Acute psycho-physiological responses to submaximal constant-load cycling under intermittent hypoxia-hyperoxia vs. hypoxia-normoxia in young males

Abstract

Background: Hypoxia and hyperoxia can affect the acute psycho-physiological response to exercise. Recording various perceptual responses to exercise is of particular importance for investigating behavioral changes to physical activity, given that the perception of exercise-induced pain, discomfort or unpleasure, and a low level of exercise enjoyment are commonly associated with a low adherence to physical activity. Therefore, this study aimed to compare the acute perceptual and physiological responses to aerobic exercise under intermittent hypoxia-hyperoxia (IHHT), hypoxia-normoxia (IHT), and sustained normoxia (NOR) in young, recreational active, healthy males.

Methods: Using a randomized, single-blinded, crossover design, 15 males (age: 24.5 ± 4.2 yrs) performed 40 min of submaximal constant-load cycling (at 60% peak oxygen uptake, 80 rpm) under IHHT (5 × 4 min hypoxia and hyperoxia), IHT (5 × 4 min hypoxia and normoxia), and NOR. Inspiratory fraction of oxygen during hypoxia and hyperoxia was set to 14% and 30%, respectively. Heart rate (HR), total hemoglobin (tHb) and muscle oxygen saturation (S_mO₂) of the right vastus lateralis muscle were continuously recorded during cycling. Participants' peripheral oxygen saturation (S_pO₂) and perceptual responses (i.e., perceived motor fatigue, effort perception, perceived physical strain, affective valence, arousal, motivation to exercise, and conflict to continue exercise) were surveyed prior, during (every 4 min), and after cycling. Prior to and after exercise, peripheral blood lactate concentration (BLC) was determined. Exercise enjoyment was ascertained after cycling. For statistical analysis, repeated measures analyses of variance were conducted.

Results: No differences in the acute perceptual responses were found between conditions (p ≥ 0.059, η_p ² ≤ 0.18), while the physiological responses differed. Accordingly, S_pO₂ was higher during the hyperoxic periods during the IHHT compared to the normoxic periods during the IHT (p < 0.001, η_p ² = 0.91). Moreover, HR (p = 0.005, η_p ² = 0.33) and BLC (p = 0.033, η_p ² = 0.28) were higher during IHT compared to NOR. No differences between conditions were found for changes in tHb (p = 0.684, η_p ² = 0.03) and S_mO₂ (p = 0.093, η_p ² = 0.16).

Conclusion: IHT was associated with a higher physiological response and metabolic stress, while IHHT did not lead to an increase in HR and BLC compared to NOR. In addition, compared to IHT, IHHT seems to improve reoxygenation indicated by a higher S_pO₂ during the hyperoxic periods. However, there were no differences in perceptual responses and ratings of exercise enjoyment between conditions. These results suggest that replacing normoxic by hyperoxic reoxygenation-periods during submaximal constant-load cycling under intermittent hypoxia reduced the exercise-related physiological stress but had no effect on perceptual responses and perceived exercise enjoyment in young recreational active healthy males.

Keywords: Blood lactate; Effort perception; Exercise enjoyment; Near-infrared spectroscopy; Perceived motor fatigue; Perceived physical strain.

Figure 1. Study design and experimental procedure.

BSL, baseline; F_iO₂, inspiratory fraction of oxygen; IHHT, intermittent hypoxic-hyperoxic training condition; IHT, intermittent hypoxic-normoxic training condition; NOR, normoxic training condition; PACES, physical activity enjoyment scale; POMS, profile of mood states; V̇O_2peak, peak oxygen consumption. Icons from PowerPoint. Figure created with PowerPoint.

Figure 2. Perceived motor fatigue (A), affective valence (B), arousal (C), motivation to exercise (D), conflict to continuous exercise (E), perceived physical strain (F), and effort perception (G).

Perceptual responses were quired immediately before (BSL) as well as after 4 (T4), 8 (T8), 20 (T20), 24 (T24), 36 (T36), and 40 min (T40) during submaximal constant-load cycling under either intermittent hypoxia-hyperoxia (IHHT), intermittent hypoxia-normoxia (IHT), or sustained normoxia (NOR). Values are presented as means and standard deviations.

Figure 3. Peripheral oxygen saturation (S_PO₂) (A), percentage changes in oxygenated hemoglobin (%ΔS_mO₂) (B), and total haemoglobin (%ΔtHb) (C) in the vastus lateralis muscle, as well as heart rate (D).

Physiological responses were measured immediately before (BSL) as well as at 4 (P4), 8 (P8), 12 (P12), 16 (P16), 20 (P20), 24 (P24), 28 (P28), 32 (P32), 36 (P36), and 40 min (P40) during submaximal constant-load cycling under either intermittent hypoxia-hyperoxia (IHHT), intermittent hypoxia-normoxia (IHT), or sustained normoxia (NOR). Values are presented as means and standard deviations. A number sign (#) denotes a difference (p < 0.05) compared to IHHT and IHT. An asterisk (*) denotes a difference (p < 0.05) compared to IHT. A cross (†) denotes a difference (p < 0.05) compared to NOR.