Effects of exercise in normobaric hypoxia on hemodynamics during muscle metaboreflex activation in normoxia

Effects of short-term repeated sprint training in hypoxia or with blood flow restriction on response to exercise

This study compared the effects of a brief repeated sprint training (RST) intervention performed with bilateral blood flow restriction (BFR) conditions in normoxia or conducted at high levels of hypoxia on response to exercise. Thirty-nine endurance-trained athletes completed six repeated sprints cycling sessions spread over 2 weeks consisting of four sets of five sprints (10-s maximal sprints with 20-s active recovery). Athletes were assigned to one of the four groups and subjected to a bilateral partial blood flow restriction (45% of arterial occlusion pressure) of the lower limbs during exercise (BFRG), during the recovery (BFRrG), exercised in a hypoxic room simulating hypoxia at FiO2 ≈ 13% (HG) or were not subjected to additional stress (CG). Peak aerobic power during an incremental test, exercise duration, maximal accumulated oxygen deficit and accumulated oxygen uptake (VO2) during a supramaximal constant-intensity test were improved thanks to RST (p < 0.05). No significant differences were observed between the groups (p > 0.05). No further effect was found on other variables including time-trial performance and parameters of the force-velocity relationship (p > 0.05). Thus, peak aerobic power, exercise duration, maximal accumulated oxygen deficit, and VO2 were improved during a supramaximal constant-intensity exercise after six RST sessions. However, combined hypoxic stress or partial BFR did not further increase peak aerobic power.

The Methodological Quality of Studies Investigating the Acute Effects of Exercise During Hypoxia Over the Past 40 years: A Systematic Review

Exercise under hypoxia and the physiological impact compared to normoxia or hypoxia has gained attention in the last decades. However, methodological quality assessment of articles in this area is lacking in the literature. Therefore, this article aimed to evaluate the methodologic quality of trials studying exercise under hypoxia. An electronic search was conducted until December 2021. The search was conducted in PubMed, CENTRAL, and PEDro using the PICO model. (P) Participants had to be healthy, (I) exercise under normobaric or hypobaric hypoxia had to be (C) compared to exercise in normoxia or hypoxia on (O) any physiological outcome. The 11-item PEDro scale was used to assess the methodological quality (internal validity) of the studies. A linear regression model was used to evaluate the evolution of trials in this area, using the total PEDro score of the rated trials. A total of n = 81 studies met the inclusion criteria and were processed in this study. With a mean score of 5.1 ± 0.9 between the years 1982 and 2021, the mean methodological quality can be described as “fair.” Only one study reached the highest score of 8/10, and n = 2 studies reached the lowest observed value of 3/10. The linear regression showed an increase of the PEDro score of 0.1 points per decade. A positive and small tendency toward increased methodologic quality was observed. The current results demonstrate that a positive and small tendency can be seen for the increase in the methodological quality in the field of exercise science under hypoxia. A “good” methodological quality, reaching a PEDro score of 6 points can be expected in the year 2063, using a linear regression model analysis. To accelerate this process, future research should ensure that methodological quality criteria are already included during the planning phase of a study.

Acute Exercise with Moderate Hypoxia Reduces Arterial Oxygen Saturation and Cerebral Oxygenation without Affecting Hemodynamics in Physically Active Males

Hemodynamic changes during exercise in acute hypoxia (AH) have not been completely elucidated. The present study aimed to investigate hemodynamics during an acute bout of mild, dynamic exercise during moderate normobaric AH. Twenty-two physically active, healthy males (average age; range 23–40 years) completed a cardiopulmonary test on a cycle ergometer to determine their maximum workload (W_max). On separate days, participants performed two randomly assigned exercise tests (three minutes pedaling at 30% of W_max): (1) during normoxia (NORMO), and (2) during normobaric AH at 13.5% inspired oxygen (HYPO). Hemodynamics were assessed with impedance cardiography, and peripheral arterial oxygen saturation (SatO₂) and cerebral oxygenation (Cox) were measured by near-infrared spectroscopy. Hemodynamic responses (heart rate, stroke volume, cardiac output, mean arterial blood pressure, ventricular emptying rate, and ventricular filling rate) were not any different between NORMO and HYPO. However, the HYPO test significantly reduced both SatO₂ (96.6 ± 3.3 vs. 83.0 ± 4.5%) and Cox (71.0 ± 6.6 vs. 62.8 ± 7.4 A.U.) when compared to the NORMO test. We conclude that an acute bout of mild exercise during acute moderate normobaric hypoxia does not induce significant changes in hemodynamics, although it can cause significant reductions in SatO₂ and Cox.

Ethnic Differences on Cardiac Rhythms and Autonomic Nervous System Responses During a High-Altitude Trek: A Pilot Study Comparing Italian Trekkers to Nepalese Porters

Altitude hypoxia exposure results in increased sympathetic activity and heart rate due to several mechanisms. Recent studies have contested the validity of heart rate variability (HRV) analysis on sympathetic activity measurement. But the plethora of HRV metrics may provide meaningful insights, particularly if linked with cardiovascular and autonomic nervous system parameters. However, the population-specific nature of HRV and cardiorespiratory response to altitude hypoxia are still missing. Six Italian trekkers and six Nepalese porters completed 300 km of a Himalayan trek. The ECG analysis was conducted at baseline, and before (bBC) and after (aBC) the high-altitude (HA) circuit. Urine was collected before and after the expedition in Italians, for assessing catecholamines. Heart rate increased with altitude significantly (p < 0.001) in the Italian group; systolic (p = 0.030) and diastolic (p = 0.012) blood pressure, and mean arterial pressure (p = 0.004) increased with altitude. Instead, pulse pressure did not change, although the Nepalese group showed lower baseline values than the Italians. As expected, peripheral oxygen saturation decreased with altitude (p < 0.001), independently of the ethnic groups. Nepalese had a higher respiratory rate (p = 0.007), independent of altitude. The cardiac vagal index increased at altitude, from baseline to bBC (p = 0.008). Higuchi fractal dimension (HFD) showed higher basal values in the Nepalese group (p = 0.041), and a tendency for the highest values at bBC. Regarding the urinary catecholamine response, exposure to HA increased urinary levels, particularly of norepinephrine (p = 0.005, d = 1.623). Our findings suggest a better cardiovascular resilience of the Nepalese group when compared with Italians, which might be due to an intrinsic adaptation to HA, resulting from their job.

Systolic and Diastolic Functions After a Brief Acute Bout of Mild Exercise in Normobaric Hypoxia

Acute hypoxia (AH) is a challenge to the homeostasis of the cardiovascular system, especially during exercise. Research in this area is scarce. We aimed to ascertain whether echocardiographic, Doppler, and tissue Doppler measures were able to detect changes in systolic and diastolic functions during the recovery after mild exercise in AH. Twelve healthy males (age 33.5 ± 4.8 years) completed a cardiopulmonary test on an electromagnetically braked cycle-ergometer to determine their maximum workload (W_max). On separate days, participants performed randomly assigned two exercise sessions consisting in 3 min pedalling at 30% of W_max: (1) one test was conducted in normoxia (NORMO) and (2) one in normobaric hypoxia with FiO₂ set to 13.5% (HYPO). Hemodynamics were assessed with an echocardiographic system. The main result was that the HYPO session increased parameters related to myocardial contractility such as pre-ejection period and systolic myocardial velocity with respect to the NORMO test. Moreover, the HYPO test enhanced early transmitral filling peak velocities. No effects were detected for left ventricular volumes, as end-diastolic, end-systolic, and stroke volume were similar between the NORMO and the HYPO test. Results of the present investigation support the hypothesis that a brief, mild exercise bout in acute normobaric hypoxia does not impair systolic or diastolic functions. Rather, it appears that stroke volume is well preserved and that systolic and early diastolic functions are enhanced by exercise in hypoxia.

Case study: physical capacity and nutritional status before and after climbing two peaks with different altitude (4897-6812 m)

Vinson and Ama Dablam are summits of different altitudes (4897 and 6812 m respectively). There are no published studies comparing physiological adaptations occurring after climbing both peaks yet. This case study compares changes in certain physiological parameters and body composition of a mountaineer who ascended both peaks. The athlete was a mountaineer who already climbed the 7 Summits^©. Baseline body composition, physical capacity, and cerebral oxygenation during effort were measured before and after his departure. Body composition was estimated by electrical bio-impedance, while physical capacity was measured with an incremental exercise test (treadmill) conducted in normoxia and in hypoxia corresponding to about 4000 m. Hypoxia was obtained with a hypoxic gas generator. During tests, cerebral oxygenation was estimated with near infrared spectroscopy. The ascent of mount Vinson and Ama Dablam took 4 and 15 days respectively. The ascent of mount Vinson resulted in a 2.0 kg drop in body mass and a reduction in body fat (from 15.5% to 12.1%). The ascent of Ama Dablam reduced body mass by 3.7 kg, with an increase in body fat from 11.9% to 14.7%. Physical capacity was almost unchanged after both expeditions, although there was a reduction in maximum heart rate in relation to workload after Ama Dablam. Finally, after Ama Dablam there was an increase in cerebral oxygenation during effort both in normoxia and hypoxia. It was concluded that the longer duration and the higher altitude during the Ama Dablam expedition resulted in more evident physiological changes.

Muscle Oxygen Delivery in the Forearm and in the Vastus Lateralis Muscles in Response to Resistance Exercise: A Comparison Between Nepalese Porters and Italian Trekkers

Altitude ascending represents an intriguing experimental model reproducing physiological and pathophysiological conditions sharing hypoxemia as the denominator. The aim of the present study was to investigate fractional oxygen extraction and blood dynamics in response to hypobaric hypoxia and to acute resistance exercises, taking into account several factors including different ethnic origin and muscle groups. As part of the “Kanchenjunga Exploration & Physiology” project, six Italian trekkers and six Nepalese porters took part in a high altitude trek in the Himalayas. The measurements were carried out at low (1,450 m) and high altitude (HA; 4,780 m). Near-infrared spectroscopy (NIRS)-derived parameters, i.e., Tot-Hb and tissue saturation index (TSI), were gathered at rest and after bouts of 3-min resistive exercise, both in the quadriceps and in the forearm muscles. TSI decreased with altitude, particularly in forearm muscles (from 66.9 to 57.3%), whereas the decrement was less in the quadriceps (from 62.5 to 57.2%); Nepalese porters were characterized by greater values in thigh TSI than Italian trekkers. Tot-Hb was increased after exercise. At altitude, such increase appeared to be higher in the quadriceps. This effect might be a consequence of the long-term adaptive memory due to the frequent exposures to altitude. Although speculative, we suggest a long-term adaptation of the Nepalese porters due to improved oxygenation of muscles frequently undergoing hypoxic exercise. Muscle structure, individual factors, and altitude exposure time should be taken into account to move on the knowledge of oxygen delivery and utilization at altitude.

Blood Pressure Response to Muscle Metaboreflex Activation is Impaired in Men Living with HIV

We investigated the muscle metaboreflex contribution to blood pressure response during dynamic handgrip exercise in men living with HIV (MLHIV) vs. without HIV (Controls). Pressor and heart rate responses were evaluated during metaboreflex activation through post-exercise muscle ischemia (PEMI) method and control exercise session (CER) in 17 MLHIV and 21 Controls. Protocols were performed randomly on the same day, being both sessions composed of 12 min, as follows: a) 3 min at rest, b) 3 min of dynamic handgrip exercise at 30% of maximal voluntary contraction, c) 3 min of recovery post-exercise with vascular occlusion (occlusion only in PEMI), and d) 3 min of recovery post-exercise without vascular occlusion. To assess metaboreflex response, differences between PEMI and CER in recovery post-exercise were calculated for blood pressure and heart rate. Systolic and mean blood pressure (P<0.01) were superior in the last 2 min of recovery with vascular occlusion at PEMI in relation to CER for both groups. No difference was found between groups for blood pressure and heart rate (P>0.05). However, metaboreflex response for systolic blood pressure was lower in MLHIV vs. Controls (4.05±4.63 vs. 7.61±3.99 mmHg; P=0.01). In conclusion, pressor response during metaboreceptor stimulation was attenuated in men living with HIV, which may suggest loss of muscle metaboreflex sensibility.

A brief bout of exercise in hypoxia reduces ventricular filling rate and stroke volume response during muscle metaboreflex activation

Purpose

The hemodynamic consequences of exercise in hypoxia have not been completely investigated. The present investigation aimed at studying the hemodynamic effects of contemporary normobaric hypoxia and metaboreflex activation.

Methods

Eleven physically active, healthy males (age 32.7 ± 7.2 years) completed a cardiopulmonary test on an electromagnetically braked cycle-ergometer to determine their maximum workload (W_max). On separate days, participants performed two randomly assigned exercise sessions (3 minutes pedalling at 30% of W_max): (1) one in normoxia (NORMO), and (2) one in normobaric hypoxia with FiO₂ set to 13.5% (HYPO). After each session, the following protocol was randomly assigned: either (1) post-exercise muscle ischemia (PEMI) to study the metaboreflex, or (2) a control exercise recovery session, i.e., without metaboreflex activation. Hemodynamics were assessed with impedance cardiography.

Results

The main result was that the HYPO session impaired the ventricular filling rate (measured as stroke volume/diastolic time) response during PEMI versus control condition in comparison to the NORMO test (31.33 ± 68.03 vs. 81.52 ± 49.23 ml·s⁻¹,respectively, p = 0.003). This caused a reduction in the stroke volume response (1.45 ± 9.49 vs. 10.68 ± 8.21 ml, p = 0.020). As a consequence, cardiac output response was impaired during the HYPO test.

Conclusions

The present investigation suggests that a brief exercise bout in hypoxia is capable of impairing cardiac filling rate as well as stroke volume during the metaboreflex. These results are in good accordance with recent findings showing that among hemodynamic modulators, ventricular filling is the most sensible variable to hypoxic stimuli.