Effects of high-intensity interval training with hyperbaric oxygen

Abstract

Hyperbaric Oxygen (HBO2) has been proposed as a pre-conditioning method to enhance exercise performance. Most prior studies testing this effect have been limited by inadequate methodologies. Its potential efficacy and mechanism of action remain unknown. We hypothesized that HBO2 could enhance aerobic capacity by inducing mitochondrial biogenesis via redox signaling in skeletal muscle. HBO2 was administered in combination with high-intensity interval training (HIIT), a potent redox stimulus known to induce mitochondrial biogenesis. Aerobic capacity was tested during acute hypobaric hypoxia seeking to shift the limiting site of whole body V̇O2 from convection to diffusion, more closely isolating any effect of improved oxidative capacity. Healthy volunteers were screened with sea-level (SL) V̇O2peak testing. Seventeen subjects were enrolled (10 men, 7 women, ages 26.5±1.3 years, BMI 24.6±0.6 kg m-2, V̇O2peak SL = 43.4±2.1). Each completed 6 HIIT sessions over 2 weeks randomized to breathing normobaric air, "HIIT+Air" (PiO2 = 0.21 ATM) or HBO2 (PiO2 = 1.4 ATM) during training, "HIIT+HBO2" group. Training workloads were individualized based on V̇O2peak SL test. Vastus Lateralis (VL) muscle biopsies were performed before and after HIIT in both groups. Baseline and post-training V̇O2peak tests were conducted in a hypobaric chamber at PiO2 = 0.12 ATM. HIIT significantly increased V̇O2peak in both groups: HIIT+HBO2 31.4±1.5 to 35.2±1.2 ml kg-1·min-1 and HIIT+Air 29.0±3.1 to 33.2±2.5 ml kg-1·min-1 (p = 0.005) without an additional effect of HBO2 (p = 0.9 for interaction of HIIT x HBO2). Subjects randomized to HIIT+HBO2 displayed higher skeletal muscle mRNA levels of PPARGC1A, a regulator of mitochondrial biogenesis, and HK2 and SLC2A4, regulators of glucose utilization and storage. All other tested markers of mitochondrial biogenesis showed no additional effect of HBO2 to HIIT. When combined with HIIT, short-term modest HBO2 (1.4 ATA) has does not increase whole-body V̇O2peak during acute hypobaric hypoxia. (ClinicalTrials.gov Identifier: NCT02356900; https://ichgcp.net/clinical-trials-registry/NCT02356900).

Keywords: high-altitude; high-intensity interval training; hyperbaric oxygenation; mitochondrial turnover; oxygen consumption.

Conflict of interest statement

The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.

Copyright © 2022 Alvarez Villela, Dunworth, Kraft, Harlan, Natoli, Suliman and Moon.

Figures

FIGURE 1

Study design. After a sea-level screening VO2peak test, subjects underwent a V̇O2peak test at altitude and were then randomized to HIIT + Air or HIIT + HBO2. After six HIIT sessions, subjects underwent a final V̇O2peak test at altitude. Abbreviations: ATM, atmospheres; HBO2, hyperbaric oxygen; HIIT, high-intensity interval training; PiO2, pressure of inspired oxygen; VL, vastus lateralis; V̇O2, oxygen consumption.

FIGURE 2

High-Intensity Interval Training. Timeline of a single 30-min HIIT session as a function of percent of V̇O2peak workload (W).

FIGURE 3

Mitochondrial protein expression. Expression of the following skeletal muscle proteins was measured by western blot: (A) Mfn2, mitofusin-2; (B) Drp1, dynamin-1-like protein; (C) Citrate synthase; (D) ATPase6, mitochondrial ATP synthase subunit a; (E) COI, cytochrome c oxidase subunit 1; and (F) ND1, NADH-ubiquinone oxidoreductase chain 1. Reference proteins were either GAPDH or Porin. Statistical analysis was 2-way ANOVA with repeated measures and Fisher’s LSD post-hoc test. *p <0.05 shows significant within group comparison (i.e. baseline vs. post-HITT). Groups: air, black bars; HBO2, grey bars.

FIGURE 4

Mitochondrial gene expression. mRNA levels of the following genes were measured by quantitative PCR: (A)NRF2, nuclear respiratory factor 2; (B)PPARGC1A, peroxisome proliferator-activated receptor gamma coactivator 1-alpha; (C)TFAM, mitochondrial transcription factor a; (D)POLG, DNA polymerase subunit gamma-1; and (E)POLMRT, mitochondrial DNA-directed RNA polymerase. Reference mRNA was 18S and shown as fold-change. Mitochondrial DNA copy number was measured in (F) by PCR with 18S rDNA as reference and shown as fold-change. Statistical analysis was 2-way ANOVA with repeated measures and Fisher’s LSD post-hoc test. *p <0.05 shows significant within group comparison (i.e. baseline vs. post-HITT) and #p <0.05 shows significant between group comparisons (i.e. air, black bars vs. HBO2, grey bars).

FIGURE 5

Antioxidant response. Antioxidant protein expression of (A) SOD2, superoxide dismutase-2; (B) HO-1, heme oxygenase-1; and (C) catalase were measured by western blot and referenced to GAPDH expression. Statistical analysis was 2-way ANOVA with repeated measures and Fisher’s LSD post-hoc test. *p <0.05 shows significant within group comparison (i.e. baseline vs. post-HITT) and #p <0.05 shows significant between group comparisons (i.e. air, black bars vs. HBO2, grey bars).

FIGURE 6

Glucose-related gene expression. mRNA levels of the following genes were measured by quantitative PCR: (A)SLC2A1, Solute carrier family 2, facilitated glucose transporter member 1; (B)SLC2A4, Solute carrier family 2, facilitated glucose transporter member 4; (C)HK1, hexokinase-1; and (D)HK2, hexokinase-2. Reference mRNA was 18S and shown as fold-change. Statistical analysis was 2-way ANOVA with repeated measures and Fisher’s LSD post-hoc test. *p <0.05 shows significant within group comparison (i.e. baseline vs. post-HITT) and #p <0.05 shows significant between group comparisons (i.e. air, black bars vs. HBO2, grey bars).