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1.
Artigo em Inglês | MEDLINE | ID: mdl-34855522

RESUMO

Simulated military operational stress (SMOS) provides a useful model to better understand resilience in humans as the stress associated with caloric restriction, sleep deficits, and fatiguing exertion degrades physical and cognitive performance. Habitual physical activity may confer resilience against these stressors by promoting favorable use-dependent neuroplasticity, but it is unclear how physical activity, resilience, and corticospinal excitability (CSE) relate during SMOS. PURPOSE: To examine associations between corticospinal excitability, physical activity, and physical performance during SMOS. METHODS: Fifty-three service members (age: 26±5yrs, 13 women) completed a five day and night intervention composed of familiarization, baseline, SMOS (two nights/days), and recovery days. During SMOS, participants performed rigorous physical and cognitive activities while receiving half of normal sleep (two 2h blocks) and caloric requirements. Lower and upper limb CSE were determined with transcranial magnetic stimulation (TMS) stimulus-response curves. Self-reported resilience, physical activity, military-specific physical performance (TMT) and endocrine factors were compared in individuals with high (HIGH) and low CSE based on a median split of lower limb CSE at baseline. RESULTS: HIGH had greater physical activity and better TMT performance throughout SMOS. Both groups maintained physical performance despite substantial psychophysiological stress. Physical activity, resilience, and TMT performance were directly associated with lower limb CSE. CONCLUSION: Individual differences in physical activity coincide with lower (but not upper) limb CSE. Such use-dependent corticospinal excitability directly relates to resilience and physical performance during SMOS. Future studies may use non-invasive neuromodulation to clarify the interplay among CSE, physical activity, and resilience and improve physical and cognitive performance.

2.
Eur J Sport Sci ; : 1-15, 2021 Aug 17.
Artigo em Inglês | MEDLINE | ID: mdl-34346851

RESUMO

Adaptation to military operational stress is a complex physiological response that calls upon the sympathetic nervous system (SNS), hypothalamic pituitary adrenal (HPA) axis and immune system, to create a delicate balance between anabolism and catabolism and meet the demands of an ever-changing environment. As such, resilience, the ability to withstand and overcome the negative impact of stress on military performance, is likely grounded in an appropriate biological adaptation to encountered stressors. Neuroendocrine [i.e. cortisol, epinephrine (EPI), norepinephrine (NE), neuropeptide-Y (NPY), and brain derived neurotropic factor (BDNF)], inflammatory [i.e. interleukin 6 (IL-6), IL-1ß, IL-4, IL-10 and tumour necrosis factor (TNF)-α], as well as growth and anabolic [i.e. insulin-like growth factor-I (IGF-I), testosterone, and dehydroepiandrosterone (DHEA)] biomarkers independently and interactively function in stress adaptations that are associated with a soldier's physical and psychological performance. In this narrative review, we detail biomarkers across neuroendocrine, inflammatory, and growth stimulating domains to better elucidate the biological basis of a resilient soldier. The findings from the reviewed studies indicate that military readiness and resiliency may be enhanced through better homeostatic control, better regulated inflammatory responses, and balanced anabolic/catabolic processes. It is unlikely that one class of biomarkers is better for assessing physiological resilience. Therefore, a biomarker panel that can account for appropriate balance across these domains may be superior in developing monitoring frameworks. Real-time physiological monitoring to assess biomarkers associated with resilience will be possible pending more sophisticated technologies and provide a field-expedient application for early identification and intervention of at-risk soldiers to improve military resiliency.

3.
Sleep ; 2021 Aug 25.
Artigo em Inglês | MEDLINE | ID: mdl-34432067

RESUMO

STUDY OBJECTIVES: Within-subject stability of certain sleep features across multiple nights is thought to reflect the trait-like behavior of sleep. However, to be considered a trait, a parameter must be both stable and robust. Here, we examined the stability (i.e., across the same sleep opportunity periods) and robustness (i.e., across sleep opportunity periods that varied in duration and timing) of different sleep parameters. METHODS: Sixty-eight military personnel (14 W) spent 5 nights in the sleep laboratory during a simulated military operational stress protocol. After an adaptation night, participants had an 8-hour sleep opportunity (23:00-07:00) followed by 2 consecutive nights of sleep restriction and disruption which included two 2-hour sleep opportunities (01:00-03:00; 05:00-07:00) and, lastly, another 8-hour sleep opportunity (23:00-07:00). Intra-class correlation coefficients were calculated to examine differences in stability and robustness across different sleep parameters. RESULTS: Sleep architecture parameters were less stable and robust than absolute and relative spectral activity parameters. Further, relative spectral activity parameters were less robust than absolute spectral activity. Absolute alpha and sigma activity demonstrated the highest levels of stability that were also robust across sleep opportunities of varying duration and timing. CONCLUSIONS: Stability and robustness varied across different sleep parameters, but absolute NREM alpha and sigma activity demonstrated robust trait-like behavior across variable sleep opportunities. Reduced stability of other sleep architecture and spectral parameters during shorter sleep episodes as well as across different sleep opportunities has important implications for study design and interpretation.

4.
Physiol Behav ; 236: 113413, 2021 07 01.
Artigo em Inglês | MEDLINE | ID: mdl-33811909

RESUMO

PURPOSE: To study the impact of 48 h of simulated military operational stress (SMOS) on executive function, in addition to the role of trait resilience (RES) and aerobic fitness (FIT) on executive function performance. Associations between executive function and neuropeptide-Y (NPY), brain-derived neurotropic factor (BDNF), insulin-like growth factor-I (IGF-I), oxytocin, and α-klotho (klotho) were assessed to elucidate potential biomarkers that may contribute to cognitive performance during a multi-factorial stress scenario. METHODS: Fifty-four service members (SM) (26.4 ± 5.4 years, 178.0 ± 6.5 cm, 85.2 ± 14.0 kg) completed the 5-day protocol, including daily physical exertion and 48 h of restricted sleep and caloric intake. Each morning subjects completed a fasted blood draw followed by Cognition, a 10-part cognitive test battery assessing executive function. SMs were grouped into tertiles [low (L-), moderate (M-), high (H-)] based on Connor Davidson Resilience Score (RES) and V˙O2peak (FIT). Repeated measures ANOVA were run to analyze the effect of day on cognitive performance and biomarker concentration. Separate two-way mixed ANOVAs were run to determine the interaction of group by day on cognitive function. Friedman test with Bonferroni-corrected pairwise comparisons were used if assumptions for ANOVA were not met. Associations between changes in biomarkers and cognitive performance were analyzed using parametric and non-parametric correlation coefficients. RESULTS: SMOS reduced SM vigilance -11.3% (p < 0.001) and working memory -5.6% (p = 0.015), and increased risk propensity +9.5% (p = 0.005). H-RES and H-FIT SMs demonstrated stable vigilance across SMOS (p > 0.05). Vigilance was compromised during SMOS in L- and M-RES (p = 0.007 and p = 0.001, respectively) as well as L- and M-FIT (p = 0.001 and p = 0.031, respectively). SMOS reduced circulating concentrations of α-klotho -7.2% (p = 0.004), NPY -6.4% (p = 0.001), and IGF-I -8.1% (p < 0.001) from baseline through the end of the protocol. BDNF declined -19.2% after the onset of sleep and caloric restriction (p = 0.005) with subsequent recovery within 48 h. Oxytocin remained stable (p > 0.05). Several modest associations between neuroendocrine biomarkers and cognitive performance were identified. CONCLUSION: This study demonstrates H-FIT and H-RES may buffer the impact of SMOS on vigilance. SMOS negatively impacted circulating neuroendocrine biomarkers. While BDNF returned to baseline concentrations by the end of the 5 d protocol, NPY, IGF-I, and α-klotho may require a longer recovery period. These data suggest that the military may benefit by training and/or selection processes targeting at augmenting trait resilience and aerobic fitness for increased readiness.


Assuntos
Função Executiva , Militares , Biomarcadores , Cognição , Exercício Físico , Humanos , Memória de Curto Prazo , Aptidão Física
5.
Eur J Sport Sci ; : 1-34, 2021 Apr 10.
Artigo em Inglês | MEDLINE | ID: mdl-33840352

RESUMO

Combat roles are physically demanding and expose service personnel to operational stressors such as high levels of physical activity, restricted nutrient intake, sleep loss, psychological stress, and environmental extremes. Women have recently integrated into combat roles, but our knowledge of the physical, physiological, and psycho-cognitive responses to these operational stressors in women is limited. The aim of this narrative review was to evaluate the evidence for sex-specific physical, physiological, and psycho-cognitive responses to real, and simulated, military operational stress. Studies examining physical and cognitive performance, body composition, metabolism, hypothalamic-pituitary-gonadal axis, and psychological health outcomes were evaluated. These studies report that women expend less energy and lose less body mass and fat-free mass, but not fat mass, than men. Despite having similar physical performance decrements as men during operational stress, women experience greater physiological strain than men completing the same physical tasks, but this may be attributed to differences in fitness. From limited data, military operational stress suppresses hypothalamic-pituitary-gonadal, but not hypothalamic-pituitary-adrenal, axis function in both sexes. Men and women demonstrate different psychological and cognitive responses to operational stress, including disturbances in mood, with women having a higher risk of post-traumatic stress symptoms compared with men. Based on current evidence, separate strategies to maximize selection and combat training are not warranted until further data directly comparing men and women are available. However, targeted exercise training programs may be advisable to offset the physical performance gap between sexes and optimize performance prior to inevitable declines caused by intense military operations.

7.
J Sci Med Sport ; 23(5): 529-534, 2020 May.
Artigo em Inglês | MEDLINE | ID: mdl-31870679

RESUMO

OBJECTIVES: To investigate tactically-related physical performance and body composition recovery following U.S. Army Ranger training. DESIGN: Prospective cohort. METHODS: Physical performance was comprehensively assessed using a tactically-related performance battery (i.e., Ranger Athlete Warrior assessment) in 10 male Soldiers at baseline (BL) two-weeks (P1), and six-weeks (P2) post-Ranger School. Body composition was determined using DXA. A one-way repeated measures ANOVA was used followed by Bonferroni-adjusted pairwise comparisons when group differences existed (p≤0.05). Pearson correlation coefficients were used to establish associations between changes in fitness and body composition. RESULTS: All performance domains except the bench press and deadlift worsened following training. Speed/mobility (Illinois agility test, seconds - BL: 16.20±0.86 vs. P2: 18.66±2.09), anaerobic capacity (300-yard shuttle run, seconds - BL: 62.95±6.17 vs. P2: 67.23±5.91), core strength (heel clap, repetitions - BL: 15.80±4.08 vs. P2: 11.50±4.95), and aerobic endurance (beep test, stage - BL: 9.95±2.18 vs. P2: 7.55±1.07) had not recovered by P2. Only upper body muscular endurance and strength (metronome push-up and pull-up, respectively) were similar to BL by P2. Percent body fat increased from 15.62±3.94 (BL) to 19.33±2.99 (P2) (p<0.001). There were no significant associations between changes in body composition and performance. CONCLUSIONS: A comprehensive characterization of physical performance and body composition revealed Rangers did not experience full recovery of fitness six weeks after training. Optimal recovery strategies are needed to return Soldiers to a state of readiness following arduous training.


Assuntos
Composição Corporal , Militares , Força Muscular , Resistência Física , Aptidão Física , Adulto , Teste de Esforço , Humanos , Masculino , Estudos Prospectivos , Estados Unidos , Adulto Jovem
8.
Work ; 63(3): 347-353, 2019.
Artigo em Inglês | MEDLINE | ID: mdl-31256104

RESUMO

BACKGROUND: Standing desks are a low cost option for the reduction of sedentary behavior. OBJECTIVE: This study evaluated changes in utility and health outcomes during a standing desk intervention. METHODS: Thirty-five participants (BMI >25) who reported sitting an average of≥six hours per workday were recruited. Participants were randomized into a control or intervention group. Eleven were enrolled in the control group and 24 in the intervention group. Participants in the intervention group were outfitted with an adjustable standing desktop accessory while participants in the control group maintained a standard work desk. Self-reported and objective measures of sedentary time during an eight hour workday were captured for a baseline and intervention period. Changes in health outcomes and workplace satisfaction were assessed after six months. RESULTS: Self-recorded sedentary behavior decreased by 25% after six months though no changes in health outcomes were observed. Subjective assessments of standing time were over-estimated by 10% (compared to accelerometer recordings) in the intervention group. The intervention group reported higher levels of satisfaction with comfort, customizability, and overall personal workplace. CONCLUSIONS: Despite a decrease in sedentary behavior, no changes in health outcomes occurred after a six month intervention. Future studies should incorporate objective measures of diet and physical activity to assess compensatory behaviors that may offset sedentary reduction. More sensitive health outcome measures should also be considered.


Assuntos
Comportamento Sedentário , Posição Ortostática , Local de Trabalho/normas , Acelerometria/métodos , Adulto , Feminino , Humanos , Masculino , Pessoa de Meia-Idade , Satisfação Pessoal , Postura Sentada , Fatores de Tempo , Local de Trabalho/estatística & dados numéricos
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