Oxygen supplementation has often been used as an aid for athletic individuals who ascend to high altitudes before acclimatization or experience symptoms of altitude sickness. The effectiveness of oxygen supplementation in augmenting arterial blood oxygen levels (5,23,25) could have contributed to hyperoxia supplements, gaining popularity in the ergogenic aid market. A search on Google for the term “Personal Oxygen Supplement” revealed at least 10 companies in the United States marketing small cylinders of 90–95% oxygen for the purposes of enhancing sport performance. However, the efficacy of such products is in need of evaluation. There is increasing need for additional research to determine the efficacy of such products due to the fact that hyperoxic supplements are being made available to the general public, with promises of enhancing exercise performance and recovery.
The introduction of supplemental oxygen into a participant's airway has been previously evaluated. Administering oxygen-enriched air into the participant's airway has been found to increase V[Combining Dot Above]O2 and improve maximum physical performance when the exercise takes place in a controlled laboratory setting (12). Although oxygen content of arterial blood was significantly different in hyperoxic conditions compared with hypoxic conditions, these treatments were found to be isocapnic (26,29,30,33,34). These findings could suggest a possible ergogenic role for oxygen supplements (OS).
However, other studies suggest that enhanced performance that results from supplemental oxygen may only be due to the maintenance of cerebral oxygenation when administered during exercise (4,20). Recent work suggests that oxygen delivery is not considered to be the limiting factor in maximal exercise performance, and recovery has not been significantly affected by the breathing of oxygen-enriched air (1,13,18,24,31). Also, the use of supplemental oxygen before exercise has not resulted in any significantly different physiological effects documented in recovery, as compared with ambient air (21,22,34).
In addition to the effects of supplemental oxygen on a participant's physical performance, studies have also been completed to assess the relationship between the percent of oxygen in inspired air and the participant's cognitive function during exercise. Oxygen has been shown to significantly improve impaired reaction times that are often experienced in hypoxic conditions (17). Some evidence suggests that, independent of inspired oxygen concentration, moderate exercise can increase levels of arousal and focus, subsequently improving cognitive function and reaction time (2,3,11,14). Not all studies have reached similar conclusions and suggest that exercise has generally shown no significant effect on cognitive performance. Cognitive function is governed by allocable resources, and severe bouts of exercise can compromise information processing and memory (10,19,28). The relationship between exercise and cognitive function is an area that requires additional research.
Previous studies have only examined the effects of hyperoxia before, during, or after exercise. The effects of supplemental oxygen administered in a controlled experiment both during exercise and recovery from a submaximal effort has yet to be examined. The introduction of air concentrated with oxygen into the respiratory pathway could potentially change both respiratory rate and augment the Haldane's effect, which could be seen as changes in V[Combining Dot Above]CO2 and minute ventilation during exercise. The purpose of this study was to determine the effects of a personal OS that delivers intermittent hyperoxia on performance during exhaustive exercise, respiratory responses during exhaustive exercise, and cognitive function after exhaustive exercise.
Experimental Approach to the Problem
The present investigation was a repeated measures, single-blind, placebo-controlled study. Participants were scheduled for 3 laboratory visits at 1 week of intervals. The 3 laboratory visits consisted of 1 maximum oxygen consumption assessment (V[Combining Dot Above]O2max) and 2 runs to exhaustion at 80% of V[Combining Dot Above]O2max speed. During the 2 runs to exhaustion at 80% of V[Combining Dot Above]O2max speed, participants received intermittent hyperoxic treatment through a personal OS or placebo treatment in a random order. This crossover design was used to counteract the likely improvements in performance that naturally occur with repeated trials of exercise to exhaustion. The intermittent hyperoxic treatment was a 90% OS, and placebo treatment was a compressed air canister that provided a sound similar to that of the hyperoxic treatment. Participants were dosed before exercise testing, at 5-minute intervals during exercise testing, immediately when exercise testing ceased, and after 2 minutes of active recovery walking during both runs to exhaustion at 80% of V[Combining Dot Above]O2max speed. Doses were administered at 5-minute intervals based on the manufacturer's recommendations for use of the supplement. Expired gases were sampled and analyzed with the ParvoMedic TrueOne 2400 metabolic measurement system (Parvo Medics, Sandy, UT, USA). Cognitive function was quantified using the psychomotor vigilance testing (PVT) (27). Psychomotor vigilance testing was performed for 5 minutes before and after each run to exhaustion at 80% of V[Combining Dot Above]O2max speed (in miles per hour). This test consisted of random stimuli, administered through a handheld palm-based computer device, and tracked mean reaction time, delay times, and false reactions (Figure 1).
The subjects of this single-blind placebo-controlled study were 20 apparently healthy college students (9 men and 11 women) aged 22.8 ± 2.46 years; all subjects were greater than 18 years of age (Table 1). All procedures were approved by the international review board before any testing. Before obtaining written consent, all participants were provided with written and oral explanations regarding procedures and potential risks. After obtaining written consent from each participant, the participant's age, height, and weight were recorded. All participants underwent a 3-site skinfold thickness assessment using Skinfold Caliper Model SH5020 (Saehan Corp., Changwon, Korea) to evaluate body fat percentage (15,16).
Graded Exercise Testing
Participants received the same graded exercise test format using the same equipment in the Human Performance Laboratory that was used for subsequent runs to exhaustion. The subjects ran on a Track Master TMX 425 treadmill (Full Vision Inc., Newton, KS, USA) during the assessment. Participant's expired air was sampled and analyzed with a ParvoMedic TrueOne 2400 metabolic measurement system (ParvoMedics). The system used a mixing chamber and was set to sample expired air every 10 seconds. The system was calibrated before each test according to the manufacturer's specifications. Drift in the sensors was not appreciable during testing. Listed accuracy for the gas sensors in the unit are: paramagnetic O2 analyzer ±0.1%, infrared CO2 analyzer ±0.1%, and pneumotach ±2%.
The Bruce protocol was used for the assessment (32). The test was concluded when the oxygen consumption was determined to have reached a plateau, or the participant volitionally ceased exercise. In this investigation, all but 3 subjects demonstrated a plateau in oxygen consumption (<100 ml O2 change with increasing workload) at the conclusion of the test. For the 3 remaining subjects, a V[Combining Dot Above]O2peak was determined from the best stage completed at an respiratory exchange ratio value of greater than 1.15. Heart rate during the test was determined through a Polar Wear Link heart rate sensor (Polar Electro Inc., Lake Success, NY, USA) that was linked to a receptor on the metabolic measurement system.
Run to Exhaustion
After completing the first laboratory visit and determining each individual's V[Combining Dot Above]O2max (ml·kg−1·min−1), each participant's V[Combining Dot Above]O2max was converted into a maximum speed in miles per hour using a metabolic equation (V[Combining Dot Above]O2 [ml·kg−1·min−1] = [0.2 × speed] + [0.9 × speed × grade] + 3.5 ml·kg−1·min−1) and solving for speed. Participants then ran to exhaustion during 2 separate trials at 80% of their previously established V[Combining Dot Above]O2max speed. Participants ran on the same Track Master TMX 425 treadmill (Full Vision Inc.). Participants also wore the same mouthpiece, headgear, and heart rate monitor. Respiratory intake took place through a flexible hose that originated from behind the participant to best facilitate the blind nature of the study (Figure 2). Respiratory gases were monitored continuously during the runs; however, analysis of oxygen consumption could not be undertaken due to the variability in inspired oxygen concentration produced by the use of the personal OS. Participants were blind to their 80% speed in miles per hour and instructed to run until reaching exhaustion. Participants were randomly assigned an order of treatment (placebo-compressed air or personal OS) and were informed that treatment was to be administered immediately into intake air hose (pilot testing did not reveal any effect on administration in this manner as compared with directly into the mouthpiece; however, this did not allow the participant to see the canister that was used) at the beginning of each trial, every 5 minutes during each trial, immediately at exhaustion, and 2 minutes into the active cool-down. During both runs to exhaustion, participants were asked to assess their level of perceived exertion on the Borg's scale, as well as the level of pain in their legs on a 10-point analog pain scale, at 2-minute intervals.
Leg Muscle Pain and Exertion Ratings
Subjects were familiarized to both scales and responses during exercise, as they were prompted to respond during the V[Combining Dot Above]O2max assessment during the first laboratory visit. Leg muscle pain was measured using the 0-10 Numeric Pain Rating Scale (Mosby Inc., Philadelphia, PA, USA). Participants received instruction to rate only muscle pain in the legs when prompted to respond with the 0-10 pain scale. The pain scale had 10 total ratings with verbal descriptors for the following: 0 = no pain, 2 = mild pain, 5 = moderate pain, 8 = severe pain, 10 = worst possible pain (7,8). Overall ratings of perceived exertion were assessed through the Borg's 6-20 rating of perceived exertion (RPE) scale. Subjects were instructed to respond to the RPE scale based on total exercise exertion. This numeric scale had 15 total ratings, beginning with 6 and ending with 20. Verbal descriptors accompany the following: 6 = no exertion at all, 7 = extremely light, 9 = very light, 11 = light, 13 = somewhat hard, 15 = hard, 17 = very hard, 19 = extremely hard, 20 = maximal exertion (6,9). Both the pain rating scale and the RPE scale were used every 2 minutes to assess pain and exertion during the run to exhaustion at 80% of V[Combining Dot Above]O2max.
Psychomotor Vigilance Testing
To quantify the effects of hyperoxia on cognitive function after exhaustive exercise, a PVT, 5 minutes in duration, was administered to all participants before and after both of their runs to exhaustion at 80% of their V[Combining Dot Above]O2max. In an effort to avoid the potential of practice effects occurring during subsequent testing dates, participants were familiarized during their initial laboratory visit, when the V[Combining Dot Above]O2max assessment was completed. The PVT is a test of simple visual reaction time and was developed at the Walter Reed Army Institute of Research (7,27). The PVT was used continuously over the course of 5 minutes to assess mean reaction time. The test used variable intervals of time in which a target stimulus was displayed on the screen of a Palm handheld device. The program was set to display approximately 100 stimuli in a 300-second (5-minute total test time) period at randomly spaced intervals (27). This program then computed a mean reaction time to each stimulus. Both right-handed and left-handed individuals were accommodated.
Personal Oxygen Supplement
The hyperoxia treatment used in this study was supplemental oxygen (High Pressure TruO2; Second Wind O2 LLC, Highland Park, IL, USA), consisting of 90% oxygen in a 20 L compressed gas cylinder. This supplement was designed by the manufacturer to deliver a dose of 90% oxygen (balance of ambient air and nitrogen) towards the nose and mouth. The device delivers approximately 250 ml of hyperoxic air per press of the trigger, with multiple trigger presses suggested per dose. However, based on the design, some of the supplement will be lost, as not all will be inspired. This supplement was previously evaluated for the ability to augment oxygen concentrations in inspired air during pilot testing. Previous pilot tests resulted in an increase in inspired oxygen from 20.9 to 22.4% at a simulated light-to-moderate exercise minute ventilation of 50 L·min−1, and inspired oxygen remained elevated for approximately 50 seconds after administration. Previous pilot tests also revealed that interdose variability was present and most likely caused by variation in finger pressure on the triggering mechanism (CV, 2.1%). The simulated minute ventilation of 50 L·min−1 was achieved using a 3-L precision calibration syringe (Hans Rudolph Inc., Shawnee, KS, USA) with the plunger operated in cadence with a metronome with the gases from the cylinder being monitored through the ParvoMedic TrueOne 2400 metabolic measurement system (ParvoMedics). Participants received treatments during their last 2 laboratory visits. The placebo consisted of an aerosol can of compressed air. The placebo was sprayed behind the participant, but facing away from their respiratory intake hose because of the aerosol nature of the canister, to maintain the efficacy of the blind study. The hyperoxia supplement was sprayed directly into the participants' respiratory intake hose. Although some supplements will be lost to the surrounding atmosphere, and this loss is consistent with the intended use of the product. In regards to dosage, both types of treatments were administered, 2 doses at the beginning of each trial, 1 dose at 5-minute intervals during each trial, 2 doses immediately at exhaustion, and 1 dose at 2 minutes into the active cool-down. Treatment administration and dosage followed manufacturer's recommendations. Each administration of the hyperoxia supplement resulted in approximately 1.3 L of the 90% oxygen being delivered.
All data are given in mean ± SD. Before analysis, all data were checked for normality through Kolmogorov-Smirnov test, which were found to be nonsignificant (p > 0.1). Performance on the run to exhaustion trials was analyzed through repeated measures analysis of variance (ANOVA) with order (supplement/placebo) as a between-subject effect. Given the use of a time trial to exhaustion, the effect of order was investigated. Repeated measures ANOVA was used to examine changes in respiratory function during both the first dose of the run to exhaustion trial and after exercise. Similarly, repeated measures ANOVAs were used to examine changes in ventilation, heart rate, and cognitive function during recovery from the exhaustive exercise. Generalized estimation equation (GEE) analysis was used to examine the pain and RPE data over the entire run to exhaustion. A modern statistical software package was used (IBM SPSS Statistics for Windows, Version 21.0; IBM Corp., Armonk, NY, USA). Alpha levels were set a priori at p ≤ 0.05.
Time to Exhaustion
Mean times were 1057.6 ± 619.8 seconds for the oxygen trials and 992.5 ± 463.1 seconds for the placebo trials (Figure 3). Performance between treatments was evaluated and not found to be different (p = 0.335,
= 0.052), and order (Placebo first, personal OS first) was not significant within the model (p = 0.305,
Respiratory Measures During Exercise
Overall mean minute ventilation during 50 seconds after hyperoxia supplementation was 82.5 ± 7.5 L·min−1 and after placebo was 82.6 ± 7.6 L·min−1. Minute Ventilation (Ve, L·min−1) data points were collected every 10 seconds during a 50-second period (based on the pilot data suggesting this time frame for elevation in lung oxygen content) after the first dosing for both oxygen and placebo trials, and there were no main effects for treatment (p = 0.986,
≤ 0.001). The analysis similarly did not reveal any significant treatment × time interaction (p = 0.570,
= 0.039) (Figure 4). Similar data points for V[Combining Dot Above]CO2 (L·O2·min−1) were also analyzed. Overall mean V[Combining Dot Above]CO2 during 50 seconds after hyperoxia supplementation was 2.82 ± 0.26 L·min−1 and after placebo was 2.82 ± 0.26 L·min−1. The main effects of treatment (p = 0.946,
≤ 0.001) and the interaction effect for treatment × time (p = 0.500,
= 0.045) showed no significant differences (Figure 5).
Recovery From Exercise
Mean heart rate during recovery was 162 ± 4 b·min−1 for the oxygen treatment and 161 ± 4 b·min−1 for the placebo. Analysis of heart rate data did not result in any significant main effects for treatment (p = 0.582,
= 0.031) or treatment by time interaction effects (p = 0.646,
= 0.038). Overall mean V[Combining Dot Above]CO2 during recovery after hyperoxia supplementation was 1.78 ± 0.21 L·min−1 and after placebo was 1.73 ± 0.20 L·min−1. Analysis of V[Combining Dot Above]CO2 during recovery showed insignificant main effects for both treatment (p = 0.344,
= 0.079) and interaction for treatment × time (p = 0.832,
Psychomotor Vigilance Testing
During the intermittent hyperoxia condition, the initial reaction time was 0.269 ± 0.033 seconds and after exercise was 0.263 ± 0.370 seconds. In the placebo condition, the initial reaction time was 0.289 ± 0.133 seconds and after exercise was 0.261 ± 0.027 seconds. Results of the PVT again did not reveal any significant main effects for treatment (p = 0.395,
= 0.038) or treatment × time interaction effects (p = 0.475,
= 0.027) for mean reaction time over the 5-minute test. Similar results for main effect for treatment (p = 0.535,
= 0.016) and treatment × time interaction (p = 0.125,
= 0.042) were found when minor lapses in attention were analyzed (Figure 6).
Rating of Perceived Exertion and Pain During Exercise
The mean RPE scores were 13.9 ± 3.7 for the intermittent hyperoxia treatment and 13.9 ± 3.6 for the placebo. The results of the GEE analysis for the Borg's 6-20 RPE did not demonstrate a significant treatment effect within the model (Wald's χ2 ≤ 0.001, p = 0.996). The mean 10-point analog pain scale scores were 5.7 ± 2.8 for the intermittent hyperoxia treatment and 5.4 ± 2.7 for the placebo. Similar results were obtained for the 10-point analog pain scale scores with treatment not being a significant predictor in the model (Wald's χ2 = 2.907, p = 0.088).
The purpose of this study was to determine the effects of a personal OS on performance during exhaustive exercise, respiratory responses during exhaustive exercise, and cognitive function after exhaustive exercise. This study was the first to explore, in 1 experiment, the effects of these types of supplements on physical and mental performance during exercise and recovery. The results indicate that the intermittent hyperoxia generated through the personal oxygen cylinder had no significant effect on the participants' performance in terms of time to exhaustion, when compared with the placebo. The respiratory responses, specifically minute ventilation (Ve, L·min−1) and V[Combining Dot Above]CO2 (L·O2·min−1), showed no significant difference between hyperoxia and the placebo, suggesting that respiratory rate is not suppressed, and carbon dioxide clearance is not enhanced by doses of oxygen concentrated air. During the recovery phase of exercise (first 2 minutes after exhaustion), the participants' heart rate and V[Combining Dot Above]CO2 (L·O2·min−1) showed no significant difference between hyperoxia and the placebo. In regards to effects on cognitive function, the PVT showed no significant difference in mean reaction time of participants over the 5-minute period for the supplement derived intermittent hyperoxia compared with the placebo. The participant's responses to the Borg's 6-20 RPE and the 10-point analog pain scale were also nonsignificant when results for supplement were compared with the placebo.
When considering previous research studies, the results of this study were found to be in contrast with some and in agreement with others. In contrast to previous findings that suggest administering oxygen-enriched air into the participant's airway may increase V[Combining Dot Above]O2max and improve maximum physical performance in exercises, the results of this study indicated that personal OSs designed to deliver intermittent hyperoxia did not yield such improvements to physical performance (13). The difference in these findings might be attributable to the nature of the delivery mechanism found in these forms of supplements. Regardless of delivery mechanism, the results of this study did agree with previous studies, which indicate that oxygen delivery is not considered to be the limiting factor in maximal exercise performance (1,13,18,24,31). All variables observed in the recovery phase (first 2 minutes after exhaustion) showed no significant difference with use of the personal OS and the placebo. This supported the findings of Ozgurbuz et al. (21), Robbins et al. (22), and Winter et al. (34), which stated that breathing supplemental oxygen has not resulted in any significantly different physiological effects documented in recovery, as compared with ambient air. The results of this study indicate no differences between normoxia and intermittent hyperoxia in regards to cognitive function and reaction time after exhaustive exercise, which is in contrast to previous studies that have shown that oxygen significantly improves impaired reaction times that are often experienced in hypoxic conditions (17). Again, this may in part be due to the delivery mechanism employed by these supplements.
The present investigation was not without limitations. One limitation was the lack of literature regarding the dosing schemes for the use of personal OSs. In the absence of any input from previous research, the manufacturer's recommended dosing scheme was used. If a larger dose of the product was administered more frequently, different results may have been obtained. Results regarding participant's cognitive function may have been limited as well. Reaction time, determined through PVT, before the trial runs to exhaustion could have been involuntarily affected because of the participant's pre-exercise arousal. Pre-exercise arousal's influence on the PVT before exercise, as well as the run to exhaustion influencing the PVT after exercise, may have masked the possible effect of oxygen on overall reaction time. Although, if the pre-arousal did mask the effect of the supplement, the effect size would have likely been trivial.
As was previously stated, hyperoxia supplements are gaining popularity in the ergogenic aid market with a number of manufacturers supporting the use of personal oxygen cylinders to augment sports performance, and the aim of this study was to explore the efficacy of such products. The present investigation does not support the use of personal OSs for exercise performance, exercise recovery, or postexercise cognitive performance. It is important that strength and conditioning professionals are armed with accurate and relevant data when making decisions regarding the use of supplements. Given the results of this study, personal hyperoxic products do not seem to provide the desired results that would be expected from an effective ergogenic aid. Athletes, coaches, trainers, and recreational exercisers are encouraged to consider the results of this study when considering the use of similar supplements.
The present investigation was conducted with partial funding provided by Second Wind O2 LLC. The results of this study do not constitute an endorsement by the National Strength and Conditioning Association.
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Keywords:Copyright © 2014 by the National Strength & Conditioning Association.
aerobic; ergogenic; psychomotor; reaction time; RPE