PubMed · 11085121
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M Ariyoshi. 2000. [Jogging].. https://pubmed.ncbi.nlm.nih.gov/11085121/
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Phylogenetic data support an origin of mitochondria from the alpha-proteobacterial order Rickettsiales. This high-rank taxon comprises exceptionally obligate intracellular endosymbionts of eukaryotic cells, and includes family Rickettsiaceae and a group of microorganisms termed Rickettsia-like endosymbionts (RLEs). Most detailed phylogenetic analyses of small subunit rRNA and chaperonin 60 sequences consistently show the RLEs to have emerged before Rickettsiaceae and mitochondria sister clades. These data suggest that the origin of mitochondria and Rickettsiae has been preceded by the long-term mutualistic relationship of an intracellular bacterium with a pro-eukaryote, in which an invader has lost many dispensable genes, yet evolved carrier proteins to exchange respiration-derived ATP for host metabolites as envisaged in classic endosymbiont theory.
The purpose of this study was to quantify the metabolic demand of simulated shipboard fire-fighting procedures currently practised by men and women in the Royal Navy (RN) and to identify a minimum level of cardiovascular fitness commensurate with satisfactory performance. Thirty-four males (M) and 15 females (F) volunteered as subjects for this study (n=49). Maximal oxygen uptake (VO2max) and heart rate (fcmax) of each subject was assessed during a standardized treadmill test. During the main trials, volunteers were randomly assigned to complete several 4-min simulated shipboard fire-fighting tasks (boundary cooling (BC), drum carry (DC), extinguisher carry (EC), hose run (HR), ladder climb (LC)), at a work rate that was endorsed as a minimum acceptable standard. Heart rate (fc) and oxygen uptake (VO2) were recorded at 10-s intervals during rest, exercise and recovery. Participants completed all tasks within an allocated time with the exception of the DC task, where 11 subjects (all females) failed to maintain the endorsed work rate. The DC task elicited the highest (p<0.01) group mean peak metabolic demand (PMD) in males (43 ml min(-1) kg(-1)) and females (42 ml min(-1) kg (-1)) who were able to maintain the endorsed work rate. The BC task elicited the lowest PMD (23 ml min(-1) kg(-1)), whilst the remaining three tasks elicited a remarkably similar PMD of 38-39 ml min(-1) kg(-1). The human endurance limit while wearing a self-contained breathing apparatus (SCBA) dictates that RN personnel are only able to fire-fight for 20-30 min, while wearing a full fire-fighting ensemble (FFE) and performing a combination of the BC, HR and LC tasks, which have a group mean metabolic demand of 32.8 ml min(-1) kg(-1). Given that in healthy subjects fire-fighting can be sustained at a maximum work intensity of 80% VO2max when wearing SCBA for this duration, it is recommended that all RN personnel achieve a VO2max of 41 ml min(-1) kg(-1) as an absolute minimum standard. Subjects with a higher VO2max than the above quoted minimum are able to complete the combination of tasks listed with greater metabolic efficiency and less fatigue.
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