Physiologia, Volume 3, Issue 4 (December 2023) – 12 articles

The objective of the present review was to evaluate the time-course of recovery of biochemical marker levels and physical performance after strenuous military training, and identify which biomarkers are affected. A systematic literature search was conducted using the databases MedLine (Ovid) and Web of Science (WoS) to identify studies until January 2023. Varying relevant search terms were used, related to military training, Special Forces, physical performance, and biomarkers. Records were based on strict inclusion and exclusion criteria. Twelve studies met the inclusion criteria and were selected for this review. A variety of physiological and psychological markers were measured, and military training lasted from 4 to 62 days, with recovery periods varying from 24 h to 6 weeks. Among these studies, full recovery was observed in two studies, while seven studies showed almost full (79–90%) recovery, and in three studies, 44–63% of markers recovered after the measured recovery period. However, in some studies, additional markers could be defined as recovered, depending on the criterion for recovery. In the majority of the studies, most of the measured variables recovered during the follow-up, but often, some variables remained unrecovered, and at times, only modest recovery was seen. It is important to point out that recovery duration depends on the duration and intensity of the military training stressor. Overall, resolution varies between the markers, and sometimes, recovery might not occur, even after prolonged recovery. Therefore, it is important to measure the recovery status of soldiers with both biomarkers and physical performance markers, especially after strenuous training, to maximize operational capability during prolonged missions. Full article

Firefighters are exposed to dangerous and often traumatic events due to the nature of their occupational demands. This repeated exposure to trauma combined with stressful work demands increases their risk for negative physiological and psychological health outcomes. The high prevalence of adverse health outcomes highlights the need for interventions to improve resiliency in firefighters. Resiliency is the ability to reduce the effect of crisis, rebound from adversity, and recover to pre-stimulus homeostasis. When traumatic exposures are unavoidable, as is the case with firefighters, it is important to buffer the resulting consequences on health. While resilience has a genetic component, interventions targeting physiological, psychological, and social components have been successful at improving resilience. These factors are of specific interest as increases in resilience have been linked to improved PTSD symptomology/severity, depression, anxiety, autonomic nervous system activation, hypothalamus–pituitary axis balance, and brain-derived neurotrophic factor. Therefore, the purpose of this review is to identify physiological and psychological components associated with resiliency and discuss strategies that may improve those components to ultimately increase resiliency in firefighters. The strategies discussed include exercise, social support, and mindfulness. Full article

The roles of 17β estradiol (E2) and progesterone (P4), the primary female sex hormones, are pivotal in regulating various aspects of metabolism. E2 influences food intake, energy expenditure, adipose tissue distribution, and insulin sensitivity across multiple tissues. Meanwhile, P4 impacts energy expenditure, electrolyte balance, amino acid oxidation, muscle protein synthesis, and glucose metabolism. The interactions between these hormones affect macronutrient utilization, both at rest and during exercise. Acknowledging the need to incorporate sex hormone perturbations in research, this paper explores the current landscape of study design and menstrual cycle tracking for female-specific sport research. It emphasizes the importance of standardization in terminology, hormone phases, reference values, and affordable hormone detection methods to advance our understanding of how the menstrual cycle influences female athletes. Full article

Background: There are no published data on the training-load magnitude or distribution in elite international-level boxers preparing for a major competition nor on the training load’s relationship with objective and subjective training markers. Methods: Twelve elite boxers (eight males and four females) preparing for the 2018 Commonwealth Games were monitored during training for 12 weeks. The training load (TL), change in creatine kinase (ΔCK), and wellness variables were measured daily but were amalgamated into average weekly values over the 12-week period for weekly comparisons. The relationships between the TL, ΔCK, and wellness variables were also assessed. Results: The significant (p < 0.001) main effects of the week with large and moderate effect sizes were noted for the TL and ΔCK, respectively, with weeks 9 and 12 in the competition-specific and taper phases showing the greatest differences, respectively. For wellness, only the muscle condition showed a significant change over time (p < 0.001). There were significant (p < 0.05) small–moderate correlations between the TL, ΔCK, and wellness variables. Conclusions: This is the first study to describe the weekly training loads and responses to training of elite international boxers across a 12-week pre-competition training period in preparation for a major competition. The findings within this study report that elite international boxers have high chronic training loads that change between training blocks to put emphasis on different qualities. Monitoring the indirect muscle damage through CK may provide further information on the internal training responses in boxers. Full article

Chemotherapy-induced peripheral neuropathy (CIPN) is a dose-limiting side-effect resulting from numerous neurotoxic chemotherapies that damages the peripheral nerves, alters sensations in the hands and feet, causes burning and shooting pains, and impairs a patient’s quality of life (QoL). There are limited established interventions to help improve CIPN symptoms. There is only one pharmacological agent (Duloxetine) for treatment of CIPN; however, it only has mild benefit, signaling a critical need for alternative management options to manage patient symptoms. Multiple studies suggest therapeutic benefits of exercise in cancer care to improve physical and psychological functioning; however, the benefits regarding CIPN symptoms and physical function are less clear. This narrative review synthesizes research articles investigating the effect and mechanisms induced by different exercise programs for patients with taxane-induced peripheral neuropathy (TIPN) symptoms and function. The overall incidence, manifestations, characteristics, and mechanisms of CIPN are also discussed. While some studies in this narrative review demonstrated that exercise programs may have benefits on sensory and motor TIPN symptoms in some but not all patients, there are consistent benefits of improved QoL and physical function across most patients. This narrative review highlights the need for future research to confirm the effects of exercise for TIPN, with a focus on other important components, including the effect of exercise adherence, type, and supervision level. Full article

Breath-hold diving has been traditionally practiced for professional and recreational reasons and has recently emerged as a competitive sport. The physiological response during breath-holding, also known as diving response, consists mainly of bradycardia and peripheral vasoconstriction. Elite apneists can suppress the urge to breathe, sustain greater arterial desaturation and develop pronounced bradycardia, thus accomplishing impressively long breath-hold times. This study explored physiological responses during static apnea and their association with apnea duration in breath-hold divers with high physiological adaptations acquired from long-term apnea training. Nine well-trained competitive divers held their breath for as long as possible while floating motionlessly in a swimming pool (26–27 °C), simulating an actual “static apnea competition”. Long apnea durations (302 ± 60 s) as well as severe oxygen desaturation (minSaO₂ 46 ± 11%) and bradycardia (minHR 49 ± 8 bpm) were achieved. Apnea duration was positively correlated with forced vital capacity (r = 0.771) and apnea duration until initiation of desaturation (r = 0.736) and negatively correlated with minSaO₂ (r = −0.672) (p < 0.05). Moreover, minHR during apnea was correlated with pre-apneic hemoglobin concentration (r = 0.685) (p < 0.05). The prolonged apnea durations achieved by the well-trained divers in this study, while performing maximum immersed static apnea under competitive simulated conditions, were related to their high lung volumes and their delayed and profound O₂ desaturation, whereas their bradycardic response was not a decisive factor. Full article

Background: The purpose of this study is to ascertain the reliability of two 15-s sprint cycling tests in men and women to estimate the maximum lactate accumulation rate (VLamax). Methods: Eighteen men and twelve women completed two sprint sessions over 1 week. A 10 min warm-up preceded the obtaining of a 3 µL blood lactate (BLC) sample, after which a 15 s sprint was completed; cyclists then rested passively while multiple lactate samples were taken until the levels peaked. Trial differences and reliability across trials were analyzed using a paired-sample t-test, Pearson’s correlation, Intraclass correlation (ICC), and Bland–Altman analysis with α = 0.05 for all tests; data are reported as mean ± sd. Results: Power (W) was similar across trials (773.0 ± 143.5 vs. 758.2 ± 127.4; p = 0.333) and the coefficient of variation (CV) of 4.7%. VLamax (mM·L⁻¹·s⁻¹) was similar (0.673 ± 0.024 vs. 0.635 ± 0.237; p = 0.280), but only moderately reliable across trials with CV, ICC, and R values of 18.6%, 0.661, and 0.67, respectively. Pre-BLC and peak BLC CV were 45.6 and 23.3%, respectively. Conclusions: A 15 s VLamax cycling sprint is moderately reliable, possibly affected both by the lactate measurement and other variables used in the calculation. More research may offer ways to improve reliability. Full article

Soybeans are vulnerable to drought and temperature increases potentially induced by climate change. Hydraulic dysfunction and stomatal closure to avoid excessive transpiration are the main problems caused by drought. The vulnerability of soybeans to drought will depend on the intensity and duration of water stress. The purpose of this study was to determine if the use of cover crops (CCs) can influence the gas exchange potential of glyphosate-tolerant soybeans when the vapor pressure deficit (Vpd) increases. This two-year study was conducted in an open experimental field comprising direct seeding plots with or without CCs. Stomatal conductance (Gs) was measured five times on the same identified leaves following glyphosate-based herbicide application. These leaves were then collected in order to observe the stomata and foliar traits with a scanning electron microscope. The Vpd was calculated concomitantly to Gs measurements at the leaf surface. The results suggest that the use of CCs promotes phenotypic change in soybean leaves (more elaborate venation and a higher abaxial stomatal density), which in turn may enhance their tolerance to drier conditions. In 2019, Gs could be up to 29% higher in plots with CCs compared to those without CCs with similar Vpd values. This study shows that the benefits of using CCs can be observed via the morphological development strategies of the crop plants and their higher tolerance to drought. Full article

This study examined the effects of two different acute bouts of treadmill running (e.g., steady-state moderate-intensity exercise (SSE) and high-intensity interval exercise (HIIE)) on adipokine (e.g., adiponectin, leptin, and omentin) concentrations in individuals with moderate stages of chronic kidney disease (CKD). Fourteen participants (8 females and 6 males) (age 58.7 ± 9.7, height (cm) 168.5 ± 9.7, weight (kg) 83.5 ± 18.2) were classified as having moderate stages of CKD (stages G3a and G3b; estimated glomerular filtration rate (eGFR) between 59 and 30 mL/min/1.73 m²). Participants completed 30 min of either SSE at 65% oxygen consumption reserve (VO₂R) or HIIE for 3 min at a 90% VO₂R separated by 2 min of slow walking (20% VO₂R) in a randomized, crossover design on a treadmill. Venous blood samples were obtained at baseline, 1 h, and 24 h post exercise. Data were analyzed using a two by three repeated measures ANOVA (p < 0.05). There were no significant differences in adiponectin (p < 0.353), leptin (p < 0.084), and omentin (p < 0.235) concentrations between SSE and HIIE. Similarly, no significant differences were seen between the sampled time points for either aerobic exercise condition. In conclusion, this study demonstrated there were no changes in adiponectin, leptin, or omentin concentrations when performing an acute bout of HIIE or SSE for 30 min, at 1 or 24 h post exercise. Future studies should seek to either increase the duration of the exercise bout or identify different adipokines to examine for patients experiencing moderate stages of CKD. Full article

The physiological mechanisms for releasing and resolving gravitational ischemia in the brain, and their susceptibility to malfunction, may play an important role in a variety of neurological illnesses. An astronaut on a space walk in a micro-gravity environment may be susceptible to neuro-ocular symptoms associated with unopposed gravity-resistance mechanisms for partially preventing gravitational ischemia in the brain, and for attenuating its impact—mechanisms which may be required for normal brain physiology on Earth. Astronauts on the International Space Station typically breathe a mixture of gasses similar in composition to what they breathed on Earth, following the 1967 death of three astronauts, including Ed White, by fire on the Apollo 1 spacecraft, which was carrying 100% oxygen. For the last decade, astronauts have been studied extensively by flight physicians regarding the commonly experienced symptoms of VIIP, or ‘visual impairment and intracranial pressure’ syndrome. In this paper, we compare VIIP syndrome to the neuro-ocular and Parkinson’s-like symptoms which occurred during and after the 1918–1919 influenza pandemic. The common denominator may be gravitational ischemia in the brain, and the mirror-imaging failed mechanisms for its release (in influenza) versus unopposed gravity-resistance mechanisms (in astronauts). Some research has suggested that astronauts may benefit from breathing oxygen concentrations somewhat higher than 20%, and under slightly elevated pressure. These may possibly prevent maladaptive mechanisms leading to Alzheimer’s- or Parkinson’s-like illness by compensating for impaired mechanisms for releasing and resolving gravitational ischemia in the brain. Full article

Insufficient physical activity (PA) is associated with low cardiorespiratory fitness, which favors cardiovascular and other noncommunicable diseases. Additionally, it evidentially affects mental health. Considering the WHO PA guidelines, CrossFit^® represents a versatile exercise program that combines aerobic and resistance training with mobility and could help reduce disease incidences among sedentary people. Yet, long-term CrossFit research is sparse. We conducted a nine-month intervention (≥2 CrossFit workouts/week) in 16 beginners (14 males, 35 ± 6.8 years, 180 ± 8.6 cm, 85. 5 ± 19.1 kg). As a primary endpoint, VO₂max was assessed at baseline, four, and nine months. A repeated-measures ANOVA and Pearson correlation were conducted. Well-being was investigated by the WHO-5 Index pre- and post-intervention. For exploratory purposes, body composition and heart rate recovery (HRR) were tracked. In a second step, all males were categorized into two groups based on body fat percentage and analyzed by repeated measures ANOVA again. The main outcome was an 11.5% VO₂max improvement with a large effect (p < 0.01, ${\eta }_p^2$ = 0.27). Strong negative correlations between baseline VO₂max and its progression after nine months (p = 0.006, r = −0.654) were found. Well-being increased by 8.7% (p = 0.024, d = 0.51). HRR improved both at 1 min (p < 0.05, ${\eta }_p^2$ = 0.34) and at 5 min (p < 0.05, ${\eta }_p^2$ = 0.27) post-exercise. Resting metabolic rate increased by 2.2% (p = 0.042). Analysis by group revealed improved HRR at 1 min (p < 0.05, ${\eta }_p^2$ = 0.62) only for the “high body fat” group. This study reveals the potential of CrossFit to enhance physiological and psychological health in beginners. For more robust results, larger sample sizes with a higher proportion of women are needed. Full article

Background: Although there is much literature demonstrating weight changes in professional mixed martial arts (MMA) athletes, there is minimal data comparing male and female MMA athletes. Therefore, the purpose of the current study was to compare weight changes between professional male and female MMA athletes leading up to competition. Methods: One hundred and three professional flyweight MMA athletes competing for the Ultimate Fighting Championship (UFC) were used for the study. Weight was obtained at multiple time points leading up to the competition. Two-way ANOVAs and post hoc t-tests were used, and significance was set at p ≤ 0.05. Results: ANOVA revealed there was a significant main effect of condition for weight changes (p < 0.001) and a significant main effect of sex on weight changes (p = 0.002) prior to competition. Post hoc analysis revealed that males lost more weight prior to the official weigh-in and gained more weight prior to competition when compared to females (p ≤ 0.05). Conclusion: MMA athletes lose weight prior to the official weigh-in and gain weight prior to competition. Moreover, male MMA athletes lose more weight prior to and gain more weight after when compared to female MMA athletes competing in the UFC’s flyweight division. Full article