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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. To examine associations between corticospinal excitability, physical activity, and physical performance during SMOS. Fifty-three service members (age: 26 ± 5 yr, 13 women) completed a 5-day and -night intervention composed of familiarization, baseline, SMOS (2 nights/days), and recovery days. During SMOS, participants performed rigorous physical and cognitive activities while receiving half of normal sleep (two 2-h 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. 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. 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 noninvasive neuromodulation to clarify the interplay among CSE, physical activity, and resilience and improve physical and cognitive performance. NEW & NOTEWORTHY We demonstrate that individual differences in physical activity levels coincide with lower limb corticospinal excitability. Such use-dependent corticospinal excitability directly relates to resilience and physical performance during a 5-day simulation of military operational stress with caloric restriction, sleep restriction and disruption, and heavy physical and cognitive exertion.

Background Preliminary evidence indicates that non–rapid eye movement (NREM) sleep is implicated in enhancing working memory (WM) performance across days in healthy individuals. While REM sleep has been implicated in other forms of memory, its role in WM remains unclear. Further, the relationship between sleep changes and WM improvement is largely unknown in posttraumatic stress disorder (PTSD). Examining the relationship between changes in sleep and WM improvement in healthy participants and participants with PTSD may inform cognitive enhancement strategies and intervention targets. Methods Repeated assessments of WM and overnight measurement of NREM and REM sleep parameters were performed in 79 participants (participants with PTSD: n = 33) during a 48-hour laboratory stay. Relationships between sleep parameter changes, WM performance changes, and clinical characteristics were analyzed in PTSD and healthy groups. Results A between-night enhancement in both NREM and REM sleep parameters in frontoparietal areas predicted across-day better WM performance in healthy participants, particularly in those with improved performance. In contrast, in participants with PTSD, an enhancement of these sleep parameters predicted a worse WM performance and was also associated with more PTSD-related sleep disturbances. Conclusions This study shows that higher sleep activity in frontoparietal areas leads to enhanced WM performance in healthy individuals, whereas in individuals with PTSD, it likely reflects the presence of sleep disturbances that interfere with WM improvement. Interventions focused on addressing sleep disturbances could therefore ameliorate cognitive impairments in individuals with PTSD.

The double-cone coil (D-CONE) is frequently used in transcranial magnetic stimulation (TMS) experiments that target the motor cortex (M1) lower-limb representation. Anecdotal evidence and modeling studies have shed light on the off-target effects of D-CONE TMS but the physiological extent remains undetermined. To characterize the off-target effects of D-CONE TMS based on bilateral corticospinal responses in the legs and hands. Thirty (N = 30) participants (9 women, age: 26 ± 5yrs) completed a stimulus–response curve procedure with D-CONE TMS applied to the dominant vastus lateralis (cVL) and motor-evoked potentials (MEPs) recorded in each active VL and resting first dorsal interosseous (FDI). As a positive control (CON), the dominant FDI was directly targeted with a figure-of-eight coil and MEPs were similarly recorded in each active FDI and resting VL. MEPMAX, V50 and MEP latencies were compared with repeated-measures ANOVAs or mixed-effects analysis and Bonferroni-corrected pairwise comparisons. Off-target responses were evident in all muscles, with similar MEPMAX in the target (cVL) and off-target (iVL) leg (p = 0.99) and cFDI compared with CON (p = 0.99). cFDI and CON MEPMAX were greater than iFDI (p

Warfighter performance may be compromised through the impact of load carriage on dynamic postural stability. Men and women may experience this impact to differing extents due to postural stability differences. Therefore, the authors investigated the effect of load magnitude on dynamic postural stability in men and women during a landing and stabilization task. Dynamic postural stability of 32 subjects (16 women) was assessed during the unilateral landing of submaximal jumps under 3 load conditions: +0%, +20%, and +30% body weight. Dynamic postural stability was measured using the dynamic postural stability index, which is calculated from ground reaction force data sampled at 1200 Hz. Two-way mixed-measures analysis of variance compared dynamic postural stability index scores between sexes and loads. Dynamic postural stability index scores were significantly affected by load (P = .001) but not by sex or by the sex by load interaction (P > .05). Dynamic postural stability index scores increased between the 0% (0.359 ± 0.041), 20% (0.396 ± 0.034), and 30% (0.420 ± 0.028) body weight conditions. Increased load negatively affects dynamic postural stability with similar performance decrements displayed by men and women. Men and women warfighters may experience similar performance decrements under load carriage conditions of similar relative magnitudes.

Transcranial magnetic stimulation (TMS) is increasingly used to examine lower extremity corticospinal excitability (CSE) in clinical and sports research. Because CSE is task-specific, there is growing emphasis on the use of ecological tasks. Nevertheless, the comparative reliability of CSE measurements during established (e.g. knee extensions; KE) and more recent ecological (e.g. squats; SQT) lower extremity tasks has received less attention. The aim of this study was to compare the test–retest reliability of CSE, force, and muscle activity (EMG) during isometric SQT and KE. 19 right-footed men (age: 25 ± 5 yrs) with similar fitness and body composition performed SQT (N = 7) or KE (N = 12) on two consecutive days. Force and EMG were recorded during maximum voluntary isometric contractions (MVC). Corticospinal excitability was determined in the dominant leg during light (15% MVC) contractions based on motor evoked potential (MEP) stimulus–response-curves (SRC). Test-retest reliability, absolute agreement, and consistency were determined for force, EMG, and SRC MEP maximum (MEPMAX) and rising phase midpoint (V50). As a secondary analysis, all outcomes were compared between groups with mixed-methods ANCOVAs (Task × Time, covariate: body-fat-percentage). Compared with SQT, KE displayed better test–retest reliability and agreement for MEPMAX whereas V50, force, and EMG were similarly reliable. Force (p = 0.01) and MEPMAX (p = 0.02) were also greater during KE despite a similar V50 (p = 0.11). Differences in test–retest reliability, absolute agreement, and between-group comparisons highlight the need to carefully select lower limb TMS assessment tasks and encourage future efforts to balance ecological validity with statistical sensitivity.

Introduction Alertness, essential for optimal performance, may be modulated by acute stressors including: sleep loss, caloric restriction, cognitive load, and physical exertion. Prior sleep may attenuate sleep loss-related alertness decrements, thereby influencing performance and safety. We examined the effects of prior sleep and changes in alertness throughout the day and across days during a simulated military operational stress (SMOS) protocol. Methods As part of a 5-day SMOS protocol, fifty-eight active-duty or recently-separated military personnel (45 men; 26±6 years) completed subjective (Profile of Mood States, Vigor subscale) and objective (3-minute Psychomotor Vigilance Task; PVT) alertness assessments each morning (~0900) and evening (~2200). PVT outcomes included median reaction time (RT) and lapses. Day 2 (D2) reflected baseline testing, in which participants received an 8-hour sleep opportunity (2300-0700) and 100% of their estimated caloric need. Day 4 (D4) reflected peak stress, after two nights of participants receiving two 2-hour sleep opportunities (0100-0300, 0500-0700) and 50% of their estimated caloric need. Mixed effects ANOVAs were used to assess the effects of day (D2, D4) and time (Morning, Evening) on alertness. D2 and D4 reflected alertness at baseline and peak stress, respectively. Separate ANOVAs were performed to assess the effects of prior sleep: the Pittsburgh Sleep Quality Index (PSQI) assessed at intake, baseline polysomnography-measured sleep efficiency (SE), and baseline frontal slow wave activity (SWA; 0.5-4Hz). All analyses controlled for age. Results No significant interaction or main effects of day and time were found for Vigor or PVT lapses. Participants with higher PSQI scores reported lower Vigor (p=.01, η_p^2=.11). A significant interaction was found for PVT RT (p=.04, η_p^2=.07); morning RT was slower on D4 than D2, while evening RT did not differ across days. SE and SWA did not significantly influence alertness. Conclusion SMOS led to objective alertness deficits in the morning but not evening. Subjective alertness did not change during SMOS but was influenced by prior sleep quality (PSQI). Thus, both circadian and prior sleep-related factors influence performance during operational stress. Fatigue mitigation strategies delivered before and during military operations may support performance and safety. Support (if any) Department of Defense Award #W81XWH-17-2-0070

Youth at Clinical High Risk (CHR) represent a unique population enriched for precursors of major psychiatric disorders. Sleep disturbances are consistently reported in CHR individuals. However, there is a dearth of studies investigating quantifiable objective measures of sleep dysfunction in CHR youth. In this study, sleep high density (hd)-EEG recordings were collected in twenty-two CHR and twenty healthy comparison (HC) subjects. Sleep architecture parameters, as well as sleep EEG power spectra in five frequency bands, were computed and compared between CHR and HC groups during non-rapid eye movement (NREM) sleep. Furthermore, correlation analyses between sleep EEG power spectra, sleep architecture parameters, and clinical symptoms, assessed with the Scale of Prodromal Symptoms (SOPS), were conducted in CHR participants. Our results show that CHR individuals had more Wakefulness After Sleep Onset (WASO) compared to HC participants. CHR also showed a higher NREM sleep gamma EEG power, which was observed in a large fronto-parieto-occipital area, relative to HC. Additionally, higher NREM gamma activity in lateral fronto-occipital regions was associated with more WASO, and increased NREM gamma power in medial fronto/parietal areas correlated with worse SOPS negative symptoms. Altogether, these findings suggest that topographically specific increases in EEG gamma activity during NREM sleep represent neurophysiological signatures underlying some of the objectively assessed sleep disturbances and clinical symptoms of CHR individuals.

Background Pulmonary function tests (PFTs) are currently recommended for liver transplant candidates. We hypothesized that PFTs may not provide added clinical value to the evaluation of liver transplant patients. Methods We conducted a retrospective cohort study of adult cadaveric liver transplants from 2012 to 2018. Abnormal PFTs were defined as restrictive disease of diffusing capacity of the lungs for carbon monoxide (DLCO) Results We analyzed data on 415 liver transplant patients (358 abnormal PFT results and 57 normal results). The liver transplant patients with abnormal PFTs had no difference in number of intensive care unit (ICU) days ( P = .68), length of stay ( P = .24), or intubation days ( P = .33). There were no differences in pulmonary complications including pleural effusion ( P = .30), hemo/pneumothorax ( P = .74), pneumonia ( P = .66), acute respiratory distress syndrome ( P = .57), or pulmonary edema ( P = .73). The significant finding between groups was a higher rate of reintubation in liver transplant patients with normal PFTs ( P = .02). There was no difference in graft survival ( P = .53) or patient survival ( P = .42). Discussion Abnormal PFTs, found in 86% of liver transplant patients, did not correlate with complications, graft failure, or mortality. PFTs contribute to the high cost of liver transplants but do not help predict which patients are at risk of postoperative complications.

Background Astronauts are required to perform a variety of cognitively demanding tasks in the face of multiple prolonged stressors in isolated, confined and extreme (ICE) environments. Short-term ICE environmental exposure can negatively affect cognitive performance, alter emotional responses, and increase reaction time in affordance-based tasks; however, these domains have not been studied simultaneously in prolonged ICE settings. Coastal and Inland Antarctic stations are excellent analogs for spaceflight based on overlapping environmental features such as limited external communication and confinement in extreme conditions. Our purpose was to investigate the effects of 5-month ICE environment analogs, and co-occurring emotional responses, on cognitive performance and affordance perception. Methods Participants assigned to either Inland or Coastal stations completed the Psychomotor Vigilance Test (PVT), Spaceflight Cognitive Assessment Tool for Windows (WinSCAT), Perception-Action Coupling Task (PACT), and Mental Health Checklist (MHCL) each month for five consecutive months. A series of 1-way ANOVAs were conducted to evaluate WinSCAT, PVT, and PACT performance across time. A series of backward stepwise linear regressions were conducted to determine if duration of ICE environment exposure (months 1–5), station (Coastal and Inland), gender (male and female), education (college degree and no degree), and time of day, in addition to Positive Adaptation, Poor Self-Regulation, and Anxious Apprehension MHCL subscales, were related to cognitive performance outcomes, including WinSCAT composite, PVT median reaction time and lapses, and PACT accuracy and lapses. Results A within-subjects’ effect indicated improvements across WinSCAT composite score, PACT Accuracy, and PACT lapses. Final regression models were significant across all outcomes, and indicate an improvement in WinSCAT and PACT performance during the winter over, assigned station and education level marginally contributed to the observed variance in cognitive performance. Conclusion Sustained attention, cognitive performance, and affordance perception and actualization outcomes were marginally affected, or improved, during a prolonged ICE environmental exposure.

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 0.05). 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 0.05). 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.

Introduction Individuals with post-traumatic stress disorder (PTSD) experience altered sleep and daytime function, including deficits in working memory (WM), the ability to store and manipulate information over short timeframes. As sleep contributes to WM, understanding how sleep parameters influence changes in WM may provide insight into potential intervention targets to improve or restore daytime function. Here, we investigated the relationship between sleep and WM improvement in Veterans with and without PTSD. Methods Forty-eight post-911 Veterans without PTSD (Control) and 37 with PTSD (PTSD) completed a 48-hour lab stay during which WM was assessed using a n-back task. Nighttime polysomnography, using high-density (64-channels) electroencephalography, quantified time spent in non-REM and REM sleep and log-transformed spectral activity for non-REM sleep in delta (.5-4Hz), theta (4-8Hz), alpha (8-12Hz), sigma (12-16Hz), and beta (16-32Hz) bands. Pearson’s correlations were used to assess associations between baseline sleep and baseline WM on 1-back trials. Within control and PTSD groups, independent samples t-tests were used to compare changes in sleep across nights between improvers and non-improvers categorized by 1-back accuracy changes across days. Results Proportions of improvers and non-improvers were similar between groups (χ 2 = .023, p = .880). Within either group, baseline sleep did not relate to baseline WM and changes in time spent in each sleep stage did not differ between improvers and non-improvers. Within the control group, improvers (n = 15; 3.67 ± 3.56) had a greater increase (t = -2.826, p = .007) in delta activity than non-improvers (n = 33; .77 ± 3.20), but this relationship was not observed in the PTSD group (11 improvers, 26 non-improvers). Conclusion Increased delta activity related to improved WM in the Control but not PTSD group. This suggests individuals with PTSD do not improve WM through non-REM sleep but that it may be a useful intervention target. Support USAMRMC MOMRP PT-130572 (PI: Reifman)

The file attached to this record is the author's final peer reviewed version. The Publisher's final version can be found by following the DOI link. Objectives: Astronauts must adapt behaviors to changing affordances (action possibilities) when exposed to operational stressors such as sleep deprivation. The inability to correctly perceive affordances may cause astronauts to attempt behaviors that place them at greater risk. This study investigated the effects of sleep deprivation on affordance perception performance during 30-day NASA Human Exploration Research Analog missions. Methods: Sixteen participants completed a perception-action coupling task (PACT) over days 22-25 of the missions. Participants completed sessions on day 22 (1800) and 24 (1200 and 1730) under normal sleep conditions and sessions on day 25 (0430, 1200 and 1445) after a night of sleep deprivation. During PACT, participants judge whether virtual balls afford posting (can fit) through virtual apertures. The ratio of ball-to-aperture size ranges from 0.2-1.8 (afforded trials 1). A two-way repeated measures ANOVA was used to analyze the effect of time and trial type (afforded versus unafforded) on response time (RST) and accuracy (ACC). Results: For RST, significant main effects of time (F2.666, 39.984 = 7.685, p = .001) and trial type (F1, 15 = 17.554, p = .001) were observed. Afforded RST was greater than unafforded RST. ACC decreased across time (F2.724, 20.939 = 5.137, p = 0.005) but did not differ between trial types. No significant interaction effects were observed. Conclusion: Decrements in affordance-based behaviors were observed under increasing levels of sleep deprivation and subjects responded slower to trials where the task-specific affordance was available. These decrements may relate to changes in operational performance.

Recent studies have concluded that athletes have increased risk of musculoskeletal injury following sport-related concussion. While an underlying explanation is still unknown, perceptual-motor control may be implicated in this increased risk. Some authors have purported that indirect perception (i.e., a “top-down” view of neuromuscular control) may be disrupted following sport-related concussion. Direct perception theory states that the athlete and environment are inextricably linked in a continuous perception–action coupling loop. That is, the athlete is able to directly perceive opportunities for action (e.g., “affordances”) in the environment. Based on these notions, the aim of the current paper was to introduce a theoretical model that argues that sport-related concussion may dysregulate the direct perception process, potentially increasing behavioral risk of musculoskeletal injury during sport. Our model is integrated with a sport-related concussion clinical treatment model, which highlights individualized profiles that characterize the heterogeneous response to sport-related concussion. These profiles have a typical constellation of symptoms (e.g., anxiety, fatigue, ocular dysfunction, etc.), which themselves have been associated with disrupted perception–action coupling, independent of sport-related concussion. Therefore, we argue that athletes who have not re-established perception–action coupling loops following sport-related concussion may be at increased risk of subsequent musculoskeletal injury.

Background Intentional self-inflicted injuries present unique challenges in treatment and prevention. We hypothesized intentional self-inflicted injuries would have higher in-hospital and postdischarge mortality than nonintentional self-inflicted injuries trauma. Methods Adult patients evaluated 2008 to 2012 were identified in our trauma registry and matched with mortality data from the National Death Index. Intentional self-inflicted injuries were identified using E-Codes. Readmissions were identified and analyzed. Intentional self-inflicted injuries patients who died in-hospital were compared with those surviving to discharge. Univariate analysis was performed using nonparametric tests. Kaplan-Meier curves were plotted to compare mortality ≤5 years postdischarge between intentional self-inflicted injuries and non-intentional self-inflicted injuries patients. Results In the study, 8,716 patient records were evaluated with 245 (2.8%) classified as intentional self-inflicted injuries. Eighteen (7.8%) patients with intentional self-inflicted injuries had multiple admissions, compared with 352 (4.4%) patients with nonintentional self-inflicted injuries with readmissions ( P = . 0210). In-hospital mortality was higher for intentional self-inflicted injuries compared with patients with non-intentional self-inflicted injuries (18.7% vs 4.9%, P 0001). Survival analysis demonstrated that patients with intentional self-inflicted injuries had significantly lower postdischarge mortality at multiple time points. Conclusion Patients with intentional self-inflicted injuries trauma have high in-hospital mortality, but low postdischarge mortality. We attribute this to high lethality mechanisms but appropriate psychiatric treatment and rehabilitation. However, the high intentional self-inflicted injuries readmission rate indicates further study of intentional self-inflicted injuries follow-up is warranted. Better prevention strategies are needed to identify and intervene in patients at-risk for intentional self-inflicted injuries.

BACKGROUND: The perception-action coupling task (PACT) was designed as a more ecologically valid measure of alertness/reaction times compared to currently used measures by aerospace researchers. The purpose of this study was to assess the reliability, within-subject variability, and systematic bias associated with the PACT.METHODS: There were 16 subjects (men/women = 9 / 7; age = 27.8 ± 3.6 yr) who completed 4 identical testing sessions. The PACT requires subjects to make judgements on whether a virtual ball could fit into an aperture. For each session, subjects completed nine cycles of the PACT, with each cycle lasting 5 min. Judgement accuracy and reaction time parameters were calculated for each cycle. Systematic bias was assessed with repeated-measures ANOVA, reliability with intraclass correlation coefficients (ICC), and within-subject variability with coefficients of variation (CVTE).RESULTS: Initiation time (Mean = 0.1065 s) showed the largest systematic bias, requiring the elimination of three cycles to reduce bias, with all other variables requiring, at the most, one. All variables showed acceptable reliability (ICC > 0.70) and within-subject variability (CVTE < 20%) with only one cycle after elimination of the first three cycles.CONCLUSIONS: With a three-cycle familiarization period, the PACT was found to be reliable and stable.Connaboy C, Johnson CD, LaGoy AD, Pepping G-J, Simpson RJ, Deng Z, Ma L, Bower JL, Eagle SR, Flanagan SD, Alfano CA. Intersession reliability and within-session stability of a novel perception-action coupling task. Aerosp Med Hum Perform. 2019; 90(2):77-83.

A 27-year-old primigravida patient with diastrophic dysplasia (DTD) presented to our obstetrics clinic at 8 weeks' gestational age. Diastrophic dysplasia is a rare, autosomal-recessive abnormality that presents multiple challenges to perinatal anesthetic management, including difficult airway management and relative contraindications to neuraxial anesthesia. The patient underwent elective cesarean delivery at 35 weeks' gestational age under general anesthesia. In this report, we describe our preoperative evaluation and management strategy that involved a multidisciplinary care team.

Questions about medication use during pregnancy and lactation are a concern for women and healthcare providers. Unfortunately, there is little experience with the use of most medications in human pregnancy and lactation at the time they are marketed. Even when information is available, it may not be readily accessible to women and healthcare providers. Nevertheless, medication use by pregnant and breastfeeding women may be beneficial, and even essential, to ensure the health of both mother and child. In addition, almost half of pregnancies in the United States each year are unintended, and medication exposures may occur in the early weeks of gestation before a pregnancy is recognized. For these reasons, it is critical that up-to-date information about the effects of medication use during pregnancy and lactation and the management of maternal conditions be available to women and healthcare providers. A comprehensive, coordinated public health approach that builds on and expands existing activities is neede...

Obesity is a major health problem. Effective treatment requires understanding the homeostatic responses to caloric restriction.The aim was to study Roux-en-Y gastric bypass patients longitudinally for 6 months after surgery to identify major factors modulating fat loss.We studied 13 patients (11 females and two males) aged 41.2 ± 2 yr. Mean body mass index was 44.6 ± 1.2 kg/m(2), with 50 ± 1% body fat (58.3 kg). Selection excluded patients with confounding comorbidities or treatments.Caloric intake was reduced 742 ± 82 kcal/d by 1 month and 450 kcal/d between 2 and 4 months postoperatively. By 6 months, relative to baseline, body mass index decreased 24.8 ± 1.1%; percentage body fat, 37.3 ± 3.2% (21.7 kg); fat free mass (FFM), 9.7 ± 1.2%; and resting metabolic rate (RMR), 18.1 ± 4.3%. RMR correlated with FFM at all times (r = 0.71; P0.0001), but FFM explained no more than 50% of RMR variance. Exercise capacity (treadmill walking, 53 m/min with increasing grade) improved with time. Mean nonexercise physical activity level was low (1.2, or 20% of RMR), with considerable variance among individuals. Fat loss did not correlate with the aggregate energy deficit or its individual components. Resting or postexercise respiratory exchange ratio (RER) was lowest, whereas plasma β-OH-butyrate and glycerol were highest, between 1 and 2 months after surgery. RER increased linearly with mild exercise, and fat loss correlated positively with physical activity level and RER.Although the ultimate cause for weight loss is the energy deficit, the variance in fat loss correlated with glucose oxidation, suggesting that glucose partition between oxidation (muscle) and storage (adipose tissue) is an important factor affecting fat loss in individuals submitted to Roux-en-Y gastric bypass.