The use of ergogenic aids to augment training adaptations is a popular strategy among athletes and fitness enthusiasts. Recently, respiratory muscle training and elevation-simulating masks have gained popularity as a means to enhance athletic performance and fitness by simulating altitude-like conditions. Specifically, the Elevation Training Mask (ETM) is a device worn during training and that the manufacturer describes as an “adjustable inhalation resistance exercise device.” It is designed to simulate altitude training (approximately 914–5,486 m) through oxygen restriction because the flux valves are designed to limit the amount of air entering the mask (2). However, a common misconception among consumers wearing the “elevation mask” is that the ETM simulates altitude by creating a hypobaric (reduced partial pressure of oxygen) environment when, in fact, there are limited supporting data (5). Although modest hypoxemia created by the ETM during exercise has been demonstrated (5), the mechanism of oxygen desaturation does not mimic that of altitude, and more research is needed to identify the specific physiological mechanism. A reduced breathing frequency imparted by the mask's flux valve system and resistance caps, whereas wearing the ETM during exercise is considered a potential factor resulting in arterial hypoxemia. This, in addition to a rebreathing of expired carbon dioxide, is likely responsible rather than a reduced partial pressure of oxygen in the atmosphere and a subsequent shift of the oxygen-dissociation curve (5). In addition, the magnitude of oxygen desaturation is less than that of terrestrial altitude, suggesting that wearing the ETM does not produce a hypoxic stimulus great enough to elicit physiologic responses within the body that would be experienced at true elevation (5).
Rather than acting as a hypoxic altitude simulator, the peripheral air resistance generated by ETM intake flux valves may directly stress breathing musculature, thereby identifying the ETM as more of a respiratory muscle trainer (RMT). In theory, a RMT may induce respiratory muscle fatigue and increase respiratory muscle strength, lung capacity, and oxygen efficiency over time. Respiratory muscle fatigue has been identified as a major factor contributing to exercise limitation during short-term maximal exercise and, thus, highlights the potential benefit of increasing respiratory muscle strength through RMT (11). As indicated by Porcari et al. (18), 6 weeks of high-intensity interval training while wearing an ETM resulted in significant increases in ventilatory threshold (VT) and power output at VT. However, no changes were found in hematological variables pre-to-post training, suggesting that the ETM functions more like an RMT than a tool that simulates high-altitude training (18).
Limited research is available regarding adaptations in strength performance when an ETM is combined with a resistance exercise program (18). Acute hypoxic exposure combined with resistance training has been shown to optimize muscle growth because of the increased accumulation of certain hormones and metabolites that serve as key components in the signaling of critical anabolic pathways (13,21). In addition, resistance training during hypoxic exposure has been shown to contribute to advanced fiber-type recruitment that may contribute to greater increases in maximal strength (23). The ETM manufacturers also claim to benefit high-intensity and high-volume resistance training performance under the assumption that oxygen restriction may result in adaptations relating to an enhanced buffering capacity (2). In theory, an improved buffering capacity could augment muscular endurance and improve high-intensity exercise tolerance; however, it is not currently known if the ETM would compromise the ability to train at high enough intensities to elicit said adaptations. Regardless, the ETM has been heavily marketed toward anaerobic activities of short-term maximal intensity such as short-distance sprints, football, basketball, and mixed martial arts.
Given that the acute impact on the physiological responses resulting from use of the ETM has yet to be evaluated in a controlled, laboratory environment, the purpose of this study was to investigate the acute effects of the ETM on resistance exercise performance, markers of metabolic stress, and ratings of mental fatigue in recreational weightlifters. We hypothesized that wearing the ETM during bouts of resistance training would diminish the subject's potential of achieving a desired total volume of work during the back squat, bench press, and maximal effort sprint while hindering the ability to complete desired workloads great enough to achieve muscular strength, hypertrophy, and peak anaerobic power. In addition, we hypothesized that the restriction of breathing would provide sufficient psychological discomfort to diminish feelings of mental alertness, energy, and focus during the resistance training bouts.
Experimental Approach to the Problem
Resistance-trained men were recruited to participate in a randomized, cross-over design study to examine the acute effects of wearing an ETM on strength and anaerobic sprint performance. Subjects first completed a familiarization session before the start of the study to gain familiarity with the strength training equipment, nonmotorized treadmill, and the training and testing exercise protocols. Informed consent, medical history, and personal information were also collected during this time. Subjects reported to the Human Performance Laboratory within 1 week of the familiarization session for baseline testing that included body composition analysis and maximal strength testing for the bench press and back squat exercises. Subjects then completed the first of 2 experimental testing sessions on a nonconsecutive day (within 3–7 days of baseline testing). Subjects were randomly assigned to complete the first of 2 experimental conditions wearing either the mask (ETM) or no mask (NM), so that an equal number of subjects completed either the ERM or NM condition first. The ETM consists of a silicone mask and flexible neoprene head strap that covers the nose and mouth and uses an adjustable flux valve system with multilevel resistance caps (Figure 1).
During each experimental testing session, baseline measures for blood lactate, oxygen saturation, and subjective measures of fatigue were assessed before performance testing. Subjects then completed a 10-minute dynamic warm-up and then wore either the mask (ETM) or nothing to serve as the control (NM) during the performance testing. Subjects then completed a standardized exercise protocol for the bench press, back squat, and sprint exercises. One week after the first testing session, subjects completed the second experimental testing session using an identical testing protocol under the opposite treatment condition.
Twenty-five healthy resistance-trained men were initially recruited to participate in this study. Five subjects did not complete both experimental trials and were dropped from the final data analysis. Descriptive statistics of the subjects who completed both conditions are presented in Table 1.
All subjects were initially recruited on the basis of their previous resistance training experience and were selected to participate if entrance criteria were met. Subjects were allowed to participate in the study if they had been regularly participating in a resistance training program for at least 2 years and were able to bench press at least their body weight and back squat >1.5 times their body weight. All subjects were over the age of 18. Before testing, subjects provided written informed consent in accordance with the University of Wisconsin-La Crosse Institutional Review Board for Protection of Human Subjects.
Session 1: Familiarization
During the familiarization session, subjects completed 2 sets of 10 repetitions using approximately 50% of their estimated 5-repetition maximum (5RM) for the back squat and bench press exercises, respectively. Subjects completed sets both with and without the ETM to familiarize themselves with the equipment. Subjects also completed a practice of 25-second sprint test (100% effort) on a nonmotorized treadmill (NMT-Force II Treadmill; Woodway USA, Waukesha, WI, USA) both with and without the ETM.
Session 2: Baseline
During the baseline testing session, subjects were assessed for height, weight, and body composition using air displacement plethysmography (Bod Pod; Cosmed, Chicago, IL, USA). Baseline measurements of maximal strength in the back squat and bench press exercises were evaluated using a 5RM test on a Smith Machine (Plyopower Technologies, Lismore, Australia) and supervised by the same researcher.
Subjects were instructed to drink only water and not to eat or exercise for the preceding 2 hours. On arrival to the laboratory, height and body mass were recorded to the nearest 0.01 cm and 0.02 kg, respectively, using a stadiometer and digital scale (Bod Pod; Cosmed). Body composition was then assessed using air displacement plethysmography (Bod Pod; Cosmed). Previous studies indicate air displacement plethysmography to be an accurate and reliable means to assess changes in body composition (25). Body mass and body volume were then used to estimate body fat percentage (% fat) based on the Brozek equation (8).
First, subjects completed 2 warm-up sets of 5–10 repetitions at a load corresponding to approximately 50% of their estimated 5RM with 3 minutes of rest allowed between sets. Subjects then began performing sets of 5 repetitions of increasing weight with 3 minutes of recovery between attempts until determination of their 5RM using methods modified from the National Strength and Conditioning Association guidelines for maximal strength testing (24). All 5RM determinations were made within 5 attempts. To be considered a successful back squat attempt, subjects were instructed to squat down until the tops of the thighs were parallel to the floor. For a repetition to be considered successful during the bench press, subjects were instructed to lower the bar to their chest during the eccentric phase and return to full extension during the concentric phase. These values were also used to validate the entrance criteria regarding minimal strength requirements for participation in the study. After maximal strength testing, subjects completed an additional 25-second practice sprint test (100% effort) on the NMT to gain further familiarity with the equipment and protocols as previously described (14).
Sessions 3, 4: Experimental Testing
During the ETM condition, the mask was adjusted according to the manufacturer's recommendations for a setting to simulate an “altitude resistance” of 2,743 m based on previous pilot work. Before the testing session, subjects completed a questionnaire to assess their baseline subjective feelings of focus, energy, alertness, and fatigue using a 5-point Likert scale, which has been previously used in our laboratory (9). Baseline fingertip blood samples were taken and assessed for lactate [La] using a handheld lactate analyzer (Lactate Plus; Nova Biomedical, Waltham, MA, USA). Test-to-test reliability with this device in our laboratory has yielded high reliability with a mean intraclass coefficient of 0.977. Baseline oxygen saturation (SpO2) was assessed using a finger pulse oximeter (Allegiance, McGaw Park, IL, USA) before testing. Subjects then completed a 5-minute standardized warm-up consisting of dynamic movements similar to the familiarization session.
Immediately after the warm-up, subjects were instructed to complete 6 sets of 10 repetitions (or as many as possible) of back squat at a load corresponding to 85% of their predetermined 5RM with 2 minutes of rest between each set. Subjects were instructed to complete each repetition as explosively as possible. Subjects then completed a seventh set to failure using the same load. During the ETM trial, subjects wore the ETM during all testing periods and during rest periods between sets. Total training volume completed was recorded. Bar velocity was assessed using a linear position transducer (Tendo Fitrodyne, Sports Machines; Tendo, Trencin, Slocak Republic), which was attached to the right side of the bar. Peak and average velocity were recorded for each repetition completed during the protocol. The Fitrodyne is a reliable measure of velocity yielding a high intraclass correlation coefficient of R = 0.97 (95% CI, 0.95–0.98) in resistance-trained men for lower-body exercises (10).
The subjective questionnaire was administered, and blood lactate was evaluated approximately 1 minute after the last repetition of the seventh set. Oxygen saturation was recorded at 1, 2, and 3 minutes after the last repetition of the seventh set. Subjects were instructed to continue wearing the ETM until all data were collected at which time they were allowed to remove the ETM and rest for 10 minutes. After the rest period, subjects completed the same protocol for the bench press exercise. After the bench press data collection, subjects were allowed to remove the ETM and rest.
After a 20-minute rest period, subjects put the mask on and completed a 25-second maximal effort sprint test on the NMT against a workload set to 18% of the subject's body mass. Subjects were given a 5-second countdown and instructed to sprint as fast as possible for the entire 25 seconds. All sprints were started from a self-selected crouched, split stance position as previously described (14). Dependent variables for the sprint test included peak velocity, average velocity, and total work completed over the 25-second sprint. Peak velocity values were determined by isolating the greatest peak velocity across individual running strides using Pacer Performance Software (Innervations, Perth, Western Australia). MATLAB (MathWorks, Natick, MA, USA) software was used to determine the average velocity and total work achieved during the sprint test using measurements acquired from each individual running stride.
Blood lactate levels were assessed immediately after the 25-second sprint test followed by the completion of the subjective questionnaire. Oxygen saturation levels were recorded at 1, 2, and 3 minutes after sprint. Subjects were instructed to continue wearing the ETM until data were collected. Subjects were allowed to return to normal activity habits with the exception of performing back squat and bench press exercises 72 hours before testing. Subjects were instructed to complete a 2-day food log before each testing session that was analyzed for total energy and macronutrient intake using the commercially available nutrition analysis program (MyFitnessPal, Under Armour, Inc., Baltimore, MD, USA). Subjects were instructed to consume the same food before each testing session to ensure that exercise performance was not influenced by acute dietary changes.
Standard descriptive characteristics were used to describe the subject population and to evaluate the responses to wearing the ETM. Differences in total repetitions and volume achieved during the squat and bench press exercises as well as differences in peak velocity, average velocity, and total work during sprint tests between conditions were compared using paired-sample t tests.
Differences in peak velocity, repetitions, and volume achieved per set of back squat and bench press exercises between conditions were analyzed using a 2-way (treatment × set) analysis of variance (ANOVA) with repeated measures for each set. Differences in blood lactate, oxygen saturation, as well as differences in energy, alertness, focus, and fatigue between conditions were also analyzed using 2-way (treatment × time) ANOVA with repeated measures for time. Pairwise comparisons were made using Tukey's post hoc procedures. The alpha level was set at p ≤ 0.05 to achieve statistical significance for all analyses. All analyses were conducted using the Statistical Package for the Social Sciences (SPSS version 23; SPSS, Inc., Chicago, IL, USA).
Some adverse side effects were reported throughout the study in relation to wearing the ETM. Two subjects voluntarily terminated testing reporting that the physiological discomfort associated with the breathing restriction of the ETM hindered the ability to complete the testing sessions. In addition, one subject experienced severe dizziness and lightheadedness while wearing the ETM and was also excluded from the study. One subject was not able to complete the first testing session because of aggravation of a previous injury, and one subject was not able to complete the last testing session because of a scheduling conflict. In addition, only data from 19 of the 20 subjects were included in the analysis of the sprint test because a technical issue produced improper data recording.
A summary of the number of repetitions completed during the back squat and bench press exercise protocols is presented in Table 2. The number of repetitions completed during the bench press significantly declined (p < 0.001) during subsequent sets for both conditions beginning at set 3 with no significant set by condition interaction observed (p = 0.08).
A summary of peak velocities achieved per set for the back squat and bench press exercises is presented in Figures 2 and 3, respectively. Peak velocity declined in both the back squat (p < 0.001) and bench press (p < 0.001) during subsequent sets for both conditions beginning at set 5 when repetitions were collapsed and expressed as an average for sets 1–6. Peak velocity was greater during the NM condition (p < 0.001) for the bench press with post hoc analysis revealing that these differences occurred beginning at set 5 when repetitions were collapsed and expressed as an average for sets 1–6. When repetitions were expanded to include peak velocities across all 7 sets, a main effect for condition was observed and the peak velocity achieved during the NM condition was greater for both back squat (p = 0.04) and bench press (p = 0.04). A greater peak velocity (p = 0.04) was achieved during the sprint test in the NM condition compared with the ETM. There was no difference in the average velocity (p = 0.85) or total work completed (p = 0.81) between conditions during the sprint test.
A summary of blood lactate measurements throughout the experimental protocol is included in Table 3. When compared between conditions, blood lactate values were higher after the bench press (p < 0.001) and sprint test (p < 0.001) in the NM condition.
A summary of oxygen saturation measurements after the back squat, bench press, and sprint test can be seen in Figures 4–6, respectively. Oxygen saturation levels were lower (p < 0.001) than baseline measurements at minutes 1, 2, and 3 after the back squat, bench press, and sprint test during both conditions. Lower oxygen saturation levels (p <0.01) were observed at 1-minute after squat during the ETM condition when compared with the NM condition.
A main effect for time was observed regarding ratings of energy as evidenced by decreases in ratings of energy after bench press and sprint test (p < 0.001) when compared with baseline for both conditions. No significant condition × time interaction was observed (p = 0.75) for ratings of energy. A main effect for time was observed for fatigue as evidenced by increases in ratings of fatigue after squat, bench press, and sprint test (p < 0.001) when compared with baseline for both conditions with no significant condition × time interaction observed (p = 0.52). Significantly lower ratings of alertness and focus for task were found after squat, bench press, and sprint test in the ETM condition compared with the no ETM condition as evidenced by a significant time × condition interaction (p < 0.001).
The primary purpose of the current study was to investigate the acute effects of the ETM on resistance exercise performance, maximal effort sprint performance, and markers of metabolic stress in trained recreational weightlifters. A secondary aim was to examine the effects of the ETM on ratings of mental alertness, energy, and focus. To the best of our knowledge, this is the first study to examine the effects of the ETM on resistance exercise performance. The study used a protocol designed to elicit a high degree of fatigue and a protocol that may be used in a hypertrophy-focused program (i.e., 6 sets of 10 repetitions, 85% of 5RM) (22). According to the results of the current study, the use of the ETM did not attenuate the total training volume achieved by the participants. Contrary to our preliminary hypotheses, no difference was observed in repetitions achieved per set, repetitions achieved to failure, or total repetitions across all sets in the back squat and bench press exercise protocols. In addition, wearing the ETM did not affect total volume load (repetitions × workload) achieved in either back squat or bench press, suggesting that wearing the ETM does not hinder the ability to complete a desired workload when using a muscle hypertrophy-focused protocol.
Previous research has indicated that declines in peak velocity during resistance training offer a strong indicator of muscle fatigue and are the primary driving force behind reductions in power output (16,17,20). In this study, a decrease in peak velocity was observed during set 5 and subsequent sets in the back squat and bench press for both conditions, suggesting the onset of muscular fatigue. When expressed as an average across all sets for both back squat and bench press, peak velocity was found to be lower in the ETM condition. The ability to maintain a higher working velocity output during multiple sets throughout a training session could potentially result in enhanced training adaptations in muscular strength and power over time as described by Oliver et al. (16). Therefore, wearing the ETM may hinder long-term training adaptations by diminishing velocity and subsequent power output during single training sessions. Analysis of performance during the maximal effort sprint test yielded similar results to that of the resistance training session because peak velocity achieved under the ETM condition was lower than the peak velocity achieved without the ETM. However, the ETM did not seem to negatively influence average velocity or total work achieved during the sprint test. In summary, the use of the ETM for speed and power development may attenuate training outcomes because the potential to achieve maximal velocity during training may be compromised.
Previous research has demonstrated that blood lactate values can be used as an indicator of exercise intensity because increased levels suggest a greater reliance on the anaerobic energy and coincide with the onset of metabolic acidosis (4,19). The results of the current study suggest that wearing the ETM during resistance training sessions may result in diminished metabolic stress, as evidenced by lower blood lactate levels. Specifically, blood lactate values collected on completion of each exercise were found to be lower in the ETM condition after squat (6.6%; although nonsignificant), bench press (20.0%), and sprint (12.3%) compared with lactate values in the no ETM condition. Because total number of back squat and bench press repetitions did not differ between conditions, the differences in blood lactate were not likely a result of training volume differences. Furthermore, the similar SpO2 level between conditions eliminates decreases in arterial oxygen saturation or oxygen availability as possible explanations for the differing blood lactate values. It is possible that differences in muscle fiber recruitment patterns during the different conditions may have influenced blood lactate levels. The observed differences in bar velocity may be indicative of shifts in fiber recruitment, specifically a reduction of fast-twitch muscle fiber utilization. This, in turn, may have led to decreases in blood lactate levels as fast-twitch muscle fibers produce the greatest lactate response because of a greater reliance on anaerobic glycolysis (6–8). Therefore, a reduction in fast-twitch fiber recruitment, as evidenced by the lower velocity of movement, may explain the reduction in blood lactate values observed in the ETM condition. The lower peak velocity in tandem with lower blood lactate values suggests that wearing the ETM may have diminished training intensity.
Although limitation of muscle fiber recruitment resulting from the ETM provides a plausible explanation for the direct relationship between lower peak velocities and concomitantly lower blood lactate values, the reason why muscle fiber recruitment may have been limited when wearing the ETM is not clear and warrants further investigation. A possible explanation, however, lies within a body of evidence that demonstrates motor performance can be directly influenced by focus of attention (15,25). The “constrained action hypothesis” suggests that holding an external focus during activity facilitates motor performance through promotion of automatic control of the movement being performed (12). By contrast, adopting an internal focus of attention induces more deliberate and conscious control of the movement, thereby constraining or disrupting “normal” automatic control processes (12). Although subjects were instructed to perform each repetition as explosively as possible, it is possible that when subjects performed the back squat and bench press while wearing the ETM, their external focus of pressing the barbell shifted to an internal focus of controlling breathing against the restriction of the ETM ultimately distracting them. Likewise, during the sprint test, subjects likely focused more on breathing rather than sprinting as fast as possible. Such a shift of focus toward breathing rather than pressing the barbell or sprinting as explosively as possible may have contributed to the lack of significant differences observed in performance.
Analysis of oxygen saturation was performed in the current study to further examine the influence of ETM on the potential states of hypoxia created during resistance training. The results of the current study suggest that the ETM may serve more as a RMT rather than a hypoxic training device. Oxygen saturation levels recorded at 1, 2, and 3 minutes after exercise were found to be lower when compared with baseline for the no ETM and ETM conditions during the back squat, bench press, and sprint test. It should be noted that the observed reductions in SpO2 represent a normal drop in SpO2 that can be expected during high-intensity exercise (3). A lower SpO2 was found at 1-minute after squat as the ETM produced an oxygen saturation level lower than that observed with no ETM. However, this oxygen saturation was less than 1% lower than that observed without the ETM and continued to fit within the range of normal SpO2 values during high-intensity exercise. Granados et al. (5) found similar responses in oxygen saturation levels in a study comparing the physiologic responses of the ETM and a sham mask. When worn during a 20-minute treadmill workout (60% of V̇o2max), SpO2 levels averaged 94, 91, and 89% for the sham, 2,743, and 4,572 m altitude settings, respectively. It should be noted that this study also used an altitude setting of 2,743 m. Granados et al. (5) observed lower SpO2 values compared with this study, however, the nature of the exercise performed and type of training, (i.e., anaerobic vs. continuous aerobic training), likely contributed to such differences as the resistance training protocol used allowed for rest periods between sets that permitted SpO2 values to recover. Nonetheless, SpO2 levels observed in this study and the study by Granados et al. (5) were much less than what occurs at terrestrial altitude as oxygen saturation levels at 2,743 m of altitude typically fall to 89% (1) compared with the average 96.7% observed in the current study while wearing the ETM. Granados et al. (5) postulated that the modest hypoxemia observed while wearing the ETM was likely due to a combination of reduced breathing frequency imparted by the ETM resistance caps and the rebreathing of expired carbon dioxide that accumulated in the mask's large dead space (∼240 ml) rather than hypoxia shifting the oxygen-dissociation curve leading to reduced arterial oxygen saturation. It can then be assumed that, such SpO2 levels, whether classified as hypoxemic or not, are not comparable with that of true altitude exposure and are presumably not great enough to elicit metabolite buildup on the same order of magnitude as true elevation. Therefore, the ETM likely does not provide any additional benefit to the signaling of anabolic factors necessary to optimize muscle growth (13,21) as has been previously theorized, based on the results of the current study.
To our surprise, analysis of questionnaire ratings scored on the Likert scale did not provide evidence that wearing the ETM during bouts of resistance training impacts mental factors of exercise performance. In fact, no differences were found in ratings of energy, fatigue, alertness, or focus on task for any exercise between conditions. These findings revealed that wearing the ETM during high-intensity resistance training was not well tolerated, which is in opposition to findings by Granados et al. (5) who found only modest elevations in RPE and anxiety while wearing the ETM. It should also be noted that 3 subjects were excluded from the study because of excessive side effects and psychological discomfort associated with restriction of breathing or overwhelming feelings of claustrophobia associated with full coverage of the nose and mouth. It is highly recommended that individuals wishing to exercise with the ETM allow for appropriate familiarization with wearing the mask to reduce the likelihood of adverse responses to the ETM.
A major limitation of this study lies in the fact that a sham mask was not included as a condition. Inclusion of a sham mask may have provided insight as to whether the constrained action hypothesis was a predominant factor contributing to lower peak velocities achieved while wearing the mask. Although the ETM is commonly interpreted as a hypoxic training device, results indicate that the ETM did not produce any differences in oxygen saturation when compared with sprint or resistance training without the use of ETM and do not reflect SpO2 levels associated with true elevation. Therefore, it was suggested that the ETM functions more as an RMT device. Additional research that includes short-term training studies are also warranted to provide support for this phenomenon and to identify if continued training with the ETM would minimize the observed reductions in peak velocity and how it would influence training adaptations over time. It is also worth mentioning that the use of the ETM during resistance exercise and sprint training was not well tolerated as 3 subjects were unable to complete the protocol while wearing the ETM. In addition, the ETM negatively influenced subjective ratings of alertness and focus for task during the training session.
Results of the current study suggest that the use of the ETM during resistance training does not hinder the ability to achieved desired workloads or training volume during resistance training. However, the use of the ETM does seem to negatively influence peak velocity during both the back squat and bench press exercises, which may attenuate training outcomes over time. The ETM may also negatively impact subjective ratings of focus and alertness during strenuous bouts of activity. Therefore, athletes who are training for maximal power development may want to exercise caution when considering and implementing an ETM into a training program because it may hinder velocity of movement during training and result in physical discomfort. Furthermore, the use of an ETM during training may impose a risk of adverse events, which should also be considered before implementing the device into a training program.
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