Combined effects of exercise and different levels of acute hypoxic severity: A randomized crossover study on glucose regulation in adults with overweight.

Purpose: The aim of this study was to investigate the influence of manipulating hypoxic severity with low-intensity exercise on glucose regulation in healthy overweight adults. Methods: In a randomized crossover design, 14 males with overweight (age: 27 ± 5 years; body mass index (BMI) 27.1 ± 1.8 kg⋅m2) completed three exercise trials involving 60 min aerobic exercise cycling at 90% lactate threshold in normoxia (NM, FiO2 = 20.9%), moderate hypoxia (MH, FiO2 = 16.5%) and high hypoxia (HH, FiO2 = 14.8%). A post-exercise oral glucose tolerance test (OGTT) was performed. Venous blood samples were analyzed for incremental area under the curve (iAUC), plasma glucose and insulin, as well as exerkine concentrations (plasma apelin and fibroblast growth factor 21 [FGF-21]) pre- and post-exercise. A 24-h continuous glucose monitoring (CGM) was used to determine interstitial glucose concentrations. Heart rate, oxygen saturation (SpO2) and perceptual measures were recorded during exercise. Results: Post-exercise OGTT iAUC for plasma glucose and insulin concentrations were lower in MH vs. control (p = 0.02). Post-exercise interstitial glucose iAUC, plasma apelin and FGF-21 were not different between conditions. Heart rate was higher in HH vs. NM and MH, and MH vs. NM (p < 0.001), while SpO2 was lower in HH vs. NM and MH, and MH vs. NM (p < 0.001). Overall perceived discomfort and leg discomfort were higher in HH vs. NM and MH (p < 0.05), while perceived breathing difficulty was higher in HH vs. NM only (p = 0.003). Conclusion: Compared to higher hypoxic conditions, performing acute aerobic-based exercise under moderate hypoxia provided a more effective stimulus for improving post-exercise glucose regulation while concomitantly preventing excessive physiological and perceptual stress in healthy overweight adults.

Influence of exercise intensity and hypoxic exposure on physiological, perceptual and biomechanical responses to treadmill running.

Acute physiological, perceptual and biomechanical consequences of manipulating both exercise intensity and hypoxic exposure during treadmill running were determined. On separate days, eleven trained individuals ran for 45 s (separated by 135 s of rest) on an instrumented treadmill at seven running speeds (8, 10, 12, 14, 16, 18 and 20 km.h-1) in normoxia (NM, FiO2 = 20.9%), moderate hypoxia (MH, FiO2 = 16.1%), high hypoxia (HH, FiO2 = 14.1%) and severe hypoxia (SH, FiO2 = 13.0%). Running mechanics were collected over 20 consecutive steps (i.e. after running ∼25 s), with concurrent assessment of physiological (heart rate and arterial oxygen saturation) and perceptual (overall perceived discomfort, difficulty breathing and leg discomfort) responses. Two-way repeated-measures ANOVA (seven speeds × four conditions) were used. There was a speed × condition interaction for heart rate (p = 0.045, ηp2 = 0.22), with lower values in NM, MH and HH compared to SH at 8 km.h-1 (125 ± 12, 125 ± 11, 128 ± 12 vs 132 ± 10 b.min-1). Overall perceived discomfort (8 and 16 km.h-1; p = 0.019 and p = 0.007, ηp2 = 0.21, respectively) and perceived difficulty breathing (all speeds; p = 0.023, ηp2 = 0.37) were greater in SH compared to MH, whereas leg discomfort was not influenced by hypoxic exposure. Minimal difference was observed in the twelve kinetics/kinematics variables with hypoxia (p > 0.122; ηp2 = 0.19). Running at slower speeds in combination with severe hypoxia elevates physiological and perceptual responses without a corresponding increase in ground reaction forces.Highlights The extent to which manipulating hypoxia severity (between normoxia and severe hypoxia) and running speed (from 8 to 20 km.h-1) influence acute physiological and perceptual responses, as well as kinetic and kinematic adjustments during treadmill running was determined.Running at slower speeds in combination with severe hypoxia elevates heart rate, while this effect was not apparent at faster speeds.Arterial oxygen saturation was increasingly lower as running speed and hypoxic severity increased.Overall perceived discomfort (8 and 16 km.h-1) and perceived difficulty breathing (all speeds) were lower in moderate hypoxia than in severe hypoxia, whereas leg discomfort remained unchanged with hypoxic exposure.