Matthew Phillips

Central role of nitric oxide synthase in AICAR and caffeine-induced mitochondrial biogenesis in L6 myocytes

5-Aminoimidazole-4-carboxamide-ribonucleoside (AICAR) and caffeine, which activate AMP-activated protein kinase (AMPK) and cause sarcoplasmic reticulum calcium release, respectively, have been shown to increase mitochondrial biogenesis in L6 myotubes. Nitric oxide (NO) donors also increase mitochondrial biogenesis. Since neuronal and endothelial NO synthase (NOS) are calcium dependent and are also phosphorylated by AMPK, we hypothesized that NOS inhibition would attenuate the activation of mitochondrial biogenesis in response to AICAR and caffeine. L6 myotubes either were not treated (control) or were exposed acutely or for 5 h/day over 5 days to 100 microM of N(G)-nitro-L-arginine methyl ester (L-NAME, NOS inhibitor), 100 microM S-nitroso-N-acetyl-penicillamine (SNAP) (NO donor) +/- 100 microM L-NAME, 2 mM AICAR +/- 100 microM L-NAME, or 5 mM caffeine +/- 100 microM L-NAME (n = 12/treatment). Acute AICAR administration increased (P < 0.05) phospho- (P-)AMPK, but also increased P-CaMK, with resultant chronic increases in peroxisome proliferator-activated receptor-gamma coactivator-1 alpha (PGC-1 alpha), cytochrome-c oxidase (COX)-1, and COX-4 protein expression compared with control cells. NOS inhibition, which had no effect on AICAR-stimulated P-AMPK, surprisingly increased P-CaMK and attenuated the AICAR-induced increases in COX-1 and COX-4 protein. Caffeine administration, which increased P-CaMK without affecting P-AMPK, increased COX-1, COX-4, PGC-1 alpha, and citrate synthase activity. NOS inhibition, surprisingly, greatly attenuated the effect of caffeine on P-CaMK and attenuated the increases in COX-1 and COX-4 protein. SNAP increased all markers of mitochondrial biogenesis, and it also increased P-AMPK and P-CaMK. In conclusion, AICAR and caffeine increase mitochondrial biogenesis in L6 myotubes, at least in part, via interactions with NOS.

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.

Validating 'fit for duty' tests for Australian volunteer fire fighters suppressing bushfires.

INTRODUCTION This study compared fire fighters work-rates and performance between the Pack Hike Test (PHT), Field Walk Test (FWT) and critical bushfire suppression tasks. METHODS Nineteen volunteer fire fighters undertook the PHT, whilst a further 11 also performed the FWT. All 30 fire fighters completed four critical tasks. Physical, physiological and subjective ratings were measured during tasks and tests. RESULTS Peak and mean heart rate during the Hose Drag was lower than during the FWT. Mean velocities for the PHT and FWT were higher than in all tasks except Hose Drag. Finishing times in the PHT and FWT were strongly correlated with finishing times for three and four of the critical tasks. CONCLUSIONS The PHT and FWT may be valid fit for duty tests for Australian rural fire fighters though the clear differences between the tests and some tasks may prompt fire agencies to consider other tests that more accurately simulate bushfire suppression work.

Frequency, Intensity, Time And Type Of Tasks Performed During Wildfire Suppression

Objective: To quantify the frequency, intensity, duration, and type of tasks performed by Australian rural fire crews when suppressing wildfires. Methods: Twenty-eight Australian rural firefighters worked across four, six-hour shifts fighting to curtail the spread of wildfire. Each firefighter wore a heart rate monitor and personal global positioning system (GPS) unit and was followed by a researcher filming their work activity. Video footage of each firefighter was synchronized with their heart rate and GPS data to quantify the frequency, intensity and duration of individual fireground tasks. Fireground tasks were isolated using a previously conducted job task analysis. Results: Firefighters performed 32 distinct fireground tasks. Task frequencies ranged from once to 103 times per six-hour shift. Individual tasks lasted 4 ± 2 s to 461 ± 387 s, were performed at speeds ranging from 0.12 ± 0.08 m•s-1 to 0.79 ± 0.40 m•s-1 and elicited mean heart rates that ranged between 97 ± 16 beats•min-1 (55.7 ± 8.7 percentage of age-predicted maximum heart rate (HRmax)) and 157 ± 15 beats•min-1 (86.2 ± 10.8%HRmax). Conclusion: Fireground tasks were, generally speaking, shorter, slower, and elicited lower heart rates than equivalent tasks previously simulated and reported in the literature. The differences between naturally occurring and simulated tasks question the value of isolated task simulations for conducting physical demands analyses en-route to developing job-specific fitness tests.

Oxygen Uptake and Heart Rate during Simulated Wildfire Suppression Tasks Performed by Australian Rural Firefighters

Objective: Australian rural fire crews safeguard the nation against the annual devastation of wildfire. We have previously reported that experienced firefighters identified seven physically demanding tasks for Australian rural fire crews suppressing wildfires. These firefighters rated the operational importance, typical duration, core fitness components, and likely frequency of the seven tasks. The intensity of these duties remains unknown. The aim of this study was to quantify the oxygen uptake (VO2), heart rate (HR) and movement speed responses during simulations of these physically demanding wildfire suppression tasks. Method: Twenty six rural firefighters (20 men, six women) performed up to seven tasks, during which time their HR and movement speed were recorded. The VO2 for each task was also calculated from the analysis of expired air collected in Douglas bags. Firefighters’ HR and movement speed were measured using HR monitors and portable global positioning system units, respectively. Results: The hose work tasks elicited a VO2 of 21-27 mL·kg-1·min-1 and peak HR of 77-87% age-predicted maximal HR (HRmax). Hand tool tasks were accompanied by VO2 of 28-34 mL·kg-1·min-1 and peak HR of 85-95%HRmax. Firefighters’ movement speed spanned 0.2 ± 0.1 to 1.8 ± 0.2 m·s-1 across the seven tasks. The cardiovascular responses in the hand tool tasks were, in most cases, higher (P<0.05) than during those elicited by the hose work tasks. Conclusions: The cardiovascular responses elicited during simulations of physically demanding wildfire suppression approximated those reported for similar tasks in urban and forestry fire fighting jurisdictions. The findings may prompt Australian rural fire agencies to consider cardiovascular disease risk screening and physical selection testing to ensure that healthy and fit firefighters are deployed to the fire ground.