Individuals with adverse childhood experiences explore less and underweight reward feedback.

Adverse childhood experiences (ACEs) are extreme stressors that lead to negative psychosocial outcomes in adulthood. Nonhuman animals explore less after exposure to early stress. Therefore, in this preregistered study, we hypothesized that reduced exploration following ACEs would also be evident in human adults. Further, we predicted that adults with ACEs, in a foraging task, would adopt a decision-making policy that relies on the most-recent reward feedback, a rational strategy for unstable environments. We analyzed data from 145 adult participants, 47 with four or more ACEs and 98 with fewer than four ACEs. In the foraging task, participants evaluated the trade-off between exploiting a known patch with diminishing rewards and exploring a novel one with a fresh distribution of rewards. Using computational modeling, we quantified the degree to which participants' decisions weighted recent feedback. As predicted, participants with ACEs explored less. However, contrary to our hypothesis, they underweighted recent feedback. These unexpected findings indicate that early adversity may dampen reward sensitivity. Our results may help to identify cognitive mechanisms that link childhood trauma to the onset of psychopathology.

Reviewing explore/exploit decision-making as a transdiagnostic target for psychosis, depression, and anxiety.

In many everyday decisions, individuals choose between trialling something novel or something they know well. Deciding when to try a new option or stick with an option that is already known to you, known as the "explore/exploit" dilemma, is an important feature of cognition that characterises a range of decision-making contexts encountered by humans. Recent evidence has suggested preferences in explore/exploit biases are associated with psychopathology, although this has typically been examined within individual disorders. The current review examined whether explore/exploit decision-making represents a promising transdiagnostic target for psychosis, depression, and anxiety. A systematic search of academic databases was conducted, yielding a total of 29 studies. Studies examining psychosis were mostly consistent in showing that individuals with psychosis explored more compared with individuals without psychosis. The literature on anxiety and depression was more heterogenous; some studies found that anxiety and depression were associated with more exploration, whereas other studies demonstrated reduced exploration in anxiety and depression. However, examining a subset of studies that employed case-control methods, there was some evidence that both anxiety and depression also were associated with increased exploration. Due to the heterogeneity across the literature, we suggest that there is insufficient evidence to conclude whether explore/exploit decision-making is a transdiagnostic target for psychosis, depression, and anxiety. However, alongside our advisory groups of lived experience advisors, we suggest that this context of decision-making is a promising candidate that merits further investigation using well-powered, longitudinal designs. Such work also should examine whether biases in explore/exploit choices are amenable to intervention.

Modulation of cold-induced shivering activity by intermittent and continuous voluntary suppression.

This investigation assessed the physiological effects of voluntary suppression of shivering thermogenesis in response to whole body cooling. Eleven healthy volunteers underwent passive air cooling (10°C), across three visits: NO_SUP, where participants allowed their body to freely regulate against the cold; FULL_SUP, where participants constantly suppressed shivering; INT_SUP, where participants intermittently suppressed shivering (5 min phases), interspersed with 5 min free regulation. Shivering was assessed via electromyography (EMG), mechanomyography (MMG), and whole body oxygen uptake (V̇o2), whereas body temperature and heat exchange were assessed via skin temperature, rectal temperature, and heat flux sensors. A 29% increase was observed in shivering onset time in the FULL_SUP trial compared with NO_SUP (P = 0.032). Assessing shivering intensity, EMG activity decreased by 29% (P = 0.034), MMG activity decreased by 35% (P = 0.031), whereas no difference was observed in V̇o2 (P = 0.091) in the FULL_SUP trial compared with NO_SUP. Partitioning the no-suppression and suppression phases of the INT_SUP trial, acute voluntary suppression significantly decreased V̇o2 (P = 0.001), EMG (P < 0.001), and MMG (P = 0.012) activity compared with the no-suppression phases. Shivering activity was restored in the no-suppression phases, equivalent to that in the NO_SUP trial (P > 0.3). No difference was observed in thermal metrics between conditions up to 60 min (P > 0.4). Humans can both constantly and periodically suppress shivering activity, leading to a delay in shivering onset and a reduction in shivering intensity. Following suppression, regular shivering is resumed.

Dietary nitrate supplementation increases nitrate and nitrite concentrations in human skin interstitial fluid.

Acute dietary nitrate (NO3-) supplementation can increase [NO3-], but not nitrite ([NO2-]), in human skeletal muscle, though its effect on [NO3-] and [NO2-] in skin remains unknown. In an independent group design, 11 young adults ingested 140 mL of NO3--rich beetroot juice (BR; 9.6 mmol NO3-), and 6 young adults ingested 140 mL of a NO3--depleted placebo (PL). Skin dialysate, acquired through intradermal microdialysis, and venous blood samples were collected at baseline and every hour post-ingestion up to 4 h to assess dialysate and plasma [NO3-] and [NO2-]. The relative recovery rate of NO3- and NO2- through the microdialysis probe (73.1% and 62.8%), determined in a separate experiment, was used to estimate skin interstitial [NO3-] and [NO2-]. Baseline [NO3-] was lower, whereas baseline [NO2-] was higher in the skin interstitial fluid relative to plasma (both P < 0.001). Acute BR ingestion increased [NO3-] and [NO2-] in the skin interstitial fluid and plasma (all P < 0.001), with the magnitude being smaller in the skin interstitial fluid (e.g., 183 ± 54 vs. 491 ± 62 µM for Δ[NO3-] from baseline and 155 ± 190 vs. 217 ± 204 nM for Δ[NO2-] from baseline at 3 h post BR ingestion, both P ≤ 0.037). However, due to the aforementioned baseline differences, skin interstitial fluid [NO2-] post BR ingestion was higher, whereas [NO3-] was lower relative to plasma (all P < 0.001). These findings extend our understanding of NO3- and NO2- distribution at rest and indicate that acute BR supplementation increases [NO3-] and [NO2-] in human skin interstitial fluid.

Body mapping of skin friction coefficient and tactile perception during the dynamic skin-textile interaction.

The clothing fabric and skin interact continuously across the many regions of users' bodies during wear, which can lead to both physical skin damage and discomfort. Therefore, this investigation aimed to explore the regional differences in skin friction, tactile perception, and sensitivity in both females and males during the skin-textile interaction. The static and dynamic friction coefficient and textile perception (texture, stickiness, pleasantness, and discomfort) were measured across the 36 selected testing body areas by using a friction measurement device. The results revealed there was a significant difference in skin friction, tactile perceptions, and sensitivity across the various body regions. The anterior neck had the highest skin friction in both females and males, and participants generally rated higher texture perception in their anterior aspects compared to posterior and lateral regions. There was no significant difference in skin friction, tactile perception ratings, and sensitivity between females and males. Practitioner summary: This study sought to examine regional variations in skin friction, tactile perception, and sensitivity during the skin-textile interaction. There was a significant difference in skin friction, tactile perceptions, and sensitivity across the various body regions and no significant sex effect on skin friction, tactile perception ratings, and sensitivity.

Are adolescents more optimal decision-makers in novel environments? Examining the benefits of heightened exploration in a patch foraging paradigm.

Adolescence is a period of heightened exploration relative to adulthood and childhood. This predisposition has been linked with negative behaviours related to risk-taking, including dangerous driving, substance misuse and risky sexual practices. However, recent models have argued that adolescents' heightened exploration serves a functional purpose within the lifespan, allowing adolescents to develop experiential knowledge of their surroundings. Yet, there is limited evidence that heightened exploration in adolescence is associated with positive outcomes. To address this, the present pre-registered study utilised a foraging paradigm with a sample of adolescents aged 16-17 (N = 68) and of adults aged 21 and above (N = 69). Participants completed a patch foraging task, which required them to choose between exploiting a known resource which gradually yields fewer rewards, and exploring a novel, unknown resource with a fresh distribution of rewards. Findings demonstrated that adolescents explored more than adults, which - in the context of the current task-represented more optimal patch foraging behaviour. These findings indicate that adolescents' heightened exploration can be beneficial, as they were able to effectively navigate unknown environments and accrue rewards more successfully than adults. This provides evidence that heightened exploration in adolescence, relative to adulthood, can lead to positive outcomes and contributes to our understanding of the role increased novelty-seeking plays at this point in the lifespan.

Independent and combined impact of hypoxia and acute inorganic nitrate ingestion on thermoregulatory responses to the cold.

PURPOSE: This study assessed the impact of normobaric hypoxia and acute nitrate ingestion on shivering thermogenesis, cutaneous vascular control, and thermometrics in response to cold stress. METHOD: Eleven male volunteers underwent passive cooling at 10 °C air temperature across four conditions: (1) normoxia with placebo ingestion, (2) hypoxia (0.130 FiO2) with placebo ingestion, (3) normoxia with 13 mmol nitrate ingestion, and (4) hypoxia with nitrate ingestion. Physiological metrics were assessed as a rate of change over 45 min to determine heat loss, and at the point of shivering onset to determine the thermogenic thermoeffector threshold. RESULT: Independently, hypoxia expedited shivering onset time (p = 0.05) due to a faster cooling rate as opposed to a change in central thermoeffector thresholds. Specifically, compared to normoxia, hypoxia increased skin blood flow (p = 0.02), leading to an increased core-cooling rate (p = 0.04) and delta change in rectal temperature (p = 0.03) over 45 min, yet the same rectal temperature at shivering onset (p = 0.9). Independently, nitrate ingestion delayed shivering onset time (p = 0.01), mediated by a change in central thermoeffector thresholds, independent of changes in peripheral heat exchange. Specifically, compared to placebo ingestion, no difference was observed in skin blood flow (p = 0.5), core-cooling rate (p = 0.5), or delta change in rectal temperature (p = 0.7) over 45 min, while nitrate reduced rectal temperature at shivering onset (p = 0.04). No interaction was observed between hypoxia and nitrate ingestion. CONCLUSION: These data improve our understanding of how hypoxia and nitric oxide modulate cold thermoregulation.

An examination of five theoretical foundations associated with localized thermosensory testing.

PURPOSE: To assess five theoretical foundations underlying thermosensory testing using local thermal stimuli. METHODS: Thermal sensation, discomfort and the confidence of thermal sensation scores were measured in 9 female and 8 male volunteers in response to 17 physical contact temperature stimuli, ranging between 18-42 °C. These were applied to their dorsal forearm and lateral torso, across two sessions. RESULTS: Thermal sensation to physical temperature relationships followed a positive linear and sigmoidal fit at both forearm (r2 = 0.91/r2 = 0.91, respectively) and lateral torso (r2 = 0.90/ r2 = 0.91, respectively). Thermal discomfort to physical temperature relationships followed second and third-order fits at both forearm (r2 = 0.33/r2 = 0.34, respectively) and lateral torso (r2 = 0.38/r2 = 0.39, respectively) test sites. There were no sex-related or regional site differences in thermal sensation and discomfort across a wide range of physical contact temperatures. The median confidence of an individual's thermal sensation rating was measured at 86%. CONCLUSION: The relation between thermal sensation and physical contact temperature was well described by both linear and sigmoidal models, i.e., the distance between the thermal sensation anchors is close to equal in terms of physical temperatures changes for the range studied. Participants rated similar thermal discomfort level in both cold and hot thermal stimuli for a given increase or decrease in physical contact temperature or thermal sensation. The confidence of thermal sensation rating did not depend on physical contact temperature.

Mental fatigue independent of boredom and sleepiness does not impact self-paced physical or cognitive performance in normoxia or hypoxia.

This study investigated the individual and combined effects of mental fatigue (MF) and hypoxia (HYP) on physical and cognitive performance. Fifteen males (24 ± 3 years) completed one familiarization session and six experimental trials, including: 1) normoxia (0.209 FiO2) and no MF; 2) normoxia (0.209 FiO2) with MF; 3) mild normobaric HYP (0.13 FiO2) and no MF; 4) mild normobaric HYP (0.13 FiO2) with MF; 5) severe normobaric HYP (0.10 FiO2) and no MF; 6) severe normobaric HYP (0.10 FiO2) with MF. Each condition included a 15-min self-paced time trial, followed by a 60-s isometric maximal voluntary contraction of the biceps brachii. MF was induced using a 16-min individualized cognitive test prior to exercise performance. Following each time trial, participants performed the Tower of Hanoi cognitive test. A main effect of HYP was observed on average power output, oxygen consumption and muscle oxygenation (P ≤ 0.004), with no effect of MF (P ≥ 0.599). Voluntary activation of the biceps brachii was also reduced in HYP (68.42 ± 5.64%, P = 0.039). No effect of MF or HYP was observed on cognitive performance (P ≥ 0.138). HYP impacted physical performance, whilst MF had no effect on self-paced physical or cognitive performance.

Reliability and validity of methods in the assessment of cold-induced shivering thermogenesis.

PURPOSE: To compare two analytical methods for the estimation of the shivering onset inflection point, segmental regression and visual inspection of data, and to assess the test-retest reliability and validity of four metrics of shivering measurement; oxygen uptake (V̇O2), electromyography (EMG), mechanomyography (MMG) and bedside shivering assessment scale (BSAS). METHODS: Ten volunteers attended three identical experimental sessions involving passive deep-body cooling via cold water immersion at 10 °C. V̇O2, EMG, and MMG were continuously assessed, while the time elapsed at each BSAS stage was recorded. Metrics were graphed as a function of time and rectal temperature (Tre). Inflection points for intermittent and constant shivering were visually identified for every graph and compared to segmental regression. RESULTS: Excellent agreement was seen between segmental regression and visual inspection (ICC, 0.92). All measurement metrics presented good-to-excellent test-retest reliability (ICC's > 0.75 and 0.90 respectively), with the exception of visual identification of intermittent shivering for V̇O2 measurement (ICC, 0.73) and segmental regression for EMG measurement (ICC, 0.74). In the assessment of signal-to-noise ratio (SNR), EMG showed the largest SNR at the point of shivering onset followed by MMG and finally V̇O2. CONCLUSIONS: Segmental regression provides a successful analytical method for identifying shivering onset. Good-to-excellent reliability can be seen across V̇O2, EMG, MMG, and BSAS, yet given the observed lag times, SNRs, along with known advantages/disadvantaged of each metric, it is recommended that no single metric is used in isolation. An integrative, real-time measure of shivering is proposed.

Counterpoint to "Infrared cameras overestimate skin temperature during rewarming from cold exposure".

We evaluated the paper by Maley et al. (2020) in this journal "Infrared cameras overestimate skin temperature during rewarming from cold Exposure" for the evidence provided in support of its title and conclusions. Several methodological issues were identified as well as issues with the data interpretation: 1: Only one camera was used but a conclusion was made for 'cameras' in general; 2: The camera accuracy (±2 °C) is too low to do a meaningful comparison without using local reference values or an on-site calibrator with higher accuracy; 3: Thermistor measurements are taken as a gold standard while issues such as temperature gradients and taping are known; 4: Both methods are not compared at the same location and a natural, physiological, gradient may be present between their locations; 5. The impact of the sensor and tape on delays in the change of the underlying tissue temperature is not considered; 6: Only a single pixel was used for the analysis, which has been shown to be problematic. We concluded that the paper by Maley et al. does not provide conclusive evidence that infrared cameras overestimate skin temperature during rewarming from cold exposure.

A comparison of methods used for inducing mental fatigue in performance research: individualised, dual-task and short duration cognitive tests are most effective.

Despite research indicating the negative impact that mental fatigue has on physical and cognitive performance, whether this is a result of mental fatigue or a state of under-arousal remains unclear. The current research aimed to explore the effectiveness of the methods being used to induce mental fatigue. Twelve participants attended six sessions in which two cognitive tests, the AX-continuous performance test (AX-CPT) and the TloadDback test, were compared for their effectiveness in inducing mental fatigue. Both tests were set at a standard processing speed (1.2 ms) for two conditions, and a further condition involved the individualisation of the TloadDback test. Participants presented significantly higher physiological and psychological arousal (p < 0.05) in the individualised dual-task test compared to the AX-CPT. The individualised TloadDback test is a more effective method of inducing mental fatigue compared to the AX-CPT, as it sustains physiological arousal whilst inducing measurable reductions in mental resources. Practitioner summary: Mental fatigue negatively impacts physical and cognitive performance. It is unclear whether the current methods being used to induce mental fatigue are effective. This study compared different methods and confirmed that short, individualised and dual-task tests are most effective for inducing mental fatigue whilst maintaining arousal.

The use of infrared thermal imaging to measure spatial and temporal sweat retention in clothing.

In our previous laboratory study a 'destructive' gravimetric method was developed to quantify local garment sweat absorption. While this currently is the only methodology that permits direct and analytical measurements of garment regional sweat absorption, the latter approach is time-consuming and expensive, therefore, of limited applicability. As such, in this study, we wanted to assess whether infrared thermography could be used as an indirect method to estimate garment regional sweat absorption, right after exercise, in a 'non-destructive' fashion. Spatial and temporal sweat absorption data, obtained in our previous study, were correlated with spatial and temporal temperature data obtained in the same experiment with an infrared thermal camera. The data suggest that infrared thermography is a good tool to qualitatively predict regional sweat absorption in garments at separate individual time points; however, temporal changes are not predicted well, due to a moisture content threshold above which variations in sweat content cannot be discriminated by further temperature changes.

Spatial and temporal migration of sweat: from skin to clothing.

PURPOSE: Moisture accumulation in clothing affects human performance and productivity through its impact on thermal balance and various aspects of discomfort. Building on our laboratory's work on mapping sweat production across the body, this study aimed to obtain detailed spatial and temporal maps showing how this sweat migrates into a single clothing layer (T-shirt) during physical exercise. METHOD: Eight male participants performed running exercise in a warm environment. Garment sweat absorption was mapped over a total running time of 50 min, in 10 separated running trials of different durations (5 min increments). After running, the garment was dissected into 22 different parts and local sweat absorption (ABSlocal) was quantified by weighing each garment part before and after drying. From ABSlocal, garment total sweat absorption (ABStotal) was estimated. RESULTS: After 50 min, Tcore rose from 37 ± 0.2 to 38.6 ± 0.3 °C, HR increased from 69 ± 15 to 163 ± 12 bpm (p < 0.001), GSL was 586 ± 86 g m-2. Clear patterns of sweat absorption reduction from superior-to-inferior and from medial-to-lateral T-shirt zones were observed, with the mid back medial and the low front hem showing the highest, respectively. CONCLUSIONS: Quantitative data on garment total and regional sweat absorption were obtained and considerable variation between different garment zones was identified. These data can support the development of sport and personal protective clothing with the end goal to prevent workers' heat-related injuries as well as maximise human performance and productivity.

Anchoring biases affect repeated scores of thermal, moisture, tactile and comfort sensations in transient conditions.

In this study, we addressed potential biases which can occur when sensorial scores of temperature, wetness and discomfort are repeatedly reported, in transient exercise conditions. We pointed out that, when repeatedly reported, previous sensorial scores can be set by the participants as reference values and the subsequent score may be given based on the previous point of reference, the latter phenomenon leading to a bias which we defined as 'anchoring bias'. Indeed, the findings shown that subsequent sensorial scores are prone to anchoring biases and that the bias consisted in a systematically higher magnitude of sensation as compared to when reported a single time only. As such, the study allowed recognition, quantification and mitigation of the identified bias which can improve the methodological rigour of research studies involving assessments of sensorial data in transient conditions.

Localized and systemic variations in central motor drive at different local skin and muscle temperatures.

This study investigated the ability to sustain quadriceps central motor drive while subjected to localized heat and metaboreceptive feedback from the contralateral leg. Eight active males each completed two counter-balanced trials, in which muscle temperature (Tm) of a single-leg (TEMP-LEG) was altered to 29.4°C (COOL) or 37.6°C (WARM), while the contralateral leg (CL-LEG) remained thermoneutral: 35.3°C and 35.2°C Tm in COOL and WARM, respectively. To activate metaboreceptive feedback, participants first performed one 120-s isometric maximal voluntary contraction (MVC) of the knee extensors in the TEMP-LEG, immediately followed by postexercise muscle ischemia (PEMI) via femoral blood flow occlusion. To assess central motor drive of a remote muscle group immediately following PEMI, another 120-s MVC was subsequently performed in the CL-LEG. Voluntary muscle activation (VA) was assessed using the twitch interpolation method. Perceived mental effort and limb discomfort were also recorded. In a cooled muscle, a significant increase in mean force output and mean VA (force, P < 0.001; VA, P < 0.05), as well as a significant decrease in limb discomfort (P < 0.05) occurred during the sustained MVC in the TEMP-LEG. However, no differences between Tm were observed in mean force output, mean VA, or limb discomfort during the sustained MVC in the CL-LEG (force, P = 0.33; VA, P > 0.68; and limb discomfort, P = 0.73). The present findings suggest that elevated local skin temperature and Tm can increase limb discomfort and decrease central motor drive, but this does not limit systemic motor activation of a thermoneutral muscle group.

Post-warm-up muscle temperature maintenance: blood flow contribution and external heating optimisation.

PURPOSE: Passive muscle heating has been shown to reduce the drop in post-warm-up muscle temperature (Tm) by about 25% over 30 min, with concomitant sprint/power performance improvements. We sought to determine the role of leg blood flow in this cooling and whether optimising the heating procedure would further benefit post-warm-up T m maintenance. METHODS: Ten male cyclists completed 15-min sprint-based warm-up followed by 30 min recovery. Vastus lateralis Tm (Tmvl) was measured at deep-, mid- and superficial-depths before and after the warm-up, and after the recovery period (POST-REC). During the recovery period, participants wore water-perfused trousers heated to 43 °C (WPT43) with either whole leg heating (WHOLE) or upper leg heating (UPPER), which was compared to heating with electrically heated trousers at 40 °C (ELEC40) and a non-heated control (CON). The blood flow cooling effect on Tmvl was studied comparing one leg with (BF) and without (NBF) blood flow. RESULTS: Warm-up exercise significantly increased Tmvl by ~3 °C at all depths. After the recovery period, BF Tmvl was lower (~0.3 °C) than NBF Tmvl at all measured depths, with no difference between WHOLE versus UPPER. WPT43 reduced the post-warm-up drop in deep-Tmvl (-0.12 °C ± 0.3 °C) compared to ELEC40 (-1.08 ± 0.4 °C) and CON (-1.3 ± 0.3 °C), whereas mid- and superficial-Tmvl even increased by 0.15 ± 0.3 and 1.1 ± 1.1 °C, respectively. CONCLUSION: Thigh blood flow contributes to the post-warm-up Tmvl decline. Optimising the external heating procedure and increasing heating temperature of only 3 °C successfully maintained and even increased T mvl, demonstrating that heating temperature is the major determinant of post-warm-up Tmvl cooling in this application.

The interaction between peripheral and central fatigue at different muscle temperatures during sustained isometric contractions.

Changes in central fatigue have been linked to active and passive changes in core temperature, as well as integration of sensory feedback from thermoreceptors in the skin. However, the effects of muscle temperature (Tm), and thereby metaboreceptor and local afferent nerve temperature, on central fatigue (measured using voluntary activation percentage) during sustained, high muscle fatigue exercise remain unexamined. In this study, we investigated Tm across the range of cold to hot, and its effect on voluntary activation percentage during sustained isometric contractions of the knee extensors. The results suggest that contrary to brief contractions, during a sustained fatiguing contraction Tm significantly (P < 0.001) influences force output (-0.7%/°C increase) and central fatigue (-0.5%/°C increase), showing a negative relationship across the Tm continuum in moderately trained individuals. The negative relationship between voluntary activation percentage and Tm indicates muscle temperature may influence central fatigue during sustained and high muscle fatigue exercise. On the basis of on an integrative analysis between the present data and previous literature, the impact of core and muscle temperature on voluntary muscle activation is estimated to show a ratio of 5.5 to 1, respectively. Accordingly, Tm could assume a secondary or tertiary role in the reduction of voluntary muscle activation when body temperature leaves a thermoneutral range.

The interactive effect of cooling and hypoxia on forearm fatigue development.

PURPOSE: To examine the effect of separate and combined exposure to hypoxia [normoxia (FIO2 = 0.21) vs. moderate altitude (FIO2 = 0.13)] and temperature [thermoneutral (22 °C) vs. cold (5 °C)] on muscle fatigue development in the forearm, after repeated low-resistance contractions. METHODS: Eight males were exposed for 70 min to four separate conditions in a balanced order. Conditions were normoxic-thermoneutral (N), hypoxic-thermoneutral, normoxic-cold and hypoxic-cold. After 15-min seated rest, participants carried out intermittent dynamic forearm exercise at 15 % maximal isometric voluntary contraction (MVC) for eight consecutive, 5-min work bouts. Each bout was separated by 110 s rest during which MVC force was collected. RESULTS: When exposed to hypoxia and cold independently, the exercise protocol decreased MVC force of the finger flexors by 8.1 and 13.9 %, respectively, compared to thermoneutral normoxia. When hypoxia and cold were combined, the decrease in MVC force was 21.4 % more than thermoneutral normoxia, reflecting an additive effect and no interaction. EMG relative to force produced during MVC, increased by 2 and 1.2 µV per kg (36 and 23 % of N) for cold and hypoxia, respectively. When the stressors were combined the effect was additive, increasing to 3.1 µV per kg (56 % of N). CONCLUSION: When compared to exercise in thermoneutral normoxic conditions, both cold and hypoxia significantly reduce brief MVC force output. This effect appears to be of mechanical origin, not a failure in muscle fibre recruitment per se. Additionally, the reduction in force is greater when the stressors are combined, showing an additive effect.

Nitrate ingestion blunts the increase in blood pressure during cool air exposure: a double-blind, placebo-controlled, randomized, crossover trial.

Cold exposure increases blood pressure (BP) and salivary flow rate (SFR). Increased cold-induced SFR would be hypothesized to enhance oral nitrate delivery for reduction to nitrite by oral anaerobes and to subsequently elevate plasma [nitrite] and nitric oxide bioavailability. We tested the hypothesis that dietary nitrate supplementation would increase plasma [nitrite] and lower BP to a greater extent in cool compared with normothermic conditions. Twelve males attended the laboratory on four occasions. Baseline measurements were completed at 28°C. Subsequently, participants ingested 140 mL of concentrated nitrate-rich (BR; ∼13 mmol nitrate) or nitrate-depleted (PL) beetroot juice. Measurements were repeated over 3 h at either 28°C (Norm) or 20°C (Cool). Mean skin temperature was lowered compared with baseline in PL-Cool and BR-Cool. SFR was greater in BR-Norm, PL-Cool, and BR-Cool than PL-Norm. Plasma [nitrite] at 3 h was higher in BR-Cool (592 ± 239 nM) versus BR-Norm (410 ± 195 nM). Systolic BP (SBP) at 3 h was not different between PL-Norm (117 ± 6 mmHg) and BR-Norm (113 ± 9 mmHg). SBP increased above baseline at 1, 2, and 3 h in PL-Cool but not BR-Cool. These results suggest that BR consumption is more effective at increasing plasma [nitrite] in cool compared with normothermic conditions and blunts the rise in BP following acute cool air exposure, which might have implications for attenuating the increased cardiovascular strain in the cold.NEW & NOTEWORTHY Compared with normothermic conditions, acute nitrate ingestion increased plasma [nitrite], a substrate for oxygen-independent nitric oxide generation, to a greater extent during cool air exposure. Systolic blood pressure was increased during cool air exposure in the placebo condition with this cool-induced blood pressure increase attenuated after acute nitrate ingestion. These findings improve our understanding of environmental factors that influence nitrate metabolism and the efficacy of nitrate supplementation to lower blood pressure.