The interactive effect of sustained sleep restriction and resistance exercise on skeletal muscle transcriptomics in young females.

Both sleep loss and exercise regulate gene expression in skeletal muscle, yet little is known about how the interaction of these stressors affects the transcriptome. The aim of this study was to investigate the effect of nine nights of sleep restriction (SR), with repeated resistance exercise (REx) sessions, on the skeletal muscle transcriptome of young, trained females. Ten healthy females aged 18-35 yr old undertook a randomized cross-over study of nine nights of SR (5 h time in bed) and normal sleep (NS; ≥7 h time in bed) with a minimum 6-wk washout. Participants completed four REx sessions per condition (days 3, 5, 7, and 9). Muscle biopsies were collected both pre- and post-REx on days 3 and 9. Gene and protein expression were assessed by RNA sequencing and Western blot, respectively. Three or nine nights of SR had no effect on the muscle transcriptome independently of exercise. However, close to 3,000 transcripts were differentially regulated (false discovery rate < 0.05) 48 h after the completion of three resistance exercise sessions in both NS and SR conditions. Only 39% of downregulated genes and 18% of upregulated genes were common between both conditions, indicating a moderating effect of SR on the response to exercise. SR and REx interacted to alter the enrichment of skeletal muscle transcriptomic pathways in young, resistance-trained females. Performing exercise when sleep restricted may not provide the same adaptive response for individuals as if they were fully rested.NEW & NOTEWORTHY This study investigated the effect of nine nights of sleep restriction, with repeated resistance exercise sessions, on the skeletal muscle transcriptome of young, trained females. Sleep restriction and resistance exercise interacted to alter the enrichment of skeletal muscle transcriptomic pathways in young, resistance-trained females. Performing exercise when sleep restricted may not provide the same adaptive response for individuals as if they were fully rested.

Alpha-lactalbumin and sleep: A systematic review.

Insufficient sleep is a growing global problem, with poor sleep associated with many negative health and performance outcomes. Previous reviews investigating the effect of diet on sleep have highlighted the amino acid tryptophan as a promising sleep-promoting nutrient, with the richest food source of tryptophan, ⍺-lactalbumin, requiring further investigation. Therefore, this systematic review aimed to review the existing evidence of association between ⍺-lactalbumin and sleep. Four electronic databases (CINAHL Complete, Embase, MEDLINE Complete, and SPORTDiscus with Full Text) were searched from database inception to March 2023, with primary research articles included if they contained α-lactalbumin as an independent variable, an outcome measure of sleep or sleepiness, and participants were ≥ 18 years old. Eight studies were reviewed, with four studies recruiting athletic populations (50%) and four recruiting healthy participants (50%). Sleep or sleepiness was measured objectively in six studies (75%), with two studies employing polysomnography and four utilizing actigraphy to assess sleep. Across the studies, 20-60 g of ⍺-lactalbumin was supplemented, with five studies (63%) observing a positive association between α-lactalbumin and sleep. Sleep-onset latency was the primary sleep metric improved following evening supplementation of α-lactalbumin (≤ 3.5 hr pre-sleep), with no studies observing any negative associations with sleep. Data from this review suggest that individuals that have difficulty initiating sleep may benefit most from pre-sleep α-lactalbumin supplementation. Further research is required to establish the effect that α-lactalbumin has on sleep architecture, through the use of more comprehensive sleep analysis tools such as portable electroencephalography or polysomnography, in combination with stringent dietary controls.

Sleep of recruits throughout basic military training and its relationships with stress, recovery, and fatigue.

OBJECTIVE: Studies in basic military training (BMT) examining sleep are largely cross-sectional, and do not investigate relationships between sleep, stress, recovery and fatigue. The aims of this study were to (1a) quantify changes in recruits' sleep quantity and quality over 12 weeks of BMT; (1b) quantify changes in recruits' perceptions of stress, fatigue and recovery over BMT; and (2) explore relationships between sleep, and perceptions of stress, fatigue and recovery. METHODS: 45 recruits (37 male; 8 female, age: 25.2 ± 7.2 years, height: 176.2 ± 10.0 cm, mass: 76.8 ± 15.0 kg) wore ActiGraph GT9X's for 12 weeks of BMT, collecting sleep duration, efficiency and awakenings. Subjective sleep quality, fatigue were measured daily, with stress and recovery measured weekly. Multi-level models assessed relationships between sleep, and stress, recovery, and fatigue. RESULTS: Objective daily means for sleep duration were 6.3 h (± 1.2 h) and 85.6% (± 5.5%) for sleep efficiency. Main effects were detected for all mean weekly values (p < 0.05). Sleep quality showed the strongest relationships with stress, recovery and fatigue. The best model to explain relationships between, stress, recovery and fatigue, included sleep quality, sleep duration, sleep efficiency and awakenings. CONCLUSIONS: The reported mean sleep duration of 6.3 h per night may negatively impact training outcomes across BMT. Combining both subjective and objective measures of sleep best explained relationships between sleep metrics stress, fatigue and recovery. Perceived sleep quality was most strongly related to change in stress, recovery, or post-sleep fatigue.

Evening Whey Protein Intake, Rich in Tryptophan, and Sleep in Elite Male Australian Rules Football Players on Training and Nontraining Days.

OBJECTIVES: To investigate the effect of evening whey protein supplementation, rich in tryptophan, on sleep in elite male Australian Rules Football players. DESIGN: Double-blinded, counterbalanced, randomized, cross-over study. METHODS: Sleep was assessed using wrist activity monitors and sleep diaries in 15 elite male Australian Football League players on two training and nontraining days following evening consumption of an isocaloric whey protein supplement or placebo in preseason. A 5-day preintervention period was implemented to determine habitual dietary intake and baseline sleep measures. These habitual data were used to inform the daily dietary intake and timing of ingestion of the evening whey protein supplement or placebo on the intervention days. The whey protein supplement or placebo was consumed 3 hr prior to habitual bedtime. RESULTS: Separate one-way repeated-measures analyses of covariance revealed no differences between the whey protein supplement and the placebo on sleep duration, sleep onset latency, sleep efficiency, or wake after sleep onset on either training or nontraining days. CONCLUSIONS: Evening whey protein supplementation, rich in tryptophan, does not improve acute sleep duration or quality in elite male Australian Football League players. However, elite athletes may be able to ingest a high protein/energy intake close to bedtime without impairing sleep, which is important for athlete recovery. Future research should investigate the effect of evening protein intake, high in tryptophan, on sleep duration and quality, including sleep staging during periods of restricted sleep and in poor-sleeping athletes.

Recovery of Cognitive Performance Following Multi-Stressor Military Training.

OBJECTIVE: This project aimed to assess the impact of an 8-day military training exercise on cognitive performance, and track its recovery in periods of reduced training load and partially restored sleep. BACKGROUND: Military personnel often work in challenging multi-stressor environments, where sleep loss is inevitable. Sleep loss can impair multiple cognitive domains, which can have disastrous consequences in military contexts. METHOD: A total of 57 male and female soldiers undergoing the Australian Army combat engineer Initial Employment Training course were recruited and tracked over a 16-day study period which included an 8-day field-based military training exercise. Cognitive performance was assessed via a computerised battery at seven time points across four sequential study periods; 1) baseline (PRE), 2) military field training exercise which included total sleep deprivation (EX-FIELD), 3) training exercise at simulated base with restricted sleep opportunities (EX-BASE), and 4) a 3-day recovery period (REC). Subjective load, fatigue, and sleep were evaluated continuously via questionnaire and actigraphy. RESULTS: Psychomotor speed, reaction time, visual tracking and vigilance were impaired following the EX-FIELD period (p < 0.05). The majority of affected measures recovered 2 days following EX-FIELD, being no different in EX-BASE compared to PRE. CONCLUSION: The sensitivity of the cognitive tests to sleep restriction, and recovery, indicates they can help assess operational readiness in military personnel. Future studies should explore other indicators of, and strategies to preserve, operational readiness in military personnel. APPLICATION: This study highlights the impact of work-induced fatigue on cognitive performance, and would interest authorities seeking to preserve operational readiness.

Monitoring Effects of Sleep Extension and Restriction on Endurance Performance Using Heart Rate Indices.

ABSTRACT: Roberts, SSH, Aisbett, B, Teo, W-P, and Warmington, S. Monitoring effects of sleep extension and restriction on endurance performance using heart rate indices. J Strength Cond Res 36(12): 3381-3389, 2022-Heart rate (HR) indices are useful for monitoring athlete fatigue or "readiness to perform." This study examined whether HR indices are sensitive to changes in readiness following sleep restriction (SR) and sleep extension (SE). Nine athletes completed a crossover study with 3 conditions: SR, normal sleep (NS), and SE. Each condition required completion of an endurance time trial (TT) on 4 consecutive days (D1-D4). Athletes slept habitually before D1; however, time in bed was reduced by 30% (SR), remained normal (NS), or extended by 30% (SE), on subsequent nights (D1-D3). Daily resting HR and HR variability were recorded. The maximal rate of HR increase and HR recovery was determined from a constant-load test before TTs. Exercise intensity ratios incorporating mean HR, mean power (W), and perceived exertion (RPE) were recorded at steady state during constant-load tests (W:HR SS ) and during TTs (W:HR TT , RPE:HR TT ). Compared with D4 of NS, RPE:HR TT was lower on D4 of SE ( p = 0.008)-when TT performances were faster. Compared with D1 of SR, RPE:HR TT was higher on D3 and D4 of SR ( p < 0.02). Moderate correlations were found between percentage changes in W:HR TT and changes in TT finishing time in SR ( r = -0.67, p = 0.049) and SE ( r = -0.69, p = 0.038) conditions. Intensity ratios incorporating mean HR seem sensitive to effects of sleep duration on athlete readiness to perform. When interpreting intensity ratios, practitioners should consider potential effects of prior sleep duration to determine whether sleep-promoting interventions are required (e.g., SE).

Informal management of health and safety risks associated with alarm response by Australian firefighters.

Fire-fighters use informal strategies to manage risks to health and safety during operations. It is not known whether such strategies are used during the high-risk alarm response period. The aim of this study was to determine if informal risk management strategies are employed by Australian firefighters during the alarm response procedure, and if these strategies differ between salaried and retained personnel. Forty-six metropolitan firefighters (all male; mean age 38 years ± 10 years; 22 salaried; 24 retained) participated in semi-structured group interviews. A general inductive data analysis approach revealed that firefighters use multiple informal risk management strategies. Some similar themes were reported by both salaried and retained personnel, for example leveraging team dynamics, communication about sleep and fatigue, stress adaptation, informal debriefs, and enhancing physical preparedness. These findings could be used by fire services to tailor risk management approaches during the alarm response period. Practitioner summary: Identifying informal risk management strategies firefighters use during alarm response will allow their development, refinement and dissemination, and may help other firefighters and emergency service workers to manage these risks. This qualitative study reveals multiple informal strategies that firefighters employ during alarm response to keep themselves and their team-mates safe.

Bidirectional associations between emergency nurses' occupational and leisure physical activity: An observational study.

Emergency nursing is a physically demanding occupation yet research suggests they do not meet current physical activity guidelines. Current interventions have had limited effectiveness increasing nurses' physical activity, possibly due to a failure to acknowledge physical activity in another domain (e.g., occupational). This study aimed to determine the bidirectional associations between emergency nurses' occupational and leisure time activity levels on work days. Data from 49 emergency nurses (44 females and five males) wearing an ActiGraph accelerometer and completing work and sleep diaries for up to four weeks were analysed. An activPAL inclinometer was simultaneously worn by 41 nurses. Time spent in different activity levels and postural positions during work and leisure time were determined. Multi-level analyses examined bidirectional associations between emergency nurses' activity levels at work and during their leisure time. Moderate- to vigorous-intensity physical activity prior to a morning shift was associated with more sedentary time and less physical activity at work. Conversely, occupational stepping time was associated with more sitting, standing and stepping time after each shift. These findings provide critical insights into how and when researchers should intervene to facilitate adequate recovery for nurses' post-shift and balance competing demands on their leisure time.

The accumulation of, and associations between, nurses' activity levels within their shift in the emergency department.

The aim of this study was to examine emergency nurses' activity levels and associations between hourly activity levels within-shifts. Fifty emergency nurses (45 females, 5 males) wore ActiGraph accelerometers and completed work diaries for up to 4 weeks. A sub-group (n = 42) also wore activPALs. Multilevel analyses examined temporal associations between hourly periods. In any hourly period, increased time spent in moderate- to vigorous-intensity physical activity (MVPA) was associated with less time spent in MVPA in the following hourly period. In any afternoon hourly period, increased time spent in MVPA was associated with more time spent in light-intensity physical activity in the following hourly period. No other associations were significant. Emergency nurses maintain activity levels within-shifts, except when more time spent in MVPA was associated with less time spent in MVPA in the following hour; a potential recovery strategy. Future research should determine how emergency nurses maintain their activity levels within-shifts. Practitioner Summary: Emergency nursing is physically demanding; however, it is unknown how active they are during hourly periods within-shifts. Emergency nurses' activity levels were maintained within hourly periods of a shift. Except for an increase in MVPA in 1 h was associated with a decrease in MVPA in the following hour. Abbreviations: CPR: cardiopulmonary resusitation; LPA: light-intensity physical activity; MPA: moderate-intenisty physical activity; MVPA: moderate- to vigorous-intensity physical activity; SED: sedentary.

Salivary cortisol profiles of on-call from home fire and emergency service personnel.

Working on-call with a night call resulted in a depressed (lower) cortisol awakening response (CAR) peak and post-awakening cortisol area under the curve with respect to ground (AUCG) the following day compared to when off-call. This may be due to exposure to noise, physical exertion, and stressful events during night callouts. There was no anticipatory effect to working on-call in any of the cortisol measures examined. This study, of male fire and emergency service workers who operate on-call from home, had two aims: (1) examine CAR and diurnal cortisol profile following a night on-call with a call, on-call without a call, and off-call; and, (2) explore whether there is an anticipatory effect of working on-call from home on diurnal cortisol profiles. Participants wore activity monitors, completed sleep and work diaries and collected seven saliva samples a day (0 min, 30 min, 60 min, 3 h, 6 h, 9 h, and 12 h after final awakening) for one week. CAR peak, reactivity and area under the curve with respect to increase (AUCI), post-awakening cortisol AUCG, diurnal cortisol slope and AUCG, and mean 12-h cortisol concentrations were calculated. The final analysis included 26 participants for Aim 1 (22 off-call nights, 68 nights on-call without a call, and 20 nights on-call with a call) and 14 participants for Aim 2 (25 days leading up to a night off-call and 92 days leading up to a night on-call). Generalized estimating equations models were constructed for each variable of interest. Aim 1: CAR peak and post-awakening cortisol AUCG were 8.2 ± 3.4 nmol/L and 5.7 ± 2.4 units lower, respectively, following a night on-call with a call compared to an off-call night. Aim 2: the day before a night on-call was not a significant predictor in any model. The lower CAR peak and post-awakening cortisol AUCG following a night on-call with a call compared to following an off-call night may be due to exposure to noise, physical exertion, and stressful events during night callouts. The lack of difference between the day before a night on-call and the day before an off-call night suggests there may not be an anticipatory effect on cortisol when on-call from home.

Effects of total sleep deprivation on endurance cycling performance and heart rate indices used for monitoring athlete readiness.

This study investigated effects of total sleep deprivation on self-paced endurance performance, and heart rate (HR) indices of athletes' "readiness to perform". Endurance athletes (n = 13) completed a crossover experiment comprising a normal sleep (NS) and sleep deprivation (SD) condition. Each required completion of an endurance time-trial (TT) on consecutive days (D1, D2) separated by normal sleep or total sleep deprivation. Finishing time, perceived exertion (RPE), mood, psychomotor vigilance (PVT), and HR responses were assessed. Time on D2 of SD was 10% slower than D2 of NS (64 ± 7 vs 59 ± 4 min, P < 0.01), and 11% slower than D1 of SD (58 ± 5 min, P < 0.01). Subjective to objective (RPE:mean HR) intensity ratio was higher on D2 of SD compared with D2 of NS and D1 of SD (P < 0.01). Mood disturbance and PVT mean response time increased on D2 of SD compared with D2 of NS and D1 of SD. Anaerobic threshold and change in TT time were correlated (R = -0.73, P < 0.01). Sleep helps to optimise endurance performance. Subjective to objective intensity ratios appear sensitive to effects of sleep on athletes' readiness. Research examining more subtle sleep manipulation is required.

Adding sleep restriction to the equation: impact on wildland firefighters' work performance and physiology in hot conditions.

PURPOSE: To examine the effects of sleep restriction on firefighters' physical task performance, physical activity, and physiological and perceived exertion during simulated hot wildfire conditions. METHODS: 31 firefighters were randomly allocated to either the hot (n = 18, HOT; 33 °C, 8-h sleep opportunity) or hot and sleep restricted (n = 13, HOT + SR; 33 °C, 4-h sleep opportunity) condition. Intermittent, self-paced work circuits of six firefighting tasks were performed for 3 days. Firefighters self-reported ratings of perceived exertion. Heart rate, core temperature, and physical activity were measured continuously. Fluids were consumed ad libitum, and all food and fluids consumed were recorded. Urine volume and urine specific gravity (USG) were analysed and sleep was assessed using polysomnography (PSG). RESULTS: There were no differences between the HOT and HOT + SR groups in firefighters' physical task performance, heart rate, core temperature, USG, or fluid intake. Ratings of perceived exertion were higher (p < 0.05) in the HOT + SR group for two of the six firefighting tasks. The HOT group spent approximately 7 min more undertaking moderate physical activity throughout the 2-h work circuits compared to the HOT + SR group. CONCLUSION: Two nights of sleep restriction did not influence firefighters' physical task performance or physiological responses during 3 days of simulated wildfire suppression. Further research is needed to explore firefighters' pacing strategies during real wildfire suppression.

Job task characteristics of Australian emergency services volunteers during search and rescue operations.

Search and rescue operations are necessary in locating, assisting and recovering individuals lost or in distress. In Australia, land-based search and rescue roles require a range of physically demanding tasks undertaken in dynamic and challenging environments. The aim of the current research was to identify and characterise the physically demanding tasks inherent to search and rescue operation personnel within Australia. These aims were met through a subjective job task analysis approach. In total, 11 criterion tasks were identified by personnel. These tasks were the most physically demanding, frequently occurring and operationally important tasks to these specialist roles. Muscular strength was the dominant fitness component for 7 of the 11 tasks. In addition to the discrete criterion tasks, an operational scenario was established. With the tasks and operational scenario identified, objective task analysis procedures can be undertaken so that practitioners can implement evidence-based strategies, such as physical selection procedures and task-based physical training programs, commensurate with the physical demands of search and rescue job roles. Practitioner Summary: The identification of physically demanding tasks amongst specialist emergency service roles predicates health and safety strategies which can be incorporated into organisations. Knowledge of physical task parameters allows employers to mitigate injury risk through the implementation of strategies modelled on the precise physical demands of the role.

Whole-body vibration and occupational physical performance: a review.

INTRODUCTION: In the occupational environment, there are a considerable number of stressors that can affect physical performance in job tasks. Whole-body vibration (WBV), which arises from vehicle transit, is one such stressor that has been demonstrated to alter human function in several ways. This study identifies the known physical changes to human function which result from WBV, to comment on changes which may translate to performance in physically demanding occupational tasks. METHODS: A systematic review is performed on the literature relating to changes in the neuromuscular, physiological and biomechanical properties of the human body, when exposed to WBV. Selection criteria are constructed to synthesise articles which strictly relate to in-vehicle WBV and physical responses. RESULTS: In total, 29 articles were identified which satisfied the criteria for inclusion. A range of physical responses produced from WBV are presented; however, little consistency exists in study design and the responses reported. DISCUSSION: Given the inconsistency in the reported responses, the precise changes to human function remain unknown. However, there is sufficient evidence to warrant the design of studies which investigate occupationally relevant physical performance changes following WBV.

The impact of sleep restriction while performing simulated physical firefighting work on cortisol and heart rate responses.

PURPOSE: Physical work and sleep restriction are two stressors faced by firefighters, yet the combined impact these demands have on firefighters' acute stress responses is poorly understood. The purpose of the present study was to assess the effect firefighting work and sleep restriction have on firefighters' acute cortisol and heart rate (HR) responses during a simulated 3-day and 2-night fire-ground deployment. METHODS: Firefighters completed multiple days of simulated physical work separated by either an 8-h (control condition; n = 18) or 4-h sleep opportunity (sleep restriction condition; n = 17). Salivary cortisol was sampled every 2 h, and HR was measured continuously each day. RESULTS: On day 2 and day 3 of the deployment, the sleep restriction condition exhibited a significantly higher daily area under the curve cortisol level and an elevated cortisol profile in the afternoon and evening when compared with the control condition. Firefighters' HR decreased across the simulation, but there were no significant differences found between conditions. CONCLUSION: Findings highlight the protective role an 8-h sleep opportunity between shifts of firefighting work has on preserving normal cortisol levels when compared to a 4-h sleep opportunity which resulted in elevated afternoon and evening cortisol. Given the adverse health outcomes associated with chronically high cortisol, especially later in the day, future research should examine how prolonged exposure to firefighting work (including restricted sleep) affects firefighters' cortisol levels long term. Furthermore, monitoring cortisol levels post-deployment will determine the minimum recovery time firefighters need to safely return to the fire-ground.

Acute Psychophysiological Relationships Between Mood, Inflammatory and Cortisol Changes in Response to Simulated Physical Firefighting Work and Sleep Restriction.

This study examined how changes in wildland firefighters' mood relate to cytokine and cortisol levels in response to simulated physical firefighting work and sleep restriction. Firefighters completed 3 days of simulated wildfire suppression work separated by an 8-h (control condition; n = 18) or 4-h sleep opportunity (sleep restriction condition; n = 17) each night. Firefighters' mood was assessed daily using the Mood Scale II and Samn-Perelli fatigue scale. Participants also provided samples for the determination of salivary cortisol and pro- (IL-6, IL-8, IL-1ß, TNF-α) and anti-inflammatory (IL-4, IL-10) cytokine levels. An increase in the positive mood dimension Happiness was related to a rise in IL-8 and TNF-α in the sleep restriction condition. A rise in the positive mood dimension Activation among sleep restricted firefighters was also related to higher IL-6 levels. An increase in the negative mood dimension Fatigue in the sleep restriction condition was associated with increased IL-6, TNF-α, IL-10 and cortisol levels. In addition, an increase in Fear among sleep restricted firefighters was associated with a rise in TNF-α. Elevated positive mood and immune activation may reflect an appropriate response by the firefighters to these stressors. To further understand this relationship, subsequent firefighting-based research is needed that investigates whether immune changes are a function of affective arousal linked to the expression of positive moods. Positive associations between negative mood and inflammatory and cortisol levels to physical work and restricted sleep provide useful information to fire agencies about subjective fire-ground indicators of physiological changes.

The acute physiological stress response to an emergency alarm and mobilization during the day and at night.

The purpose of this study was to investigate the acute physiological stress response to an emergency alarm and mobilization during the day and at night. Sixteen healthy males aged 25 ± 4 years (mean ± SD) spent four consecutive days and nights in a sleep laboratory. This research used a within-participants design with repeated measures for time, alarm condition (alarm or control), and trial (day or night). When an alarm sounded, participants were required to mobilize immediately. Saliva samples for cortisol analysis were collected 0 min, 15 min, 30 min, 45 min, 60 min, 90 min, and 120 min after mobilization, and at corresponding times in control conditions. Heart rate was measured continuously throughout the study. Heart rate was higher in the day (F(20,442) = 9.140, P < 0.001) and night (F(23,459) = 8.356, P < 0.001) alarm conditions compared to the respective control conditions. There was no difference in saliva cortisol between day alarm and day control conditions. Cortisol was higher (F(6,183) = 2.450, P < 0.001) following the night alarm and mobilization compared to the night control condition. The magnitude of difference in cortisol between night control and night alarm conditions was greater (F(6,174) = 4.071, P < 0.001) than the magnitude of difference between the day control and day alarm conditions. The augmented heart rate response to the day and night alarms supports previous observations in field settings. Variations in the cortisol responses between conditions across the day and night may relate to differences in participants' ability to interpret the alarm when sleeping versus when awake.

The effects of military body armour on trunk and hip kinematics during performance of manual handling tasks (.).

Musculoskeletal injuries are reported as burdening the military. An identified risk factor for injury is carrying heavy loads; however, soldiers are also required to wear their load as body armour. To investigate the effects of body armour on trunk and hip kinematics during military-specific manual handling tasks, 16 males completed 3 tasks while wearing each of 4 body armour conditions plus a control. Three-dimensional motion analysis captured and quantified all kinematic data. Average trunk flexion for the weightiest armour type was higher compared with control during the carry component of the ammunition box lift (p < 0.001) and sandbag lift tasks (p < 0.001). Trunk rotation ROM was lower for all armour types compared with control during the ammunition box place component (p < 0.001). The altered kinematics with body armour occurred independent of armour design. In order to optimise armour design, manufacturers need to work with end-users to explore how armour configurations interact with range of personal and situational factors in operationally relevant environments. Practitioner Summary: Musculoskeletal injuries are reported as burdening the military and may relate to body armour wear. Body armour increased trunk flexion and reduced trunk rotation during military-specific lifting and carrying tasks. The altered kinematics may contribute to injury risk, but more research is required.

Fighting fire and fatigue: sleep quantity and quality during multi-day wildfire suppression.

This study examined firefighters' sleep quantity and quality throughout multi-day wildfire suppression, and assessed the impact of sleep location, shift length, shift start time and incident severity on these variables. For 4 weeks, 40 volunteer firefighters' sleep was assessed using wrist actigraphy. Analyses revealed that the quantity of sleep obtained on fire days was restricted, and pre- and post-sleep fatigue ratings were higher, compared to non-fire days. On fire days, total sleep time was less when: (i) sleep location was in a tent or vehicle, (ii) shifts were greater than 14 h and (iii) shifts started between 05:00 and 06:00 h. This is the first empirical investigation providing objective evidence that firefighters' sleep is restricted during wildfire suppression. Furthermore, sleep location, shift length and shift start time should be targeted when designing appropriate controls to manage fatigue-related risk and preserve firefighters' health and safety during wildfire events. Practitioner Summary: During multi-day wildfire suppression, firefighters' sleep quantity was restricted, and pre- and post-sleep fatigue ratings were higher, compared to non-fire days. Furthermore, total sleep time was less when: (i) sleep occurred in a tent/vehicle, (ii) shifts were >14 h and (iii) shifts started between 05:00 and 06:00 h.

Associations between firefighters' physical activity across multiple shifts of wildfire suppression.

The aim of this study was to examine the associations between firefighters' physical activity levels across consecutive wildfire suppression shifts and to determine whether sleep duration moderated these associations. Forty volunteer firefighters (31 males, 9 females) wore an activity monitor to concurrently measure physical activity and sleep duration. Sedentary time and time spent in light- (LPA), moderate- (MPA), and vigorous-intensity physical activity (VPA) during each shift were determined using monitor-specific cut points. During any given shift, every additional 60 min spent in LPA was associated with 7.2 min more LPA and 27.6 min MPA the following shift. There were no other significant positive or negative associations. No significant moderating effect of total sleep time was observed. Firefighters are able to maintain and/or increase their physical activity intensity between consecutive shifts. Further research is needed to understand firefighters pacing and energy conservation strategies during emergency wildfire deployments. Practitioner Summary: To examine associations between firefighters' physical activity levels across consecutive shifts during a multi-day emergency wildfire and determine whether sleep duration moderated these associations. Firefighters are able to maintain and/or increase their physical activity intensity between consecutive shifts. No significant moderating effect of total sleep time was observed.