Reliability of simulated combat tasks performed by Brazilian Air Force cadets.

The Brazilian Air Force (BAF) has developed physical evaluations focused on the demands required in combat scenarios, giving rise to the Simulated Tasks (STs). Therefore, the purpose of the present study was to determine test-retest reliability and investigate learning effects of the five STs established among the BAF. Fifty-six subjects performed five STs three times, after completing a previous familiarisation session. Repeated measures analysis of variance (ANOVA) was used to determine the occurrence of learning effects, and the intraclass correlation coefficient (ICC) was used to identify the reliability of each ST. ANOVA revealed no significant differences in the subject's scores across trials for all the STs, and the ICCs ranged from 0.75 to 0.92 (p < 0.01). In conclusion, this study identified that the five STs showed no learning effects across three successive trials and exhibited high levels of reliability.

Understanding the reliability and learning effects of the STs established among the Brazilian Air Force is crucial for their potential implementation. The subjects performed five STs three times, over the course of seven days. The results highlighted no evidence of learning effects, and high levels of reliability.

Heart rate variability of elite female rowers in preparation for and during the national selection regattas: a pilot study on the relation to on water performance.

Elite athletes require a delicate balance of physiological and psychological stress and recovery-essential for achieving optimal performance. Monitoring heart rate variability (HRV) provides a non-invasive estimation of both physiological and psychological stress levels, offering potentially valuable insights into health, performance, and adaptability. Previous studies, primarily conducted on male participants, have shown an association between HRV and performance in the context of rowing training. However, given the rigorous nature of rowing training, it is crucial to investigate HRV in elite rowers, particularly during the U.S. national selection regattas (NSR). Purpose: To comprehensively analyze elite female rowers, evaluating acute changes in HRV and subjective psychometrics during the NSR. Methods: Five elite female rowers (26 ± 2 years, 180 ± 8 cm, 82 ± 8 kg, 19 ± 6%fat) were recruited and tracked prior to and during NSR I and II. Morning HRV measures were completed using photoplethysmography (HRV4training) along with self-reported levels of fatigue, soreness, rating of perceived exertion, mentally energy and physical condition. Results: Significant decreases were observed in log transformed root-mean square of successive differences (LnRMSSD; p = 0.0014) and fatigue (p = 0.01) from pre-to-during NSR, while mental energy (p = 0.01), physical condition (p = 0.01), and motivation (p = 0.006) significantly increased. These psychometric measures returned to pre-NSR levels, at post-NSR (all p < 0.05), though HRV remained slightly suppressed. NSR on-water performance was not correlated to LnRMSSD or the change in LnRMSSD (p > 0.05). Discussion: HRV and psychometric measures are sensitive to the stress of elite rowing competition in females. However, HRV was not associated with on-water rowing performance during an elite rowing competition.

Biomarkers of oxidative stress, diet and exercise distinguish soldiers selected and non-selected for special forces training.

INTRODUCTION: The metabolomic profiles of Soldiers entering the U.S. Special Forces Assessment and Selection course (SFAS) have not been evaluated. OBJECTIVES: To compare pre-SFAS blood metabolomes of Soldiers selected during SFAS versus those not selected, and explore the relationships between the metabolome, physical performance, and diet quality. METHODS: Fasted blood samples and food frequency questionnaires were collected from 761 Soldiers prior to entering SFAS to assess metabolomic profiles and diet quality, respectively. Physical performance was assessed throughout SFAS. RESULTS: Between-group differences (False Discovery Rate < 0.05) in 108 metabolites were detected. Selected candidates had higher levels of compounds within xenobiotic, pentose phosphate, and corticosteroid metabolic pathways, while non-selected candidates had higher levels of compounds potentially indicative of oxidative stress (i.e., sphingomyelins, acylcarnitines, glutathione, amino acids). Multiple compounds higher in non-selected versus selected candidates included: 1-carboxyethylphenylalanine; 4-hydroxy-nonenal-glutathione; α-hydroxyisocaproate; hexanoylcarnitine; sphingomyelin and were associated with lower diet quality and worse physical performance.  CONCLUSION: Candidates selected during SFAS had higher pre-SFAS levels of circulating metabolites that were associated with resistance to oxidative stress, higher physical performance and higher diet quality. In contrast, non-selected candidates had higher levels of metabolites potentially indicating elevated oxidative stress. These findings indicate that Soldiers who were selected for continued Special Forces training enter the SFAS course with metabolites associated with healthier diets and better physical performance. Additionally, the non-selected candidates had higher levels of metabolites that may indicate elevated oxidative stress, which could result from poor nutrition, non-functional overreaching/overtraining, or incomplete recovery from previous physical activity.

Anthropometrics and body composition predict performance during a simulated direct-fire engagement.

This study determined anthropometric and body composition predictors of performance during a simulated direct-fire engagement. Healthy subjects (N = 33, age = 25.7 ± 7.0 yr) underwent anthropometric and body composition assessments before completing a simulated direct-fire engagement - consisting of marksmanship with cognitive workload assessment and a fire-and-move drill (16 × 6-m sprints) while wearing combat load. Susceptibility to enemy fire was modelled on sprint duration. Partial correlations and multiple linear regressions established the relationships between predictors and performance outcomes, controlling for age and sex. Significance was p ≤ 0.05. Higher percent body fat, fat mass, fight load index predicted greater susceptibility to enemy fire (r = 0.40 to 0.42) and lower cognitive performance (r= -0.45 to -0.49). Higher BMI also predicted lower cognitive performance (r= -0.49). Shorter stature/hand length predicted higher marksmanship accuracy (r= -0.40), while higher fat-free mass/fat-free mass index predicted slower reaction times (r = 0.36-0.41). These data suggest anthropometric and body composition measures modulate combat effectiveness and reinforce body composition standards in military organisations.Practitioner summary: This study identified field-expedient anthropometric and body composition predictors of a simulated direct-fire engagement that evaluated survivability (i.e. susceptibility to enemy fire) and lethality (i.e. marksmanship, cognitive performance) outcomes. Our findings suggest that anthropometric and body composition measures may play a role in soldier survivability and lethality during simulated direct-fire engagements.

Metabolomics of testosterone enanthate administration during severe-energy deficit.

INTRODUCTION: Testosterone administration attenuates reductions in total body mass and lean mass during severe energy deficit (SED). OBJECTIVES: This study examined the effects of testosterone administration on the serum metabolome during SED. METHODS: In a double-blind, placebo-controlled clinical trial, non-obese men were randomized to receive 200-mg testosterone enanthate/wk (TEST) (n = 24) or placebo (PLA) (n = 26) during a 28-d inpatient, severe exercise- and diet-induced energy deficit. This study consisted of three consecutive phases. Participants were free-living and provided a eucaloric diet for 14-d during Phase 1. During Phase 2, participants were admitted to an inpatient unit, randomized to receive testosterone or placebo, and underwent SED for 28-d. During Phase 3, participants returned to their pre-study diet and physical activity habits. Untargeted metabolite profiling was conducted on serum samples collected during each phase. Body composition was measured using dual-energy X-ray absorptiometry after 11-d of Phase 1 and after 25-d of Phase 2 to determine changes in fat and lean mass. RESULTS: TEST had higher (Benjamini-Hochberg adjusted, q < 0.05) androgenic steroid and acylcarnitine, and lower (q < 0.05) amino acid metabolites after SED compared to PLA. Metabolomic differences were reversed by Phase 3. Changes in lean mass were associated (Bonferroni-adjusted, p < 0.05) with changes in androgenic steroid metabolites (r = 0.42-0.70), acylcarnitines (r = 0.37-0.44), and amino acid metabolites (r = - 0.36-- 0.37). Changes in fat mass were associated (p < 0.05) with changes in acylcarnitines (r = - 0.46-- 0.49) and changes in urea cycle metabolites (r = 0.60-0.62). CONCLUSION: Testosterone administration altered androgenic steroid, acylcarnitine, and amino acid metabolites, which were associated with changes in body composition during SED.

Effects of acute arginine supplementation on neuroendocrine, metabolic, cardiovascular, and mood outcomes in younger men: A double-blind, placebo-controlled trial.

OBJECTIVES: Arginine is an amino-acid supplement and precursor for nitric-oxide synthesis, which affects various biologic processes. The objective of this study was to determine the effects of arginine supplementation on growth hormone (GH) and metabolic parameters. METHODS: Thirty physically active, healthy men (age 18-39 y; body mass index: 18.5-25 kg/m2) were randomized in a double-blind, placebo-controlled, crossover trial. Arginine (10 g) and placebo (0 g) beverages were consumed after an overnight fast. Blood samples were collected at baseline and 1.5, 3.0, and 24 h after supplementation. The primary outcomes were serum GH and metabolomics. Also, amino acids, glucose, insulin, triacylglycerols, thyroid hormones, testosterone, cortisol, dehydroepiandrosterone, and mood state were assessed. Individuals with detectable increases in GH were analyzed separately (responders: n = 16; < 0.05 ng/mL at 1.5 h). Repeated-measure analyses of variance estimated the treatment effects at each timepoint. RESULTS: Arginine levels increased at 1.5 h (146%) and 3.0 h (95%; P ≤ 0.001) and GH (193%) and thyroid-stimulating hormone (TSH; 10%) levels at 24 h (P < 0.05) after arginine versus placebo consumption. Arginine versus placebo increased glucose levels at 1.5 h (5%) and 3.0 h (3%; P ≤ 0.001). Arginine versus placebo did not affect other dependent measures, including mood state (P > 0.05), but changes in the urea, glutamate, and citric-acid pathways were observed. Among responders, arginine versus placebo increased GH at 1.5 h (37%), glucose at 1.5 h (4%) and 3.0 h (4%), and TSH at 24 h (9%; P < 0.05). Responders had higher levels of benzoate metabolites at baseline and 1.5 h, and an unknown compound (X-16124) at baseline, 1.5 h, and 24 h that corresponds to a class of gut microbes (P < 0.05). CONCLUSIONS: Arginine supplementation modestly increased GH, glucose, and TSH levels in younger men. Responders had higher benzoate metabolites and an unknown analyte attributed to the gut microbiome. Future studies should examine whether the increased prevalence of these gut microorganisms corresponds with GH response after arginine supplementation.

Lower-body muscular power and exercise tolerance predict susceptibility to enemy fire during a tactical combat movement simulation.

This study examined if field-expedient physical fitness/performance assessments predicted performance during a simulated direct-fire engagement. Healthy subjects (n = 33, age = 25.7 ± 7.0 years) completed upper- and lower-body strength and power assessments and a 3-min all-out running test to determine critical velocity. Subjects completed a simulated direct-fire engagement that consisted of marksmanship with cognitive workload assessment and a fire-and-move drill (16 × 6-m sprints) while wearing a combat load. Susceptibility to enemy fire was modelled on average sprint duration during the fire-and-move drill. Stepwise linear regression identified predictors for the performance during the simulated direct-fire engagement. Critical velocity (ß = -0.30, p < 0.01) and standing broad jump (ß = -0.67, p < 0.001) predicted susceptibility to enemy fire (R2 = 0.74, p < 0.001). All predictors demonstrated poor relationships with marksmanship accuracy and cognitive performance. These data demonstrate the importance of exercise tolerance and lower-body power during simulated direct-fire engagements and provide potential targets for interventions to monitor and enhance performance and support soldier survivability. Practitioner Summary: This study identified field-expedient physical fitness/performance predictors of a simulated direct-fire engagement which evaluated susceptibility to enemy fire, marksmanship, and cognitive performance. Our findings suggest that high-intensity exercise tolerance and lower-body power are key determinants of performance that predicted susceptibility to enemy fire.

Effects of Caffeine on Exercise Duration, Critical Velocity, and Ratings of Perceived Exertion During Repeated-Sprint Exercise in Physically Active Men.

Caffeine improves short-to-moderate distance running performance, but the effect of caffeine on repeated sprints are equivocal. This research determined if caffeine improved exercise tolerance during repeated-sprint exercise. iCV is a running velocity that distinguishes intermittent running velocities (velocities ≤ iCV) that are sustainable from those resulting in a predictable time to exhaustion (velocities > iCV). Seven physically active men (age = 21.6 ± 1.5 years, body mass = 72.8 ± 5.1 kg, VO2max = 56.9 ± 9.8 mL/kg/min) ingested caffeine (5 mg/kg) or placebo (crossover design) 60 min prior to an intermittent critical velocity (iCV) test. The treadmill grade and velocity at VO2max (vVO2max) were used for iCV testing, and consisted of 3 bouts (10 sec running and 10 sec passive rest) at 130, 110 and 120% vVO2max. Each bout continued until volitional exhaustion and was separated by 20 min of passive rest. Total distance and duration were recorded to determine exercise tolerance using the iCV model. Caffeine ingestion increased running duration at 110% vVO2max (p = 0.02), but not at 120 (p = 0.93) and 130% vVO2max (p = 0.14). Caffeine did not improve iCV model parameters. A single dose of caffeine consumed 60 min before repeated-sprints can improve performance at 110% vVO2max, but not at higher velocities.

Acute Caffeine Supplementation Does Not Improve Performance in Trained CrossFit® Athletes.

Caffeine's ergogenic effects persist during various exercise modalities; however, information establishing its efficacy during CrossFit® protocols is limited. This study aimed to determine the effects of caffeine supplementation on CrossFit® performance. Twenty CrossFit®-trained men (age = 26.7 ± 6.2 years, experience = 3.7 ± 2.9 years) were randomized in a double-blind, crossover design. Participants completed two sessions separated by a seven-day washout period, 60 min after consuming 5 mg/kg body mass of caffeine or a placebo. In each session, participants completed as many rounds as possible in 20 min of five pull-ups, 10 push-ups, and 15 air squats. CrossFit® performance was the total number of repetitions completed in 20 min. Paired-samples t-tests were used to compare CrossFit® performance between caffeine and placebo conditions and to test for a potential learning effect between the first and second sessions. CrossFit® performance was not significantly different during the caffeine condition compared to the placebo (468.6 ± 114.7 vs. 466.7 ± 94.3 repetitions, p = 0.861). A significant learning effect was identified between the first and second sessions (452.4 ± 101 vs. 483.8 ± 106.5 repetitions, p = 0.001), with no significant effect of treatment order (p = 0.438). Caffeine's ergogenic effect were not present during the CrossFit® workout "Cindy"; however, future research should include familiarization sessions and examine other CrossFit® workouts in novice and women participants.

Retraction: Stein, J.A. et al. The Effects of Acute Caffeine Supplementation on Performance in Trained CrossFit Athletes. Sports 2019, 7, 95.

All authors of the published article [1] have agreed to retract it based on the basis of a data entry error (Figure 1) [...].

The Effects of Acute Caffeine Supplementation on Performance in Trained CrossFit Athletes.

Caffeine's ergogenic effects persist during various exercise modalities; however, information establishing its efficacy during CrossFit protocols is limited. Our study aimed to determine the effects of caffeine supplementation on CrossFit performance. Thirteen CrossFit-trained men (age = 28.5 ± 6.6 years, experience = 49.2 ± 36.3 months) were randomized in a double-blind, crossover design. Participants completed two sessions separated by a seven-day washout period, 60 min after consuming 5 mg/kg body mass of caffeine or a placebo. In each session, participants completed as many rounds as possible in 20 min of 5 pull-ups, 10 push-ups, and 15 air squats. CrossFit performance was the total number of repetitions completed in 20 min. Paired samples t-tests were used to compare CrossFit performance between caffeine and placebo conditions and to test for a potential learning effect between the first and second sessions. CrossFit performance was significantly higher during the caffeine condition compared to the placebo (461.4 ± 103 vs. 425.0 ± 93.5 repetitions, p < 0.05). No significant learning effect was identified between the first and second sessions (445.6 ± 95.0 vs. 440.8 ± 105.0 repetitions, p = 0.73) nor was there a significant treatment order effect (p = 0.40). Caffeine's ergogenic effect is present during CrossFit; however, future investigations should establish caffeine's efficacy during other CrossFit protocols and among female athletes.