Among them are those which involve insulin, insulin-like growth factor (IGF-1), and IGF-binding proteins (IGFBPs). Different types and degrees of exercise, as well as an athlete's fitness, may induce a range of responses regarding concentrations and time needed for the alteration. The idea of the work was to find out whether and how insulin/IGF axis responds to additional physical activity in the already trained subjects and if so, is the adaptation potentially beneficial from the aspect of metabolic control.

METHODS

The effect of 4-week intensive training on campus (preparatory training) on the levels of insulin, IGF-1, and IGFBPs during maximal progressive exercise test (MPET) on a treadmill was compared to the results obtained during MPET conducted after a regular training season of a female elite handball team (n = 17, age: 17 ± 1 years, height: 171 ± 8 cm, weight: 65 ± 8 kg, body mass index: 22 ± 1 kg/m2 at the beginning of the study; there were no significant changes at the end). Serum samples were obtained from players immediately before the test (basal), at the end of the test after reaching the point of maximal oxygen consumption (VO2max), and after recovery.

RESULTS

The concentration of insulin decreased at VO2max, but remained higher in players after preparatory training (12.2 ± 2.5 mU/L vs. 8.9 ± 4.4 mU/L, p = 0.049). The level of IGFBP-1 decreased in players at VO2max in either case of training, but it remained much higher in tests performed after the preparatory regime than before (p = 0.029). Concentrations of IGF-1, IGFBP-2, -3, and -4 did not change significantly.

CONCLUSION

The inverse relation between insulin and IGFBP-1 was lost during MPET, as these 2 molecules changed in the same direction. The results obtained suggest less severe stress-induced depression of insulin and IGFBP-1 after preparatory training. But another metabolic mechanism cannot be excluded, and that is potentially impaired insulin sensitivity resulting in higher level of IGFBP-1.

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±295.7<mid; 828.6±104.2=post; 833.7±481.2ng/mL; p=0.008) and Acid Labile Subunit (ALS) changed over the exercise training (pre-; 16.2±1.3=mid-; 17.6±1.8>post-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.

Role of IGF Binding Proteins in Regulating Metabolism

Insulin-like growth factors (IGFs) circulate in extracellular fluids bound to a family of binding proteins. Although they function in a classical manner to limit the access of the IGFs to their receptors they also have a multiplicity of actions that are independent of this property; they bind to their own receptors or are transported to intracellular and intranuclear sites to influence cellular functions that may directly or indirectly modify IGF actions. The availability of genetically modified animals has helped to determine their functions in a physiological context. These results show that many of their actions are cell type- and context-specific, and have led to a broader understanding of how these proteins function coordinately with IGF-I and -II to regulate growth and metabolism.

Consumption of a calcium and vitamin D-fortified food product does not affect iron status during initial military training: a randomised, double-blind, placebo-controlled trial

Ca/vitamin D supplementation maintains bone health and decreases stress fracture risk during initial military training (IMT); however, there is evidence that Ca may negatively affect the absorption of other critical micronutrients, particularly Fe. The objective of this randomised, double-blind, placebo-controlled trial was to determine whether providing 2000 mg/d Ca and 25µg/d vitamin D in a fortified food product during 9 weeks of military training affects Fe status in young adults. Male (n98) and female (n54) volunteers enrolled in US Army basic combat training (BCT) were randomised to receive a snack bar with Ca/vitamin D (n75) or placebo (snack bar without Ca/vitamin D;n77) and were instructed to consume 2 snack bars/d between meals throughout the training course. Circulating ionised Ca was higher (P<0·05) following BCT among those consuming the Ca/vitamin D bars compared with placebo. Fe status declined in both groups over the course of BCT. Transferrin saturation, serum ferritin and Hb were reduced (P<0·05) and soluble transferrin receptor increased (P<0·05) following BCT. There were no differences (P>0·05) in markers of Fe status between placebo and Ca/vitamin D groups. Collectively, these data indicate that Ca/vitamin D supplementation through the use of a fortified food product consumed between meals does not affect Fe status during IMT.

Chronic activity-based therapy does not improve body composition, insulin-like growth factor-I, adiponectin, or myostatin in persons with spinal cord injury

Spinal cord injury (SCI) induces dramatic changes in body composition including reductions in fat-free mass (FFM) and increases in fat mass (FM).

OBJECTIVE

To examine changes in body composition in response to chronic activity-based therapy (ABT) in persons with SCI.

DESIGN

Longitudinal exercise intervention.

METHODS

Seventeen men and women with SCI (mean age=36.1±11.5 years) completed 6 months of supervised ABT consisting of load bearing, resistance training, locomotor training, and functional electrical stimulation. At baseline and after 3 and 6 months of ABT, body weight, body fat, and FFM were assessed using dual-energy X-ray absorptiometry, and fasting blood samples were obtained to assess changes in insulin-like growth factor-I (IGF-I), adiponectin, and myostatin.

RESULTS

Across all subjects, there was no change (P>0.05) in body weight, percent body fat, or FFM of the leg, arm, or trunk, whereas whole-body FFM declined (P=0.02, 50.4±8.4 to 49.2±7.4 kg). No changes (P=0.21-0.41) were demonstrated in IGF-I, adiponectin, or myostatin during the study.

CONCLUSIONS

Chronic ABT focusing on the lower extremity does not slow muscle atrophy or alter body fat, body mass, or regional depots of FFM in persons with SCI. Further, it does not induce beneficial changes in adiponectin, myostatin, or IGF-I. Alternative exercise-based therapies are needed in SCI to reverse muscle atrophy and minimize the onset of related health risks.

Calcium and vitamin D supplementation maintains parathyroid hormone and improves bone density during initial military training: a randomized, double-blind, placebo controlled trial

Calcium and vitamin D are essential nutrients for bone health. Periods of activity with repetitive mechanical loading, such as military training, may result in increases in parathyroid hormone (PTH), a key regulator of Ca metabolism, and may be linked to the development of stress fractures. Previous studies indicate that consumption of a Ca and vitamin D supplement may reduce stress fracture risk in female military personnel during initial military training, but circulating markers of Ca and bone metabolism and measures of bone density and strength have not been determined. This randomized, double-blind, placebo-controlled trial sought to determine the effects of providing supplemental Ca and vitamin D (Ca+Vit D, 2000mg and 1000IU/d, respectively), delivered as 2 snack bars per day throughout 9weeks of Army initial military training (or basic combat training, BCT) on PTH, vitamin D status, and measures of bone density and strength in personnel undergoing BCT, as well as independent effects of BCT on bone parameters. A total of 156 men and 87 women enrolled in Army BCT (Fort Sill, OK; 34.7°N latitude) volunteered for this study. Anthropometric, biochemical, and dietary intake data were collected pre- and post-BCT. In addition, peripheral quantitative computed tomography was utilized to assess tibia bone density and strength in a subset of volunteers (n=46). Consumption of supplemental Ca+Vit D increased circulating ionized Ca (group-by-time, P=0.022), maintained PTH (group-by-time, P=0.032), and increased the osteoprotegerin:RANKL ratio (group-by-time, P=0.006). Consistent with the biochemical markers, Ca+Vit D improved vBMD (group-by-time, P=0.024) at the 4% site and cortical BMC (group-by-time, P=0.028) and thickness (group-by-time, P=0.013) at the 14% site compared to placebo. These data demonstrate the benefit of supplemental Ca and vitamin D for maintaining bone health during periods of elevated bone turnover, such as initial military training. This trial was registered with ClincialTrials.gov, NCT01617109.

Energy balance and body composition during US Army special forces training

Small Unit Tactics (SUT) is a 64-day phase of the Special Forces Qualification Course designed to simulate real-world combat operations. Assessing the metabolic and physiological responses of such intense training allows greater insights into nutritional requirements of soldiers during combat. The purpose of this study was to examine energy balance around specific training events, as well as changes in body mass and composition. Data were collected from 4 groups of soldiers (n = 36) across 10-day periods. Participants were 28 ± 5 years old, 177 ± 6 cm tall, and weighed 83 ± 7 kg. Doubly labeled water (D218O) was used to assess energy expenditure. Energy intake was calculated by subtracting energy in uneaten foods from known energy in distributed foods in individually packaged combat rations or in the dining facility. Body composition was estimated from skinfold thickness measurements on days 0 and 64 of the course. Simulated urban combat elicited that largest energy deficit (11.3 ± 2.3 MJ·day−1 (2700 ± 550 kcal·day−1); p < 0.05), and reduction in body mass (3.3 ± 1.9 kg; p < 0.05), during SUT, while energy balance was maintained during weapons familiarization training and platoon size raids. Over the entire course body mass decreased by 4.2 ± 3.7 kg (p < 0.01), with fat mass decreasing by 2.8 ± 2.0 kg (p < 0.01) and fat-free mass decreasing by 1.4 ± 2.8 kg (p < 0.05). The overall reduction in body mass suggests that soldiers were in a negative energy balance during SUT, with high energy deficit being observed during strenuous field training.

Differential effects of military training on fat-free mass and plasma amino acid adaptations in men and women

Fat-free mass (FFM) adaptations to physical training may differ between sexes based on disparities in fitness level, dietary intake, and levels of plasma amino acids (AA). This investigation aimed to determine FFM and plasma AA responses to military training, examine whether adaptations differ between male and female recruits, and explore potential associations between FFM and AA responses to training. Body composition and plasma AA levels were assessed in US Army recruits (n = 209, 118 males, 91 females) before (baseline) and every three weeks during basic combat training (BCT), a 10-week military training course. Body weight decreased in men but remained stable in women during BCT (sex-by-time interaction, P < 0.05). Fifty-eight percent of recruits gained FFM during BCT, with more (P < 0.05) females (88%) gaining FFM than males (36%). Total plasma AA increased (P < 0.05) during BCT, with greater (P < 0.05) increases observed in females (17%) then in males (4%). Essential amino acids (EAA) and branched-chain amino acids (BCAA) were increased (P < 0.05) in females but did not change in males (sex-by-time interaction, P < 0.05). Independent of sex, changes in EAA (r = 0.34) and BCAA (r = 0.27) from baseline were associated with changes in FFM (P < 0.05); greater (P < 0.05) increases in AA concentrations were observed for those who gained FFM. Increases in FFM and plasma AA suggest that BCT elicits a more pronounced anabolic response in women compared to men, which may reflect sex-specific differences in the relative intensity of the combined training and physiological stimulus associated with BCT.

Female recruits sustaining stress fractures during military basic training demonstrate differential concentrations of circulating IGF-I system components: a preliminary study

OBJECTIVE

Stress fracture injuries sustained during military basic combat training (BT) are a significant problem and occur at a higher rate in female recruits than male recruits. Insulin-like growth factor-I (IGF-I) is an easily measured biomarker that is involved in bone formation and positively correlated with bone mineral density, especially in women. This study examined the response of the IGF-I system between female soldiers that sustained a stress fracture (SFX, n=13) during BT and female soldiers who did not (NSFX, n=49).

DESIGN

Female soldiers (n=62, 18.8 ± 0.6 yr) from 2 companies of a gender-integrated combat battalion in the Israeli Defense Forces participated in this study. Height, weight and blood draws were taken upon entry to BT (preBT) and after a four-month BT program (postBT). Stress fractures were diagnosed by bone scan. Serum was analyzed for total IGF-I, free IGF-I, IGF binding proteins (IGFBP)1-6, BAP, calcium, CTx, IL1β, IL6, PINP, PTH, TNFα, TRAP, and 25(OH)D. Statistical differences between SFX and NSFX groups and time points were assessed by RM ANOVA with Fisher post-hoc (p≤0.05).

RESULTS

The SFX group was significantly taller and had lower BMI than NSFX (p≤0.05). Serum concentrations of total IGF-I, bioavailable IGF-I, other bone biomarkers, and cytokines were not significantly different between SFX and NSFX preBT. Serum IGFBP-2 and IGFBP-5 were significantly higher in the SFX compared to the NSFX preBT (p≤0.05). In both groups, total IGF-I increased pre to postBT (p≤0.05). Additionally, a significant difference was observed in the bioavailable IGF-I response pre to postBT for both groups. The SFX group demonstrated a significant decrease in bioavailable IGF-I pre to postBT (preBT: 0.58 ± 0.58 ng/mL; postBT 0.39 ± 0.48; p≤0.05) whereas the NSFX group demonstrated a significant increase in bioavailable IGF-I pre to postBT (preBT: 0.53 ± 0.37 ng/mL; postBT: 0.63 ± 0.45; p≤0.05).

CONCLUSIONS

Our study demonstrated that serum IGF-I changes during basic training and that women sustaining stress fractures during BT significantly decreased bioavailable IGF-I, whereas their uninjured counter parts increased bioavailable IGF-I. These results suggest that stress fracture susceptibility may be related to differential IGF-I system concentrations and response to physical training.