Atherosclerosis42.docx - Muscle cross sectional area While...

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Muscle cross sectional area While RTH is in its infancy, there a few studies that have reported augmented changes in muscle CSA [111-114]. A novel study that compared the effects of 5 wk of low-intensity (20% 1RM) resistance exercise in hypoxia and normoxia, reported greater increases in muscle CSA of the knee extensors and flexors in hypoxia compared to the identical training in normoxia (6.1 ?? 5.1 vs. 2.9 ?? 2.75) [111]. Similarly, Nishimura et al. [112] reported a significant increase in elbow flexor and extensor muscle CSA following 6 wk of moderate-intensity (70% 1RM) in hypoxia (16% inspired O2), whilst no significant change was observed after identical training normoxia. In contrast, Friedmann et al. [115] reported that 4 wk of low-intensity (20% 1RM)/high repetition knee extension exercise in hypoxia (12% inspired O2) did not induced any significant changes in muscle CSA. Nonetheless, no significant changes were also observed in the normoxic group, therefore, it was suggested that RTH was not a superior training modality to the identical training normoxia. While there are disparities in these investigations, it is important to consider the influence of the methodological designs on the changes in muscle CSA. Particularly, the program durations as Friedman et al. [115] employed a training study of 4 wk, which may not be sufficient to stimulate muscular hypertrophy. Collectively, this data suggest that RTH may be beneficial to promote skeletal muscle hypertrophy, which is similar to that observed following BFR training, and beyond those achieved by training in normoxia. Hormonal and metabolic responses To date, there are only two studies that assessed the acute hormonal and metabolic response to RTH [116, 117]. Kon et al. [116] investigated the effects of bench press and leg press exercise at 70% 1RM consisting of 5 sets of 10 repetitions combined with one minute rest intervals in systemic hypoxia (13% inspired O2) and normoxia (21% inspired O2). It was reported that the hypoxic group demonstrated significantly greater increases in both blood lactate (1.3- fold) and GH (mean value 12.9 ?? 2.5 vs. 7.7 ?? 1.9 ng/mL) responses compared to the normoxic group. Similar findings were reported from the same research group when resistance exercise was performed at 50% 1RM consisting of 5 sets of 14 repetitions at 13% inspired O2 [117]. However, it was also reported that there was no significant difference in both serum testosterone and IGF-1 following low-intensity resistance exercise in both hypoxia and normoxia [116, 117]. These findings are in agreement with the responses observed following BFR training, where the GH response is typically augmented, whilst
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testosterone and IGF-1 do not appear to be significantly altered. More recently, two studies have investigated the effects of moderate- intensity resistance exercise (70% 1RM) in systemic hypoxia over eight week duration [113, 114]. Both studies assessed the GH response on the first and last resistance exercise session and it was reported that the hypoxic group observed a significantly greater increase GH concentrations compared to the normoxic group. Further to this, peak
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