Change in heart rate variability during two firefighting work cycles.

This study aimed to determine whether the change in heart rate variability from pre to post firefighting is modulated by different work cycles. Thirteen male firefighters underwent two firefighting simulations that comprised two identical 25-min work bouts intercalated by a passive recovery period of either 20 min (T20) or 5 min (T5). The square root of the mean squared differences of successive R-R intervals (RMSSD) and aural temperature were measured at rest before (PRE) and after (POST) firefighting simulations. The decrease in RMSSD was different between firefighting simulations (T20: -10 ± 21.2 ms, T5: -19.9 ± 20.9 ms, interaction, p = 0.02). Post-firefighting aural temperature was greater (p = 0.05) in T5 (37.18 ± 0.53 °C) than in T20 (36.88 ± 0.49 °C). In conclusion, a shorter recovery period of 5 min between firefighting work bouts decreases post-firefighting heart rate variability, possibly attributed to a lower parasympathetic reactivation and a higher absolute value of body temperature.

Cardiorespiratory Fitness of Police Recruits: Normative Reference Values and Temporal Trend.

ABSTRACT: Poirier, S, Houle, J, Lajoie, C, and Trudeau, F. Cardiorespiratory fitness of police recruits: normative reference values and temporal trend. J Strength Cond Res 37(1): 207-212, 2023-Several studies have highlighted the increased risk of cardiovascular diseases (CVDs) among police officers. Given the longitudinal association between cardiorespiratory fitness (CRF) in early adulthood and later appearance of CVD, the identification of police recruits exhibiting lower CRF could allow the implementation of targeted CVD prevention strategies. Unfortunately, norm-referenced values for the CRF of Canadian police recruits are not yet available. Thus, this research aimed to provide norm-referenced values for the CRF of police recruits in the province of Quebec (Canada) and to evaluate the temporal trend in the CRF of police recruits over a 14-year period. First, a model was developed to estimate maximal oxygen consumption (V̇O2max) based on the results of the physical ability test (PAT) used for the recruitment of police officers in Quebec. Based on the previously developed model, the CRF of police recruits who completed the PAT from 2004 to 2017 was retrospectively assessed using administrative records. The analysis of 7,234 PAT results including 2,150 females (29.7%) and 5,084 males (70.3%) suggests that police recruits generally present high levels of CRF with an average estimated V̇O2max of 53.3 ml·min-1·kg-1 for males and 43.8 ml·min-1·kg-1 for females. Furthermore, our analyses showed significant but small positive correlations between estimated V̇O2max and time periods of PAT performance for male (rs = 0.105, p < 0.001) and female recruits (rs = 0.125, p < 0.001). Overall, our results suggest that the CRF of police recruits in Quebec is considerably higher than that of their North American peers.

Cardiorespiratory fitness in police recruits: Assessing the validity of the 20-meter shuttle run test for recruitment purposes.

BACKGROUND: Although the 20-meter shuttle run test (20MSR) is frequently used by police organisations for recruitment purposes, to our knowledge no study has yet assessed the accuracy of this test to estimate maximal oxygen consumption (VO2max) in police recruits. OBJECTIVE: The primary objective of this study was to assess the validity of the 20MSR as a predictor of VO2max in police cadets. METHODS: 49 police cadets completed both an indirect calorimetry VO2max assessment and a 20MSR. Based on their results, estimated VO2max was calculated using an established equation. Furthermore, two models estimating the VO2max was also developed using the final stage completed and sex as independent variables in the first model (model A) as well as the final half-stage completed and sex in the second model (model B). RESULTS: A strong and significant bivariate correlation was found between measured VO2max and the final stage completed at the 20MSR (r = 0.874, p < 0.001). Nevertheless, limits of agreement analysis showed relatively large agreement errors between measured VO2max and estimated VO2max based on the established equation (0.46±6.29 ml·min-1·kg-1), model A (0.00±5.58 ml min-1 kg-1), and model B (0.00±5.48 ml min-1·kg-1). CONCLUSIONS: Although the 20MSR can be a useful tool to estimate cardiorespiratory fitness for research and conditioning purposes, the large agreement errors found in this study suggest that results at the 20MSR should be interpreted with caution when making "pass or fail" decisions.

Fitness components associated with performance of a law enforcement physical employment standard in police cadets.

BACKGROUND: The physical preparation of cadets for both physical employment standards (PES) and police job performance is a major concern for police organizations. Identifying fitness components associated with both PES performance and work performance can provide essential information for the physical training of police cadets. Therefore, the objective of this study was to assess the association of fitness components with performance of the Standardized Physical Abilities Test (SPAT), a new law enforcement PES. METHODS: A sample of 41 police cadets was recruited to take part in this cross-sectional study. First, the participants were assessed using six fitness assessments (standing broad jump, medicine ball put, grip strength test, visuomotor reaction time (VMRT) test, modified agility T-test, and 600-meter run). In a second experiment, participants performed the SPAT. RESULTS: Bivariate correlation analysis showed moderate to strong associations between each fitness assessment and SPAT performance. Based on stepwise multiple regression analysis, results at the VMRT Test, the medicine ball put, and the agility T-test accounted for 66.0% of the variability in SPAT performance (R2=0.660; P<0.001). CONCLUSIONS: Overall, our results suggest that exercise prescriptions for police cadets should focus on power, agility, and VMRT. Furthermore, our results show that performance in a PES can be estimated rather precisely based on low-cost fitness assessments. Therefore, such methodology could be used to develop fitness assessments specific to PES requirements.

Programmed vs. Thirst-Driven Drinking during Prolonged Cycling in a Warm Environment.

We compared the effect of programmed (PFI) and thirst-driven (TDFI) fluid intake on prolonged cycling performance and exercise associated muscle cramps (EAMC). Eight male endurance athletes (26 ± 6 years) completed two trials consisting of 5 h of cycling at 61% V˙O2peak followed by a 20 km time-trial (TT) in a randomized crossover sequence at 30 °C, 35% relative humidity. EAMC was assessed after the TT with maximal voluntary isometric contractions of the shortened right plantar flexors. Water intake was either programmed to limit body mass loss to 1% (PFI) or consumed based on perceived thirst (TDFI). Body mass loss reached 1.5 ± 1.0% for PFI and 2.5 ± 0.9% for TDFI (p = 0.10). Power output during the 20 km TT was higher (p < 0.05) for PFI (278 ± 41 W) than TDFI (263 ± 39 W), but the total performance time, including the breaks to urinate, was similar (p = 0.48) between conditions. The prevalence of EAMC of the plantar flexors was similar between the drinking conditions. Cyclists competing in the heat for over 5 h may benefit from PFI aiming to limit body mass loss to <2% when a high intensity effort is required in the later phase of the race and when time lost for urination is not a consideration.

Shortened Recovery Period Between Firefighting Work Bouts Increases Cardiac Response Disproportionately With Metabolic Rate.

OBJECTIVE: To compare physiological responses between two firefighting simulations with different recovery periods, one having work bouts intercalated by a shortened recovery period. METHODS: Thirteen male firefighters participated in two different simulations, which comprised two identical 25-minute effort bouts (E1 and E2) intercalated by a recovery period of either 20 (T20) or 5 (T5) minutes. RESULTS: From E1 to E2, the increase of mean heart rate (HR) (26 ±â€Š5 vs 14 ±â€Š5 bpm, P < 0.001) and mean VO2 (1.8 ±â€Š0.4 vs 1.3 ±â€Š0.4 mL kg min, P < 0.001) was higher in T5 than in T20. CONCLUSION: Results indicate that a shortened recovery time between firefighting work bouts intensifies cardiac strain disproportionately with metabolic rate, since mean HR increased by 19.3% and 10.8% while mean VO2 increased by only 7.2% and 5.0% in T5 and T20, respectively.

Cardiovascular health profile among Québec male and female police officers.

To document the cardiovascular health profile of Québec police officers (PO). Participants answered an online questionnaire evaluating the presence of cardiovascular disease (CVD) risk factors and symptoms. Two thousand, ninety-nine (2,099) male (age: 40.8 ± 9.2 years) and 756 female (age: 37.9 ± 7.9 years) PO participated in this study. The prevalence of obesity (body mass index ≥30 kg/m2) and diagnosed hypertension was respectively 21.1, and 14.3% in male and 7.3 and 4.1% in female PO. According to 2013 American College of Sports Medicine guidelines, 27.0 and 48.0% of male and 12.1 and 56.7% of female PO were categorized as being at moderate and high CVD risk, respectively. These findings suggest that Québec police departments should help PO to adopt and maintain a healthy lifestyle to decrease CVD risk.

Physiological and Psychological Adaptations of Trained Cyclists to Spring Cycling Camps.

The purpose of our study was to assess physiological adaptations and measure mood outcomes following a cycling training camp in competitive athletes. Fourteen competitive athletes (8 males, 6 females) performed 2 incremental tests to exhaustion before and after a training camp. Volume and intensity (load) of the training regimen were recorded. Submaximal and maximal metabolic data were analysed, as well as economy variables (gross mechanical efficiency and cycling economy). Skeletal muscle adaptations were assessed using near infrared spectroscopy (NIRS). For both genders (n = 14), peak power output, peak power output-W/kg ratio and peak power output-B[La] were significantly increased (p < 0.05) after the cycling training camp (p < 0.05). Significant increases occurred for gross mechanical efficiency measured at the lactate threshold (+4.9%) and at the same precamp lactate threshold power output (+2.9%). At the lactate threshold and Post Camp Lactate Threshold Power, cycling economy increased by 5.2 and 2.9%, respectively (p < 0.05). These power measurements were significantly correlated with individual fluctuations in deoxyhaemoglobin in the vastus lateralis for male cyclists only. Profile of Mood State questionnaire results showed that subcategories "Tension-Anxiety", "Confusion", "Fatigue" and "Total Global Score" significantly decreased after the training camp. Cycling training camps were associated with positive adaptations (increased cycling economy, gross mechanical efficiency and power output) as well as some mental benefits. This indicates that despite some significant physiological adaptations participants probably did not overreach during their CTC.

Cardiovascular Disease Risk Factors in Québec Male Firefighters.

OBJECTIVE: We aimed to document the prevalence of cardiovascular disease (CVD) risk factors and symptoms in Québec firefighters. METHODS: Seven hundred and seventy-nine (779) male firefighters (age: 41.6 ±â€Š10.4 years; body mass index [BMI]: 28.0 ±â€Š3.6 kg/m) answered an online questionnaire evaluating lifestyle and the presence of CVD risk factors and symptoms. RESULTS: The prevalence of obesity (BMI is more than or equal to 30 kg/m), diagnosed hypertension, diagnosed dyslipidemia, and diagnosed type 2 diabetes mellitus was respectively 23.6%, 12.2%, 17.4%, and 1.7%. Among survey participants, 34.5% were categorized as moderate and 43.6% as high CVD risk, according to American College of Sports Medicine guidelines. CONCLUSIONS: A high proportion of Québec firefighters are at moderate to high risk of CVD. These findings suggest that Québec fire departments should help all firefighters to adopt and maintain a healthy lifestyle.

Energy expenditure at work in physical education teachers.

The objective of this study was to quantify work energy expenditure (EE) in physical education (PE) teachers. Sixty-four (64) physical educators (49 men, 15 women) had their individualized linear function between heart rate (HR) and oxygen consumption measured by laboratory testing. HR was then recorded on 2 different days at work to estimate EE, correlated with a diary of daily tasks. Average absolute EE was low-to-moderate (2.7 ± 1.4 to 4.6 ± 2.5 kcal·min(-1)) and low when expressed in relative values (15.3 ± 6.1% to 24.8 ± 7.6% of VO2max). However, these physical educators often reached very high intensities (from 7.5 ± 7.9% to 23.8 ± 22.3% of work time at 100 bpm and more). PE teaching requires a light-to-moderate EE with more intense periods of physical activity. The variety of tasks performed (office work, supervision and monitoring, mixed participation and active participation) significantly influenced EE.

Infarct size is increased in female post-MI rats treated with rapamycin.

Rapamycin represents a recognized drug-based therapeutic approach to treat cardiovascular disease. However, at least in the female heart, rapamycin may suppress the recruitment of putative signalling events conferring cardioprotection. The present study tested the hypothesis that rapamycin-sensitive signalling events contributed to the cardioprotective phenotype of the female rat heart after an ischemic insult. Rapamycin (1.5 mg/kg) was administered to adult female Sprague-Dawley rats 24 h after complete coronary artery ligation and continued for 6 days. Rapamycin abrogated p70S6K phosphorylation in the left ventricle of sham rats and the noninfarcted left ventricle (NILV) of 1-week postmyocardial-infarcted (MI) rats. Scar weight (MI 0.028 +/- 0.006, MI+rapamycin 0.064 +/- 0.004 g) and surface area (MI 0.37 +/- 0.08, MI+rapamycin 0.74 +/- 0.03 cm2) were significantly larger in rapamycin-treated post-MI rats. In the NILV of post-MI female rats, rapamycin inhibited the upregulation of eNOS. Furthermore, the increased expression of collagen and TGF-beta3 mRNAs in the NILV were attenuated in rapamycin-treated post-MI rats, whereas scar healing was unaffected. The present study has demonstrated that rapamycin-sensitive signalling events were implicated in scar formation and reactive fibrosis. Rapamycin-mediated suppression of eNOS and TGF-beta3 mRNA in post-MI female rats may have directly contributed to the larger infarct and attenuation of the reactive fibrotic response, respectively.

The cardiac neural stem cell phenotype is compromised in streptozotocin-induced diabetic cardiomyopathy.

Neural stem cells were identified in the rat heart and during scar formation and healing participated in sympathetic fiber sprouting and angiogenesis. In the setting of diabetes, impaired wound healing represents a typical pathological feature. These findings provided the impetus to test the hypothesis that experimental diabetes adversely influenced the phenotype of cardiac neural stem cells. Streptozotocin (STZ)-induced diabetic rats were associated with elevated plasma glucose levels, significant loss of body weight and left ventricular contractile dysfunction. In the heart of STZ-diabetic rats, the density of nestin immunoreactive processes emanating from cardiac neural stem cells were reduced. The latter finding was reaffirmed as nestin protein expression was significantly decreased in the heart of STZ-diabetic rats and associated with a concomitant reduction of nestin mRNA. Employing the TUNEL assay, the loss of nestin expression in STZ-diabetic rats was not attributed to widespread cardiac neural stem cell apoptosis. Insulin administration to STZ-diabetic rats with established hyperglycaemia led to a modest recovery of nestin protein expression in cardiac neural stem cells. By contrast, the administration of insulin immediately after STZ injection improved plasma glucose levels and significantly attenuated the loss of nestin protein expression. These data highlight the novel observation that nestin protein expression in cardiac neural stem cells was significantly reduced in STZ-induced type I diabetic rats. The aberrant cardiac neural stem cell phenotype may compromise their biological role and predispose the diabetic heart to maladaptive healing following ischemic injury.

Female rats fed a high-fat diet were associated with vascular dysfunction and cardiac fibrosis in the absence of overt obesity and hyperlipidemia: therapeutic potential of resveratrol.

It remains presently unknown whether vascular reactivity is impaired and whether maladaptive cardiac remodeling occurs before the onset of overt obesity and in the absence of hyperlipidemia. Normal female rats were fed a high-fat diet for 8 weeks and were associated with a modest nonsignificant increase of body weight (standard diet, 300 +/- 10, versus high-fat diet, 329 +/- 14 g) and a normal plasma lipid profile. In rats fed a high-fat diet, systolic (171 +/- 7 mm Hg) and diastolic blood pressures (109 +/- 3) were increased compared to a standard diet (systolic blood pressure, 134 +/- 8; diastolic blood pressure, 96 +/- 5 mm Hg), and acetylcholine-dependent relaxation of isolated aortic rings (high-fat diet, 22 +/- 5%, versus standard diet, 53 +/- 8%) was significantly reduced. Furthermore, perivascular fibrosis was detected in the heart of rats fed a high-fat diet. The exogenous addition of resveratrol (trans-3,5,4'-trihydroxystilbene) (0.1 microM) to aortic rings isolated from rats fed a high-fat diet restored acetylcholine-mediated relaxation (47 +/- 9%). The administration of resveratrol (20 mg/kg/day for 8 weeks) to rats fed a high-fat diet prevented the increase in blood pressure and preserved acetylcholine-dependent relaxation of isolated aortic rings. However, resveratrol therapy failed to attenuate the perivascular fibrotic response. These data have demonstrated that a high-fat diet fed to normal female rats can elicit a hypertensive response and induce perivascular fibrosis before the development of overt obesity and in the absence of hyperlipidemia. Resveratrol therapy can prevent the hypertensive response in female rats fed a high-fat diet but is without effect on the progression of perivascular fibrosis.

Disparate regulation of signaling proteins after exercise and myocardial infarction.

INTRODUCTION: The signaling proteins extracellular signal-regulated kinase (ERK1/2) and protein kinase B (PKB) were implicated in the development of pathological cardiac hypertrophy. The present study examined whether the progression of physiological eccentric cardiac hypertrophy was associated with ERK1/2 and PKB recruitment. METHODS AND RESULTS: Following 1 and 3 wk of voluntary exercise, female Sprague-Dawley rats ran a total distance of 55 +/- 10 and 195 +/- 19 km, respectively. Left ventricular hypertrophy was detected in 3-wk-exercised rats, albeit prepro-ANP protein expression was unchanged. ERK1/2 was not recruited in the left ventricle (LV) of either 1-wk-exercised rats or the hypertrophied LV of 3-wk-exercised rats. In 1-wk-exercised rats, PKB Thr308 and Ser473 phosphorylation were significantly reduced, whereas a selective increase of PKB Ser473 phosphorylation was observed in the hypertrophied LV of 3-wk-exercised rats. In both 1- and 3-wk-exercised rats, an upward electrophoretic mobility band shift of p70 ribosomal S6 kinase (p70 S6K) was detected. In 1-wk post-myocardial-infarcted (MI) female Sprague-Dawley rats, scar formation was associated with increased left ventricular end-diastolic pressure. In the hypertrophied noninfarcted left ventricle (NILV), ERK1/2, p70 S6K, PKB Ser473, and Thr308 phosphorylation were increased. CONCLUSIONS: These data support the premise that ERK1/2 and PKB were differentially regulated during the development of eccentric physiological and pathological cardiac hypertrophy. It remains to be determined whether the chronic activation of either ERK1/2 and/or PKB in the NILV of post-MI rats may contribute in part to maladaptive cardiac remodelling.

The rapid onset of hyperglycaemia in ZDF rats was associated with a widespread alteration of metabolic proteins implicated in glucose metabolism in the heart.

The present study tested the hypothesis that the phosphorylation and regulation of metabolic proteins implicated in glucose homeostasis were impaired in the heart of the type 2 diabetic Zucker-diabetic-fatty (ZDF) rat model. The onset of hyperglycaemia in ZDF rats was not uniform, instead it either progressed rapidly (3-4 weeks) or was delayed (6-8 weeks). In both the early and late onset hyperglycaemic ZDF rats, AMPKalpha Thr172 phosphorylation in the heart was significantly decreased. In the early onset hyperglycaemic ZDF rats, PKB Ser473 phosphorylation was reduced, whereas Thr308 phosphorylation was significantly increased. In the late onset hyperglycaemic ZDF rats, PKB Ser473 phosphorylation was unchanged, but Thr308 phosphorylation remained elevated. Cardiac GLUT4 protein and mRNA expression were significantly reduced in the early onset hyperglycaemic ZDF rats, whereas increased protein expression was observed in the late onset hyperglycaemic ZDF rats. In conclusion, the present study has demonstrated that following a more rapid onset of hyperglycaemia, the type 2 diabetic heart is more prone to alterations in the signaling proteins implicated in glucose metabolism.

Exercise training enhanced the expression of myocardial proteins related to cell protection in spontaneously hypertensive rats.

Exercise training could potentially exert beneficial effects on the signaling events associated with cardiac cell apoptosis. Spontaneously hypertensive rats (SHR) were trained 5 days/week on a treadmill (18 m/min for 120 min/day) between the ages of 4 weeks and 1 week, corresponding to the hypertensive accelerating phase. The effect of exercise training on the expression of anti-apoptotic proteins HSP-72, Bcl-2 and protein kinase B (PKB), and the apoptotic proteins Bax and glycogen synthase kinase-3 (GSK-3) was examined. Exercise had a significant acute lowering effect on blood pressure, but this decrease did not attenuate the progressive increase in blood pressure. In the left ventricles of exercised SHR, PKB phosphorylation of both Ser473 and Thr308 residues was significantly increased by 166% and 120%, respectively, compared to sedentary SHR. PKB phosphorylation significantly correlated with GSK-3beta phosphorylation. HSP-72 and Bcl-2 protein expression were increased in the left ventricle of exercised SHR, and associated with the concomitant increased expression of the protein Bax. Thus, the Bcl-2/Bax ratio was not changed by exercise training, suggesting that the anti-apoptotic mechanism was effective in compensating the increase in the expression of the pro-apoptotic protein Bax in the myocardium of the SHR.

Exercise training attenuated the PKB and GSK-3 dephosphorylation in the myocardium of ZDF rats.

Cardiac dysfunction is a severe secondary effect of Type 2 diabetes. Recruitment of the protein kinase B/glycogen synthase kinase-3 pathway represents an integral event in glucose homeostasis, albeit its regulation in the diabetic heart remains undefined. Thus the following study tested the hypothesis that the regulation of protein kinase B/glycogen synthase kinase-3 was altered in the myocardium of the Zucker diabetic fatty rat. Second, exercise has been shown to improve glucose homeostasis, and, in this regard, the effect of swimming training on the regulation of protein kinase B/glycogen synthase kinase-3 in the diabetic rat heart was examined. In the sedentary Zucker diabetic fatty rats, glucose levels were elevated, and cardiac glycogen content increased, compared with wild type. A 13-wk swimming regimen significantly reduced plasma glucose levels and cardiac glycogen content and partially normalized protein kinase B-serine473, protein kinase B-threonine308, and glycogen synthase kinase-3alpha phosphorylation in Zucker diabetic fatty rats. In conclusion, hyperglycemia and increased cardiac glycogen content in the Zucker diabetic fatty rats were associated with dysregulation of protein kinase B/glycogen synthase kinase-3 phosphorylation. These anomalies in the Zucker diabetic fatty rat were partially normalized with swimming. These data support the premise that exercise training may protect the heart against the deleterious consequences of diabetes.