Abstract Monitoring CO₂ storage sites over decades requires cost-effective, reliable strategies to ensure containment and conformance. Conventional approaches such as repeated 3D/4D seismic surveys are expensive and logistically challenging, particularly offshore. The SPARSE project, developed under ACT4, introduces a sparse node-based multiphysics monitoring concept that integrates seismic, electromagnetics, gravity, and deformation measurements. This approach was designed to reduce survey frequency while maintaining sensitivity to pressure and saturation changes. Results from onshore field trials at Carbon Management Canada’s Newell County site and offshore feasibility studies based on the Smeaheia CO₂ storage model are presented. Onshore tests demonstrated the feasibility of using permanent seismic sources, distributed acoustic sensing, and electromagnetic configurations within a sparse monitoring framework. Offshore modeling indicated that seismic, electromagnetic, and gravity signals could detect plume arrival, monitor its development over time, and distinguish between different migration scenarios under realistic noise conditions. These findings supported the feasibility of sparse node multiphysics monitoring as a scalable and cost-efficient approach for long-term CO2 storage assurance, complementing conventional methods and informing future deployment.

Gravity sensors for high-precision monitoring or mapping can be grouped into 1) Relative spring, 2) Absolute free-fall, 3) Absolute cold atom, and 4) Superconducting. While all can provide valuable data, few comparisons of performance or cost have been published. Here we report on performance of CG-6 relative gravimeters and discuss how it relates to other sensors.The Scintrex CG-6 sensor has weight of 5.5 kg and volume of 10,8 litre, which is less than previous quartz sensors. While the manufacturer specifies 5 µGal repeatability, Francis (2021) reported better performance and improved drift, noise level, tilt susceptibility and temperature influence. Mao et al., (2022) reported uncertainty down to 0.1 µGal in the laboratory. We have analysed more than 2000 survey records from as diverse environments as the desert and the seafloor. Station repeatability is a robust measure of the precision for surveys with multiple station visits and sensors. Data redundancy allows in-situ calibration of scale factors and parameters for tilt and temperature corrections. Up to 10oC temperature difference between night and day gave no remaining correlation between sensor temperature and gravity residuals, but some diurnal drift periodicity, and repeatabilities

The capacity to tolerate high G loads in the head-to-seat direction (+Gz tolerance) is critical for pilots flying high-performance aircraft. The adaptive effects of repeated +Gz loading on relaxed +Gz tolerance and G-protective sympathetic reflex pressor responses were investigated. Twelve men were exposed to increased +Gz loads in a relaxed state, during 15 × 40 min sessions across 5 wk. Before and after the training regimen, relaxed +Gz tolerance was investigated during rapid onset-rate (ROR) and gradual onset-rate (GOR) G exposures, and cardiovascular responses were investigated during exposures to 2.5 G in the belly-to-back direction (+Gx) as well as during orthostatic provocations and pressure manipulations of the carotid baroreceptors. The G training increased (P = 0.04) the ROR G tolerance by 17% but did not affect GOR G tolerance, orthostatic tolerance, or the sensitivity and operational pressure range of the carotid baroreflex pressor response. The training reduced (P < 0.001) the arterial pressure response to +Gx exposure. The results suggest that repeated high +Gz exposures do not improve the overall vascular sympathetic response to high +Gz nor the responsiveness of the vascular branch of the carotid baroreflex, but, judging by the arterial pressure responses to +Gx loads, reduces the responsiveness of the vestibulosympathetic reflex. That the G training improved the ROR +Gz tolerance is attributable to local vascular adaptation, in terms of increased stiffness in dependent precapillary vessels resulting from the iterative increments in local transmural pressures.NEW & NOTEWORTHY Five weeks of repeated exposures to head-to-seat directed G load in the relaxed state increased the capacity to tolerate rapid but not gradual G elevations, suggesting unaffected overall vascular sympathetic responses to high G. The G training did not affect the responsiveness of the vascular branch of the carotid baroreflex but reduced the vestibulosympathetic reflex response. The improved tolerance to rapid G elevations is attributable to increased stiffness in dependent precapillary vessels.

To evaluate whether a sustained period of normobaric O2 breathing would modulate acral-skin vasoreactivity and thermosensitivity to localised cooling. Eight healthy men performed a 30-min normoxic and hyperoxic (100

We examined whether finger vasomotor and thermoperceptual responses to local cooling would be modulated by sustained cognitive loading. Finger temperature, circulatory [i.e., cutaneous vascular conductance (CVC)] and perceptual responses were monitored, in 12 healthy men, during and after a 30-min hand-immersion in 8°C-water, performed either immediately after a 60-min continual execution of a cognitive task (cognitive→cold trial), or during the simultaneous performance of the cognitive task (cognitive + cold trial). Subjects' responses were compared with those obtained in a control cold-provocation trial, wherein they watched an emotionally neutral documentary. The cognitive task temporarily enhanced the perceived levels of mental effort and fatigue in both intervention trials. During cooling in the cognitive→cold trial, the area under the curve (AUC) for finger CVC was enhanced [49 (23) PU·mmHg-1·min vs. control: 36 (22) PU·mmHg-1·min], the cold-induced increase in mean arterial pressure was blunted [2 (4) mmHg vs. control: 8 (4) mmHg] (P < 0.01), and the thermal discomfort was alleviated [2.2 (0.5) vs. control: 2.5 (0.7); P = 0.05]. In the cognitive + cold trial, no intertrial differences were noted during the cold-water immersion (P ≥ 0.28), but AUC for finger CVC was augmented during the last part of the rewarming [29 (12) PU·mmHg-1·min vs. control: 24 (11) PU·mmHg-1·min; P = 0.05]. Present findings demonstrate that 1) in moderately mentally fatigued individuals, finger cold-induced vasoconstriction is transiently attenuated, and thermal discomfort is mitigated, and 2) superimposition of cognitive loading on cold stress does not alter finger vasoreactivity or thermosensitivity during cooling, but facilitates reperfusion following cooling.NEW & NOTEWORTHY The study examined whether finger vasoreactivity and thermosensitivity to local cooling would be modulated by two different paradigms of enhanced cognitive strain evoked by the prolonged execution of a mentally demanding task. When localized cold stress was applied in moderately mentally fatigued individuals, finger cold-induced vasoconstriction was temporarily attenuated, and thermal discomfort was mitigated. The simultaneous application of cognitive loading and local cooling did not potentiate finger vasoconstriction during cooling but facilitated digit reperfusion following cooling.

Previous studies have suggested that, during prolonged cold exposure, shivering thermogenesis may gradually be attenuated, supposedly reflecting a state of central fatigue (aka 'thermoregulatory fatigue') provoked by extended shivering activity, that precipitates hypothermia. The purpose of this study was to revisit the validity of this notion. Twelve noncold-acclimatized men participated in three ∼10-h sessions, during which they performed repeatedly three 120-min cold-water immersions. To induce discrete amounts of heat-producing thermoeffector output, presumptively leading to distinct levels of fatigue during each session, subjects were submersed, within each session, in either severely (15°C), moderately (20°C), or slightly (28°C) cold water. The cold-induced elevation in thermogenic rate was similar across the three repeated immersions performed within the 15°C (∼130 W·m2) and 20°C (∼100 W·m2) sessions (P ≥ 0.43). In the 28°C-session, the metabolic heat production was augmented by ∼7% in the second and third immersions compared with the first immersion (P = 0.01). No intrasession differences were noted with regards to the body-core cooling rate, the cold-induced drop in skin temperature and forearm cutaneous vascular conductance, or the stress-hormone (salivary α-amylase and cortisol concentrations) and thermoperceptual responses (P > 0.05). The present findings, therefore, demonstrate that the ability to generate heat remains intact during prolonged iterative exposure to a high-heat loss environment in a single day, regardless of the severity of cold stressor. The intermittent application of slight cold stress (i.e., 28°C water) appears to mediate metabolic sensitization, reflecting either the circadian rhythmicity of heat-producing thermoeffector activity, or perhaps the rapid induction of metabolic adaptation.NEW & NOTEWORTHY The study evaluated whether centrally mediated thermoregulatory fatigue is provoked by prolonged exposure to uncompensable cold. Regardless of the severity of cold stressor, the ability to produce endogenous heat remains intact during prolonged iterative exposure to a high-heat loss environment.

Regional cerebral and peripheral tissue (de)oxygenation responses to breath-holding (apnea) have predominantly been examined during isolated attempts. How these responses evolve across repeated efforts remains unclear, as previous studies either averaged data across bouts or focused solely on the final repetition. Accordingly, this study mapped the (de)oxygenation dynamics across successive breath-holds. Fifteen nondivers performed three repeated maximal static breath-holds, separated by 2-min rest intervals. Systemic cardiovascular variables, gas exchange, and cerebral frontal cortex and forearm muscle (de)oxygenation were assessed. At each breath-hold onset, a transient fall in cerebral oxygenated hemoglobin (cO2Hb) and arterial pressure occurred, coinciding with tachycardia. A cardiovascular steady state followed, which persisted until the onset of involuntary breathing movements (IBMs). At IBM onset, cO2Hb increased only during the first attempt (Δ8 ± 5 µM, P < 0.001), with smaller changes in subsequent breath-holds (apnea-2, Δ3 ± 6 µM; apnea-3, Δ3 ± 5 µM, P ≤ 0.014). Cerebral deoxygenated hemoglobin (cHHb) increased progressively across breath-holds (apnea-1, Δ3 ± 4 µM; apnea-2, Δ5 ± 4 µM; apnea-3, Δ7 ± 5 µM, P ≤ 0.001), whereas arterial pressure increases were of similar magnitude (P ≥ 0.064). Forearm (de)oxygenation profiles were comparable across attempts (P ≥ 0.085). In nine subjects, a triphasic peripheral response emerged: initial rapid decline in O2Hb and rise in HHb at breath-holding onset, a transient intermediate plateau, and further divergence near IBM onset. Breath-holds were terminated at successively lower cO2Hb, cerebral tissue oxygen index, and end-tidal oxygen, and higher cHHb (P ≤ 0.034), but similar end-tidal carbon dioxide levels (P > 0.912). The magnitude and timing of regional (de)oxygenation responses vary greatly over repeated breath-holds. Cerebral oxygenation showed a pronounced increase during the first attempt but progressively smaller changes across subsequent bouts. In contrast, peripheral tissue oxygenation demonstrated a time-dependent decline across successive attempts.NEW & NOTEWORTHY In nondivers, regional cerebral (de)oxygenation responses varied greatly across repeated breath-holds, whereas peripheral tissue responses were comparable. At IBM onset, cerebral oxygenation increased significantly during the first breath-hold but showed progressively smaller changes in subsequent attempts. In the periphery, a triphasic (de)oxygenation pattern was identified. Its final phase-characterized by a further oxygenation decline-coincided with increased cerebral oxygenation, supporting the concept of sympathetically mediated vasoconstriction and selective blood redistribution toward vital organs.

Abstract Eccentric upper‐body exercise performed 24 h prior to high‐altitude decompression has previously been shown to aggravate venous gas emboli (VGE) load. Yet, it is unclear whether increasing the muscle mass recruited (i.e., upper vs. whole‐body) during eccentric exercise would exacerbate the decompression strain. Accordingly, this study aimed to investigate whether the total muscle mass recruited during eccentric exercise influences the decompression strain. Eleven male participants were exposed to a simulated altitude of 24,000 ft for 90 min on three separate occasions. Twenty‐four hours before each exposure, participants performed one of the following protocols: (i) eccentric whole‐body exercise (ECCw; squats and arm‐cycling exercise), (ii) eccentric upper‐body exercise (ECCu; arm‐cycling), or (iii) no exercise (control). Delayed onset muscle soreness (DOMS) and isometric strength were evaluated before and after each exercise intervention. VGE load was evaluated at rest and after knee‐ and arm‐flex provocations using the 6‐graded Eftedal–Brubakk scale. Knee extensor (−20 ± 14%, P = 0.001) but not elbow flexor (−12 ± 18%, P = 0.152) isometric strength was reduced 24 h after ECCw. ECCu reduced elbow flexor isometric strength at 24 h post‐exercise (−18 ± 10%, P < 0.001). Elbow flexor DOMS was higher in the ECCu (median 6) compared with ECCw (5, P = 0.035). VGE scores were higher following arm‐flex provocations in the ECCu (median (range), 3 (0–4)) compared with ECCw (2 (0–3), P = 0.039) and control (0 (0–2), P = 0.011), and in ECCw compared with control (P = 0.023). VGE were detected earlier in ECCu (13 ± 20 min) compared with control (60 ± 38 min, P = 0.021), while no differences were noted between ECCw (18 ± 30 min) and control or ECCu. Eccentric exercise increased the decompression strain compared with control. The VGE load varied depending on the body region but not the total muscle mass recruited. Highlights What is the central question of this study? Does exercise‐induced muscle damage (EIMD) resulting from eccentric exercise influence the presence of venous gas emboli (VGE) during a 90 min continuous exposure at 24,000 ft? What is the main finding and its importance? EIMD led to an earlier manifestation and greater VGE load compared with control. However, the decompression strain was dependent on the body region but not the total muscle mass recruited.

This study shows that breath-holds (apneas) preceded by a 12-h overnight fast coupled with a 30-s hyperventilation as opposed to normal breathing may increase the likelihood of a hypoxic blackout through delaying the excitation of hypercapnic ventilatory sensory chemoreflexes. Evidently, this risk is exacerbated over a series of repeated maximal attempts, possibly due to a shift in preapneic gas tensions facilitated by an unintentional increase in tidal volume breathing.

When entering a coordinated flight turn without visual references, the perception of roll-angular displacement is determined by vestibular cues, and/or probably by assessment of the gravitoinertial (G) load (G magnitude) and its translation into the corresponding bank angle. Herein, we examined whether repeated exposures to hypergravity (G training) in a centrifuge, would advance, not only the ability to accurately assess the G load but also the capacity to detect or estimate the corresponding roll inclination of the centrifuge gondola. To this end, in nine men without piloting experience, the subjective estimation of G load and roll tilt were assessed, in complete darkness, during 5-min coordinated turns in the centrifuge, performed at 1.1 G (25° roll-tilt angle) and 2.0 G (60° roll tilt angle). These trials were conducted before and after 5 wk of G training {3 × 40-min sessions·wk-1; protocol: 20 × 1 min at G levels close to the individual relaxed G-level tolerance [range: ∼2.6 G (∼67°)-3.6 G (74°)], separated by 1-min intervals at idle speed (1.4 G)}, whereas continual feedback to the subjects was limited to the G load. As expected, G training improved subjects' capacity to assess G load, especially at 2.0 G (P = 0.006). The perception of roll tilt, however, was consistently underestimated (by ∼70%-80%), and not enhanced by G training (P ≥ 0.51). The present findings demonstrate that prolonged repeated G-induced roll-tilts in a centrifuge gondola, while external feedback is restricted to graviception, enhance the capacity to perceive G load, but fail to advance the ability to detect or consciously estimate the magnitude of roll-angular displacement during a coordinated turn.NEW & NOTEWORTHY During a coordinated flight turn without external visual references, the pilot typically underestimates the aircraft bank angle, because unreliable information of roll tilt is conveyed by the vestibular system. The present results demonstrate that prolonged repeated gravitoinertial (G)-induced roll-tilts in a centrifuge gondola, while external feedback is restricted to graviception, enhance the capacity to perceive G load, but fail to advance the ability to consciously estimate the magnitude of roll angular displacement.

Without visual references, nonpilots exposed to coordinated flight turns underestimate the bank angle, because of discordant information of the roll-angular displacement from the otoliths, consistently signaling vertical position, versus the semicircular canals, enabling detection of the displacement. Pilots may also use their ability to perceive the G load and knowledge of the relation between load and angle to assess the bank angle. Our aim was to investigate whether the perception of bank angle can be improved by spatial orientation training in a centrifuge. Sixteen pilots/pilot students assessed their roll tilt, in complete darkness, during both real coordinated flight turns and gondola centrifugation, at roll tilts of 30 degrees and 60 degrees. The experiments were repeated after a 3-wk period, during which eight of the subjects performed nine training sessions in the centrifuge, comprising feedback on roll angle vs. G load, and on indicating requested angles. Before training, the subjects perceived in the aircraft and centrifuge, respectively: 37 (17)degrees, 38 (14)degrees during 60 degrees turns and 19 (12)degrees, 20 (10)degrees during 30 degrees turns. Training improved the perception of angle during the 60 degrees [to 60 (7)degrees, 55 (10)degrees; P <= 0.04] but not the 30 degrees [21 (10)degrees, 15 (9)degrees; P >= 0.30] turns; the improvement disappeared within 2 yr after training. Angle assessments did not change in the untrained group. The results suggest that it is possible to, in a centrifuge, train a pilot's ability to perceive large but not discrete-to-moderate roll-angular displacements. The transient training effect is attributable to improved capacity to perceive and translate G load into roll angle and/or to increased reliance on semicircular canal signals.

AbstractThis study aimed to investigate the effect of eccentric exercise on exercise‐induced muscle damage (EIMD) and inflammation on high‐altitude‐induced venous gas emboli (VGE). Subjects were exposed to an altitude of 24,000 ft. for 90 min, with either prior eccentric exercise (ECC) or no exercise (Control) 24 h before. Blood samples were collected at baseline (T0), before (T1), and after (T2) altitude exposures. VGE load was evaluated using the Eftedal‐Brubakk (ΕΒ) scale. Creatine kinase (CK) and myoglobin were used to assess muscle damage, while interleukin‐6 (IL‐6), tumor necrosis factor alpha (TNF‐α), C‐reactive protein (CRP), and fibrinogen were used to evaluate inflammation. ECC showed higher EB‐scores during altitude exposures [median(range), 3(0–5)] than Control [1(0–4), p = 0.019]. Increases in myoglobin (+35%, p = 0.012), CK (+130%, p < 0.001), IL‐6 (+72%, p = 0.02), and CRP (+63%, p = 0.004) were observed from T0 to T1 in ECC, but not Control. Significantly higher levels of myoglobin (p = 0.033), CK (p < 0.001), IL‐6 (p = 0.016), and CRP (p = 0.002) were noted in the ECC compared to Control at T1. IL‐6 increased from T1 to T2 in ECC (p = 0.005), with higher levels than Control at T2 (p = 0.046). A correlation was found between EB‐scores and T1 myoglobin levels (rs = 0.450; p = 0.004), and to T1‐T2 IL‐6 changes (rs = 0.396; p = 0.037). Eccentric EIMD followed by inflammation is associated with a higher decompression strain, with VGE load aggravating systemic inflammation.

PURPOSE:There is a scarcity of information regarding the effect of upper-body eccentric exercise on biomarkers of muscle damage. This study sought to investigate the effect of eccentric arm cycling on muscle damage [exercise-induced muscle damage (EIMD)]. METHOD:Ten subjects performed a 15 min eccentric arm cycling protocol (cadence 49 ± 7 rpm, power absorbed 248 ± 34 W). Maximal voluntary contraction (MVC) of the elbow flexors was evaluated at rest and at 5 min, 24 h, and 48 h post-exercise. In addition, blood samples were drawn at rest and thereafter at 30 min, 24 h, and 48 h intervals after exercise for quantification of creatine kinase (CK), myoglobin, lactate dehydrogenase (LDH) and endothelin (ET-1) concentrations. Delayed onset muscle soreness (DOMS) was assessed using a category ratio scale (0-10). RESULTS:Myoglobin was increased from baseline at 30 min post-exercise (+114%, 46.08 ± 22.17 µg/L, p = 0.018). Individual peak values were higher than baseline values for CK (+72.8%, 204 ± 138 U/L, p = 0.046) and LDH (+17%, 3.3 ± 0.88 nmole/min/mL, p = 0.017), but not for ET-1 (+9%, 1.4 ± 0.48 pg/mL, p = 0.45). DOMS was reported at 24 h (median 4) and 48 h (median 4) post-exercise and MVC of the elbow flexors were reduced from baseline (216 ± 44 N) at 5 min (-34%, 147 ± 61 N, p < 0.001), 24 h (-17%, 181 ± 56 N, p = 0.005) and 48 h (-9%, 191 ± 54 N, p = 0.003). CONCLUSION:Eccentric arm cycling incites EIMD with reduced MVC and elevation of myoglobin, CK and LDH.

BACKGROUND:During a simulated coordinated turn in a gondola centrifuge, experienced pilots show a substantial inter-individual variability in visual measures of perceived roll tilt. Because of the centrifuge's small radius, the pattern of stimuli to the semicircular canals during acceleration of the centrifuge differs in certain respects from that of an aircraft entering a turn.OBJECTIVE:To explore whether these differences may be of significance for the pilot's roll- plane orientation and whether individual characteristics revealed in the centrifuge correspond to those during real flight.METHOD:8 fixed-wing air-force pilots were tested in a centrifuge and a high-performance aircraft. The centrifuge was accelerated to 2 G (gondola inclination 60°) within 10 s. The duration at 2 G was 6 minutes. Similar profiles were created in the aircraft. The subjective visual horizontal (SVH) was measured using an adjustable luminous line in darkness. Each pilot was tested on three occasions: centrifuge (2 runs), aircraft (2 turns), centrifuge (2 runs). For each 2-G exposure, initial and final SVH values were established via curve fitting.RESULT:Despite a large inter-individual variability (±SD), group means were similar in the aircraft (initial: 43.0±20.6°; final: 22.5±14.8°) and centrifuge (initial: 40.6±17.0°; final: 20.5±16.0°). Further, individual peculiarities in response patterns were similar in the two conditions. For both the initial and final SVH tilt there was a high correlation between centrifuge and aircraft.CONCLUSION:The correspondence between conditions suggests that the centrifuge is an adequate means for demonstrating the fundamental motion pattern of coordinated flight and also for establishing the individual pilot's ability to perceive an aircraft's roll attitude.Findings are discussed in connection with vestibular learning and the possibility of underlying differences between pilots in the keenness for semicircular canal and somatosensory cues.

Animal studies have shown that recent musculoskeletal injuries increase the risk of decompression sickness (DCS). However, to date no similar experimental study has been performed in humans. The aim was to investigate if exercise-induced muscle damage (EIMD)—as provoked by eccentric work and characterized by reduced strength and delayed-onset muscle soreness (DOMS)—leads to increased formation of venous gas emboli (VGE) during subsequent hypobaric exposure. Each subject (n = 13) was on two occasions exposed to a simulated altitude of 24,000 ft for 90 min, whilst breathing oxygen. Twenty-four hours prior to one of the altitude exposures, each subject performed 15 min of eccentric arm-crank exercise. Markers of EIMD were reduction in isometric m. biceps brachii strength and DOMS as assessed on the Borg CR10 pain scale. The presence of VGE was measured in the right cardiac ventricle using ultrasound, with measurements performed at rest and after three leg kicks and three arm flexions. The degree of VGE was evaluated using the six-graded Eftedal–Brubakk scale and the Kisman integrated severity score (KISS). Eccentric exercise induced DOMS (median 6.5), reduced the biceps brachii strength (from 230 ± 62 N to 151 ± 8.8 N) and increased the mean KISS at 24,000 ft, both at rest (from 1.2 ± 2.3 to 6.9 ± 9.2, p = 0.01) and after arm flexions (from 3.8 ± 6.2 to 15.5 ± 17.3, p = 0.029). EIMD, induced by eccentric work, provokes release of VGE in response to acute decompression.

The study examined intra- and interlimb variations in cutaneous vessel responsiveness to acute and repeated transmural pressure elevations. In 11 healthy men, red blood cell flux was assessed via laser-Doppler flowmetry on both glabrous and nonglabrous skin regions of an arm (finger and forearm) and leg (toe and lower leg), across a wide range of stepwise increasing distending pressures imposed in the vessels of each limb separately. The pressure-flux cutaneous responses were evaluated before and after 5 wk of intermittent (40 min, 3 sessions per week) exposures to hypergravity (∼2.6–3.3 G; G training). Before and after G training, forearm and lower leg blood flux were relatively stable up to ∼210 and ∼240 mmHg distending pressures, respectively; and then they increased two- to threefold ( P < 0.001). Finger blood flux dropped promptly ( P < 0.001), regardless of the G training ( P = 0.64). At ≤120-mmHg distending pressures, toe blood flux enhanced by ∼40% ( P ≤ 0.05); the increase was augmented after the G training ( P = 0.01). At high distending pressures, toe blood flux dropped by ∼70% in both trials ( P < 0.001). The present results demonstrate that circulatory autoregulation is more pronounced in glabrous skin than in nonglabrous skin, and in nonglabrous sites of the leg than in those of the arm. Repetitive high-sustained gravitoinertial stress does not modify the pressure-flow relationship in the dependent skin vessels of the arm nor in the nonglabrous sites of the lower leg. Yet it may partly inhibit the myogenic responsiveness of the toe’s glabrous skin.

Purpose We evaluated the hypothesis that repetitive gravitoinertial stress would augment the arterial-pressure response to peripheral sympathetic stimulation. Methods Before and after a 5-weeks G-training regimen conducted in a human-use centrifuge, twenty healthy men performed a hand cold-pressor test, and nine of them also a foot cold-pressor test (4 min; 4 °C water). Arterial pressures and total peripheral resistance were monitored. Results The cold-induced elevation ( P ≤ 0.002) in arterial pressures and total peripheral resistance did not vary between testing periods, either in the hand [mean arterial pressure: Before = + 16% vs. After = + 17% and total peripheral resistance: Before = + 13% vs. After = + 15%], or in the foot [mean arterial pressure: Before = + 19% vs. After = + 21% and total peripheral resistance: Before = + 16% vs. After = + 16%] cold-pressor tests ( P > 0.05). Conclusion Present results demonstrate that 5 weeks of prolonged iterative exposure to hypergravity does not alter the responsiveness of sympathetically mediated circulatory reflexes.

During coordinated flight and centrifugation, pilots show interindividual variability in perceived roll tilt. The study explored how this variability is related to perceptual and cognitive functions. Twelve pilots underwent three 6-min centrifugations on two occasions (G levels: 1.1G, 1.8G, and 2.5G; gondola tilts: 25°, 56°, and 66°). The subjective visual horizontal (SVH) was measured with an adjustable luminous line and the pilots gave estimates of experienced G level. Afterward, they were interrogated regarding the relationship between G level and roll tilt and adjusted the line to numerically mentioned angles. Generally, the roll tilt during centrifugation was underestimated, and there was a large interindividual variability. Both knowledge on the relationship between G level and bank angle, and ability to adjust the line according to given angles contributed to the prediction of SVH in a multiple regression model. However, in most cases, SVH was substantial smaller than predictions based on specific abilities.

Abstract Sjöberg, M, Eiken, O, Norrbrand, L, Berg, HE, and Gutierrez-Farewik, EM. Lumbar loads and muscle activity during flywheel and barbell leg exercises. J Strength Cond Res 37(1): 27–34, 2023—It is anticipated that flywheel-based leg resistance exercise will be implemented in future long-duration space missions, to counter deconditioning of weight-bearing bones and postural muscles. The aim was to examine low back loads and muscle engagements during flywheel leg press (FWLP) and flywheel squat (FWS) and, for comparisons, free-weight barbell back squat (BBS). Eight resistance-trained subjects performed 8 repetition maximums of FWLP, FWS, and BBS. Motion analysis and inverse dynamics-based musculoskeletal modeling were used to compute joint loads and muscle forces. Muscle activities were measured with electromyography (EMG). At the L4–L5 level, peak vertebral compression force was similarly high in all exercise modes, whereas peak vertebral posteroanterior shear force was greater (p < 0.05) in FWLP and BBS than in FWS. Among the back-extensor muscles, the erector spinae longissimus exerted the greatest peak force, with no difference between exercises. Peak force in the lumbar multifidus was lower (p < 0.05) during FWLP than during FWS and BBS. Peak EMG activity in the lumbar extensor muscles ranged between 31 and 122% of maximal voluntary isometric contraction across muscles and exercise modes, with the greatest levels in the lumbar multifidus. The vertebral compression forces and muscle activations during the flywheel exercises were sufficiently high to presume that when implementing such exercise in space countermeasure regimens, they may be capable of preventing muscle atrophy and vertebral demineralization in the lumbar region.

Divers are at enhanced risk of hypothermia, due to the independent action of the inspired inert gases on thermoregulation. Thus, narcosis induced by acute (≤2 h) exposure to either hyperbaric nitrogen or normobaric nitrous oxide (N2O) impairs shivering thermogenesis and accelerates body core cooling. Animal-based studies, however, have indicated that repeated and sustained N2O administration may prevent N2O-evoked hypometabolism. We, therefore, examined the effects of prolonged intermittent exposure to 30% N2O on human thermoeffector plasticity in response to moderate cold. Fourteen men participated in two ∼12-h sessions, during which they performed sequentially three 120-min cold-water immersions (CWIs) in 20°C water, separated by 120-min rewarming. During CWIs, subjects were breathing either normal air or a normoxic gas mixture containing 30% N2O. Rectal and skin temperatures, metabolic heat production (via indirect calorimetry), finger and forearm cutaneous vascular conductance (CVC; laser-Doppler fluxmetry/mean arterial pressure), and thermal sensation and comfort were monitored. N2O aggravated the drop in rectal temperature (P = 0.01), especially during the first (by ∼0.3°C) and third (by ∼0.4°C) CWIs. N2O invariably blunted the cold-induced elevation of metabolic heat production by ∼22%-25% (P < 0.001). During the initial ∼30 min of the first and second CWIs, N2O attenuated the cold-induced drop in finger (P ≤ 0.001), but not in forearm CVC. N2O alleviated the sensation of coldness and thermal discomfort throughout (P < 0.001). Thus, the present results demonstrate that, regardless of the cumulative duration of gas exposure, a subanesthetic dose of N2O depresses human thermoregulatory functions and precipitates the development of hypothermia.NEW & NOTEWORTHY Human thermoeffector plasticity was evaluated in response to prolonged iterative exposure to 30% N2O and moderate cold stress. Regardless of the duration of gas exposure, N2O-induced narcosis impaired in a persistent manner shivering thermogenesis and thermoperception.