Altitude training involves living and/or training at high altitude for numerous weeks and has been used for decades by athletes to improve their performance both at sea level and at altitude (1,6,7). Additionally, there is sufficient empirical evidence of a decline in aerobic performance at altitudes as low as 1,500 m (19), while anaerobic performance does not seem to be impacted by the level of elevation during testing (3). These detriments in aerobic performance at altitude are often attributed to the reduction in both barometric pressure and the partial pressure of oxygen (PO2). Furthermore, there is also the increased risk of suffering from acute mountain sickness (AMS), which can lead to additional decreases in performance, and, in extreme cases, may result in life-threatening conditions such as high-altitude cerebral edema or high-altitude pulmonary edema (19).
Present day military operations often require the deployment of personnel in elevated regions without the benefit of an acclimatization period (18,19), which may require 1–3 weeks for physiological changes to occur (3,16,17,19). Any decrease in performance because of decrease in atmospheric pressure or symptoms of AMS may result in significant reductions in personnel capabilities to carry out their assignments accurately. The majority of studies investigating the effects of living and/or training at altitude on performance focus on elite-level athletes (2–4,13,21).
Intermittent hypoxic training (IHT) involves the user to be subjected to brief exposures, typically 1–2 hours, of simulated high-altitude conditions to elicit a reduction in PO2 below normal levels (i.e., hypoxia) (20). Intermittent hypoxic training can be performed while the user is exercising, allowing them to “live low-train high.” This practice has become increasingly popular amongst athletes despite limited, inconclusive evidence of any increased release of erythropoietin from previous studies (8,11,15). Yet, a review by Gore et al. (10) identified multiple nonhematological processes such as angiogenesis, energy transport and production, and pH regulation that may lead to enhanced endurance performance on completion of hypoxic training. Initial studies examining IHT and elite athletes have shown an increase in various performance parameters such as, but not limited to, lactate threshold, maximal aerobic capacity, and hemoglobin mass (2,5,14). Furthermore, a recent review by Fulco et al. (9) concluded that treatments using hypobaric hypoxia (reduced barometric pressure [PB] with 20.9% O2) proved a more effective acclimatization method to both reduce the risk and symptoms of AMS as well as to improve aerobic performance than those using normobaric hypoxia (sustained PB with <20.9% O2) treatments. However, there is still a lack of research-based evidence on the potential utility of IHT for tactical athletes and military applications.
Another possible implication of the increased research efforts into the effects of IHT is the apparent increase in the number of commercially available products designed to simulate training at elevation. One such device is the ventilatory training mask (training mask) used for this study (Figure 1), which has been designed and marketed as a method to simulate training at altitude by restricting airflow. The training masks increase the effort of breathing, which may possibly lead to respiratory muscle training, and introduce low levels of hypoxemia through the buildup of expired CO2 in the mask itself (11). From a functional perspective, these training masks could potentially serve as an acclimatization tool for military personnel living or training near sea levels at a far lesser cost than traditional IHTs. Currently, there is a dearth of research-based evidence regarding the effectiveness to improve aerobic or anaerobic performance measures using similar training masks. Although the authors acknowledge that the methodology used to carry out this study does have its limitations, we believe the training scenario used during the intervention period is one based on practicality, thus the applicability for military personnel and all tactical athletes justified such methods. Therefore, the purpose of this study was to determine the efficacy of the training mask in improving both aerobic and anaerobic performance after a 6-week intervention training period.
Experimental Approach to the Problem
To assess the potential impact of IHT to improve both aerobic and anaerobic fitness, through the use of the training mask, an intervention period of 6 weeks was used to allow for physiological changes to occur. On completion of the pretesting sessions, subjects were paired based on both branch affiliation and initial maximal aerobic capacity (V[Combining Dot Above]O2max_pre) results. One subject from each pair was then randomly assigned to either the MASK or CON group. The MASK group wore the training mask, which was set to simulate training at 2,743.2 m during each physical training (PT) session attended over the 6-week intervention period, and the CON group completed PT sessions under normal or normoxic conditions. The intervention period consisted of 2 PT sessions per week for the Air Force (AF) cadets and 4 PT sessions per week for the Army cadets for a 6-week period. Before wearing the training mask during PT sessions, each ROTC cadet wore their assigned training mask for 5 separate 15-minute sessions in a nonexercise setting to acclimate themselves to breathing with the mask. The MASK group was permitted to briefly remove the training mask for hydration purposes during PT sessions, but participants were instructed to keep the duration of the drink breaks to less than 60 seconds. All participants were asked to maintain their current exercise training routines performed outside of the PT sessions and to continue their regular dietary habits. Furthermore, to monitor use of the training mask, each participant assigned to the MASK group signed a compliance document indicating the percentage of the PT sessions during the intervention period that they wore the training mask. Limitations of the experimental approach exist in that there was no sham training masks used for the CON group nor was the study design blinded to either the subjects or the researchers. A further limitation exists in that no physiological measurements such as arterial oxygen saturation (SaO2) were collected during the PT sessions, thus making it impossible to determine whether subjects were exposed to hypoxia.
This study was approved by the university's institutional review board (IRB), and all subjects (age 19.47 ± 1.22 years, weight 73.2 ± 9.94 kg, height 174.79 ± 6.5 cm, body fat 7.85 ± 2.9%) were informed of the benefits and risks of the investigation before signing an IRB-approved informed consent form to participate in this study. All subjects were currently living at an elevation of 299.9 m. Each subject was familiarized with the testing protocol and the use of the training mask before the onset of the study. Nineteen healthy male ROTC cadets (AF, n = 11; Army, n = 8) completed the anthropometry and anaerobic portions of the study, and 17 of the 19 cadets (AF, n = 10; Army, n = 7) completed the aerobic testing protocol. Subjects were paired based on both ROTC affiliation (AF or Army) and V[Combining Dot Above]O2max to create 2 groups: a ventilatory training mask group (MASK; n = 9) and a control group (CON; n = 10). The MASK and CON groups were of similar fitness levels as determined by between-group mean V[Combining Dot Above]O2max levels measured before the intervention period. All subjects completed their regularly scheduled PT sessions under the instruction of their respective ROTC PT leaders, and all participants assigned to the MASK group completed an adherence form during the final day of posttesting and stating that they wore the device at least 75% of the time during their PT sessions.
Army ROTC cadets were required to attend 4 PT sessions per week for a total of 24 required PT sessions during the intervention period. A standard weekly schedule for the Army ROTC PT sessions, which lasted approximately 60–75 minutes per day, consisted of the following: 2 days of body weight resistance training exercises such as push-ups, core training exercises, pull-ups, and dips followed by either a 3.2- to 8-km run or repeated sprints; one day of core training exercises followed by a 5-km run and 500- to 1,000-m swim (during which cadets did not wear the masks); and 1 day of rucking 5–10 km with 15.88-kg weighted backpack. The AF cadets were required to attend 2 PT sessions per week for a total of 12 required PT sessions during the intervention period. A standard weekly AF PT schedule consisted of 2 days of approximately 40-minute duration, which included bodyweight resistance exercises such as push-ups lunges, and planks, calisthenics such as jumping jacks and squat jumps, and repeated sprints of varying distances performed in a circuit training format.
Participants completed both pre- and postassessment consisting of 2 separate days of testing for each session with a 2- to 7-day period between the first and second testing days of both the pre- and posttesting assessments. Both testing days of the postassessment were completed within 2–10 days on the completion of the intervention training period to allow for sufficient recovery from the final PT session. The first day of each testing session consisted of anthropometry and anaerobic capacity (AC) measurements, and the second day consisted of a maximal aerobic capacity measurement. As per the National Strength and Conditioning Association (NSCA) fitness testing sequencing guidelines, testing order was not randomized but was completed in identical order for pre- and posttesting (12).
Anaerobic Capacity Test
On completion of anthropometry, all participants completed a 5-minute warm-up on a Monark Ergomedic 828E stationary bicycle (AB Cykelfabriken Monark, Vansbro, Sweden). Resistance during the warm-up was set at approximately 1.0 kg, and each participant was instructed to maintain a cadence of 75–100 rpm. After the warm-up, subjects completed a 30-second Wingate Anaerobic Test (WAnT) with a resistance of 7.5% of body weight on a Velotron Cycle Ergometer (RacerMate Inc., Seattle, WA, USA) to measure fatigue index (FI), AC, and peak power (PP). On completion of the WAnT, each subject performed a 2-minute cool-down with no resistance before dismounting the Velotron Cycle Ergometer.
Aerobic Capacity Test
After the 2- to 7-day rest period after the first day of each testing session, participants returned to complete a maximal aerobic capacity test. Before the test, all participants completed a 5-minute warm-up on a Monark Ergomedic 828E stationary bicycle (AB Cykelfabriken Monark). Resistance during the warm-up was set at approximately 1.0 kg, and each participant was instructed to maintain a cadence of 75–100 rpm. On completion of the warm-up, participants completed a maximal aerobic capacity treadmill ergometer test after the Bruce protocol. The test was completed on a Trackmaster treadmill (TMX 425C, Newton, KS, USA), and expired gases were analyzed using a mixing chamber by means of a TrueOne 2400 metabolic measuring system (Parvo Medics, Salt Lake City, UT, USA). Additionally, heart rate was continuously monitored using a Polar heart rate monitor (Polar Electro FT1 and T31, Lake Success, NY, USA). All subjects met the assumptions of a true maximal aerobic capacity test.
A repeated measures analysis of variance (ANOVA) design was used to assess differences within (pre vs. post) and between groups (MASK vs. CON) for each variable. A t-test for paired samples was calculated to determine any differences between the combined group's pre- and posttest values for all variables. All statistical analyses was performed using SPSS (Ver. 21.0 for Windows; SPSS, Chicago, IL, USA) with the statistical significance set at p ≤ 0.05.
The initial sample consisted of 23 participants but was reduced to 19 because of injuries unrelated to the study incurred by participants. Of the 19 remaining participants, 2 were unable to complete the aerobic capacity test. Subject characteristics are shown in Table 1.
Table 2 demonstrates the results of the WAnT used to measure AC. Between the 2 groups, the repeated measures ANOVA indicated that there were no significant differences in the main effect between groups in FI (F(1,17) = 0.009, p = 0.924), AC (F(1,17) = 0.128, p = 0.725), or PP (F(1,17) = 0.032, p = 0.860). Based on the results from the paired samples t-test, there was a significant improvement in AC for the combined groups (p < 0.001), whereas no significant difference was found for the combined group's FI (p = 0.724) or PP (p = 0.154) (Table 3). Although significance was not reached, the MASK and CON groups displayed marginal increases in FI of 2.42 and 1.46%, respectively. Both the MASK and CON groups demonstrated minute, yet insignificant, increases in AC of 4.5 and 4.19%, respectively. Finally, the MASK and CON groups exhibited small, albeit insignificant, increases in PP of 3.14 and 4.26%, respectively (Table 2).
Based on the results from repeated measures ANOVA, there was no significant difference in the main effect between groups after the intervention period on V[Combining Dot Above]O2max or TE; V[Combining Dot Above]O2max scores (F(1,15) = 0.598, p = 0.451) and TE (F(1,15) = 0.327, p = 0.576). Based on the results from the paired samples t-test, there was no significant difference between pre- and posttest V[Combining Dot Above]O2max (p = 0.141) or TE (p = 0.307) values of the combined groups (Table 3). Although statistical significance was not reached for either group, mean V[Combining Dot Above]O2max for the MASK group displayed a minute increase of 1.81%, and the mean V[Combining Dot Above]O2max CON group exhibited a greater increase of 5.57% (Table 4). Furthermore, both the MASK and CON groups exhibited increases in TE of 0.59 and 2.20%, respectively.
The primary finding of this investigation was the lack of a significant effect, beyond that of traditional PT, of the ventilatory training mask on any of the measured variables after the completion of the intervention period. An almost identical protocol by Warren et al. (22) produced similar results, finding no difference in V[Combining Dot Above]O2max improvements between the control and experimental groups. The use of IHT has become increasingly popular in professional and Olympic sports (23), but other than marketing testimonials, there is limited empirical evidence supporting the use of such a training apparatus. Since IHT has increased in popularity as an apparent cost-effective alternative to traveling to high-altitude locations to train while still receiving the physiological benefit of training at altitude, research-based evidence regarding the efficacy of this and similar devices is warranted. Such findings will also be relevant as military branches use various methods of altitude training to prepare for high-altitude operations (18,18). Additionally, the particular mask used for this research study is significantly less expensive than current IHT equipment and would have been a cost-conscious IHT strategy.
Prior research has indicated that aerobic exercise is impacted by altitude to a greater extent than anaerobic exercise (3,18). Additionally, previous studies have also demonstrated that IHT may improve anaerobic metabolism to a greater extent than aerobic metabolism, thus leading to greater potential improvements in anaerobic exercise performance than aerobic performance at sea-level (1,13). Furthermore, strict monitoring of training intensity with respect to percentage of V[Combining Dot Above]O2max would assure precise training adherence for more accurate assessments. A review of 25 published intermittent hypoxic exposure (IHE) studies concluded that more research is needed to determine the effectiveness of shorter interval (<90 minutes)/higher altitude (>4,000 m) and extended durations (>4 hours) at elevation levels between 2,500- and 3,500-m IHE treatments (19). Thus, supplementary research may be necessary to determine the efficacy of the training masks with a greater number of exposures, longer intervention duration, or a more rigid and progressive program design.
Additionally, as the participants in this study were tested at sea-level, future research to determine the efficacy of the masks to acclimatize participants to performing at altitude may also be warranted, which may be of greater concern to teams located in mountainous locations and armed forces personnel. It should be noted that as a combined group, only AC significantly improved between the pre- and posttesting, while there was no significant difference between pre- and posttest values for FI, PP, V[Combining Dot Above]O2max, or TE (Table 3). The subjects in this study were highly trained in an attempt to increase the applicability to military personnel and tactical athletes. Therefore, it may be possible that as a group, they are near each of their respective genetic ceilings regarding ACs and aerobic capacities and thus had limited room to improve either their anaerobic or aerobic fitness levels. Although this investigation did not find any significant aerobic or AC improvements over standard PT as a result of wearing the training masks, further research incorporating the aforementioned training protocol changes does seem justified.
Based on these preliminary results and contrary to our hypothesis, the training masks used in this study could not demonstrate the same physiological benefits observed after true IHT. Our results indicate that despite the training mask being set to simulate training at approximately 2,750 m, there were no significant anaerobic or aerobic benefits from wearing the training masks. It is recommended that individuals, athletic teams, or military personnel seeking to use IHT, follow established and validated technologies, such as hypoxic rooms, and training protocols until further research determines the conditions under which a ventilatory training mask improves exercise conditioning.
The authors acknowledge both the Cadets and the Cadre of the U.S. Army and AF ROTC Units who participated in this study. The authors declare that no conflicts of interest, past or present, existed throughout this investigation.
1. Álvarez-Herms J, Julià-Sánchez S, Corbi F, Pagès T, Viscor G. Anaerobic performance after endurance strength training in hypobaric environment. Sci Sports 29: 311–318, 2014.
2. Bonetti DL, Hopkins WG, Kilding AE. High-intensity kayak performance after adaptation to intermittent hypoxia. Int J Sports Physiol Perform 1: 246, 2006.
3. Burtscher M, Faulhaber M, Flatz M, Likar R, Nachbauer W. Effects of short-term acclimatization
to altitude (3200 m) on aerobic and anaerobic exercise performance. Int J Sports Med 27: 629–635, 2006.
4. Chapman RF, Stray-Gundersen J, Levine BD. Individual variation in response to altitude training
. J Appl Physiol (1985) 85: 1448–1456, 1998.
5. Czuba M, Waskiewicz Z, Zajac A, Poprzecki S, Cholewa J, Roczniok R. The effects of intermittent hypoxic training
on aerobic capacity and endurance performance in cyclists. J Sports Sci Med 10: 175, 2011.
6. Daniels J. Altitude and athletic training and performance. Am J Sports Med 7: 371–373, 1979.
7. Dick F. Training at altitude in practice. Int J Sports Med 13: S203–S206, 1992.
8. Eckardt K-U, Boutellier U, Kurtz A, Schopen M, Koller EA, Bauer C. Rate of erythropoietin formation in humans in response to acute hypobaric hypoxia. J Appl Physiol (1985) 66: 1785–1788, 1989.
9. Fulco CS, Beidleman BA, Muza SR. Effectiveness of preacclimatization strategies for high-altitude exposure. Exerc Sports Sci Rev 41: 55–63, 2013.
10. Gore CJ, Clark SA, Saunders PU. Nonhematological mechanisms of improved sea-level performance after hypoxic exposure. Med Sci Sports Exerc 39: 1600–1609, 2007.
11. Granados J, Jansen L, Harton H, Kuennen M. “Elevation training Mask” Induces hypoxemia but utilizes a novel feedback signaling mechanism. Presented at International Journal of Exercise Science: Conference Proceedings, 2014.
12. Harman E, Pandorf C. Principles of test selection and administration. In: Essentials of Strength Training and Conditioning (2nd ed.). Champaign, IL: Human Kinetics, 2000. pp. 275–307.
13. Hendriksen IJ, Meeuwsen T. The effect of intermittent training in hypobaric hypoxia on sea-level exercise: A cross-over study in humans. Eur J Appl Physiol 88: 396–403, 2003.
14. Humberstone-Gough CE, Saunders PU, Bonetti DL, Stephens S, Bullock N, Anson JM, Gore CJ. Comparison of live high: Train low altitude and intermittent hypoxic exposure. J Sports Sci Med 12: 394, 2013.
15. Knaupp W, Khilnani S, Sherwood J, Scharf S, Steinberg H. Erythropoietin response to acute normobaric hypoxia in humans. J Appl Physiol (1985) 73: 837–840, 1992.
16. Krueger GP. Environmental medicine research to sustain health and performance during military
deployment: Desert, arctic high altitude stressors. J Therm Biol 18: 687–690, 1993.
17. Levine BD. Intermittent hypoxic training
: Fact and fancy. High Alt Med Biol 3: 177–193, 2002.
18. McLellan T, Kavanagh M, Jacobs I. The effect of hypoxia on performance during 30 s or 45 s of supramaximal exercise. Eur J Appl Physiol Occup Physiol 60: 155–161, 1990.
19. Muza SR. Military
applications of hypoxic training for high-altitude operations. Med Sci Sports Exerc 39: 1625–1631, 2007.
20. Powell FL, Garcia N. Physiological effects of intermittent hypoxia. High Alt Med Biol 1: 125–136, 2000.
21. Roels B, Bentley DJ, Coste O, Mercier J, Millet GP. Effects of intermittent hypoxic training
on cycling performance in well-trained athletes. Eur J Appl Physiol 101: 359–368, 2007.
22. Warren B, Spaniol F, Bonnette R. The effects of an elevation training mask on VO2Max of male reserve officers training corps cadets. Presented at National Strength & Conditioning Association. National Conference and Exhibition, 2015.
23. Wilber RL. Introduction to altitude/hypoxic training symposium. Med Sci Sports Exerc 39: 1587–1589, 2007.
Keywords:Copyright © 2016 by the National Strength & Conditioning Association.
altitude training; acclimatization; intermittent hypoxic training; military; acute mountain sickness