Stress response to virtual reality based active shooter training: Impact of caffeine consumption

Participation in a virtual reality based active shooter training drill (VR-ASD) has been shown to increase biomarkers of stress; however, the impact of caffeine consumption on this response has not been studied. Caffeine ingestion has been shown to have favorable effects on physical and cognitive performance among athletic and tactical occupations alike. This study examined the impact of caffeine ingestion on subjective and physiological markers of stress in response to a mental stress task (MST) which involved participation in a VR-ASD and cognitive challenge consisting of mental arithmetic and a Stroop challenge. Fifty-three subjects were randomly assigned either caffeine (n = 26) or placebo (n = 27) prior to being exposed to the MST. Saliva samples, heart rate (HR), and state-anxiety inventory (SAI) scales, were collected before and after exposure to the MST. Saliva was analyzed for α-amylase (sAA), secretory IgA (SIgA), and cortisol (sCORT) concentrations. The MST resulted in significant increases in sAA, SIgA, HR, and SAI. Immediately post MST, sAA concentrations were significantly higher following the caffeine treatment compared to placebo. These data demonstrate that caffeine consumption results in significantly greater sAA concentrations post MST. This study was pre-registered as a clinical trial ("Impact of supplements on stress markers": NCT05592561).

Flaxseed oil as omega-3 polyunsaturated fatty acid source modulates cortisol concentrations and social dominance in male and female guinea pigs

Flaxseed oil is an excellent source of the essential omega-3 polyunsaturated fatty acid (PUFA) alpha-linolenic acid (ALA). Omega-3 PUFAs are important neuronal components and can counteract aggressive, depressive, and anxiety-like behavior, reduce glucocorticoid (e.g. cortisol) concentrations under chronic stress but also increase acute glucocorticoid responses. As glucocorticoids per se and glucocorticoid responsiveness can modulate the establishment of dominance hierarchies, we investigated if flaxseed oil high in ALA can promote social dominance through effects on glucocorticoid concentrations. Two male and two female groups of domestic guinea pigs (n = 9 per group) were maintained on a control or a 5% (w/w) flaxseed oil diet for four weeks. Social behaviors, hierarchy indices, locomotion, and saliva cortisol concentrations were determined during basal group housing conditions and stressful social confrontations with unfamiliar individuals of the other groups. Flaxseed groups had increased basal cortisol concentrations and showed no cortisol increase during social confrontations. Cortisol concentrations in control groups significantly increased during social confrontations. Such higher cortisol responses positively affected individual hierarchy indices in control males. However, flaxseed males became dominant irrespective of cortisol concentrations. In females, the opposite was detected, namely a higher dominant status in control compared to flaxseed females. Open-field- and dark-light-tests for anxiety-like behavior revealed no pronounced differences, but flaxseed males showed the highest locomotor activity. Flaxseed oil as an ALA source sex-specifically promoted social dominance irrespective of cortisol concentrations and responses. The underlying neuronal mechanisms remain to be determined, but a sex-specific energetic advantage may have accounted for this effect.

The perceived benefit of intraoperative stress modifiers for surgeons: an experimental simulation study in volunteers

Background

During surgery, surgeons often work under stressful conditions, which could affect patient safety. Reducing intraoperative stress for surgeons could benefit surgeons and subsequently patients. It is difficult to study stress and stress relief in real life situations due to the multitude of confounding factors. The aim of this study was to evaluate simulated intraoperative stressors on surgeons’ stress levels and the effect of an intervention (pause including a sugar-containing drink) during standardized experiments (simulated operations).

Methods

An experimental interventional study was conducted using a simulator. The healthy surgeon volunteers were randomized to intervention and control in a cross-over design. Primary endpoint was salivary cortisol difference between a pause including a sugar containing drink (intervention) and controls. Secondary endpoints were change in heart rate, change in self-perceived stress measured by the State Trait Anxiety Inventory (STAI), and experience of the intraoperative pause. Endpoints were calculated with a mixed effect analysis of covariance (ANCOVA) model.

Results

Seventeen surgeons performed 32 experiments. There was no statistically significant difference in salivary cortisol between simulations with and without a pause including a sugar-containing drink; percent reduction, 8% (0.92 (95%CI:0.72;1.18)), p-value = 0.469. The surgeons’ self-estimation of intervention was positive, but there was no statistically significant difference in heart rate or STAI.

Conclusions

The surgeons’ experience of a pause including a drink was positive but there were no differences in physiological outcomes of the intervention. Lessons learned from this study could contribute to optimizing design of future studies.

Trial registration

Clinicaltrials.gov NCT04626648, Registered November 6, 2020, retrospectively registered.

Associations of saliva cortisol and hair cortisol with generalized anxiety, social anxiety, and major depressive disorder: An epidemiological cohort study in adolescents and young adults

OBJECTIVES

Most of the observed associations of generalized anxiety disorder (GAD), social anxiety disorder (SAD) and major depressive disorder (MDD) with cortisol concentrations came from clinical and adult study samples, with inconsistent findings, partly due to method variance. We examined cross-sectional and longitudinal associations between GAD, SAD and MDD with saliva and hair cortisol as well as hair cortisol change in a population-based sample of adolescents and young adults, considering relevant co-factors.

DESIGN

Epidemiological cohort study in Dresden, Germany. Data of 1050 individuals (mean age: 17.2 years) assessed at baseline (11/2015-12/2016) and of 605 individuals assessed at 1-year follow-up (FU1) are used.

METHODS

Multivariable regression models were implemented to assess cross-sectional and longitudinal associations of DSM-5 defined 12-month diagnoses of GAD, SAD, and MDD, with short-term (saliva cortisol: cortisol awakening response (CAR) and area under the curve (AUC) as total cortisol) and long-term (hair cortisol) cortisol indices. Multivariable models were adjusted for age or "tanner" stage, waist circumference, tobacco and alcohol consumption, physical inactivity, and hair cortisol dependent confounder. Sex-specific analyses were additionally conducted.

RESULTS

Cross-sectional analyses revealed positive associations between SAD and baseline saliva cortisol in multivariable models (CAR: β-coefficient: 0.12; 95% CI: 0.01; 0.23) but could not be confirmed after adjusting for "tanner" stage or comorbid depression. Cross-sectional analyses concerning GAD and MDD in the full baseline sample yielded no significant associations. Sex-specific linear models revealed a significant inverse cross-sectional association between MDD (β-coefficient: - 2.21; 95% CI: - 3.64; - 0.79) as well as SAD (β-coefficient: - 2.21; 95% CI: - 4.03; - 0.38) with baseline hair cortisol in males, but not in females. In longitudinal analyses, no significant associations were found in the fully adjusted model, except for a positive association between hair cortisol change between baseline and FU1 and FU1-SAD (OR: 1.07; 95% CI: 1.02; 1.12).

CONCLUSIONS

Results confirmed sex-specificity and the role of pubertal development in the association between cortisol with SAD and MDD, while no association emerged regarding cortisol and GAD. Future research in adolescents focusing on the role of cortisol in the pathogenesis of anxiety and depressive disorders would benefit from considering factors like sex-specificity and puberty development as well as comorbidity.

Insufficient glucocorticoid receptor signaling and flattened salivary cortisol profile are associated with metabolic and inflammatory indices in type 2 diabetes

PURPOSE

Impaired negative feedback and hyperactivation of the hypothalamic-pituitary-adrenal (HPA) axis characterizes type 2 diabetes mellitus (T2DM). The glucocorticoid receptor (GR) is a key mediator of HPA axis negative feedback; however, its role in linking hypercortisolemia and T2DM-associated hyperglycemia, hyperlipidemia and inflammation is not yet known.

METHODS

In peripheral mononuclear cells (PBMC) from 31 T2DM patients and 24 healthy controls, we measured various GR-signaling parameters such as phosphorylated GR (pGR-S211), GRα/GRβ gene expression and GC-sensitivity [using the basal and dexamethasone (DEX)-induced leucine zipper (GILZ) and FK506 binding-protein (FKBP5) mRNA levels as well as the basal interleukin (IL)-1β protein levels]. Diurnal salivary cortisol curve parameters such as the cortisol awaking response (CAR) and area under the curve (AUC_total and AUCi) as well as inflammatory and metabolic indices were also determined.

RESULTS

T2DM patients exhibited diminished pGR-S211 protein content, increased GRβ, decreased basal GILZ and FKBP5 mRNA levels and increased IL-1β levels. Flattened DEX-induced GILZ and FKBP5 response curves and a flattened salivary cortisol profile characterized T2DM patients. Significant associations of GR measures and saliva cortisol curve parameters with biochemical and clinical characteristics were found.

CONCLUSION

Our novel data implicate an insufficient GR signaling in PBMCs in T2DM patients and HPA axis dysfunction. The significant associations of GR-signaling parameters with inflammatory and metabolic indices implicate that GR may be the critical link between HPA axis dysfunction, hypercortisolemia and diabetes-associated metabolic disturbances. Our findings provide significant insights into the contribution of GR-mediated mechanisms in T2DM aetiopathology and therapy.

Dietary fatty acids modulate cortisol concentrations and social dominance during social confrontations in adolescent male guinea pigs

The hypothalamic-pituitary-adrenal (HPA)-axis and related glucocorticoid concentrations regulate physiology and behavior, which can be modulated by nutritional conditions, particularly by the dietary fatty acid composition. Omega-3 polyunsaturated fatty acids (PUFAs) have been shown to promote hypothalamic-pituitary-adrenal (HPA)-axis functions, whereas saturated fatty acids (SFAs) in general produce adverse effects and even increase baseline glucocorticoid concentrations. Glucocorticoids (e.g. cortisol) were further documented to modulate the establishment of dominance relationships, while the involvement of dietary fatty acids remains understudied. This study focused on different effects of PUFAs and SFAs on cortisol concentrations and social dominance in male guinea pigs. Three groups of animals were maintained on diets high in PUFAs (10 % w/w walnut oil), SFAs (10 % w/w coconut fat), or on an untreated control diet starting already prenatally. During adolescence, at an age of 60, 90, and 120 days, each individual's saliva cortisol concentrations and hierarchy index (calculated by initiated and received agonistic behavior) were measured during basal group housing conditions and stressful social confrontations with unfamiliar individuals of the other groups. SFA males showed highest baseline cortisol concentrations, lowest cortisol responses to social confrontations, and became subdominant. PUFA and control males showed significant cortisol responses. However, while control males became dominant during social confrontations, the hierarchy index in PUFA males decreased with age. Individual hierarchy indices during consecutive social confrontations revealed a high consistency. The findings presented here indicate that dietary fatty acids differently affect HPA-axis functions and social dominance but the underlying mechanisms remain to be determined.

Effects of dietary fatty acids on the social life of male Guinea pigs from adolescence to adulthood

Dietary intake of polyunsaturated fatty acids (PUFAs) or saturated fatty acids (SFAs) differently modulates neurophysiological and behavioral functions in response to altered hypothalamic-pituitary-adrenal (HPA)-axis activity and an individual's development. In this context, an individual's social environment, including social interactions and social hierarchies, is closely related to hormone concentrations and possibly interacts with dietary fatty acid effects. We investigated if dietary supplementation with walnut oil (high in PUFAs) and coconut fat (high in SFAs), compared to a control group, affects body mass gain, cortisol and testosterone concentrations, plasma fatty acids, and social behavior in male domestic guinea pigs from adolescence to adulthood. For analyses of cortisol and testosterone concentrations, social interactions were included as covariates in order to consider effects of social behavior on hormone concentrations. Our results revealed that SFAs increased escalated conflicts like fights and stimulated cortisol and testosterone concentrations, which limited body mass gain and first-year survival. PUFAs did not remarkably affect social behavior and hormone concentrations, but enabled the strongest body mass gain, which probably resulted from an energetic advantage. Neither sociopositive nor agonistic behaviors explained age-specific differences in hormone concentrations between groups. However, a high number of subdominant individuals and lower testosterone concentrations were related to increased cortisol concentrations in adult PUFA males. Our findings demonstrate the importance of dietary fatty acids regarding behavioral and endocrine developmental processes and adaptations to the social environment by modulating HPA-axis function and body homeostasis.

Saliva versus serum cortisol to identify subclinical hypercortisolism in adrenal incidentalomas: simplicity versus accuracy

PURPOSE

Subclinical hypercortisolism (SCH) leads to metabolic derangements and increased cardiovascular risk. Cortisol autonomy is defined by the overnight 1 mg dexamethasone suppression test (DST). Saliva cortisol is an easier, stress-free, and cost-effective alternative to serum cortisol. We compared 23 h and post-1 mg DST saliva with serum cortisol to identify SCH in adrenal incidentalomas (AI).

METHODS

We analyzed 359 DST obtained retrospectively from 226 AI subjects (173F/53 M; 19-83 years) for saliva and serum cortisol. We used three post-DST serum cortisol cutoffs to uncover SCH: 1.8, 2.5, and 5.0 μg/dL. We determined post-DST and 23 h saliva cortisol cutoffs by ROC curve analysis and calculated their sensitivities (S) and specificities (E).

RESULTS

The sensitive 1.8 μg/dL cutoff defined 137 SCH and 180 non-functioning adenomas (NFA): post-DST and 23 h saliva cortisol S/E were: 75.2%/74.4% and 59.5%/65.9%, respectively. Using the specific 5.0 μg/dL cortisol cutoff (22 SCH/295 NFA), post-DST and 23 h saliva cortisol S/E were 86.4%/83.4% and 66.7%/80.4%, respectively. Using the intermediate 2.5 μg/dL cutoff (89 SCH/228 NFA), post-DST and 23 h saliva cortisol S/E were 80.9%/68.9% and 65.5%/62.8%, respectively.

CONCLUSION

Saliva cortisol showed acceptable performance only with the 5.0 μg/dL cortisol cutoff, as in overt Cushing's syndrome. Lower cutoffs (1.8 and 2.5 μg/dL) that identify larger samples of patients with poor metabolic outcomes are less accurate for screening. These results may be attributed to pre-analytical factors and inherent patient conditions. Thus, saliva cortisol cannot replace serum cortisol to identify SCH among patients with AI for screening DST.

Saliva cortisol in relation to aircraft noise exposure: pooled-analysis results from seven European countries

BACKGROUND

Many studies have demonstrated adverse effects of exposure to aircraft noise on health. Possible biological pathways for these effects include hormonal disturbances. Few studies deal with aircraft noise effects on saliva cortisol in adults, and results are inconsistent.

OBJECTIVE

We aimed to assess the effects of aircraft noise exposure on saliva cortisol levels and its variation in people living near airports.

METHODS

This study focused on the 1300 residents included in the HYENA and DEBATS cross-sectional studies, with complete information on cortisol sampling. All the participants followed a similar procedure aiming to collect both a morning and an evening saliva cortisol samples. Socioeconomic and lifestyle information were obtained during a face-to-face interview. Outdoor aircraft noise exposure was estimated for each participant's home address. Associations between aircraft noise exposure and cortisol outcomes were investigated a priori for male and female separately, using linear regression models adjusted for relevant confounders. Different approaches were used to characterize cortisol levels, such as morning and evening cortisol concentrations and the absolute and relative variations between morning and evening levels.

RESULTS

Statistically significant increases of evening cortisol levels were shown in women with a 10-dB(A) increase in aircraft noise exposure in terms of LA_{eq, 16h} (exp(β) = 1.08; CI95% = 1.00-1.16), L_den (exp(β) = 1.09; CI95% = 1.01-1.18), L_night (exp(β) = 1.11; CI95% = 1.02-1.20). A statistically significant association was also found in women between a 10-dB(A) increase in terms of L_night and the absolute variation per hour (exp(β) = 0.90; CI95% = 0.80-1.00). Statistically significant decreases in relative variation per hour were also evidenced in women, with stronger effects with the L_night (exp(β) = 0.89; CI95% = 0.83-0.96) than with other noise indicators. The morning cortisol levels were unchanged whatever noise exposure indicator considered. There was no statistically significant association between aircraft noise exposure and cortisol outcomes in men.

CONCLUSIONS

The results of the present study show statistically significant associations between aircraft noise exposure and evening cortisol levels and related flattening in the (absolute and relative) variations per hour in women. Further biological research is needed to deepen knowledge of the pathway between noise exposure and disturbed hormonal regulation, and specially the difference in effects between genders.

Omega-3-polyunsatured fatty acids (O3PUFAs), compared to placebo, reduced symptoms of occupational burnout and lowered morning cortisol secretion

BACKGROUND

Occupational burnout is both a serious health concern at both public and individual levels. Treatment options are psychopharmacological, psychological and physical activity-related interventions. Here, we tested whether, compared to placebo, omega-3-polyunsaturated fatty acids (O3PUFAs) have a positive impact on burnout and morning cortisol secretion.

METHOD

A total of 43 individuals (mean age: 38.4 years, 76.7% females) took part in the present double-blind and placebo-controlled intervention. Participants were randomly assigned either to the O3PUFA or to the placebo condition. At baseline and again eight weeks later, participants completed the Maslach Burnout Inventory and collected morning saliva samples for analysis of the cortisol awakening response (CAR).

RESULTS

Emotional exhaustion and depersonalization decreased, and sense of personal accomplishment increased over time, but more so in the O3PUFA condition than in the placebo condition. Likewise, CAR decreased over time, but again more so in the O3PUFA condition than in the placebo condition.

CONCLUSIONS

The present pattern of results suggests that, compared to placebo, administration of daily omega-3-polyunsaturated fatty acids for eight consecutive weeks positively influences both psychological and physiological markers of occupational burnout.

Effect of artificial shade on saliva cortisol concentrations of heat-stressed dairy calves

Responses to heat stress have not been evaluated in dairy cattle by noninvasive techniques such as analysis of saliva cortisol concentrations. The aim of the present study was the assessment of saliva cortisol levels in Holstein bull calves with (n = 8) or without supplemental shade (n = 8) in response to acute heat stress. Measurements were carried out during a 5-d period [temperature, average/max (°C); day 1 (control, all calves shaded): 22.9/29.4, day 2 (heat stress day): 28.3/38.8, day 3: 26.2/33.5, day 4: 23.7/28.7, and day 5: 21.2/24.7]. The level of thermal stress was characterized with a temperature-humidity index (THI). Saliva cortisol levels did not differ between groups during the control day. On the heat stress day, saliva cortisol levels increased from 8:00 to 12:00 by 51% and 342% in shaded and nonshaded calves, respectively, and nonshaded calves showed higher cortisol concentrations at 12:00, 16:00, and 24:00. Saliva cortisol levels peaked at 12:00 on day 3 in both groups. On days 4 and 5, saliva cortisol did not show significant daytime elevations in either group; however, group differences remained significant until 20:00 on day 4. Based on our results, measurement of saliva cortisol concentrations is a promising approach to detect acute heat stress in dairy calves, which could be reduced by artificial shading.

Road traffic noise and determinants of saliva cortisol levels among adolescents

OBJECTIVES

The understanding of determinants for saliva cortisol levels in adolescents is limited. This study investigated the role of road traffic noise exposure, noise annoyance and various other factors for saliva cortisol levels.

METHODS

We collected morning and evening saliva samples from 1751 adolescents from the BAMSE birth cohort based in Stockholm County. Façade noise levels from road traffic were estimated at the residences of the study subjects and repeated questionnaires and medical examinations provided extensive information on various exposures and conditions, including annoyance to noise from different sources. Cortisol was measured using radioimmunoassay. Associations between determinants and saliva cortisol levels were analysed using linear regression.

RESULTS

Morning saliva cortisol levels were significantly higher in females than in males (geometric mean 42.4 and 35.0 nmol/l, respectively) as well as in subjects with allergy related diseases. Height and age were related to saliva cortisol levels as well as sampling season. Road traffic noise exposure was not associated with saliva cortisol, however, annoyance to noise tended to increase the levels. Saliva cortisol levels appeared particularly high among those who were highly annoyed and exposed to road traffic noise levels ≥ 55 dB L_den (50.5 nmol/l, p = 0.02).

CONCLUSION

Our findings suggest that individual perception of noise may be of importance for saliva cortisol levels. The results also point to the complexity of using saliva cortisol as a marker of noise exposure in adolescents.

Measuring the course of anxiety in women giving birth by caesarean section: a prospective study

Background

Women undergoing elective caesarean section experience anxiety. However, course, extent and duration of anxiety have not been investigated yet. This study aimed to explore anxiety levels during the course of the day of surgery by employing and comparing subjective as well as objective measures. By examining their correlation it is intended to give methodological support for interventional studies.

Methods

This is a monocentric, prospectively planned study in which 47 women with an indication for primary caesarean section took part. Anxiety levels were evaluated using the State-Trait Anxiety Inventory (STAI-trait and STAI-state), the visual analogue scale for anxiety (VASA) as well as saliva cortisol at three time points on the day of the caesarean section (at admission, at skin closure and 2 h post surgery).

Results

Peak anxiety levels for the STAI-state and VASA were highest at admission and showed significant decreases to skin closure (p < .001). The subjective measures correlated significantly at all time points (p-values < .001). For cortisol levels the peak level of anxiety was shown at skin closure with a significant increase from admission to skin closure and a significant decrease from skin closure to 2 h post operation (p-values < .001). Additionally women with STAI-trait scores above the median showed significantly higher levels at the peaks of anxiety.

Conclusion

The study reveals the course of anxiety on the day of the caesarean section. A strong correlation of STAI-state and VASA was demonstrated. Cortisol showed a different course, which fits into its known biological kinetics. Taking into account all measures, anxiety seems to be most bothersome before surgery until skin closure. In a differentiated approach using STAI-trait scores as a discriminator we showed that the group with STAI-trait levels above the median is particularly prone to develop anxiety in the setting of the caesarean section and might therefore mostly be in need of an intervention against anxiety.

Effect of sex and time to slaughter (transportation and lairage duration) on the levels of cortisol, creatine kinase and subsequent relationship with pork quality

The study determined the effect of sex and time to slaughter on cortisol and creatine kinase levels, and pork quality in commercial crossbred pigs. Saliva samples were before collected transportation, on arrival at the abattoir, and after a 20 hour lairage period. Cortisol levels from saliva (SC), serum (SeC) and urine (UC) were determined. Creatine kinase (CK) levels were determined from serum samples. Fifteen boars vs. 15 gilts were immediately slaughtered on arrival (SOA), and the other 15 boars vs. 15 gilts were rested for 20 h before slaughter. Meat quality parameters were also determined. In both sexes, SC significantly increased in response to time to slaughter. There was a significant interaction of sex and time to slaughter on SeC. Gilts had higher CK levels and lower muscle L* values than boars. There were correlations among baseline SC, SeC, UC and most meat quality parameters. Time to slaughter influenced levels of SC, UC, CK and pork quality between boars and gilts.

Non-invasive cortisol measurements as indicators of physiological stress responses in guinea pigs

Non-invasive measurements of glucocorticoid (GC) concentrations, including cortisol and corticosterone, serve as reliable indicators of adrenocortical activities and physiological stress loads in a variety of species. As an alternative to invasive analyses based on plasma, GC concentrations in saliva still represent single-point-of-time measurements, suitable for studying short-term or acute stress responses, whereas fecal GC metabolites (FGMs) reflect overall stress loads and stress responses after a species-specific time frame in the long-term. In our study species, the domestic guinea pig, GC measurements are commonly used to indicate stress responses to different environmental conditions, but the biological relevance of non-invasive measurements is widely unknown. We therefore established an experimental protocol based on the animals' natural stress responses to different environmental conditions and compared GC levels in plasma, saliva, and fecal samples during non-stressful social isolations and stressful two-hour social confrontations with unfamiliar individuals. Plasma and saliva cortisol concentrations were significantly increased directly after the social confrontations, and plasma and saliva cortisol levels were strongly correlated. This demonstrates a high biological relevance of GC measurements in saliva. FGM levels measured 20 h afterwards, representing the reported mean gut passage time based on physiological validations, revealed that the overall stress load was not affected by the confrontations, but also no relations to plasma cortisol levels were detected. We therefore measured FGMs in two-hour intervals for 24 h after another social confrontation and detected significantly increased levels after four to twelve hours, reaching peak concentrations already after six hours. Our findings confirm that non-invasive GC measurements in guinea pigs are highly biologically relevant in indicating physiological stress responses compared to circulating levels in plasma in the short- and long-term. Our approach also underlines the importance of detailed investigations on how to use and interpret non-invasive measurements, including the determination of appropriate time points for sample collections.

Saliva collection by using filter paper for measuring cortisol levels in dogs

Four experiments were conducted to evaluate the accuracy and reliability of noninvasive evaluation of cortisol in saliva of dogs. In experiment 1, we measured the cortisol concentration in the filter paper on which 250-μL cortisol solutions had been quantitatively pipetted and in filter papers dipped in cortisol solution. In experiment 2, we collected the blood and saliva of dogs 3 times at 30-min intervals and compared the cortisol concentrations to examine whether the dynamics of cortisol in the blood and saliva are similar. The results of experiments 1 and 2 showed that the cortisol concentration can be quantitatively measured with this method and that the dynamics of cortisol concentration in the plasma and saliva collected by using filter paper are not different (P = 0.14 for experiment 1 and P = 0.51 for experiment 2). In experiment 3, to investigate the factors related to inducing stress in dogs by using the filter-paper method of collecting saliva, we compared the cortisol concentrations at 0 and 30 min after collecting the saliva of pet dogs. The dog owners completed a survey on their dogs, providing basic information and reporting the collection of their dog's saliva. We found that the cortisol concentrations increased significantly in dogs whose owners spent >2 min collecting saliva (P = 0.005), suggesting that prompt collection of saliva is necessary for accurate assessment of cortisol without induction of a stress response. In addition, the cortisol concentrations increased significantly in dogs whose teeth were not regularly brushed (P = 0.04), suggesting that regular teeth brushing mitigates the effect of the collection process on cortisol concentrations in the saliva, with minimal stress to the dogs. In experiment 4, we measured cortisol concentrations in pet dogs accustomed to having their teeth brushed by their owners, before and after interaction with their owners, to assess whether brushing induces stress in dogs. We detected that the cortisol concentrations significantly decreased after human-dog interaction (P = 0.008), suggesting that this method does not induce stress in dogs. Our study indicates that the method of saliva collection by using filter paper is effective in measuring the cortisol concentrations to evaluate stress, although certain steps are required to enhance accuracy.

Monitoring fitness, fatigue and running performance during a pre-season training camp in elite football players

OBJECTIVES

To examine the usefulness of selected physiological and perceptual measures to monitor fitness, fatigue and running performance during a pre-season, 2-week training camp in eighteen professional Australian Rules Football players (21.9±2.0 years).

DESIGN

Observational.

METHODS

Training load, perceived ratings of wellness (e.g., fatigue, sleep quality) and salivary cortisol were collected daily. Submaximal exercise heart rate (HRex) and a vagal-related heart rate variability index (LnSD1) were also collected at the start of each training session. Yo-Yo Intermittent Recovery level 2 test (Yo-YoIR2, assessed pre-, mid- and post-camp, temperate conditions) and high-speed running distance during standardized drills (HSR, >14.4 km h(-1), 4 times throughout, outdoor) were used as performance measures.

RESULTS

There were significant (P<0.001 for all) day-to-day variations in training load (coefficient of variation, CV: 66%), wellness measures (6-18%), HRex (3.3%), LnSD1 (19.0%), but not cortisol (20.0%, P=0.60). While the overall wellness (+0.06, 90% CL (-0.14; 0.02) AU day(-1)) did not change substantially throughout the camp, HRex decreased (-0.51 (-0.58; -0.45)% day(-1)), and cortisol (+0.31 (0.06; 0.57) nmol L(-1)day(-1)), LnSD1 (+0.1 (0.04; 0.06) ms day(-1)), Yo-YoIR2 performance (+23.7 (20.8; 26.6) m day(-1), P<0.001), and HSR (+4.1 (1.5; 6.6) m day(-1), P<0.001) increased. Day-to-day ΔHRex (r=0.80, 90% CL (0.75; 0.85)), ΔLnSD1 (0.51 (r=0.40; 0.62)) and all wellness measures (0.28 (-0.39; -0.17)<r<0.25 (0.14; 0.36)) were related to Δtraining load. There was however no clear relationship between Δcortisol and Δtraining load. ΔYo-YoIR2 was correlated with ΔHRex (r=0.88 (0.84; 0.92)), ΔLnSD1 (r=0.78 (0.67; 0.89)), Δwellness (r=0.58 (0.41; 0.75), but not Δcortisol. ΔHSR was correlated with ΔHRex (r = -0.27 (-0.48; -0.06)) and Δwellness (r=0.65 (0.49; 0.81)), but neither with ΔLnSD1 nor Δcortisol.

CONCLUSIONS

Training load, HRex and wellness measures are the best simple measures for monitoring training responses to an intensified training camp; cortisol post-exercise and LnSD1 did not show practical efficacy here.