Brad Aisbett

The Effect of Body Armor on Performance, Thermal Stress, and Exertion: A Critical Review

Armed forces worldwide utilize some form of body armor as part of their personal protective system. This is particularly essential in recent times because of the increased sophistication of weapons employed during modern warfare and the advent of unconventional combat methods (such as the increased use of improvised explosive devices). There is some evidence to show, however, that the usage of military body armor impairs physical performance. This review of the literature will focus on the effect of body armor on the performance of, and physiological and subjective responses during, military-style physical tasks. Because of the paucity of research investigating body armor, this review will also draw upon more generalized personal protective clothing and equipment literature from a range of physically demanding occupations (i.e., firefighting and other emergency services). The review will conclude with suggested directions for future research in this area.

Reliability and variability of day-to-day vault training measures in artistic gymnastics

Inter-day training reliability and variability in artistic gymnastics vaulting was determined using a customised infra-red timing gate and contact mat timing system. Thirteen Australian high performance gymnasts (eight males and five females) aged 11–23 years were assessed during two consecutive days of normal training. Each gymnast completed a number of vault repetitions per daily session. Inter-day variability of vault run-up velocities (at ‐18 to ‐12 m, ‐12 to ‐6 m, ‐6 to ‐2 m, and ‐2 to 0 m from the nearest edge of the beat board), and board contact, pre-flight, and table contact times were determined using mixed modelling statistics to account for random (within-subject variability) and fixed effects (gender, number of subjects, number of trials). The difference in the mean (Mdiff) and Cohens effect sizes for reliability assessment and intra-class correlation coefficients, and the coefficient of variation percentage (CV%) were calculated for variability assessment. Approach velocity (‐18 to ‐2 m, CV = 2.4–7.8%) and board contact time (CV = 3.5%) were less variable measures when accounting for day-to-day performance differences, than pre-flight time (CV = 17.7%) and table contact time (CV = 20.5%). While pre-flight and table contact times are relevant training measures, approach velocity and board contact time are more reliable when quantifying vaulting performance.

Visual guidance during competition performance and run‐through training in long jumping

To ensure precise foot placement on the take-off board, long jumpers visually regulate their stride pattern during their run-up. A relationship between how much visual guidance they use and the horizontal distance they jump has not, however, been quantified. Run-up precision is often practiced using run-throughs, which exclude the take-off and, therefore, the high physical stress of the complete long jump. The validity with which this common training method simulates the long jump approach remains, however, to be verified. Four state-standard long jumpers and two heptathletes completed two sessions, each comprising six runthroughs and six competition long jumps. A 50 Hz video camera was manually panned from an elevated platform to film each trial, to enable subsequent gait characteristic evaluations. Linear regression analyses identified that a longer visual regulation phase, measured in time, distance or number of strides, was a key predictor of long jump distance. The number of strides that were visually regulated during the long jump approach was, accordingly, positively correlated with long jump distance (r = 0.67, p = 0.001). The amount of visual regulation used during run-throughs was, however, less than half (p = 0.001) of that observed during long jump approaches. Our results should compel long jump coaches to supplement run-through training with additional visual guidance exercises, to encourage their athletes to visually regulate more of their long jump approach.

Influence of All-Out and Fast Start on 5-min Cycling Time Trial Performance

PURPOSE To examine the influence of two different fast-start pacing strategies on performance and oxygen consumption (VO2) during cycle ergometer time trials lasting ∼5 min. METHODS Eight trained male cyclists performed four cycle ergometer time trials whereby the total work completed (113 ± 11.5 kJ; mean ± SD) was identical to the better of two 5-min self-paced familiarization trials. During the performance trials, initial power output was manipulated to induce either an all-out or a fast start. Power output during the first 60 s of the fast-start trial was maintained at 471.0 ± 48.0 W, whereas the all-out start approximated a maximal starting effort for the first 15 s (mean power: 753.6 ± 76.5 W) followed by 45 s at a constant power output (376.8 ± 38.5 W). Irrespective of starting strategy, power output was controlled so that participants would complete the first quarter of the trial (28.3 ± 2.9 kJ) in 60 s. Participants performed two trials using each condition, with their fastest time trial compared. RESULTS Performance time was significantly faster when cyclists adopted the all-out start (4 min 48 s ± 8 s) compared with the fast start (4 min 51 s ± 8 s; P < 0.05). The first-quarter VO2 during the all-out start trial (3.4 ± 0.4 L·min(-1)) was significantly higher than during the fast-start trial (3.1 ± 0.4 L·min(-1); P < 0.05). After removal of an outlier, the percentage increase in first-quarter VO2 was significantly correlated (r = -0.86, P < 0.05) with the relative difference in finishing time. CONCLUSIONS An all-out start produces superior middle distance cycling performance when compared with a fast start. The improvement in performance may be due to a faster VO2 response rather than time saved due to a rapid acceleration.

Validity of an upper-body-mounted accelerometer to measure peak vertical and resultant force during running and change-of-direction tasks.

This study assessed the validity of a tri-axial accelerometer worn on the upper body to estimate peak forces during running and change-of-direction tasks. Seventeen participants completed four different running and change-of-direction tasks (0°, 45°, 90°, and 180°; five trials per condition). Peak crania-caudal and resultant acceleration was converted to force and compared against peak force plate ground reaction force (GRF) in two formats (raw and smoothed). The resultant smoothed (10 Hz) and crania-caudal raw (except 180°) accelerometer values were not significantly different to resultant and vertical GRF for all running and change-of-direction tasks, respectively. Resultant accelerometer measures showed no to strong significant correlations (r = 0.00–0.76) and moderate to large measurement errors (coefficient of variation [CV] = 11.7–23.9%). Crania-caudal accelerometer measures showed small to moderate correlations (r = − 0.26 to 0.39) and moderate to large measurement errors (CV = 15.0–20.6%). Accelerometers, within integrated micro-technology tracking devices and worn on the upper body, can provide a relative measure of peak impact force experienced during running and two change-of-direction tasks (45° and 90°) provided that resultant smoothed values are used.

Sleep restriction during simulated wildfire suppression: Effect on physical task performance

Objectives To examine the effects of sleep restriction on firefighters’ physical task performance during simulated wildfire suppression. Methods Thirty-five firefighters were matched and randomly allocated to either a control condition (8-hour sleep opportunity, n = 18) or a sleep restricted condition (4-hour sleep opportunity, n = 17). Performance on physical work tasks was evaluated across three days. In addition, heart rate, core temperature, and worker activity were measured continuously. Rate of perceived and exertion and effort sensation were evaluated during the physical work periods. Results There were no differences between the sleep-restricted and control groups in firefighters’ task performance, heart rate, core temperature, or perceptual responses during self-paced simulated firefighting work tasks. However, the sleep-restricted group were less active during periods of non-physical work compared to the control group. Conclusions Under self-paced work conditions, 4 h of sleep restriction did not adversely affect firefighters’ performance on physical work tasks. However, the sleep-restricted group were less physically active throughout the simulation. This may indicate that sleep-restricted participants adapted their behaviour to conserve effort during rest periods, to subsequently ensure they were able to maintain performance during the firefighter work tasks. This work contributes new knowledge to inform fire agencies of firefighters’ operational capabilities when their sleep is restricted during multi-day wildfire events. The work also highlights the need for further research to explore how sleep restriction affects physical performance during tasks of varying duration, intensity, and complexity.

Validity and relevance of the pack hike wildland firefighter work capacity test: a review

Fighting wildland fire is a physically demanding occupation. Wildland firefighters need to be physically fit to work safely and productively. To determine whether personnel are fit for duty, many firefighting agencies employ physical competency tests, such as the pack hike test (PHT). The PHT involves a 4.83-km hike over level terrain carrying a 20.4-kg pack within a 45-min period. The PHT was devised to test the job readiness of US wildland firefighters but is also currently used by some fire agencies in Australia and Canada. This review discusses the history and development of the PHT with emphasis on the process of test validation. Research-based training advice for the PHT is given, as well as discussion of the risks associated with completing the PHT. Different versions and modifications to the PHT have emerged in recent years and these are discussed with regard to their validity. Finally, this review addresses the relevance and validity of the PHT for Australian and Canadian wildland firefighters. Statement of Relevance: This paper reviews the history, development and validity of the PHT, an internationally recognised and utilised wildland firefighter work capacity test. It is concluded that while the PHT has general content validity for US wildland firefighters, verification of its reliability, criterion and construct validity is still needed.

The impact of sleep restriction and simulated physical firefighting work on acute inflammatory stress responses

Objectives This study investigated the effect restricted sleep has on wildland firefighters’ acute cytokine levels during 3 days and 2 nights of simulated physical wildfire suppression work. Methods Firefighters completed multiple days of physical firefighting work separated by either an 8-h (Control condition; n = 18) or 4-h (Sleep restriction condition; n = 17) sleep opportunity each night. Blood samples were collected 4 times a day (i.e., 06:15, 11:30, 18:15, 21:30) from which plasma cytokine levels (IL-6, IL-8, IL-1β, TNF-α, IL-4, IL-10) were measured. Results The primary findings for cytokine levels revealed a fixed effect for condition that showed higher IL-8 levels among firefighters who received an 8-h sleep each night. An interaction effect demonstrated differing increases in IL-6 over successive days of work for the SR and CON conditions. Fixed effects for time indicated that IL-6 and IL-4 levels increased, while IL-1β, TNF-α and IL-8 levels decreased. There were no significant effects for IL-10 observed. Conclusion Findings demonstrate increased IL-8 levels among firefighters who received an 8-h sleep when compared to those who had a restricted 4-h sleep. Firefighters’ IL-6 levels increased in both conditions which may indicate that a 4-h sleep restriction duration and/or period (i.e., 2 nights) was not a significant enough stressor to affect this cytokine. Considering the immunomodulatory properties of IL-6 and IL-4 that inhibit pro-inflammatory cytokines, the rise in IL-6 and IL-4, independent of increases in IL-1β and TNF-α, could indicate a non-damaging response to the stress of simulated physical firefighting work. However, given the link between chronically elevated cytokine levels and several diseases, further research is needed to determine if firefighters’ IL-8 and IL-6 levels are elevated following repeated firefighting deployments across a fire season and over multiple fire seasons.

Effects of work-related sleep restriction on acute physiological and psychological stress responses and their interactions: A review among emergency service personnel.

Emergency work can expose personnel to sleep restriction. Inadequate amounts of sleep can negatively affect physiological and psychological stress responses. This review critiqued the emergency service literature (e.g., firefighting, police/law enforcement, defense forces, ambulance/paramedic personnel) that has investigated the effect of sleep restriction on hormonal, inflammatory and psychological responses. Furthermore, it investigated if a psycho-physiological approach can help contextualize the significance of such responses to assist emergency service agencies monitor the health of their personnel. The available literature suggests that sleep restriction across multiple work days can disrupt cytokine and cortisol levels, deteriorate mood and elicit simultaneous physiological and psychological responses. However, research concerning the interaction between such responses is limited and inconclusive. Therefore, it is unknown if a psycho-physiological relationship exists and as a result, it is currently not feasible for agencies to monitor sleep restriction related stress based on psycho- physiological interactions. Sleep restriction does however, appear to be a major stressor contributing to physiological and psychological responses and thus, warrants further investigation.

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

Abstract 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.