On-Duty Resting Heart Rate Variability at the Fire Station Is Related to Cardiorespiratory Fitness and Physical Activity Levels in Firefighters.

OBJECTIVE: The aim of the study is to measure the association between the physical activity (PA) levels and cardiorespiratory fitness on the firefighters' cardiac autonomic function at rest at the fire station. METHODS: Anthropometry, heart rate variability, fitness, and PA levels were assessed at the fire station in 98 career Québec male firefighters. RESULTS: Partial correlations, adjusted for age, waist circumference, and perceived stress revealed that heart rate and several heart rate variability indices were significantly correlated to estimated maximal oxygen consumption and to high-intensity PA but not to moderate-intensity PA. CONCLUSIONS: These results suggest that both cardiorespiratory fitness and high-intensity physical training are related to the cardiac autonomic function of firefighters. Therefore, fire department should promote PA programs to improve physical fitness among firefighters.

Cardiovascular disease risk factors in career firefighters: A 6-year follow-up study.

This study sought to investigate the evolution of cardiovascular disease (CVD) risk factors in career firefighters. A questionnaire was sent to a cohort of 233 Québec career firefighters in 2015 and 2021 to collect demographic and occupational information and the presence of CVD risk factors. Ninety-six (96) firefighters (1 female) responded to the questionnaire in 2015 and 2021. Body weight (2015: 88.3 ± 10.9, 2021: 89.6 ± 10.7 kg, p = 0.01), body mass index (2015: 27.6 ± 3.2, 2021: 28.0 ± 3.0 kg/m2, p = 0.01), number of CVD risk factors (2015: 1.1 ± 1.0, 2021: 1.3 ± 0.9 CVD risk factors, p = 0.05), and proportion of firefighters with at least 1 CVD risk factor (2015: 71, 2021: 82%, p = 0.02) increased. Overall, our results highlight an aggravation of several CVD risk factors in Québec career firefighters over the years.

How Exergaming with Virtual Reality Enhances Specific Cognitive and Visuo-Motor Abilities: An Explorative Study.

Virtual reality (VR) is the computer simulation of a three-dimensional environment that a person can interact with using special electronic equipment, such as a headset with an integrated display. Often coupled with VR, exergames are video games that involve physical exercise. Little is known regarding the chronic effects of exergaming through VR chon cognitive functions. Eleven young participants were enrolled in this crossover exploratory study. They had to follow two trainings of 5 consecutive days, 15 min per day, interspaced by a 1-month washout period. Trainings were performed in a random order: (1) a video training using shadow boxing fitness videos (SBV) and (2) a VR training using a three-dimensional game where the aim is to cut moving cubes with a sword in each hand. Before and after each training period, a battery of cognitive tests was performed to assess executive functions, such as attention (change blindness), reaction time, response inhibition (go/no-go, Stroop task), or flexibility (trail making test). Fine motor skills were also evaluated through a Fitt's task. No effect of the SBV training was observed on any of the cognitive functions tested. On the contrary, a significant increased performance in selective attention and observation tests was found after VR training, as well as in inhibitory processes (Stroop and go/no-go). Other performances were unaffected by either VR or SBV training. The present study argues that VR exergaming is a promising tool to promote cognitive enhancement but targets specific functions according to the type of interface/game that is used.

Physiological demands and physical performance determinants of a new firefighting simulation test.

The study aimed to examine physiological responses of firefighters performing a firefighting simulation test (FST) and to determine the relationship between physical fitness parameters and FST performance. Aerobic fitness, muscular strength, muscular endurance, and anaerobic capabilities were evaluated in 37 firefighters (21-profesionals and 16-volunteers firefighters). Furthermore, participants carried out the FST during which we measured performance, respiratory gas exchange, heart rate (HR), perceived exertion and blood lactate concentrations. Males were significantly faster than females for all tasks of the FST (p < 0.01); however, final performance score (16.5 ± 2.9 and 14.5 ± 2.6 points for males and females, respectively), HR (94.0 ± 2.0% and 93.7 ± 2.3% of HRmax) and perceived exertion (8.1 ± 0.9 and 7.1 ± 1.3) were not significantly different. Prediction of FST performance by LASSO regression revealed a model that included mainly aerobic capacity and maximal strength. In conclusion, FST challenged both aerobic and anaerobic energy metabolisms for both males and females and requires various physiological abilities to perform. Practitioner Summary: For the safety of firefighters and victims, firefighters must meet minimum physical requirements. 37 firefighters performed physical tests and a new firefighting test implemented for the recruitment of firefighters in France. The results revealed that this test is strenuous and that performance is associated with cardiorespiratory fitness and muscular strength. Abbreviations: V̇O2: oxygen consumption; V̇CO2: carbon dioxyde production; V̇E: expired ventilation; RER: respiratory exchange ratio; FST: firefighting simulation test; MAS: maximal aerobic speed; HR: heart rate; RPE: rating of perceived exertion; MVC: maximum voluntary contraction; IMTP: isometric mid-thigh pull; TTE: time to exhaustion; Ppeak: peak power; Pmean: mean power; LASSO: least absolute shrinkage and selection operator; La-: blood lactate concentration.

Virtual reality does not fool the brain only: spinal excitability changes during virtually simulated falling.

Virtual reality (VR) is known to induce substantial activation of brain's motor regions. It remains unclear to what extent virtual reality can trigger the sensorimotor system, and more particularly, whether it can affect lower nervous levels. In this study, we aimed to assess whether VR simulation of challenging and stressful postural situations (Richie's plank experience) could interfere with spinal excitability of postural muscles in 15 healthy young participants. The H-reflex of the triceps surae muscles was elicited with electrical nerve stimulation while participants were standing and wearing a VR headset. Participants went through several conditions, during which stimulations were evoked: standing still (noVR), standing in VR on the ground (groundVR), standing on the edge of a building (plankVR), and falling from the building (fallingVR). Myoelectrical activity of the triceps surae muscles was measured throughout the experiment. Leg and head movements were also measured by means of accelerometers to account for body oscillations. First, no differences in head rotations and myoelectrical activity were to be noted between conditions. Second, triceps H-reflex (HMAX/MMAX) was not affected from noVR to groundVR and plankVR. The most significant finding was a drastic decrease in H-reflex during falling (-47 ± 26.9% between noVR and fallingVR, P = 0.015). It is suggested that experiencing a postural threat in VR efficiently modulates spinal excitability, despite remaining in a quiet standing posture. This study suggests that simulated falling mimics the neural adjustments observed during actual postural challenge tasks.NEW & NOTEWORTHY The present study showed a modulation of spinal excitability induced by virtual reality (VR). In the standing position, soleus H-reflex was downmodulated during a simulated falling, in the absence of apparent changes in body oscillations. Since the same behavior is usually observed during real falling, it was suggested that the visual cues provided by VR were sufficiently strong to lead the neuromuscular system to mimic the actual modulation.

Post-Exercise Cold- and Contrasting-Water Immersion Effects on Heart Rate Variability Recovery in International Handball Female Players.

This study aimed to investigate the effect of water immersion (WI) on cardiac parasympathetic reactivation during recovery from handball training sessions in elite female players during a two-week training camp. On the first three days of both weeks, players completed a crossover design with one of three 60-min delayed post-exercise WI protocols or passive rest (PAS). Recovery interventions consisted of a period of 6-min cold-WI (10°C; CWI6) and two contrasting periods cold- and hot-WI (36°C): one session included 3 min cold + 2 min hot + 3 min cold and the other session 5 × 2 min with cold at the very end. Short-term measures of heart rate variability (HRV) were collected before and after handball training sessions, and after WI. Derived parasympathetic HRV indices collected daily showed lower values post-training compared to pre-training values (p < 0.0001, large ES). Individual handball training sessions revealed similar clear depression of the vagal tone throughout the training camp. The comparison between each WI protocol and PAS revealed significant time × condition interaction particularly for CWI6. All parasympathetic indices revealed higher post-recovery values in CWI6 than PAS (p < 0.001 -p < 0.0001, with large ES ranging from 0.86 to 0.94). Surprisingly, 60-min delayed post-training WI revealed for most of parasympathetic HRV indices higher values than pre-training. This study highlighted that post-exercise parasympathetic disruption was exacerbated in response to handball training, and the 60-min delayed WI recovery interventions improved parasympathetic reactivity. Cardiac vagal tone can be highly improved with CWI6 compared to PAS. For the purpose of HRV modulations, CWI6 is recommended for short-term recovery.

Effect of Protective Equipment on Firefighters' External and Internal Workloads During a Simulated Rescue Intervention.

ABSTRACT: Marcel-Millet, P, Ravier, G, and Groslambert, A. Effect of protective equipment on firefighters' external and internal workloads during a simulated rescue intervention. J Strength Cond Res 36(8): 2291-2297, 2022-Firefighter's protective equipment is one of the main factors increasing psychophysiological demand during rescue intervention. Workload quantification defines the amount of stress placed on an individual. This study aimed to test the relationships and compare different workload methods to discriminate 3 protective equipment conditions based on simulated rescue intervention. The protective equipment was (a) personal protective clothing (PPC); (b) PPC and a self-contained breathing apparatus (SCBA), including a cylinder, a full-face piece, and a breathing regulator; and (c) PPC and only the cylinder of the SCBA (SCBAc). Workload was determined using methods based on heart rate (HR), perceived exertion (sRPE), acceleration, and an indirect method based on postexercise HR variability. Differences between conditions were analyzed with repeated-measures analyses of variance. Relationships between workload methods were determined using Pearson's correlations. Statistical significance was set at p < 0.05. The HR-based and sRPE methods showed higher values in the SCBA and SCBAc conditions than the PPC condition ( p < 0.0001); only the sRPE method had a higher workload for the SCBA condition than the SCBAc condition ( p < 0.0001). Acceleration-based workloads were lower in the SCBA and SCBAc conditions than the PPC condition ( p < 0.0001). The indirect method revealed no difference between the 3 conditions. Significant relationships were observed between the HR-based and sRPE methods ( r = 0.544-0.738). Inverse significant correlations were observed between the HR-based and sRPE methods and the acceleration workload methods ( r = -0.319 to -0.762). Although HR-based and sRPE methods might quantify the workloads, the sRPE method was more sensitive to discriminate between the SCBAc and SCBA conditions.

Does firefighters' physical fitness influence their cardiac parasympathetic reactivation? Analysis with post-exercise heart rate variability and ultra-short-term measures.

Purpose. This study assessed the influence of firefighters' physical fitness on performances and parasympathetic reactivation in rescue interventions, and tested the validity of post-exercise ultra-short-term heart rate variability. Methods. Twenty-four firefighters were assigned to two groups based on their fitness and performed three simulated interventions. The mean completion time was recorded. The post-exercise root mean square of successive differences of R-R intervals (LnRMSSD) was determined from both criterion (between 5 and 10 min) and ultra-short-term (every 1-min segment from minutes 0-6) analyses. Results. Completion time was better for the highest fitness group in the three simulated interventions while post-exercise LnRMSSD was not influenced by the firefighters' fitness. Reliability between ultra-short-term and criterion analyses differed between the segments tested; minute 5-6 revealed the highest intra-class correlations (0.86-0.97). Concerning sensitivity of both analyses, the criterion analysis revealed differences between the three rescue interventions and the fitness test, but these results were not observed with ultra-short-term measures. Conclusions. Fitness was associated with firefighters' performances but not with parasympathetic reactivation in the firefighting intervention. The ultra-short-term measures do not seem to be a suitable post-exercise LnRMSSD analysis because of the low sensitivity to reveal differences among exercise conditions.

Psychophysiological responses of firefighters to day and night rescue interventions.

This study aimed 1) to assess the psychophysiological responses throughout a rescue intervention performed during the day and at night and 2) to determine if a vibrating alarm influences these psychophysiological responses at night. Sixteen male firefighters completed a simulated intervention under three different conditions: 1) during the day with a sound alarm signal (DaySA), 2) during the night with a sound alarm signal (NightSA), 3) during the night with a vibrating alarm signal (NightVA). Cardiovascular and psychological stress were recorded throughout the interventions. During the alarm signal, HR reactivity was greater in NightSA than in DaySA (p < 0.01). Parasympathetic reactivation and self-confidence were significantly lower in NightSA than in DaySA (p < 0.05). HR reactivity was decreased in NightVA in comparison to NightSA (p < 0.05). Overall, the rescue intervention had a greater impact on the psychophysiological variables during the night than during the day, and the type of alarm had a minor effect.

The type of visual biofeedback influences maximal handgrip strength and activation strategies.

PURPOSE: This study investigated the effects of force and electromyographic (EMG) feedbacks on forearm muscle activations and handgrip maximal isometric voluntary contraction (MIVC). METHODS: Sixteen males performed a set of MIVC in four different feedback conditions: (1) NO-FB: no feedback is given to the participant; (2) FORCE-FB: participants received a visual feedback of the produced force; (3) AGO-FB: participants received a visual feedback of the EMG activity of two agonist grip muscles; (4) ANTAGO-FB: participants received a visual feedback of the EMG activity of two hand extensors muscles. Each feedback was displayed by monitoring the signal of either force or electrical activity of the corresponding muscles. RESULTS: Compared to NO-FB, FORCE-FB was associated with a higher MIVC force (+ 11%, P < 0.05), a higher EMG activity of agonist and antagonist muscles (+ 8.7% and + 9.2%, respectively, P < 0.05) and a better MIVC/EMG ratio with the agonist muscles (P < 0.05). AGO-FB was associated with a higher EMG activity of agonist muscles (P < 0.05) and ANTAGO-FB was associated with a higher EMG activity of antagonist muscles (P < 0.05). MIVC force was higher in the agonist feedback condition than in the antagonist feedback condition (+ 5.9%, P < 0.05). CONCLUSION: Our results showed that the MIVC force can be influenced by different visuals feedback, such as force or EMG feedbacks. Moreover, these results suggested that the type of feedback employed could modify the EMG-to-force relationships. Finally, EMG biofeedback could represent an interesting tool to optimize motor strategies. But in the purpose of performing the highest strength independently of the strategy, the force feedback should be recommended.

Effects on Firefighters' Nocturnal Cardiac Autonomic Activity and Sleep Quality of On-Call Nights With and Without Simulated Firefighting Interventions.

OBJECTIVE: To examine the effects on firefighters' nocturnal cardiac autonomic activity and sleep quality of one on-call night without intervention and one on-call night with intervention. METHODS: Thirteen firefighters completed three experimental nights: a control night (CON), an on-call night without intervention (0-INTER), an on-call night with one simulated intervention (1-INTER). Sleep parameters were determined from nocturnal heart rate variability (HRV), objective and subjective sleep quality. RESULTS: Derived parasympathetic HRV indices were higher in CON compared with 0-INTER and 1-INTER (P < 0.05). Subjective sleep quality and total sleep time were decreased in 1-INTER compared with CON and 0-INTER (P < 0.01). DISCUSSION: These results revealed that for firefighters, being on-call during the night with and without interventions disturbs cardiac autonomic activity. Objective and subjective sleep quality were disrupted when on-call nights were interrupted by simulated firefighting interventions.

Cardiac Parasympathetic Reactivation Following Small-Sided Games, Repeated Sprints and Circuit Training in Elite Handball Players.

To compare acute parasympathetic reactivation following usual training exercises, the acute post-exercise heart rate (HR) and heart rate variability (HRV) were analysed. Fourteen elite male handball players completed three separate sessions of 16-min small-sided games (SSGs), repeated sprints (RSs) consisting of two sets of six repetitions of a 25-m sprint with a 180° change of direction (12.5 m + 12.5 m) every 25 s and 40 min of handball-specific circuit training (CT, one brief action every 40 s). The HR was recorded during the exercises; HRV was assessed 10 min before and after exercise. The exercise HR was higher for SSGs than RSs and it was higher for RSs than CT. Comparison of the baseline and acute post-exercise HRV values showed that parasympathetic indices decreased following SSG (p < 0.01 - p < 0.0001; large effect size) and RS (p < 0.05 -p < 0.01; large effect size) interventions. For CT, recovery values remained similar to the baseline (small effect size). The comparison of the acute recovery period between exercise modalities showed that the root mean square of the successive differences (RMSSD) was lower for SSGs than RSs and CT. No difference in any HRV indices was observed between RSs and CT. Time-varying of RMSSD for successive 30 s segments during the 10 min recovery period showed lower values for SSGs than CT for all tested points; the progressive increase in the beat-to-beat interval was similar for all interventions. In conclusion, SSGs caused the greatest post-exercise vagal disruption and it is likely that CT is the exercise modality that least delays over-all recovery. These results might help coaches design better training sessions by understanding athletes' recovery status after completing their conditioning exercises.

Physiological responses and parasympathetic reactivation in rescue interventions: The effect of the breathing apparatus.

This study aimed to assess the effect of wearing a breathing apparatus during a simulated rescue intervention on psychophysiological responses and parasympathetic reactivation of firefighters. Thirty-four firefighters participated in this study which consisted of four experimental sessions conducted randomly: a maximal fitness test and three rescue interventions performed (a) with personal protective clothing (PPC); (b) with PPC and the full self-contained breathing apparatus (SCBA), including cylinder, full-face piece, and breathing regulator; and (c) with PPC and only the cylinder of the self-contained breathing apparatus (SCBAc). Physiological (heart rate [HR], breathing frequency [BF]) and perceptual (rating of perceived exertion [RPE]) responses were continuously collected during the three rescue interventions. Parasympathetic reactivation was assessed using HR recovery and variability indexes after experimental sessions. HR responses ranged between 63% and 95% of HRmax , and BF responses ranged between 22 and 55 breaths/min for the different activity tasks. Parasympathetic reactivation indexes were similar for the rescue interventions but lower than after the intermittent fitness test (P = 0.016 - P < 0.0001). Mean HR for both SCBAc (83.2 ± 4.1%HRmax ) and SCBA (83.1 ± 5.2%HRmax ) was higher in comparison with PPC (79.5 ± 5.3%HRmax ). RPE was higher for SCBA than for SCBAc which was higher than PPC. Mean BF for SCBA (34 breaths/min) was lower than PPC (40 breaths/min) and SCBAc (43 breaths/min). Based on HR, BF, and RPE, rescue interventions seem to be psychologically and physiologically stressful. Parasympathetic reactivation after PCC, SCBA, and SCBAc suggests that these conditions induce higher cardiac stress than the maximal fitness test. The study showed that SCBA increased psychophysiological perturbations.