Effects of a Single Power Strength Training Session on Heart Rate Variability When Performed at Different Simulated Altitudes

Effect of altitude training on the aerobic capacity of athletes: A systematic review and meta-analysis

Purpose

With a growing number of athletes and coaches adopting altitude training, the importance for rationalizing and optimizing such training has been emphasized. We conducted a meta-analysis to evaluate the influence of altitude training on athletes' aerobic capacity and to explore the best altitude training method to improve this capacity.

Methods

We searched Web of Science, SpringerLink, Science Direct, EBSCO, and PubMed databases combined with manual search of the references to collect studies indexed from 1979 to September 2020 on the effect of altitude training on athletes' aerobic capacity. Data from experimental studies that reported hemoglobin levels and maximum oxygen uptake in athletes before and after altitude training, or in athletes performing altitude training in comparison with a control group were analyzed. Data of the populations, intervention, comparison, outcomes and study design were extracted. Review Manager software 5.3 was used for bias evaluation.

Results

17 publications were included. In our meta-analysis, altitude training led to higher maximum oxygen uptake [standardized mean difference (SMD) = 0.67, 95% confidence interval (CI) 0.35-1.00, P < 0.001] and hemoglobin level (SMD = 0.50, 95% CI 0.11-0.90, P = 0.013) than training at lower altitude. The result of sensitivity analysis showed that results of meta-analysis were relatively stable, and there was no bias or change in the result of effect size according to the bias test. The results of subgroup analysis showed that high-altitude living and low-altitude training ("Hi-Lo" regime), with a training cycle of about three weeks at an altitude around 2500 m, had better effects than other regimes on the athletes' aerobic capacity.

Conclusions

Altitude training can improve athletes' aerobic capacity in terms of maximum oxygen uptake and hemoglobin level. Our results are limited by the number and quality of available studies. Therefore, more high-quality studies are needed to verify and extend these findings. Our study can provide scientific suggestions for the training of athletes.

Acute Effects of Whole-Body Electromyostimulation during a Single Maximal Strength Training Session

Whole-body electromyostimulation (WB-EMS) training is effective in improving training adaptation. However, WB-EMS may have side effects and contraindications that can lead to excessive muscle damage and physiological impairment. This randomized crossover study aimed to analyze the acute effects of WB-EMS on muscle damage, autonomic modulation and performance during a single maximal strength session in physically active participants. Twenty healthy and physically active participants randomly performed three maximal strength training sessions (90% 1RM) consisting of bench presses and squat exercises, with a continuous stimulus, a coordinated stimulus with concentric and eccentric phases, and without WB-EMS. Data showed no significant differences between the trials for muscle damage (blood creatine kinase levels), lactate blood levels and performance after exercise. Likewise, the heart rate, blood oxygen saturation and the rate of perceived exertion were similar during exercise between trials. The heart rate variability analysis also showed a similar autonomic response among the trials. Training with WB-EMS seemed to be safe at the observed time intervals while offering a stimulus similar to regular training in physically active participants, regardless of the delivery of the electrical stimuli. More studies are needed to assess the effectiveness of WB-EMS in improving exercise adaptations during training programs.

Remote ischemic preconditioning enhances aerobic performance by accelerating regional oxygenation and improving cardiac function during acute hypobaric hypoxia exposure

Remote ischemic preconditioning (RIPC) may improve exercise performance. However, the influence of RIPC on aerobic performance and underlying physiological mechanisms during hypobaric hypoxia (HH) exposure remains relatively uncertain. Here, we systematically evaluated the potential performance benefits and underlying mechanisms of RIPC during HH exposure. Seventy-nine healthy participants were randomly assigned to receive sham intervention or RIPC (4 × 5 min occlusion 180 mm Hg/reperfusion 0 mm Hg, bilaterally on the upper arms) for 8 consecutive days in phases 1 (24 participants) and phase 2 (55 participants). In the phases 1, we measured the change in maximal oxygen uptake capacity (VO₂max) and muscle oxygenation (SmO₂) on the leg during a graded exercise test. We also measured regional cerebral oxygenation (rSO₂) on the forehead. These measures and physiological variables, such as cardiovascular hemodynamic parameters and heart rate variability index, were used to evaluate the intervention effect of RIPC on the changes in bodily functions caused by HH exposure. In the phase 2, plasma protein mass spectrometry was then performed after RIPC intervention, and the results were further evaluated using ELISA tests to assess possible mechanisms. The results suggested that RIPC intervention improved VO₂max (11.29%) and accelerated both the maximum (18.13%) and minimum (53%) values of SmO₂ and rSO₂ (6.88%) compared to sham intervention in hypobaric hypoxia exposure. Cardiovascular hemodynamic parameters (SV, SVRI, PPV% and SpMet%) and the heart rate variability index (Mean RR, Mean HR, RMSSD, pNN50, Lfnu, Hfnu, SD1, SD2/SD1, ApEn, SampEn, DFA1and DFA2) were evaluated. Protein sequence analysis showed 42 unregulated and six downregulated proteins in the plasma of the RIPC group compared to the sham group after HH exposure. Three proteins, thymosin β4 (Tβ4), heat shock protein-70 (HSP70), and heat shock protein-90 (HSP90), were significantly altered in the plasma of the RIPC group before and after HH exposure. Our data demonstrated that in acute HH exposure, RIPC mitigates the decline in VO₂max and regional oxygenation, as well as physiological variables, such as cardiovascular hemodynamic parameters and the heart rate variability index, by influencing plasma Tβ4, HSP70, and HSP90. These data suggest that RIPC may be beneficial for acute HH exposure.

Chronic intermittent hypobaric hypoxia attenuates ischemic limb injury by promoting angiogenesis in mice

This study aimed to evaluate the protective effect of chronic intermittent hypobaric hypoxia (CIHH) against limb ischemic injury. C57BL/6 mice were randomly divided into three groups: limb ischemic injury group (Ischemia, induced by ligation and excision of the left femoral artery), limb ischemia following CIHH pretreatment group (CIHH+Ischemia, simulated a 5000 m altitude hypoxia, 6 h per day for 28 days, before induction of hind-limb ischemia), and sham group (Sham). The blood flow in the mouse models of hind-limb ischemia was examined using laser doppler imaging. The functional and morphological performance of ischemic muscle was evaluated using contraction force and hematoxylin-eosin and Masson's trichrome staining. Angiogenesis was determined by immunohistochemistry staining of the endothelial markers CD31 and CD34. The protein expressions of angiogenesis-related genes were detected using Western blot assay. Chronic ischemia resulted in reduced blood perfusion, decreased contraction tension, and morphological destruction in gastrocnemius muscle. CIHH pretreatment increased the contractile force and muscle fiber diameter and decreased necrosis and fibrosis of the ischemic muscle. Also, CIHH significantly increased the density of CD31+ and CD34+ cells and promoted the expression of angiogenesis-related molecules in ischemic muscle. These data demonstrate that CIHH has a protective effect against chronic limb ischemia by promoting angiogenesis.

Minimal Influence of Hypobaria on Heart Rate Variability in Hypoxia and Normoxia

Introduction

The present study evaluated the putative effect of hypobaria on resting HRV in normoxia and hypoxia.

Methods

Fifteen young pilot trainees were exposed to five different conditions in a randomized order: normobaric normoxia (NN, P_B = 726 ± 5 mmHg, F_IO₂ = 20.9%), hypobaric normoxia (HN, P_B = 380 ± 6 mmHg, F_IO₂≅40%), normobaric hypoxia (NH, P_B = 725 ± 4 mmHg, F_IO₂≅11%); and hypobaric hypoxia (HH at 3000 and 5500 m, HH3000 and HH5500, P_B = 525 ± 6 and 380 ± 8 mmHg, respectively, F_IO₂ = 20.9%). HRV and pulse arterial oxygen saturation (SpO₂) were measured at rest seated during a 6 min period in each condition. HRV parameters were analyzed (Kubios HVR Standard, V 3.0) for time (RMSSD) and frequency (LF, HF, LF/HF ratio, and total power). Gas exchanges were collected at rest for 10 min following HRV recording.

Results

SpO₂ decreased in HH3000 (95 ± 3) and HH5500 (81 ± 5), when compared to NN (99 ± 0). SpO₂ was higher in NH (86 ± 4) than HH5500 but similar between HN (98 ± 2) and NN. Participants showed lower RMSSD and total power values in NH and HH5500 when compared to NN. In hypoxia, LF/HF ratio was greater in HH5500 than NH, whereas in normoxia, LF/HF ratio was lower in HN than NN. Minute ventilation was higher in HH5500 than in all other conditions.

Discussion

The present study reports a slight hypobaric effect either in normoxia or in hypoxia on some HRV parameters. In hypoxia, with a more prominent sympathetic activation, the hypobaric effect is likely due to the greater ventilation stimulus and larger desaturation. In normoxia, the HRV differences may come from the hyperoxic breathing and slight breathing pattern change due to hypobaria in HN.