Strategies to mitigate acute kidney injury risk during physical work in hot environments

Prolonged physical work in the heat can reduce renal function and increase the risk of acute kidney injury (AKI). This is concerning given that the latest climate change projections forecast a rise in global temperature as well as the frequency, intensity, and duration of heatwaves. This means that outdoor and indoor workers in the agriculture or construction industries will be exposed to higher heat stress in the years ahead. Several studies indicate a higher incidence of chronic kidney disease from nontraditional origins (CKDnt) in individuals exposed to high temperatures, intense physical work, and/or recurrent dehydration. It has been proposed that prolonged physical work in the heat accompanied by dehydration results in recurrent episodes of AKI that ultimately lead to permanent kidney damage and the development of CKDnt. Thus, there is a need to identify and test strategies that can alleviate AKI risk during physical work in the heat. The purpose of this review is to present strategies that might prevent and mitigate the risk of AKI induced by physical work in the heat.

Effect of heat stress on heat shock protein expression and hypertrophy-related signaling in the skeletal muscle of trained individuals

Muscle mass is balanced between hypertrophy and atrophy by cellular processes, including activation of the protein kinase B-mechanistic target of rapamycin (Akt-mTOR) signaling cascade. Stressors apart from exercise and nutrition, such as heat stress, can stimulate the heat shock protein A (HSPA) and C (HSPC) families alongside hypertrophic signaling factors and muscle growth. The effects of heat stress on HSP expression and Akt-mTOR activation in human skeletal muscle and their magnitude of activation compared with known hypertrophic stimuli are unclear. Here, we show a single session of whole body heat stress following resistance exercise increases the expression of HSPA and activation of the Akt-mTOR cascade in skeletal muscle compared with resistance exercise in a healthy, resistance-trained population. Heat stress alone may also exert similar effects, though the responses are notably variable and require further investigation. In addition, acute heat stress in C2C12 muscle cells enhanced myotube growth and myogenic fusion, albeit to a lesser degree than growth factor-mediated hypertrophy. Though the mechanisms by which heat stress stimulates hypertrophy-related signaling and the potential mechanistic role of HSPs remain unclear, these findings provide additional evidence implicating heat stress as a novel growth stimulus when combined with resistance exercise in human skeletal muscle and alone in isolated murine muscle cells. We believe these findings will help drive further applied and mechanistic investigation into how heat stress influences muscular hypertrophy and atrophy.NEW & NOTEWORTHY We show that acute resistance exercise followed by whole body heat stress increases the expression of HSPA and increases activation of the Akt-mTOR cascade in a physically active and resistance-trained population.

A comprehensive evaluation of heat stress and heat strain in a sample of sugarcane cutters in Brazil

Sugarcane cutters are vulnerable to extreme heat and are at risk for heat-related illness and chronic kidney disease, potentially due to high heat strain. We performed a comprehensive assessment of the physiological demands of sugarcane cutters via measurements of metabolic, thermal, and cardiovascular responses. In addition, we assessed cross-shift changes in markers of kidney function. Nine male sugarcane cutters were monitored while working during the spring harvest season in Brazil. Core temperature (Tcore) and heart rate (HR) were continuously recorded, and oxygen consumption was measured during the work shift. Urine and blood samples were collected pre- and postwork shifts. Total sweat loss was calculated using body weight changes and adjusting for water ingestion and urine output. A wet-bulb globe temperature (WBGT) station was used to monitor environmental heat stress. WBGT was ≥30°C on 7 of the 8 study days. Mean and peak Tcore during the work shift were 37.96 ± 0.47°C and 38.60 ± 0.41°C, respectively, with all participants surpassing a Tcore of 38°C. Mean and peak HR during the work shift were 137 ± 14 and 164 ± 11 beats/min, respectively. Percent of maximal oxygen consumption was, on average, 53 ± 11%. Workers had a total sweat loss of 7.63 ± 2.31 L and ingested 6.04 ± 1.95 L of fluid. Kidney function (estimated glomerular filtration rate) was reduced from pre- to postwork shift (Δ -20 ± 18 mL·min·1.73 m2). We demonstrated that sugarcane cutters performing prolonged work during a period of high environmental heat stress display high levels of heat strain, high water turnover, and reduced kidney function.NEW & NOTEWORTHY We demonstrate that a shift of sugarcane cutting performed outdoors during the spring harvest season results in a high level of heat strain. In fact, all the studied workers sustained core temperatures above 38°C and heart rates above 75% of the measured maximum heart rate. Additionally, workers displayed a high water turnover with sweat loss close to 10% of their body weight. Finally, we report elevated muscle damage and reductions in kidney function following the work shift.

Reduced running performance and greater perceived exertion, but similar post-exercise neuromuscular fatigue in tropical natives subjected to a 10 km self-paced run in a hot compared to a temperate environment

Environmental heat stress impairs endurance performance by enhancing exercise-induced physiological and perceptual responses. However, the time course of these responses during self-paced running, particularly when comparing hot and temperate conditions, still needs further clarification. Moreover, monitoring fatigue induced by exercise is paramount to prescribing training and recovery adequately, but investigations on the effects of a hot environment on post-exercise neuromuscular fatigue are scarce. This study compared the time course of physiological and perceptual responses during a 10 km self-paced treadmill run (as fast as possible) between temperate (25°C) and hot (35°C) conditions. We also investigated the changes in countermovement jump (CMJ) performance following exercise in these two ambient temperatures. Thirteen recreational long-distance runners (11 men and 2 women), inhabitants of a tropical region, completed the two experimental trials in a randomized order. Compared to 25°C, participants had transiently higher body core temperature (TCORE) and consistently greater perceived exertion while running at 35°C (p < 0.05). These changes were associated with a slower pace, evidenced by an additional 14 ± 5 min (mean ± SD) to complete the 10 km at 35°C than at 25°C (p < 0.05). Before, immediately after, and 1 h after the self-paced run, the participants performed CMJs to evaluate lower limb neuromuscular fatigue. CMJ height was reduced by 7.0% (2.3 ± 2.4 cm) at 1 h after the race (p < 0.05) compared to pre-exercise values; environmental conditions did not influence this reduction. In conclusion, despite the reduced endurance performance, higher perceived exertion, and transiently augmented TCORE caused by environmental heat stress, post-exercise neuromuscular fatigue is similar between temperate and hot conditions. This finding suggests that the higher external load (faster speed) at 25°C compensates for the effects of more significant perceptual responses at 35°C in inducing neuromuscular fatigue.

The physiological, perceptual, and thermoregulatory responses to facemask use during exercise

The use of masks in public settings and when around people has been recommended to limit the spread of Coronavirus disease 2019 (COVID-19) by major public health agencies. Several different types of masks classified as either medical- or non-medical grade are commonly used among the public. However, concerns with difficulty breathing, re-breathing exhaled carbon dioxide, a decrease in arterial oxygen saturation, and a decrease in exercise performance have been raised regarding the use of mask during exercise. We review the current knowledge related to the effect of different masks during exercise on cardiorespiratory, metabolic, thermoregulatory, and perceptual responses. As such, the current literature seems to suggest that there are minimal changes to cardiovascular, metabolic, and no changes to thermoregulatory parameters with facemask use. However, differences in ventilatory parameters have been reported with submaximal and maximal intensity exercise to volitional fatigue. Literature on perceptual responses to exercise indicate an impact on ratings of perceived exertion, dyspnea, and overall discomfort dependent on mask use as well as exercise intensity. In conclusion, data from the current literature suggests a minimal impact on physiological, perceptual, and thermoregulatory responses dependent on the type of mask used during exercise.

Ibuprofen Increases Markers of Intestinal Barrier Injury But Suppresses Inflammation at Rest and After Exercise in Hypoxia

PURPOSE

The purpose of this study was to evaluate the effects of acute ibuprofen consumption (2 × 600-mg doses) on markers of enterocyte injury, intestinal barrier dysfunction, inflammation, and symptoms of gastrointestinal (GI) distress at rest and after exercise in hypobaric hypoxia.

METHODS

Using a randomized double-blind placebo-controlled crossover design, nine men (age, 28 ± 3 yr; weight, 75.4 ± 10.5 kg; height, 175 ± 7 cm; body fat, 12.9% ± 5%; V̇O 2 peak at 440 torr, 3.11 ± 0.65 L·min -1 ) completed a total of three visits including baseline testing and two experimental trials (placebo and ibuprofen) in a hypobaric chamber simulating an altitude of 4300 m. Preexercise and postexercise blood samples were assayed for intestinal fatty acid binding protein (I-FABP), ileal bile acid binding protein, soluble cluster of differentiation 14, lipopolysaccharide binding protein, monocyte chemoattractant protein-1, tumor necrosis factor α (TNF-α), interleukin-1β, and interleukin-10. Intestinal permeability was assessed using a dual sugar absorption test (urine lactulose-to-rhamnose ratio).

RESULTS

Resting I-FABP (906 ± 395 vs 1168 ± 581 pg·mL -1 ; P = 0.008) and soluble cluster of differentiation 14 (1512 ± 297 vs 1642 ± 313 ng·mL -1 ; P = 0.014) were elevated in the ibuprofen trial. Likewise, the urine lactulose-to-rhamnose ratio (0.217 vs 0.295; P = 0.047) and the preexercise to postexercise change in I-FABP (277 ± 308 vs 498 ± 479 pg·mL -1 ; P = 0.021) were greater in the ibuprofen trial. Participants also reported greater upper GI symptoms in the ibuprofen trial ( P = 0.031). However, monocyte chemoattractant protein-1 ( P = 0.007) and TNF-α ( P = 0.047) were lower throughout the ibuprofen trial compared with placebo (main effect of condition).

CONCLUSIONS

These data demonstrate that acute ibuprofen ingestion aggravates markers of enterocyte injury and intestinal barrier dysfunction at rest and after exercise in hypoxia. However, ibuprofen seems to suppress circulating markers of inflammation.

Practicing COVID-19 Public Health Measures Is Associated With Anxiety and Depression in Undergraduate University Students

Background

COVID-19 has affected mental health globally, increasing depression and anxiety. This study examined relationships between practicing COVID-19-related public health measures and depression and anxiety in young adult students.

Methods

A sample of 755 undergraduate students 18–25 years of age at a large public university completed a cross-sectional survey in fall 2020 during the pandemic (response rate = 18.9%). The survey included demographic questions, anxiety and depression screeners (GAD-7 and PHQ-9), and questions on practicing public health measures (stay-at-home orders, quarantining, social distancing, etc.) since March 2020. Multivariate logistic regression was utilized to calculated adjusted odds between practicing public health measures and anxiety and depression.

Results

The majority of respondents reported practicing public health measures; however, 53% experienced anxiety (GAD-7 score >10) and 57% experienced depression (PHQ-9 score >10) in the 2 weeks prior to completing the survey. Participants who quarantined had significantly higher odds of anxiety (AOR = 1.44; 95% CL 1.07, 1.96) and depression (AOR = 1.77; 95% CL 1.30, 2.41) than those who did not. Participants who self-isolated also had significantly higher odds of anxiety (AOR = 1.53; 95% CL 1.13, 2.08) and depression (AOR = 1.87; 95% CL 1.37, 2.56) compared to those who did not. Moving/changing living situations in response to the pandemic also increased odds of depression (AOR = 1.86; 95% CL 1.33, 2.60).

Conclusion

Young adult undergraduate students experienced a high prevalence of anxiety and depression. Quarantining, self-isolating, and moving/changing living situations increased odds of anxiety and/or depression. The public health measures necessary for COVID-19 control and prevention may adversely affect mental health.

A Metabolic Profile of Peripheral Heart Action Training

Purpose: Peripheral heart action (PHA) is a style of circuit training that alternates upper and lower body resistance exercises with minimal rest between sets. The purpose of this study was to compare the metabolic demands of PHA to traditional hypertrophy training (TRAD) and to provide between sex comparison for both types of resistance training (RT). Methods: Twenty resistance-trained individuals underwent two bouts of volume-load matched RT: PHA and TRAD. We measured oxygen uptake (VO₂), heart rate (HR), blood lactate (BL) concentration, rating of perceived exertion (RPE), excess post-exercise oxygen consumption (EPOC), and duration of each session. Results: PHA elicited significantly greater %VO₂max (p < .001), %HRmax (p < .001), RPE (p < .001), and EPOC (p < .001) compared to TRAD. PHA was also completed in less time (p < .001). Compared to TRAD, BL was significantly higher at mid-exercise (p < .001), post-exercise (p < .001), and 5-min post-exercise (p < .001) during PHA. There were no between-sex differences for BL at any time-point for TRAD. However, during PHA, BL was significantly higher for males at mid-exercise (p = .04), post-exercise (p = .02), and 5-min post-exercise (p = .002). No between-sex differences were detected for HR, VO₂, RPE, or duration for either style of RT. Conclusions: PHA is a time-effective and metabolically demanding circuit that may lead to strength and cardiorespiratory adaptations. Males produced more BL than females during PHA, but not TRAD, suggesting that they incurred more metabolic stress during the bout of circuit training.

The effect of repetition tempo on cardiovascular and metabolic stress when time under tension is matched during lower body exercise

PURPOSE

To investigate the effect of repetition tempo on cardiovascular and metabolic stress when time under tension (TUT) and effort are matched during sessions of lower body resistance training (RT).

METHODS

In a repeated-measures, cross-over design, 11 recreationally trained females (n = 5) and males (n = 6) performed 5 sets of belt squats under the following conditions: slow-repetition tempo (SLOW; 10 reps with 4-s eccentric and 2-s concentric) and traditional-repetition tempo (TRAD; 20 reps with 2-s eccentric and 1-s concentric). TUT (60 s) was matched between conditions and external load was adjusted so that lifters were close to concentric muscular failure at the end of each set. External load, total volume load (TVL), impulse (IMP), blood lactate, ratings of perceived exertion (RPE), HR, and muscle oxygenation were measured.

RESULTS

Data indicated that TVL (p < 0.001), blood lactate (p = 0.017), RPE (p = 0.015), and HR (p < 0.001) were significantly greater during TRAD while external load (p = 0.030) and IMP (p = 0.002) were significantly greater during SLOW. Whether it was expressed as minimal values or change scores, muscle oxygenation was not different between protocols.

CONCLUSION

When TUT is matched, TVL, cardiovascular stress, metabolic stress, and perceived exertion are greater when faster repetition tempos are used. In contrast, IMP and external load are greater when slower repetition tempos are used.

Exercise in hypobaric hypoxia increases markers of intestinal injury and symptoms of gastrointestinal distress

NEW FINDING

What is the central question of this study? What is the effect of hypobaric hypoxia on markers of exercise-induced intestinal injury and symptoms of GI distress? What is the main finding and its importance? Exercise performed at 4300 m of simulated altitude increased I-FABP, CLDN-3, and LBP which together suggest that exercise-induced intestinal injury may be aggravated by concurrent hypoxic exposure. Increases in I-FABP, LBP, CLDN-3 were correlated to exercise-induced GI symptoms, providing some evidence of a link between intestinal barrier injury and symptoms of GI distress.

ABSTRACT

We sought to determine the effect of exercise in hypobaric hypoxia on markers of intestinal injury and gastrointestinal (GI) symptoms. Using a randomized and counterbalanced design, 9 males completed two experimental trials: one at local altitude of 1585 m (NORM) and one at 4300 m of simulated hypobaric hypoxia (HYP). Participants performed 60-minutes of cycling at a workload that elicited 65% of their NORM VO₂ max. GI symptoms were assessed before and every 15-minutes during exercise. Pre- and post-exercise blood samples were assessed for intestinal fatty acid binding protein (I-FABP), claudin-3 (CLDN-3), and lipopolysaccharide binding protein (LBP). All participants reported at least one GI symptom in HYP compared to just 1 participant in NORM. I-FABP significantly increased from pre- to post-exercise in HYP (708±191 to 1215±518 pg mL^-1 ; p = 0.011, d = 1.10) but not NORM (759±224 to 828±288 pg mL^-1 ; p>0.99, d = 0.27). CLDN-3 significantly increased from pre- to post-exercise in HYP (13.8±0.9 to 15.3±1.2 ng mL^-1 ; p = 0.003, d = 1.19) but not NORM (13.7±1.8 to 14.2±1.6 ng mL^-1 ; p = .435, d = 0.45). LBP significantly increased from pre- to post-exercise in HYP (10.8±1.2 to 13.9±2.8 μg mL^-1 ; p = 0.006, d = 1.12) but not NORM (11.3±1.1 to 11.7±0.9 μg mL^-1 ; p>0.99, d = 0.32). I-FABP (d = 0.85), CLDN-3 (d = 0.95), and LBP (d = 0.69) were all significantly higher post-exercise in HYP compared to NORM (p≤0.05). Overall GI discomfort was significantly correlated to ΔI-FABP (r = 0.71), ΔCLDN-3 (r = 0.70), and ΔLBP (r = 0.86). These data indicate that cycling exercise performed in hypobaric hypoxia can cause intestinal injury, which might cause some commonly reported GI symptoms. This article is protected by copyright. All rights reserved.

Expanding the Gap: An Updated Look Into Sex Differences in Running Performance

Males consistently outperform females in athletic endeavors, including running events of standard Olympic distances (100 m to Marathon). The magnitude of this percentage sex difference, i.e., the sex gap, has evolved over time. Two clear trends in sex gap evolution are evident; a narrowing of the gap during the 20th century, followed by a period of stability thereafter. However, an updated perspective on the average sex gap from top 20 athlete performances over the past two decades reveals nuanced trends over time, indicating the sex gap is not fixed. Additionally, the sex gap varies with performance level; the difference in absolute running performance between males and females is lowest for world record/world lead performances and increases in lower-ranked elite athletes. This observation of an increased sex gap with world rank is evident in events 400 m and longer and indicates a lower depth in female competitive standards. Explanations for the sex difference in absolute performance and competition depth include physical (physiological, anatomical, neuromuscular, biomechanical), sociocultural, psychological, and sport-specific factors. It is apparent that females are the disadvantaged sex in sport; therefore, measures should be taken to reduce this discrepancy and enable both sexes to reach their biological performance potential. There is scope to narrow the sex performance gap by addressing inequalities between the sexes in opportunities, provisions, incentives, attitudes/perceptions, research, and media representation.

A Latent Class Analysis of Mental Health Severity and Alcohol Consumption: Associations with COVID-19-Related Quarantining, Isolation, Suicidal Ideations, and Physical Activity

The present study examined latent class cluster group patterns based on measures of depression and anxiety symptom severity and alcohol consumption during the COVID-19 pandemic. Hypothesized correlates with latent class cluster groups including quarantining, self-isolation, suicidal ideations, sitting hours per day, and physical activity (vigorous intensity exercise in minutes per week) were examined. The delimited participant sample consisted of 606 university young adults 18 to 25 years of age (M = 21.24 ± 1.62). Latent cluster analysis (LCA) modeled patterns of depression and anxiety symptom severity and alcohol consumption during the COVID-19 pandemic. Between group analysis and multinomial logistic regression analysis were used to examine relationships between latent class clusters and correlates including quarantining, self-isolation, suicidal ideations, sitting hours per day, and physical activity (vigorous intensity exercise in minutes per week). LCA results showed that six latent cluster groups provided optimal model-to-date fit based on mental health symptom severity and alcohol consumption (L 2  = 56.31, BIC = 5012.79, AIC = 4849.74, and the bootstrap L 2 p-value = .88; Entropy R 2  = .89). Identified latent class clusters were as follows: cluster one = moderate anxiety and depression severity and moderate alcohol consumption (n = 156; 25.7%); cluster two = high mental health severity and alcohol consumption (n = 133; 21.9%); cluster three = low mental health symptoms and moderate alcohol consumption (n = 105; 17.3%); cluster four = lowest mental health severity and alcohol consumption (n = 95; 15.7%); cluster five = moderate depression severity, low anxiety severity, and low alcohol consumptions (n = 74; 12.2%); and cluster six = moderate anxiety severity, low depression severity, and low alcohol consumption (n = 43; 7.1%). Multinomial logistic regression analysis results found that quarantining, self-isolation, suicidal ideations, sedentary behavior, and physical activity were differentially associated with cluster group membership. Findings from this study demonstrate associations between COVID-19 public health restrictions, suicidal ideations, and declines in mental health and increases in alcohol consumption among young adult university students.

Physical Activity Behavior and Mental Health Among University Students During COVID-19 Lockdown

Background: The coronavirus disease 2019 (COVID-19) pandemic placed social, travel, school access, and learning restrictions on University students. Excessive restriction measures have been shown to have negative impacts on mental health. Physical activity preserves mental health, and may be useful during quarantines. Purpose: Explore physical activity and sedentary behavior and associations with depression and anxiety symptoms among University students during COVID-19 restrictions in the Fall 2020 semester. Methods: Six hundred and ninety-seven undergraduates (18-25 years) from a U.S. public University completed a cross-sectional survey in fall 2020. The survey included demographic questions, the Generalized Anxiety Disorder Scale 7 (GAD-7), the Patient Health Questionnaire 9 (PHQ-9), and questions about meeting moderate to vigorous physical activity (MVPA) recommendations and sedentary behavior. Results: Forty-nine percent did not meet MVPA guidelines. Patient Health Questionnaire 9 (p = 0.002) and GAD-7 (p = 0.024) scores were higher among those who did not achieve MVPA. Sitting time (h/day) was a significant associated with depression (B = 0.29 (0.06), p < 0.05, 95% CI = 0.18, 0.41) and anxiety (B = 0.24 (0.05), p < 0.05, 95% CI = 0.13, 0.34) severity. Conclusion: Physical activity was associated with mental health among University students during COVID-19 lockdowns.

Exercise as a Useful Intervention to Reduce Alcohol Consumption and Improve Physical Fitness in Individuals With Alcohol Use Disorder: A Systematic Review and Meta-Analysis

Objective: This meta-analysis and systematic review examined the effects of exercise interventions on alcohol consumption and binge drinking in individuals with alcohol use disorder (AUD). Data sources: PubMed, Web of Science, Google Scholar, SPORTDiscus, and ERIC databases. Study Inclusion and Exclusion Criteria: Peer-reviewed randomized controlled trials published in English between 1970 and 2021. All studies compared exercise (Ex) and treatment as usual (TAU) to TAU in adults with an alcohol-related diagnosis. All forms of exercise interventions were included (e.g., aerobic exercise, yoga, resistance exercise, etc.). Data Extraction: Preferred Reporting Items for Systematic Reviews and Meta-Analyses Protocols standard and the Meta-Analyses and Systematic Reviews of Observational Studies guidelines were followed. Risk of bias was assessed using the Cochrane risk-of-bias tool as described by the Cochrane Handbook for Systematic Reviews and Interventions. Results: The literature searches retrieved a combined 2527 studies, with 1,034 studies screened after removal of duplicates and 973 (94%) rejected after reviewing titles and abstracts. Full-text review was performed on 61 studies, with seven studies meeting inclusion criteria for qualitative and meta-analysis. Across seven studies (n = 492 participants), a significant effect (Z-value = -3.37; g = -0.30; 95% CI [-0.50--0.09]; p = 0.001) was found for Ex+TAU on drinking volume. There was no effect of Ex+TAU on binge drinking. The effect of Ex+TAU on physical fitness (VO2max, ml•kg-1•min-1) was significant (Z-score = 3.70; g = 0.64; 95% CI [0.19-1.08]; p < 0.001). Conclusions: Exercise interventions may decrease alcohol consumption and improve fitness and can be an effective adjunctive treatment for individuals with alcohol-related diagnoses including AUD.

Autophagy in peripheral blood mononuclear cells is associated with body fat percentage

CONTEXT

Numerous chronic conditions including obesity exhibit autophagic dysfunction. Association of immune cell autophagic marker regulation by body fat percentage (%BF) is unknown.

OBJECTIVE

Investigate autophagy activity in peripheral blood mononuclear cells (PBMCs) of adults with distinct %BFs and obesity-related circulating inflammatory markers.

MATERIALS AND METHODS

Sixteen individuals (eight males) with %BF above (n = 8, 36.9 ± 3.6 years, 27.1 ± 8.1%BF) and below (n = 8, 37.1 ± 3.7 years, 13.3 ± 3.7%BF) their age- and sex-specific 50th percentile value based on the American College Sports Medicine guidelines participated. Body fat percentage was calculated from hydrostatic weighing. PBMCs were isolated from venous blood, and PBMC autophagic flux markers (LC3-I, LC3-II, and p62) were measured via Western blot. CRP, resistin, leptin, and adiponectin were measured via ELISA.

RESULTS

LC3-II/LC3-I ratio correlated with %BF (r=-0.56, p=.023). Insulin (p=.05) and CRP (p=.018) were higher in high %BF participants.

DISCUSSION AND CONCLUSIONS

Autophagic activity markers in PBMCs correlate with %BF, but are not different between %BF groups.

Change in Exercise Performance and Markers of Acute Kidney Injury Following Heat Acclimation with Permissive Dehydration

Implementing permissive dehydration (DEH) during short-term heat acclimation (HA) may accelerate adaptations to the heat. However, HA with DEH may augment risk for acute kidney injury (AKI). This study investigated the effect of HA with permissive DEH on time-trial performance and markers of AKI. Fourteen moderately trained men (age and VO_2max = 25 ± 0.5 yr and 51.6 ± 1.8 mL·kg⁻¹·min⁻¹) were randomly assigned to DEH or euhydration (EUH). Time-trial performance and VO_2max were assessed in a temperate environment before and after 7 d of HA. Heat acclimation consisted of 90 min of cycling in an environmental chamber (40 °C, 35% RH). Neutrophil gelatinase-associated lipocalin (NGAL) and kidney injury molecule-1 (KIM-1) were assessed pre- and post-exercise on day 1 and day 7 of HA. Following HA, VO_2max did not change in either group (p = 0.099); however, time-trial performance significantly improved (3%, p < 0.01) with no difference between groups (p = 0.485). Compared to pre-exercise, NGAL was not significantly different following day 1 and 7 of HA (p = 0.113) with no difference between groups (p = 0.667). There was a significant increase in KIM-1 following day 1 and 7 of HA (p = 0.002) with no difference between groups (p = 0.307). Heat acclimation paired with permissive DEH does not amplify improvements in VO_2max or time-trial performance in a temperate environment versus EUH and does not increase markers of AKI.

Insulin resistance is improved in high-fat fed mice by photobiomodulation therapy at 630 nm

Photobiomodulation therapy (PBMT) in the infrared spectrum exerts positive effects on glucose metabolism, but the use of PBMT at the red spectrum has not been assessed. Male Swiss albino mice were divided into low-fat control and high-fat diet (HFD) for 12 weeks and were treated with red (630 nm) PBMT or no treatment (Sham) during weeks 9 to 12. PBMT was delivered at 31.19 J/cm² , 60 J total dose per day for 20 days. In HFD-fed mice, PBMT improved glucose tolerance, insulin resistance and fasting hyperinsulinemia. PBMT also reduced adiposity and inflammatory infiltrate in adipose tissue. Phosphorylation of Akt in epididymal adipose tissue and rectus femoralis muscle was improved by PBMT. In epididymal fat PBMT reversed the reduced phosphorylation of AS160 and the reduced Glut4 content. In addition, PBMT reversed the alterations caused by HFD in rectus femoralis muscle on proteins involved in mitochondrial dynamics and β-oxidation. In conclusion, PBMT at red spectrum improved insulin resistance and glucose metabolism in HFD-fed mice.

Metabolic effects of two high-intensity circuit training protocols: Does sequence matter?

Background/objective

The integration of high-intensity interval training (HIIT) and circuit weight training (CWT) is seamless and practical for meeting recommended exercise guidelines. The purpose of this study was to determine the ideal combination of HIIT and CWT to elicit desired acute cardiorespiratory and metabolic responses in variables such as energy expenditure (EE), oxygen consumption (VO₂), heart rate (HR), blood lactate (BLa^-), excess post-exercise oxygen consumption (EPOC), rating of perceived exertion (RPE), and enjoyment.

Methods

Fourteen trained males (25.7 ± 4.4 yr) completed two exercise protocols matched for volume and recovery periods. On one day, participants performed six HIIT bouts prior to three rounds of a nine exercise CWT protocol (HIC). The second day (separated by ≥ 72 h) consisted of three rounds of three mini-circuits (three exercises per circuit) integrated with three HIIT bouts between the first and second and second and third mini-circuits (TRI). VO₂, HR, and EE were monitored throughout both protocols. EPOC for a 20-min duration, [BLa^-] (five time points), RPE, and enjoyment were measured post-exercise.

Results

Energy expenditure was significantly higher during the HIC compared to the TRI protocol (p = .012), as well as EPOC (p = .034). [BLa^-] was significantly greater immediate-, 5min-, 10min- and 20min-post-exercise following HIC as compared to TRI. Mean values for HIC and TRI were similar (p > .05) for HR and RPE.

Conclusion

Performing HIIT prior to CWT elicits a higher metabolic perturbation compared to the TRI protocol. Although a significant EE difference was detected between the two trials, the practical difference (∼20 kcal) between protocols indicates both protocols are similarly effective for caloric expenditure, metabolic and cardiorespiratory response.

Telemedicine-Based Health Coaching Is Effective for Inducing Weight Loss and Improving Metabolic Markers

BACKGROUND

To assess the efficacy of health coaching (HC) delivered through videoconferencing (VC) to favorably change physical activity (PA), weight, and metabolic markers in adults with high body mass index (BMI).

MATERIALS AND METHODS

Thirty adults (BMI ≥30 kg/m2) were randomly assigned to one of three groups: VC, in-person (IP), or control group (CG). Participants received wireless watches and weight scales to sync with their personal smartphones; recorded data were wirelessly uploaded to a secure database. Participants assigned to VC and IP received individualized HC by a multidisciplinary team (registered dietitian, exercise physiologist, and medical doctor) based on data uploaded over the 12-week intervention. Steps/day and weight loss were analyzed through analyses of covariance.

RESULTS

Within- and between-group changes in weight (kg), glucose, insulin, hemoglobin A1c (HbA1c), and Homeostasis Model Assessment estimate of insulin resistance (HOMA-IR) were analyzed through analyses of variance. Weight loss was greater (p < 0.05) for VC (8.23 ± 4.5 kg; 7.7%) than IP (3.2 ± 2.6 kg; 3.4%) and CG (2.9 ± 3.9 kg; 3.3%), respectively. Steps/day were significantly higher in VC than IP at week 4 and VC was significantly higher than the CG at weeks 6, 8, 9, and 11 (p ≤ 0.05). No within- or between-group differences were found for glucose, insulin, or HbA1C. HOMA-IR decreased for VC only (p ≤ 0.05).

CONCLUSIONS

Our innovative, multidisciplinary, telemedicine HC delivered through VC led to more favorable changes in weight loss, PA (steps/day), and HOMA-IR than IP or no HC. VC may be an economical approach to improve health and promote behavior change in obese adults.

CLINICAL TRIAL REGISTRATION NUMBER

ClinicalTrials.gov identifier NCT03278951.

Association Between Exercise-Induced Hyperthermia and Intestinal Permeability: A Systematic Review

BACKGROUND

Prolonged and strenuous physical exercise increases intestinal permeability, allowing luminal endotoxins to translocate through the intestinal barrier and reach the bloodstream. When recognized by the immune system, these endotoxins trigger a systemic inflammatory response that may affect physical performance and, in severe cases, induce heat stroke. However, it remains to be elucidated whether there is a relationship between the magnitude of exercise-induced hyperthermia and changes in intestinal permeability.

OBJECTIVE

In this systematic review, we evaluated whether an exercise-induced increase in core body temperature (T _Core) is associated with an exercise-induced increase in intestinal permeability.

METHODS

The present systematic review screened the MEDLINE/PubMed and Web of Science databases in September 2016, without any date restrictions. Sixteen studies that were performed in healthy participants, presented original data, and measured both the exercise-induced changes in T _Core and intestinal permeability were selected. These studies assessed intestinal permeability through the measurement of sugar levels in the urine and measurement of intestinal fatty acid binding protein or lipopolysaccharide levels in the blood.

RESULTS

Exercise increased both T _Core and intestinal permeability in most of the 16 studies. In addition, a positive and strong correlation was observed between the two parameters (r = 0.793; p < 0.001), and a T _Core exceeding 39 °C was always associated with augmented permeability.

CONCLUSION

The magnitude of exercise-induced hyperthermia is directly associated with the increase in intestinal permeability.

Hemodynamic and metabolic responses to self-paced and ramp-graded exercise testing protocols

Recent examinations have shown lower maximal oxygen consumption during traditional ramp (RAMP) compared with self-paced (SPV) graded exercise testing (GXT) attributed to differences in cardiac output. The current study examined the differences in hemodynamic and metabolic responses between RAMP and SPV during treadmill exercise. Sixteen recreationally trained men (aged23.7 ± 3.0 years) completed 2 separate treadmill GXT protocols. SPV consisted of five 2-min stages (10 min total) of increasing speed clamped by the Borg RPE6-20 scale. RAMP increased speed by 0.16 km/h every 15 s until volitional exhaustion. All testing was performed at 3% incline. Oxygen consumption was measured via indirect calorimetry; hemodynamic function was measured via thoracic impedance and blood lactate (BLa^-) was measured via portable lactate analyzer. Differences between SPV and RAMP protocols were analyzed as group means by using paired-samples t tests (R Core Team 2017). Maximal values for SPV and RAMP were similar (p > 0.05) for oxygen uptake (47.1 ± 3.4 vs. 47.4 ± 3.4 mL·kg^-1·min^-1), heart rate (198 ± 5 vs. 200 ± 6 beats·min^-1), ventilation (158.8 ± 20.7 vs. 159.3 ± 19.0 L·min^-1), cardiac output (26.9 ± 5.5 vs. 27.9 ± 4.2 L·min^-1), stroke volume (SV) (145.9 ± 29.2 vs. 149.8 ± 25.3 mL·beat^-1), arteriovenous oxygen difference (18.5 ± 3.1 vs. 19.7 ± 3.1 mL·dL^-1), ventilatory threshold (VT) (78.2 ± 7.2 vs. 79.0% ± 7.6%), and peak BLa^- (11.7 ± 2.3 vs. 11.5 ± 2.4 mmol·L^-1), respectively. In conclusion, SPV elicits similar maximal hemodynamic responses in comparison to RAMP; however, SV kinetics exhibited unique characteristics based on protocol. These results support SPV as a feasible GXT protocol to identify useful fitness parameters (maximal oxygen uptake, oxygen uptake kinetics, and VT).

Distinct beneficial effects of continuous vs accumulated exercise training on cardiovascular risk factors in Wistar rats

We compared the effects of continuous exercise (CE) vs accumulated exercise (AE) training on CVD risk factors and heart of young male Wistar rats. The exercise training (ET) was performed in a swimming pool for 30-60 min/day, 5 days/week over 15 weeks. CE group performed the ET in a single long daily session (30-60 min), while AE group performed the ET at the same frequency, intensity, and duration of CE rats, but in three short bouts over the course of a day (10-20 min in three daily sessions). AE training was more efficient than CE in attenuating body and fat weight gain and inhibiting visceral adipocyte hypertrophy at the same food intake level. CE training was more efficient in improving systolic blood pressure, LDL/HDL cholesterol, and serum triglyceride. Both ET protocols increased heart function, decreased lipid peroxidation, and increased intracellular Hsp72 content in the heart. This work shows distinct beneficial effects of CE vs AE training suggesting that the prescription of one or other may be preferred to prevent the increase of a specific CVD risk factor.

The temperature of water ingested ad libitum does not influence performance during a 40-km self-paced cycling trial in the heat

AIM

The aim of the present study was to evaluate the effects of the temperature of ingested water on performance during a 40-km self-paced cycling trial in the heat (35º C and 60% relative humidity).

METHODS

The study was randomized, counterbalanced, crossover and single-blinded. Ten well-trained male cycling athletes (cyclists, mountain bikers or triathletes) who were non-acclimatized to heat were subjected to four experimental situations divided into two sets. In the first set, the participants performed two trials, during which they were given either cold (10º C) or warm water (37º C) ad libitum. In these situations, the volume and timing of the water ingestion (when each bolus was ingested) were recorded and replicated in the second set, but the water temperature was reversed.

RESULTS

The performance times were unaffected by the water intake volume (P=0.425), but the water at a temperature of 37º C tended to induce lower performance times (P=0.078) during the trials (AL10=93.0±3.5 min; AL37=94.4±4.1 min; SC10=93.4±4.0; SC37=97.4±4.3 min). The water intake was greater when the water was cold (P<0.05), but the temperature did not affect the heat storage rate, rectal temperature, mean skin temperature, heart rate, blood glucose level, sweat loss, sweat rate, perceived exertion rate or plasma volume changes. However, a significant reduction in the plasma volume change from pre- to postexercise was observed (P<0.01).

CONCLUSION

The performance, thermoregulatory, cardiovascular and metabolic responses during a 40-km self-paced cycling trial in the heat were unaffected by different water temperatures.

Influence of aerobic training on cardiovascular and metabolic parameters in ederly hypertensive women

BACKGROUND

Treatment of hypertension includes pharmacological and nonpharmacological interventions. Among the nonpharmacological interventions emphasizes the practice of regular physical exercise. However, the effects of aerobic exercise training on cardiovascular and metabolic parameters in elderly hypertensive women are still controversial.

OBJECTIVES

The purpose of this study was to assess the effects of a walking program on metabolic and cardiovascular parameters at rest and during the recovery period following maximal exercise by hypertensive elderly women.

METHODS

Twelve elderly women with hypertension started a 2-week walking program. Rest blood cholesterol and anthropometric data, as well as blood pressure and heart rate at rest and after progressive maximal exercise were measured before and after training.

RESULTS

There were significant differences between the pre- and posttraining periods in VO(2)max, systolic blood pressure, diastolic blood pressure, and mean blood pressure. There were no changes in serum cholesterol levels after the training. During the recovery period following the progressive test, the fall in heart rate and mean blood pressure after 10 minutes of recovery was significantly higher after training.

CONCLUSION

The proposed walking program did not alter serum cholesterol, but it did reduce resting blood pressure, improve aerobic performance and accelerate the fall in heart rate and mean blood pressure during the postprogressive maximal aerobic exercise recovery period in elderly hypertensive women.

Run performance of middle-aged and young adult runners in the heat

The aging process may impair exercise tolerance in the heat. It is not clear whether this impairment is partly due to a reduction in aerobic capacity. To compare the exercise performance and thermoregulatory responses of middle-aged and young adults with similar aerobic capacities and training statuses, 7 middle-aged (54±2 years; 58±4 ml·kg - 1·min - 1) and 7 young (28±1 years; 61±5 ml·kg - 1·min - 1) male competitive endurance runners underwent 2 10-km self-paced and 2 fixed-workload (90% of race speed) runs until fatigue on a treadmill in hot (40°C) and moderate (20°C) environments on separate days. The runners' total time, average speed, rectal temperature, heat storage rate, physiological strain index, sweat rate, sweat sensitivity, number of heat-activated sweat glands and sweat rate per sweat gland were measured or calculated. Body fat, body surface area, body surface area per body mass, training volume and VO2max were similar between the 2 groups. No differences were observed in total time (59±3; 49±3; 27±2; 54±5 min in the middle-aged and 60±2; 49±3; 27±2; 51±4 min in the young group), average speed, rectal temperature, heat storage rate, physiological strain index, sweat rate (17±7; 15±3; 23±7; 13±2 g.m - 2.min - 1 in the middle-aged and 20±5; 14±4; 22±5; 15±4 g.m - 2.min - 1 in the young group) or sweat sensitivity between age groups (p>0.05) in any trial. The number of heat-activated sweat glands (88±14; 80±18; 90±16; 66±14 cm - 2 in the middle-aged and 43±10; 32±10; 37±11; 31±11 cm - 2 in the young group) was higher, and the sweat rate per sweat gland was smaller, in the middle-aged than the young group (p<0.05) in all of the trials. We conclude that running performance and body thermoregulation are similar between young and middle-aged runners with similar aerobic capacities and training statuses under hot and moderate conditions in self-paced and fixed-intensity runs. The decrease observed in the sweat rate per sweat gland in middle-aged men was compensated for by a higher number of heat-activated sweat glands.

Palm cooling does not reduce heat strain during exercise in a hot, dry environment

To compare the effectiveness of the rapid thermal exchange device (RTX) in slowing the development of hyperthermia and associated symptoms among hand immersed in water bath (WB), water-perfused vest (WPV), and no cooling condition (NC). Ten subjects performed 4 heat stress trials. The protocol consisted of 2 bouts of treadmill walking, separated by a cooling-rehydration period. The times to reach the predetermined rectal temperature in the first (38.5 degrees C) and second bouts (39 degrees C) were not different among RTX, NC, and WB, but was longer for the WPV in both bouts (p<0.05). Heat storage was significantly lower for WPV only in the first bout vs. the other conditions (p<0.05). Heart rate (HR) was not different at 10, 20, and 30 min during the first bout among RTX, NC, and WB, but was lower for WPV (p<0.05). HR was not different among conditions during the second bout. The RTX was not effective in slowing the development of hyperthermia.

Palm cooling to reduce heat strain in subjects during simulated armoured vehicle transport

This study examined whether palm cooling (PC) could reduce heat strain, measured through changes in core, mean skin, mean body temperatures, and thermal sensation in resting hyperthermic subjects wearing chemical protective garments. Ten male subjects performed three exercise bouts (6.1 km h(-1), 2-4% grade) in a hot, dry environment [mean (SD) air temperature 42.2 (0.5 degrees C), relative humidity 36.5 (1%)] until core temperature reached 38.8 degrees C. Subjects then simulated transport in an armoured vehicle by resting in a seated position for 50 min with either no cooling (NC), (PC at 10 degrees C) or palm cooling with vacuum application around the hand (PCVAC, 10 degrees C, 7.47 kPa negative pressure). Core, skin, and mean body temperatures with PC and PCVAC were lower (P < 0.05) than NC from 15 to 50 min of cooling, and thermal sensation was lower (P < 0.05) from 30 to 50 min, with no differences in any variables between PC and PCVAC. Maximal heat extraction averaged 42 (12 W), and core temperature was reduced by 0.38 (0.21 degrees C) after 50 min of PC. Heat extraction with PC was modest compared to other cooling approaches in the literature.

Effect of heat acclimation on heat shock protein 72 and interleukin-10 in humans

Heat acclimation (HA) results in whole body adaptations that increase heat tolerance, and in addition, HA may also result in protective cellular adaptations. We hypothesized that, after HA, basal intracellular heat shock protein (HSP) 72 and extracellular IL-10 levels would increase, while extracellular HSP72 levels decrease. Ten male and two female subjects completed a 10-day exercise/HA protocol (100-min exercise bout at 56% of maximum O2uptake in a 42.5°C DB, 27.9% RH environment); subjects exhibited classic adaptations that accompany HA. Peripheral blood mononuclear cells (PBMCs) were isolated before and after each acclimation session on days 1, 6, and 10; plasma and serum were collected before and after exercise on the 1st and 10th day of HA. SDS-PAGE was used to determine PBMC HSP72 levels during HA, and ELISA was used to measure plasma IL-10 and serum HSP72 concentrations. The increase in PBMC HSP72 from pre- to postexercise on the 1st day of HA was not significant (mean ± SD, 1.0 ± 0 vs. 1.6 ± 0.6 density units). Preexercise HSP72 levels on day 1 were significantly lower compared with the pre- and postexercise samples on days 6 and 10 (mean ± SD, day 6: 2.1 ± 1.0 and 2.2 ± 1.0, day 10: 2.0 ± 1.3 and 2.2 ± 1.0 density units, respectively, P < 0.05). There were no differences in plasma IL-10 and serum HSP72 postexercise or after 10 days of HA. The sustained elevation of HSP72 from days 6 to 10 may be evidence of a cellular adaptation to HA that contributes to improved heat tolerance and reduced heat illness risk.