COMBINING NORMOBARIC HYPOXIA WITH SHORT-TERM RESISTANCE TRAINING HAS NO ADDITIVE BENEFICIAL EFFECT ON MUSCULAR PERFORMANCE AND BODY COMPOSITION JEN-YU HO,1 TAI-YU KUO,1 KUAN-LIN LIU,1 XIANG-YI DONG,1
AND
KANG TUNG2
Departments of 1Athletic Performance; and 2Physical Education, National Taiwan Normal University, Taipei, Taiwan ABSTRACT Ho, J-Y, Kuo, T-Y, Liu, K-L, Dong, X-Y, and Tung, K. Combining normobaric hypoxia with short-term resistance training has no additive beneficial effect on muscular performance and body composition. J Strength Cond Res 28(4): 935–941, 2014— The aim of this study was to determine the effects of shortterm resistance training combined with systemic hypoxia on muscular performance and body composition. Eighteen resistance-untrained men (21.3 6 2.0 years, 172.7 6 5.5 cm, 67.3 6 9.7 kg) were matched and assigned to 2 experimental groups: performing 6 weeks of squat exercise training under normobaric hypoxia (H, FiO2 = 15%) or normoxia (N). In both groups, subjects performed 3 weekly sessions (a total of 18 sessions) of 3 sets of back squat at 10-repetition maximum with 2 minutes of rest between sets. Dynamic, isometric, and isokinetic leg strength and body composition were measured under normoxia before and after resistance training. Squat 1 repetition maximum (1RM) improved significantly (p # 0.05) after resistance training in both H and N groups (88.9 6 16.9 to 109.4 6 17.0 kg and 90.0 6 12.2 to 105.6 6 13.3 kg, respectively). However, there were no changes in maximal isometric and isokinetic leg strength, lean body mass, and fat mass after the resistance training in both groups. In addition, no significant differences were observed between H and N groups in squat 1RM, maximal isometric and isokinetic leg strength, and body composition. The major findings of this study suggest that short-term resistance training performed under normobaric hypoxia has no additive beneficial effect on muscular performance and body composition. In practical terms, our data suggest that the use of systemic hypoxia during short-term resistance training is not a viable method to further enhance
Address correspondence to Jen-Yu Ho, [email protected]. 28(4)/935–941 Journal of Strength and Conditioning Research Ó 2014 National Strength and Conditioning Association
muscular performance and body composition in previously resistance-untrained men.
KEY WORDS intermittent hypoxic training, weight training, maximal strength, lean body mass INTRODUCTION
S
ince the 1968 Summer Olympics that took place in the high elevation of Mexico City (2,240 m), studies of altitude training or hypoxia training have received more attention in the literature for its role in improving endurance performance. Nowadays, altitude or hypoxia training (i.e., preferably at 2,500 m above sea level) has become a common practice especially adopted by endurance athletes to enhance their performance at sea level or at altitude. Indeed, after 2–3 weeks’ endurance training at altitude, improvement of the oxygen transport capacity, and increase of mitochondrial density and oxidative capacity in muscles have been reported and associated with improved endurance performance at sea level (2–4). In contrast, researchers have observed muscle mass loss (210 to 215%), decrease in muscle fiber size (220 to 225%), and muscle mitochondrial density in typical mountaineers who had experienced long-term exposure (5–6 weeks) to real or simulated altitude (9,15). These detrimental effects of chronic altitude training have led to a proposed training protocol that applies hypoxic exposure only during all or a limited number of training sessions while recovering in normoxia (23). This training method, known as “living-low and training-high (LLTH)” or “intermittent hypoxic training (IHT),” would not only allow subjects to maximize the hypoxia stimulus on muscles during exercise but also get optimal conditions for muscle recovery, thus avoiding the detrimental effects of long-term hypoxic exposure on muscles. Over the past decades, LLTH or IHT has been extensively studied and now commonly adopted as part of training program, especially for endurance athletes to improve their exercise performance at sea level (5,18). Furthermore, with the advancement of technology, hypoxia can be simulated through the use of an altitude simulation tent or room making LLTH or IHT possible and VOLUME 28 | NUMBER 4 | APRIL 2014 |
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Intermittent Hypoxic Training on Muscular Performance convenient at sea level for exercise training and for experimental purposes. Although most studies have combined the altitude or IHT with endurance training, the effects of combining IHT with resistance training on muscular adaptations and performance are still mostly unknown. Resistance training has grown in popularity in past decades and has been extensively studied, especially for its role in muscular strength, power, and hypertrophy (14). Most studies have confirmed the positive effects of resistance training on muscular strength and muscle mass (8,14,24). However, coaches and researchers are still trying to develop better and more effective training methods to maximize strength and muscle mass gains over a short period. Effective training technique has always been a major area of interest because to maintain or improve muscular strength and muscle mass is very important to athletes and the general population for successful athletic performance and for good health, respectively. Recently, some researchers began to apply systemic hypoxia through the use of altitude simulation tent or room during resistance training to examine its effectiveness on maximizing muscular performance. These studies hypothesized that the application of systemic hypoxia during resistance training can provide additive beneficial effects on muscular adaptations and performance (11,12,21). The hypotheses were based on the positive results observed from occlusion training or Kaatsu training studies. Several studies combining low-intensity resistance exercise with moderate vascular occlusion have demonstrated greater growth hormone (GH) response (25) and subsequently greater increase in muscle size and strength (26). The possible physiological mechanisms could be that local hypoxia of skeletal muscles induced by blood flow restriction to the exercising muscle caused greater lactate production. The greater lactate accumulation may result from more recruitment of fast-twitch muscle fibers when muscles are forced to contract in a hypoxic condition (20). Greater lactate concentrations are involved in the stimulation of GH secretion from the pituitary gland (6,27). It is, however, important to note that the physiological mechanisms underlying muscular adaptations to occlusion training and systemic hypoxia training could be different. Thus, combining systemic hypoxia with resistance training may not provide similar beneficial effects on muscular adaptations and performance as occlusion training. Further studies are needed for clarification. Among these researchers, Kon et al. (11,12) have speculated in their studies that applying systemic hypoxia during resistance exercise can be as effective as occlusion training on inducing greater anabolic hormone responses. In agreement with their hypotheses, they reported that performing bench press and leg press at 70 and 50% of 1 repetition maximum (1RM) in normobaric hypoxic conditions (FiO2 = 13%) caused greater accumulation of metabolites and a greater anabolic hormone response than that in the normoxic condition. These anabolic hormones play a substantial role in promot-
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ing muscular strength and muscle hypertrophy to resistance training. However, the physiological mechanisms underlying muscular adaptations to systemic hypoxia training are still not clarified and may not be the same as muscular adaptations to occlusion training. Whether short-term moderate-intensity resistance training performed under systemic hypoxia can eventually lead to greater muscular strength and hypertrophy, further studies are required for clarification. Thus, the purpose of the present study was to investigate the effects of a 6-week moderate-intensity resistance training program combining systemic hypoxia on muscular performance and body composition. It was hypothesized that in comparison with normoxia, short-term moderate-intensity resistance training performed under normobaric hypoxia would significantly induce greater muscular strength and hypertrophy.
METHODS Experimental Approach to the Problem
To test the hypothesis of the study that combining systemic hypoxia with short-term resistance training would induce greater gains in muscular strength and lean body mass, we matched up and assigned 18 resistance untrained men (aged 20–25 years) into 2 experimental groups: (a) performing 6 weeks of squat exercise training in normobaric hypoxia (H group, FiO2 = 15%) and (b) performing 6 weeks of squat exercise training in normoxia (N group, FiO2 = 21%). After completing the familiarization to all experimental tests, maximal dynamic strength was assessed by measuring squat 1RM in all subjects under normoxia. In addition, isometric and isokinetic leg strength, and body composition were measured under normoxia before the resistance training. Subjects then performed 3 sets of back squat at an intensity of 10-repetition maximum (10RM) with 2 minutes of rest between sets under normobaric hypoxia (H group) or normoxia (N group) for a total of 18 training sessions (3 times per week). Weight was increased systematically during the next workout if the prescribed amount of repetitions were completed in 2 consecutive sessions. Maximal dynamic, isometric and isokinetic leg strength, and body composition were measured again under normoxia after 6 weeks of resistance training to determine the effects of combining short-term resistance training with systemic hypoxia on muscular performance and body composition. Subjects
Eighteen recreationally active male subjects (21.3 6 2.0 years, 172.7 6 5.5 cm, 67.3 6 9.7 kg) volunteered to participate in this study and were assigned to hypoxia (H) and normoxia (N) groups (n = 9 per group). Table 2 summarizes the physical characteristics of the subjects. All the subjects were primarily undergraduate and graduate students from local universities. They were either completely untrained or recreationally active and had not been involved with regular resistance training for at least 6 months before the study. Subjects were excluded from the study if they had any preexisting medical condition or orthopedic limitations that put
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Journal of Strength and Conditioning Research them at risk while performing the squat exercises. Subjects were asked to avoid intense exercise, alcohol, caffeine, or any drug for at least 24 hours before any strength tests performed before and after resistance training. In addition, subjects were encouraged to maintain their regular dietary habits during the course of the study and to refrain from any exercise training outside the study. Pretraining and post-training tests were conducted at the same time of the day for each subject. After a detailed explanation of the study procedures and associated risks, all subjects provided a written informed consent before their participation. The study was approved by the University Institutional Review Board for Human Subjects. Procedures
Squat One Repetition Maximum Test. All subjects went through a familiarization session first at which they were familiarized with the proper technique for performing the barbell squat exercise using Cybex Free Weight Squat Rack (Cybex International, Inc., Medway, MA, USA). Approximately 4–5 days after the familiarization, subject’s squat 1RM was performed under normoxia as a measure of maximal dynamic lower-body strength. Subjects were instructed to avoid consumption of alcohol and caffeine 24 hours before the strength test and to keep hydrated by drinking enough water before the test. The 1RM test used the method described by Kraemer et al. (13). Briefly, a warmup set of 8–10 repetitions at 50% of their estimated 1RM was performed followed by another warm-up set of 3–5 repetitions at 85% of estimated 1RM. After the warm-up sets, 1RM attempts were performed within 4–5 trials separated by at least 3 minutes of rest to determine their squat 1RM. Squat depth was standardized by having subjects who adopt a shoulder width stance and descend until the knee joints angle reach 908. Knee joints angle verification was monitored by the same investigator throughout the trials. One repetition maximum test was considered valid if the subjects performed correctly with correct depth and completed the entire lift in a controlled manner without assistance. Squat 1RM was conducted again under normoxia after 6 weeks of resistance training at the same time of the day as baseline performance in each subject. Isometric and Isokinetic Leg Strength Tests. Leg strength was also assessed under normoxia by performing isometric and isokinetic knee extension and flexion using an isokinetic dynamometer (System 4 Pro; Biodex Medical Systems, Inc., Shirley, NY, USA). After a general warm-up and dynamic stretching, subjects were seated in a rigid chair and firmly strapped across the chest, hip, and distal thigh. The rotational axis of the dynamometer was aligned to the lateral femoral epicondyle of the right leg, and the lower leg was firmly attached to the dynamometer lever arm above the medial malleolus. Subjects were first familiarized with the dynamometer and the testing procedures before any data
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collection. Maximal isometric contractions were performed first with the knee joint set to a static angle of 608 (08 = full knee extension). Subjects performed 3 sets of 3-second isometric knee extensions and flexions with maximal voluntary efforts. Each set was separated by 90 seconds. Subjects were instructed to contract “as fast and forcefully as possible.” After 5 minutes of rest, maximal isokinetic contractions were performed at a speed of 608 per second. Subjects performed 5 isokinetic knee extensions and flexions continuously. The maximal torque values of isometric and isokinetic tests collected were used in statistical analyses. Each subject conducted isometric and isokinetic leg strength tests before and after 6 weeks of resistance training at the same time of the day. Systemic Hypoxic Exposure. Subjects of H group were trained in the normobaric hypoxic tent (CAT-315 Walk-In Tent; Colorado Altitude Training, Louisville, CO, USA) where oxygen-depleted air (i.e., nitrogen-enriched air) was pumped from hypoxia generator into the tent (width 3 length 3 height: 228.7 3 213.5 3 183.0 cm) to create simulated hypoxic condition (FiO2 = 15%, equivalent to 2,300 m altitude) where barometric pressure in the tent was equivalent to sea level (760 mm Hg). After finishing each workout, subjects left the hypoxic tent and rest in normoxia until their next workout performed in hypoxia. To verify and maintain the normobaric hypoxic condition in the tent (FiO2 = 14.5%–15%) during each training session for H group, the oxygen concentration was continuously monitored using an oxygen analyzer (Handi Plus; Maxtec, Salt Lake City, UT, USA) throughout the experiment. Subjects then entered the tent and rest for 10 minutes before performing the squat exercise in hypoxia. Arterial oxygen saturation (SpO2) was monitored by pulse oximeter (Novametrix Medical Systems Inc., Wallingford, CT, USA). Arterial oxygen saturation was recorded after 10 minutes of rest in the tent and after the squat exercise. The other training group (N group) also performed squat exercise in the tent but the oxygendepleted air was not pumped into the tent. Therefore, N group performed the squat exercise under normoxic condition (FiO2 = 21%, barometric pressure was equivalent to 760 mm Hg). Resistance Training Program. The resistance training program was a 6-week training program and the same for both H and N groups. However, the N group trained in the tent at noon first and the H group trained in the evening because of the time required (3–4 hours) to establish the normobaric hypoxic condition (FiO2 = 15%) in the tent. During all training sessions, subjects first performed a warm-up set of 10 squats at 50% of 1RM. Subjects then performed 3 sets of squat at 10RM loads with 2 minutes of rest between sets, 3 times per week for a total of 18 training sessions. Guidelines that there should be at least 1 rest day but not more than 3 days of rest between each workout session were followed. In addition, all the training sessions for both groups were performed between February and April of the same year. VOLUME 28 | NUMBER 4 | APRIL 2014 |
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Intermittent Hypoxic Training on Muscular Performance
Figure 1. Changes in squat 1 repetition maximum before and after 6 weeks of resistance training. Values are mean 6 SD. *p # 0.05 (vs. pretraining). H = resistance training in hypoxia; N = resistance training in normoxia.
In the first training session, 10RM was determined using 75% of the 1RM in the first set. Weight was slightly added, decreased, or remained the same during the next set to achieve 10RM loads. All sets were performed to or near muscular exhaustion. Weight was increased systematically during the next workout if the prescribed amount of repetitions were completed in 2 consecutive sessions. During all training sessions, subjects were trained one on one under the supervision of instructors. Makeup sessions were allowed if subjects missed a regularly scheduled training session to finish up a total of 18 training sessions.
Body Composition Assessment. All subjects measured body composition under normoxia using bioelectrical impedance analysis (InBody 720; Biospace Co. Ltd., Seoul, South Korea) before and after 6 weeks of resistance training. Twenty-four hours before the measurements, subjects were instructed to refrain from intense exercise. Two to 3 hours before the measurements, subjects were instructed to refrain from eating and drinking. Subjects were instructed to urinate and remove their watches, shoes, and shocks before the measurements. All these controls helped to keep the possible confounding factors of exercise, diet, and hydration status to a minimum to obtain valid measurements of lean body mass and fat mass.
Statistical Analyses
The dependent variables in this study (squat 1RM, isometric and isokinetic leg strength, and body composition) were analyzed by 2 (training group: hypoxia and normoxia) 3 2 (time: pretraining and post-training) mixed factor analysis of variance. All data sets satisfied statistical requirements for the liner approaches used. When a significant F score resulted, a Fisher’s least significant difference post hoc test was used to determine the pairwise differences between mean. The testretest reliability of the tests used in this study showed intraclass R values $0.90. The level of significance for all the tests was set at p # 0.05. All data are presented as mean 6 SD.
TABLE 1. Changes in isometric and isokinetic leg strength before and after 6 weeks of resistance training.*
RESULTS Squat One Repetition
H (n = 9) Pretraining Isometric strength (N$m) Knee extension Knee flexion Isokinetic strength (N$m) Knee extension Knee flexion
N (n = 9)
Post-training
Pretraining
Post-training
166.0 6 19.9 161.9 6 28.0 168.2 6 14.6 174.7 6 21.1 113.6 6 15.7 117.0 6 15.5 117.2 6 15.1 113.3 6 18.5 151.4 6 25.5 155.8 6 36.7 149.3 6 21.5 159.7 6 17.3 97.9 6 18.5 103.7 6 24.6 107.8 6 19.6 107.8 6 15.9
*Values are mean 6 SD. H = resistance training in hypoxia; N = resistance training in normoxia.
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Changes in squat 1RM before and after resistance training are shown in Figure 1. The results of the 2-way mixed design analysis of variance (group 3 time) indicated that there was no significant interaction between group and time (p . 0.05). However, there was significant main effect for time. Squat 1RM significantly improved (p # 0.05) after 6 weeks of resistance training in
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was verified and maintained for H group. Arterial oxygen satuTABLE 2. Changes in body weight, lean body mass and fat mass before and after ration was recorded after 10 mi6 weeks of resistance training.* nutes of rest in the hypoxic H (n = 9) N (n = 9) tent and immediately after the squat exercise. Arterial oxygen Pretraining Post-training Pretraining Post-training saturation significantly dropped to 92.9% when subjects Age (y) 21.4 6 2.2 21.2 6 1.9 Height (cm) 172.7 6 5.0 172.8 6 6.2 rested for 10 minutes inside Body weight (kg) 66.5 6 8.2 66.6 6 7.8 67.9 6 9.5 67.9 6 9.1 the hypoxic tent. Arterial oxyLean body mass (kg) 31.3 6 3.3 31.1 6 2.9 31.8 6 4.1 31.9 6 4.1 gen saturation remained signifFat mass (kg) 11.1 6 6.5 11.5 6 6.9 11.5 6 4.9 11.4 6 5.2 icantly lower (91.2%) than *Values are mean 6 SD. H = resistance training in hypoxia; N = resistance training in baseline value (97.8%) after normoxia. squat exercise. Similarly, Kelly et al. (10) reported that SpO2 dropped from 98 to 92% after exposure to inspired oxygen concentration of 15%. The SpO2 data of this study ensured both H and N groups (88.9 6 16.9 to 109.4 6 17.0 kg and 90.0 that subjects’ exposure to hypoxia was correctly controlled 6 12.2 to 105.6 6 13.3 kg, respectively). However, no signifduring the hypoxia training for H group. icant differences in squat 1RM were observed between H and It is well documented that resistance training is a strong N group before and after resistance training (p . 0.05). potent factor to increase muscular strength and promote Isometric and Isokinetic Leg Strength muscle hypertrophy (8,24). The magnitude of these training Table 1 shows changes in maximal isometric and isokinetic effects is considered to be dependent on intensity of exercise leg strength before and after resistance training. There was and the acute hormonal responses to resistance exercise. no significant interaction between group and time (p . 0.05). Moderate to high intensity of resistance exercise (i.e., above Furthermore, there was no significant main effect for group 65% of 1RM) may be required to increase muscular strength or time (p . 0.05). and induce greater anabolic hormonal responses that are highly correlated to the degree of muscle hypertrophy Body Composition (16). In the present study, moderate intensity of squat exerChanges in body weight, lean body mass and fat mass before cise (75% of 1RM or equivalent to 10RM) was performed for and after resistance training are shown in Table 2. The results 6 weeks. Our results reported that squat 1RM significantly were similar to maximal isometric and isokinetic leg strength. increased 24.2 and 17.5% in H and N groups (Figure 1) after No significant changes in body weight, lean body mass, and fat 6 weeks of squat training, suggesting that the moderate mass were observed from pretraining to post-training in either intensity was sufficient to induce muscular strength gains H or N group (p . 0.05). Furthermore, no significant between after short-term resistance training. However, in contrast group differences in body composition were observed before to the study hypothesis, we failed to demonstrate greater and after 6-week resistance training (p . 0.05). strength gains in H group when compared with N group. DISCUSSION Our finding is in contrast to a previous study suggesting that resistance training under hypoxic conditions improves musThe findings of the present study provide some insight into cle strength and induces muscle hypertrophy of elbow faster the speculative beneficial effects of combining normobaric than under normoxic conditions (21). In that study, 14 male hypoxia with resistance training on muscle strength and university students performed 4 sets of 10 repetitions of hypertrophy. The primary finding of this study was that elbow extension and flexion at intensity of 70% of 1RM with 6 weeks of resistance training (a total of 18 training sessions 1 minute of rest for 6 weeks under hypoxia (FiO2 = 16%) or at moderate intensity) performed under systemic hypoxia normoxia. Elbow strength and hypertrophy were signifi(FiO2 = 15%) did not induce greater improvement in muscantly greater for the hypoxia group than normoxia group. cular strength and lean body mass than that of normoxia. Despite the lack of significant differences in strength and Our data suggest that, the use of systemic hypoxia during muscle mass between H and N groups in our study, it is short-term resistance training has no additive beneficial important to note that this previous study provided lower effects on muscular strength and muscle hypertrophy in presample size (7 subjects per group) than our study. In addiviously resistance-untrained men. tion, although Nishimura’s study examined the smaller musTo examine the hypothesis of this study, the control for cle groups (e.g., biceps and triceps), we examined the larger hypoxic exposure during hypoxia training is required. muscle groups (e.g., gluteus maximus, quads, hamstrings). During each session of hypoxia training, normobaric hypFurthermore, magnetic resonance imaging was used to oxic condition (FiO2 = 14.5–15%, with an average of 14.7%) VOLUME 28 | NUMBER 4 | APRIL 2014 |
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Intermittent Hypoxic Training on Muscular Performance assess muscle hypertrophy in Nishimura’s study. In our study, bioelectrical impedance analysis was applied to assess muscle hypertrophy. All these differences in research design may contribute to the discrepancies between these 2 studies. Further research is obviously required in view of these concerns. The time course of gains in muscle mass has been investigated in previously untrained individuals. As neural adaptations occur first during the early phase of training (19), muscle hypertrophy becomes evident after 6 weeks of training (22). Although Kon et al. (11,12) have reported that hypoxia is a potent factor for the enhancements of GH responses to moderate intensity of resistance exercise (i.e., 50 and 70% of 1RM), it is expected to see a greater strength and muscle mass gains in H group than in N group after resistance training in our study. Surprisingly, in our study, 6 weeks of squat exercise training did not show significant increases in muscle mass in both H and N groups. It is possible that longer training time (.6 weeks) may be required to induce significant muscle hypertrophy as other studies have shown significant increases in muscle mass with high-intensity resistance training performed between 10 weeks to 10 months (7,17). It is also possible that systemic hypoxic exposure during resistance training may not induce greater gains in strength and muscle mass as observed from occlusion or Kaatsu training because the physiological mechanisms underlying muscular adaptations to occlusion training could be different from systemic hypoxia training. In addition to dynamic strength, isometric strength and isokinetic strength are other common strength tests that have long been used to assess muscular performance in exercise science research. In the present study, maximal dynamic strength as measure of 1RM squat significantly increased after short-term resistance exercise. However, maximal isometric strength and maximal isokinetic strength (at a speed of 608 per second) had no significant changes after training in both H and N groups. This agrees with a previous study showing that squat 1RM significantly increased but not peak isometric force after 13 weeks of dynamic resistance training (1). Similarly, Woo et al. (28) observed no significant increase in peak torque on knee extension/flexion after 12 weeks of resistance training at moderate intensity in adolescent males. As magnitude of strength improvement might be associated with the specificity of the strength training, this may explain the lack of significant changes in isometric and isokinetic strength after training in both groups in this study. Because systemic hypoxic exposure during resistance training did not induce greater gains in dynamic strength, it is not surprising to observe the lack of differences in isometric and isokinetic strength between H and N groups after 6 weeks of resistance training in this study. In summary, the present study investigated the effects of 6-week resistance training combining normobaric hypoxia on muscular performance and body composition. Squat 1RM improved significantly after short-term resistance training in
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both H and N groups. However, no significant changes in lean body mass were observed over 6 weeks of resistance training in both groups. The results of this study failed to demonstrate greater gains in muscular strength and hypertrophy in normobaric hypoxia than normoxia. Our data suggest that the application of systemic hypoxia during short-term resistance training may not be a promising training technique to induce greater muscular strength and enhance body composition in previously resistance-untrained men.
PRACTICAL APPLICATIONS As strength and muscle mass are key factors to improve athletic performance and the quality of life, how to maximize the strength and muscle mass effectively has always been a major area of interest to coaches, athletes, and researchers around the world. In recent years, some researchers have speculated that combining systemic hypoxia through the use of simulation altitude tents or rooms with resistance training may provide additive beneficial effects on muscular strength and body composition. Their speculations were based on the beneficial effects observed from combining occlusion training or Kaatsu training with resistance training. Despite previous studies have already reported greater anabolic hormone responses to moderate-intensity resistance exercise (above 50% of 1RM) in hypoxia, unfortunately our data suggest that short-term moderate-intensity resistance training performed under normobaric hypoxia (FiO2 = 15%) may not be a viable training method for increasing greater muscular strength and hypertrophy. In practical terms, the use of systemic hypoxia during resistance training may not be effective for enhancing greater muscular performance and body composition in previously resistance-untrained men.
ACKNOWLEDGMENTS The authors thank a dedicated group of subjects for their participation in this study and the members of the Human Performance Laboratory in National Taiwan Normal University for their assistance in data collection. This study was funded by a grant for “Aim for the Top University Plan” from National Taiwan Normal University and the Ministry of Education of Taiwan. The authors declare no conflicts of interest. Furthermore, the results of this study do not constitute endorsement by the authors or the National Strength and Conditioning Association.
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Journal of Strength and Conditioning Research 5. Geiser, J, Vogt, M, Billeter, R, Zuleger, C, Belforti, F, and Hoppeler, H. Training high–living low: Changes of aerobic performance and muscle structure with training at simulated altitude. Int J Sports Med 22: 579–585, 2001. 6. Goto, K, Ishii, N, Kizuka, T, and Takamatsu, K. The impact of metabolic stress on hormonal responses and muscular adaptations. Med Sci Sports Exerc 37: 955–963, 2005. 7. Ha¨kkinen, K, Ale´n, M, and Komi, PV. Changes in isometric forceand relaxation-time, electromyographic and muscle fibre characteristics of human skeletal muscle during strength training and detraining. Acta Physiol Scand 125: 573–585, 1985. 8. Ha¨kkinen, K, Pakarinen, A, Alen, M, Kauhanen, H, and Komi, PV. Neuromuscular and hormonal responses in elite athletes to two successive strength training sessions in one day. Eur J Appl Physiol Occup Physiol 57: 133–139, 1988. 9. Howald, H, Pette, D, Simoneau, JA, Uber, A, Hoppeler, H, and Cerretelli, P. Effects of chronic hypoxia on muscle enzyme activities. Int J Sports Med 11: S10–S14, 1990. 10. Kelly, PT, Swanney, MP, Frampton, C, Seccombe, LM, Peters, MJ, and Beckert, LE. Normobaric hypoxia inhalation test vs. response to airline flight in healthy passengers. Aviat Space Environ Med 77: 1143–1147, 2006. 11. Kon, M, Ikeda, T, Homma, T, Akimoto, T, Suzuki, Y, and Kawahara, T. Effects of acute hypoxia on metabolic and hormonal responses to resistance exercise. Med Sci Sports Exerc 42: 1279–1285, 2010. 12. Kon, M, Ikeda, T, Homma, T, Akimoto, T, and Suzuki, Y. Effects of low intensity resistance exercise under acute systemic hypoxia on hormonal responses. J Strength Cond Res 26: 611–617, 2012. 13. Kraemer, WJ and Fry, AC. Strength testing: Development and evaluation of methodology. In: Physiological Assessment of Human Fitness. P.J. Maud and C Foster, eds. Champaign, IL: Human Kinetics, 1995. pp. 115–138. 14. Kraemer, WJ and Ratamess, NA. Physiology of Resistance Training: Current Issues. OrthopPhys Therapy Clin North Am Exerc Tech. Philadelphia, PA: WB. Saunders, 2000. pp. 467–513. 15. MacDougall, JD, Green, HJ, Sutton, JR, Coates, G, Cymerman, AYP, and Houston, CS. Operation Everest II: structural adaptations in skeletal muscle in response to extreme simulated altitude. Acta Physiol Scand 142: 421–427, 1991. 16. McCall, GE, Byrnes, WC, Fleck, SJ, Dickinson, A, and Kraemer, WJ. Acute and chronic hormonal responses to resistance training
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designed to promote muscle hypertrophy. Can J Appl Physiol 24: 96–107, 1999. 17. McCartney, N, Hicks, AL, Martin, J, and Webber, CE. Long-term resistance training in the elderly: Effects on dynamicstrength, exercise capacity, muscle, and bone. J Gerontol A Biol Sci Med Sci 50: B97–B104, 1995. 18. Meeuwsen, T, Hendriksen, IJ, and Holewijn, M. Training-induced increases in sea-level performance are enhanced by acute intermittent hypobaric hypoxia. Eur J Appl Physiol 84: 283–290, 2001. 19. Moritani, T and DeVries, H. Neural factors vs hypertrophy in the time course of muscle strength gain. Am J Phys Med 58: 115–130, 1979. 20. Moritani, T, Michael-Sherman, W, Shibata, M, Matsumoto, T, and Shinohara, M. Oxygen availability and motor unit activity in humans. Eur J Appl Physiol Occup Physiol 64: 552–556, 1992. 21. Nishimura, A, Sugita, M, Kato, K, Fukuda, A, Sudo, A, and Uchida, A. Hypoxia increases muscle hypertrophy induced by resistance training. Int J Sports Physiol Perform 5: 497–508, 2010. 22. Phillips, SM. Short-term training: When do repeated bouts of resistance exercise become training? Can J Appl Physiol 5: 185–193, 2000. 23. Roels, B, Millet, GP, Marcoux, CJ, Coste, O, Bentley, DJ, and Candau, RB. Effects of hypoxic interval training on cycling performance. Med Sci Sports Exerc 37: 138–146, 2005. 24. Staron, RS, Karapondo, DL, Kraemer, WJ, Fry, AC, Gordon, SE, Falkel, JE, Hagerman, FC, and Hikida, RS. Skeletal muscle adaptations during early phase of heavy-resistance training in men and women. J Appl Physiol (1985) 76: 1247–1255, 1994. 25. Takarada, Y, Nakamura, Y, Aruga, S, Onda, T, Miyazaki, S, and Ishii, N. Rapid increase in plasma growth hormone after lowintensity resistance exercise with vascular occlusion. J Appl Physiol (1985) 88: 61–65, 2000. 26. Takarada, Y, Takazawa, H, Sato, Y, Takebayashi, S, Tanaka, Y, and Ishii, N. Effects of resistance exercise combined with moderate vascular occlusion on muscular function in humans. J Appl Physiol 88: 2097–2106, 2000. 27. Viru, M, Jansson, E, Viru, A, and Sundberg, CJ. Effect of restricted blood flow on exercise-induced hormone changes in healthy men. Eur J Appl Physiol Occup Physiol 77: 517–522, 1998. 28. Woo, MT, Chen, CK, Ghosh, AK, and Thimurayan, V. Effects of a resistance training programme on isokinetic peak torque and anaerobic power of 13-16 years old Taekwondo athletes. Int J Sports Sci Eng 2: 111–121, 2008.
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AND
KANG TUNG2
Departments of 1Athletic Performance; and 2Physical Education, National Taiwan Normal University, Taipei, Taiwan ABSTRACT Ho, J-Y, Kuo, T-Y, Liu, K-L, Dong, X-Y, and Tung, K. Combining normobaric hypoxia with short-term resistance training has no additive beneficial effect on muscular performance and body composition. J Strength Cond Res 28(4): 935–941, 2014— The aim of this study was to determine the effects of shortterm resistance training combined with systemic hypoxia on muscular performance and body composition. Eighteen resistance-untrained men (21.3 6 2.0 years, 172.7 6 5.5 cm, 67.3 6 9.7 kg) were matched and assigned to 2 experimental groups: performing 6 weeks of squat exercise training under normobaric hypoxia (H, FiO2 = 15%) or normoxia (N). In both groups, subjects performed 3 weekly sessions (a total of 18 sessions) of 3 sets of back squat at 10-repetition maximum with 2 minutes of rest between sets. Dynamic, isometric, and isokinetic leg strength and body composition were measured under normoxia before and after resistance training. Squat 1 repetition maximum (1RM) improved significantly (p # 0.05) after resistance training in both H and N groups (88.9 6 16.9 to 109.4 6 17.0 kg and 90.0 6 12.2 to 105.6 6 13.3 kg, respectively). However, there were no changes in maximal isometric and isokinetic leg strength, lean body mass, and fat mass after the resistance training in both groups. In addition, no significant differences were observed between H and N groups in squat 1RM, maximal isometric and isokinetic leg strength, and body composition. The major findings of this study suggest that short-term resistance training performed under normobaric hypoxia has no additive beneficial effect on muscular performance and body composition. In practical terms, our data suggest that the use of systemic hypoxia during short-term resistance training is not a viable method to further enhance
Address correspondence to Jen-Yu Ho, [email protected]. 28(4)/935–941 Journal of Strength and Conditioning Research Ó 2014 National Strength and Conditioning Association
muscular performance and body composition in previously resistance-untrained men.
KEY WORDS intermittent hypoxic training, weight training, maximal strength, lean body mass INTRODUCTION
S
ince the 1968 Summer Olympics that took place in the high elevation of Mexico City (2,240 m), studies of altitude training or hypoxia training have received more attention in the literature for its role in improving endurance performance. Nowadays, altitude or hypoxia training (i.e., preferably at 2,500 m above sea level) has become a common practice especially adopted by endurance athletes to enhance their performance at sea level or at altitude. Indeed, after 2–3 weeks’ endurance training at altitude, improvement of the oxygen transport capacity, and increase of mitochondrial density and oxidative capacity in muscles have been reported and associated with improved endurance performance at sea level (2–4). In contrast, researchers have observed muscle mass loss (210 to 215%), decrease in muscle fiber size (220 to 225%), and muscle mitochondrial density in typical mountaineers who had experienced long-term exposure (5–6 weeks) to real or simulated altitude (9,15). These detrimental effects of chronic altitude training have led to a proposed training protocol that applies hypoxic exposure only during all or a limited number of training sessions while recovering in normoxia (23). This training method, known as “living-low and training-high (LLTH)” or “intermittent hypoxic training (IHT),” would not only allow subjects to maximize the hypoxia stimulus on muscles during exercise but also get optimal conditions for muscle recovery, thus avoiding the detrimental effects of long-term hypoxic exposure on muscles. Over the past decades, LLTH or IHT has been extensively studied and now commonly adopted as part of training program, especially for endurance athletes to improve their exercise performance at sea level (5,18). Furthermore, with the advancement of technology, hypoxia can be simulated through the use of an altitude simulation tent or room making LLTH or IHT possible and VOLUME 28 | NUMBER 4 | APRIL 2014 |
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Intermittent Hypoxic Training on Muscular Performance convenient at sea level for exercise training and for experimental purposes. Although most studies have combined the altitude or IHT with endurance training, the effects of combining IHT with resistance training on muscular adaptations and performance are still mostly unknown. Resistance training has grown in popularity in past decades and has been extensively studied, especially for its role in muscular strength, power, and hypertrophy (14). Most studies have confirmed the positive effects of resistance training on muscular strength and muscle mass (8,14,24). However, coaches and researchers are still trying to develop better and more effective training methods to maximize strength and muscle mass gains over a short period. Effective training technique has always been a major area of interest because to maintain or improve muscular strength and muscle mass is very important to athletes and the general population for successful athletic performance and for good health, respectively. Recently, some researchers began to apply systemic hypoxia through the use of altitude simulation tent or room during resistance training to examine its effectiveness on maximizing muscular performance. These studies hypothesized that the application of systemic hypoxia during resistance training can provide additive beneficial effects on muscular adaptations and performance (11,12,21). The hypotheses were based on the positive results observed from occlusion training or Kaatsu training studies. Several studies combining low-intensity resistance exercise with moderate vascular occlusion have demonstrated greater growth hormone (GH) response (25) and subsequently greater increase in muscle size and strength (26). The possible physiological mechanisms could be that local hypoxia of skeletal muscles induced by blood flow restriction to the exercising muscle caused greater lactate production. The greater lactate accumulation may result from more recruitment of fast-twitch muscle fibers when muscles are forced to contract in a hypoxic condition (20). Greater lactate concentrations are involved in the stimulation of GH secretion from the pituitary gland (6,27). It is, however, important to note that the physiological mechanisms underlying muscular adaptations to occlusion training and systemic hypoxia training could be different. Thus, combining systemic hypoxia with resistance training may not provide similar beneficial effects on muscular adaptations and performance as occlusion training. Further studies are needed for clarification. Among these researchers, Kon et al. (11,12) have speculated in their studies that applying systemic hypoxia during resistance exercise can be as effective as occlusion training on inducing greater anabolic hormone responses. In agreement with their hypotheses, they reported that performing bench press and leg press at 70 and 50% of 1 repetition maximum (1RM) in normobaric hypoxic conditions (FiO2 = 13%) caused greater accumulation of metabolites and a greater anabolic hormone response than that in the normoxic condition. These anabolic hormones play a substantial role in promot-
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ing muscular strength and muscle hypertrophy to resistance training. However, the physiological mechanisms underlying muscular adaptations to systemic hypoxia training are still not clarified and may not be the same as muscular adaptations to occlusion training. Whether short-term moderate-intensity resistance training performed under systemic hypoxia can eventually lead to greater muscular strength and hypertrophy, further studies are required for clarification. Thus, the purpose of the present study was to investigate the effects of a 6-week moderate-intensity resistance training program combining systemic hypoxia on muscular performance and body composition. It was hypothesized that in comparison with normoxia, short-term moderate-intensity resistance training performed under normobaric hypoxia would significantly induce greater muscular strength and hypertrophy.
METHODS Experimental Approach to the Problem
To test the hypothesis of the study that combining systemic hypoxia with short-term resistance training would induce greater gains in muscular strength and lean body mass, we matched up and assigned 18 resistance untrained men (aged 20–25 years) into 2 experimental groups: (a) performing 6 weeks of squat exercise training in normobaric hypoxia (H group, FiO2 = 15%) and (b) performing 6 weeks of squat exercise training in normoxia (N group, FiO2 = 21%). After completing the familiarization to all experimental tests, maximal dynamic strength was assessed by measuring squat 1RM in all subjects under normoxia. In addition, isometric and isokinetic leg strength, and body composition were measured under normoxia before the resistance training. Subjects then performed 3 sets of back squat at an intensity of 10-repetition maximum (10RM) with 2 minutes of rest between sets under normobaric hypoxia (H group) or normoxia (N group) for a total of 18 training sessions (3 times per week). Weight was increased systematically during the next workout if the prescribed amount of repetitions were completed in 2 consecutive sessions. Maximal dynamic, isometric and isokinetic leg strength, and body composition were measured again under normoxia after 6 weeks of resistance training to determine the effects of combining short-term resistance training with systemic hypoxia on muscular performance and body composition. Subjects
Eighteen recreationally active male subjects (21.3 6 2.0 years, 172.7 6 5.5 cm, 67.3 6 9.7 kg) volunteered to participate in this study and were assigned to hypoxia (H) and normoxia (N) groups (n = 9 per group). Table 2 summarizes the physical characteristics of the subjects. All the subjects were primarily undergraduate and graduate students from local universities. They were either completely untrained or recreationally active and had not been involved with regular resistance training for at least 6 months before the study. Subjects were excluded from the study if they had any preexisting medical condition or orthopedic limitations that put
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the
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Journal of Strength and Conditioning Research them at risk while performing the squat exercises. Subjects were asked to avoid intense exercise, alcohol, caffeine, or any drug for at least 24 hours before any strength tests performed before and after resistance training. In addition, subjects were encouraged to maintain their regular dietary habits during the course of the study and to refrain from any exercise training outside the study. Pretraining and post-training tests were conducted at the same time of the day for each subject. After a detailed explanation of the study procedures and associated risks, all subjects provided a written informed consent before their participation. The study was approved by the University Institutional Review Board for Human Subjects. Procedures
Squat One Repetition Maximum Test. All subjects went through a familiarization session first at which they were familiarized with the proper technique for performing the barbell squat exercise using Cybex Free Weight Squat Rack (Cybex International, Inc., Medway, MA, USA). Approximately 4–5 days after the familiarization, subject’s squat 1RM was performed under normoxia as a measure of maximal dynamic lower-body strength. Subjects were instructed to avoid consumption of alcohol and caffeine 24 hours before the strength test and to keep hydrated by drinking enough water before the test. The 1RM test used the method described by Kraemer et al. (13). Briefly, a warmup set of 8–10 repetitions at 50% of their estimated 1RM was performed followed by another warm-up set of 3–5 repetitions at 85% of estimated 1RM. After the warm-up sets, 1RM attempts were performed within 4–5 trials separated by at least 3 minutes of rest to determine their squat 1RM. Squat depth was standardized by having subjects who adopt a shoulder width stance and descend until the knee joints angle reach 908. Knee joints angle verification was monitored by the same investigator throughout the trials. One repetition maximum test was considered valid if the subjects performed correctly with correct depth and completed the entire lift in a controlled manner without assistance. Squat 1RM was conducted again under normoxia after 6 weeks of resistance training at the same time of the day as baseline performance in each subject. Isometric and Isokinetic Leg Strength Tests. Leg strength was also assessed under normoxia by performing isometric and isokinetic knee extension and flexion using an isokinetic dynamometer (System 4 Pro; Biodex Medical Systems, Inc., Shirley, NY, USA). After a general warm-up and dynamic stretching, subjects were seated in a rigid chair and firmly strapped across the chest, hip, and distal thigh. The rotational axis of the dynamometer was aligned to the lateral femoral epicondyle of the right leg, and the lower leg was firmly attached to the dynamometer lever arm above the medial malleolus. Subjects were first familiarized with the dynamometer and the testing procedures before any data
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collection. Maximal isometric contractions were performed first with the knee joint set to a static angle of 608 (08 = full knee extension). Subjects performed 3 sets of 3-second isometric knee extensions and flexions with maximal voluntary efforts. Each set was separated by 90 seconds. Subjects were instructed to contract “as fast and forcefully as possible.” After 5 minutes of rest, maximal isokinetic contractions were performed at a speed of 608 per second. Subjects performed 5 isokinetic knee extensions and flexions continuously. The maximal torque values of isometric and isokinetic tests collected were used in statistical analyses. Each subject conducted isometric and isokinetic leg strength tests before and after 6 weeks of resistance training at the same time of the day. Systemic Hypoxic Exposure. Subjects of H group were trained in the normobaric hypoxic tent (CAT-315 Walk-In Tent; Colorado Altitude Training, Louisville, CO, USA) where oxygen-depleted air (i.e., nitrogen-enriched air) was pumped from hypoxia generator into the tent (width 3 length 3 height: 228.7 3 213.5 3 183.0 cm) to create simulated hypoxic condition (FiO2 = 15%, equivalent to 2,300 m altitude) where barometric pressure in the tent was equivalent to sea level (760 mm Hg). After finishing each workout, subjects left the hypoxic tent and rest in normoxia until their next workout performed in hypoxia. To verify and maintain the normobaric hypoxic condition in the tent (FiO2 = 14.5%–15%) during each training session for H group, the oxygen concentration was continuously monitored using an oxygen analyzer (Handi Plus; Maxtec, Salt Lake City, UT, USA) throughout the experiment. Subjects then entered the tent and rest for 10 minutes before performing the squat exercise in hypoxia. Arterial oxygen saturation (SpO2) was monitored by pulse oximeter (Novametrix Medical Systems Inc., Wallingford, CT, USA). Arterial oxygen saturation was recorded after 10 minutes of rest in the tent and after the squat exercise. The other training group (N group) also performed squat exercise in the tent but the oxygendepleted air was not pumped into the tent. Therefore, N group performed the squat exercise under normoxic condition (FiO2 = 21%, barometric pressure was equivalent to 760 mm Hg). Resistance Training Program. The resistance training program was a 6-week training program and the same for both H and N groups. However, the N group trained in the tent at noon first and the H group trained in the evening because of the time required (3–4 hours) to establish the normobaric hypoxic condition (FiO2 = 15%) in the tent. During all training sessions, subjects first performed a warm-up set of 10 squats at 50% of 1RM. Subjects then performed 3 sets of squat at 10RM loads with 2 minutes of rest between sets, 3 times per week for a total of 18 training sessions. Guidelines that there should be at least 1 rest day but not more than 3 days of rest between each workout session were followed. In addition, all the training sessions for both groups were performed between February and April of the same year. VOLUME 28 | NUMBER 4 | APRIL 2014 |
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Intermittent Hypoxic Training on Muscular Performance
Figure 1. Changes in squat 1 repetition maximum before and after 6 weeks of resistance training. Values are mean 6 SD. *p # 0.05 (vs. pretraining). H = resistance training in hypoxia; N = resistance training in normoxia.
In the first training session, 10RM was determined using 75% of the 1RM in the first set. Weight was slightly added, decreased, or remained the same during the next set to achieve 10RM loads. All sets were performed to or near muscular exhaustion. Weight was increased systematically during the next workout if the prescribed amount of repetitions were completed in 2 consecutive sessions. During all training sessions, subjects were trained one on one under the supervision of instructors. Makeup sessions were allowed if subjects missed a regularly scheduled training session to finish up a total of 18 training sessions.
Body Composition Assessment. All subjects measured body composition under normoxia using bioelectrical impedance analysis (InBody 720; Biospace Co. Ltd., Seoul, South Korea) before and after 6 weeks of resistance training. Twenty-four hours before the measurements, subjects were instructed to refrain from intense exercise. Two to 3 hours before the measurements, subjects were instructed to refrain from eating and drinking. Subjects were instructed to urinate and remove their watches, shoes, and shocks before the measurements. All these controls helped to keep the possible confounding factors of exercise, diet, and hydration status to a minimum to obtain valid measurements of lean body mass and fat mass.
Statistical Analyses
The dependent variables in this study (squat 1RM, isometric and isokinetic leg strength, and body composition) were analyzed by 2 (training group: hypoxia and normoxia) 3 2 (time: pretraining and post-training) mixed factor analysis of variance. All data sets satisfied statistical requirements for the liner approaches used. When a significant F score resulted, a Fisher’s least significant difference post hoc test was used to determine the pairwise differences between mean. The testretest reliability of the tests used in this study showed intraclass R values $0.90. The level of significance for all the tests was set at p # 0.05. All data are presented as mean 6 SD.
TABLE 1. Changes in isometric and isokinetic leg strength before and after 6 weeks of resistance training.*
RESULTS Squat One Repetition
H (n = 9) Pretraining Isometric strength (N$m) Knee extension Knee flexion Isokinetic strength (N$m) Knee extension Knee flexion
N (n = 9)
Post-training
Pretraining
Post-training
166.0 6 19.9 161.9 6 28.0 168.2 6 14.6 174.7 6 21.1 113.6 6 15.7 117.0 6 15.5 117.2 6 15.1 113.3 6 18.5 151.4 6 25.5 155.8 6 36.7 149.3 6 21.5 159.7 6 17.3 97.9 6 18.5 103.7 6 24.6 107.8 6 19.6 107.8 6 15.9
*Values are mean 6 SD. H = resistance training in hypoxia; N = resistance training in normoxia.
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Changes in squat 1RM before and after resistance training are shown in Figure 1. The results of the 2-way mixed design analysis of variance (group 3 time) indicated that there was no significant interaction between group and time (p . 0.05). However, there was significant main effect for time. Squat 1RM significantly improved (p # 0.05) after 6 weeks of resistance training in
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was verified and maintained for H group. Arterial oxygen satuTABLE 2. Changes in body weight, lean body mass and fat mass before and after ration was recorded after 10 mi6 weeks of resistance training.* nutes of rest in the hypoxic H (n = 9) N (n = 9) tent and immediately after the squat exercise. Arterial oxygen Pretraining Post-training Pretraining Post-training saturation significantly dropped to 92.9% when subjects Age (y) 21.4 6 2.2 21.2 6 1.9 Height (cm) 172.7 6 5.0 172.8 6 6.2 rested for 10 minutes inside Body weight (kg) 66.5 6 8.2 66.6 6 7.8 67.9 6 9.5 67.9 6 9.1 the hypoxic tent. Arterial oxyLean body mass (kg) 31.3 6 3.3 31.1 6 2.9 31.8 6 4.1 31.9 6 4.1 gen saturation remained signifFat mass (kg) 11.1 6 6.5 11.5 6 6.9 11.5 6 4.9 11.4 6 5.2 icantly lower (91.2%) than *Values are mean 6 SD. H = resistance training in hypoxia; N = resistance training in baseline value (97.8%) after normoxia. squat exercise. Similarly, Kelly et al. (10) reported that SpO2 dropped from 98 to 92% after exposure to inspired oxygen concentration of 15%. The SpO2 data of this study ensured both H and N groups (88.9 6 16.9 to 109.4 6 17.0 kg and 90.0 that subjects’ exposure to hypoxia was correctly controlled 6 12.2 to 105.6 6 13.3 kg, respectively). However, no signifduring the hypoxia training for H group. icant differences in squat 1RM were observed between H and It is well documented that resistance training is a strong N group before and after resistance training (p . 0.05). potent factor to increase muscular strength and promote Isometric and Isokinetic Leg Strength muscle hypertrophy (8,24). The magnitude of these training Table 1 shows changes in maximal isometric and isokinetic effects is considered to be dependent on intensity of exercise leg strength before and after resistance training. There was and the acute hormonal responses to resistance exercise. no significant interaction between group and time (p . 0.05). Moderate to high intensity of resistance exercise (i.e., above Furthermore, there was no significant main effect for group 65% of 1RM) may be required to increase muscular strength or time (p . 0.05). and induce greater anabolic hormonal responses that are highly correlated to the degree of muscle hypertrophy Body Composition (16). In the present study, moderate intensity of squat exerChanges in body weight, lean body mass and fat mass before cise (75% of 1RM or equivalent to 10RM) was performed for and after resistance training are shown in Table 2. The results 6 weeks. Our results reported that squat 1RM significantly were similar to maximal isometric and isokinetic leg strength. increased 24.2 and 17.5% in H and N groups (Figure 1) after No significant changes in body weight, lean body mass, and fat 6 weeks of squat training, suggesting that the moderate mass were observed from pretraining to post-training in either intensity was sufficient to induce muscular strength gains H or N group (p . 0.05). Furthermore, no significant between after short-term resistance training. However, in contrast group differences in body composition were observed before to the study hypothesis, we failed to demonstrate greater and after 6-week resistance training (p . 0.05). strength gains in H group when compared with N group. DISCUSSION Our finding is in contrast to a previous study suggesting that resistance training under hypoxic conditions improves musThe findings of the present study provide some insight into cle strength and induces muscle hypertrophy of elbow faster the speculative beneficial effects of combining normobaric than under normoxic conditions (21). In that study, 14 male hypoxia with resistance training on muscle strength and university students performed 4 sets of 10 repetitions of hypertrophy. The primary finding of this study was that elbow extension and flexion at intensity of 70% of 1RM with 6 weeks of resistance training (a total of 18 training sessions 1 minute of rest for 6 weeks under hypoxia (FiO2 = 16%) or at moderate intensity) performed under systemic hypoxia normoxia. Elbow strength and hypertrophy were signifi(FiO2 = 15%) did not induce greater improvement in muscantly greater for the hypoxia group than normoxia group. cular strength and lean body mass than that of normoxia. Despite the lack of significant differences in strength and Our data suggest that, the use of systemic hypoxia during muscle mass between H and N groups in our study, it is short-term resistance training has no additive beneficial important to note that this previous study provided lower effects on muscular strength and muscle hypertrophy in presample size (7 subjects per group) than our study. In addiviously resistance-untrained men. tion, although Nishimura’s study examined the smaller musTo examine the hypothesis of this study, the control for cle groups (e.g., biceps and triceps), we examined the larger hypoxic exposure during hypoxia training is required. muscle groups (e.g., gluteus maximus, quads, hamstrings). During each session of hypoxia training, normobaric hypFurthermore, magnetic resonance imaging was used to oxic condition (FiO2 = 14.5–15%, with an average of 14.7%) VOLUME 28 | NUMBER 4 | APRIL 2014 |
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Intermittent Hypoxic Training on Muscular Performance assess muscle hypertrophy in Nishimura’s study. In our study, bioelectrical impedance analysis was applied to assess muscle hypertrophy. All these differences in research design may contribute to the discrepancies between these 2 studies. Further research is obviously required in view of these concerns. The time course of gains in muscle mass has been investigated in previously untrained individuals. As neural adaptations occur first during the early phase of training (19), muscle hypertrophy becomes evident after 6 weeks of training (22). Although Kon et al. (11,12) have reported that hypoxia is a potent factor for the enhancements of GH responses to moderate intensity of resistance exercise (i.e., 50 and 70% of 1RM), it is expected to see a greater strength and muscle mass gains in H group than in N group after resistance training in our study. Surprisingly, in our study, 6 weeks of squat exercise training did not show significant increases in muscle mass in both H and N groups. It is possible that longer training time (.6 weeks) may be required to induce significant muscle hypertrophy as other studies have shown significant increases in muscle mass with high-intensity resistance training performed between 10 weeks to 10 months (7,17). It is also possible that systemic hypoxic exposure during resistance training may not induce greater gains in strength and muscle mass as observed from occlusion or Kaatsu training because the physiological mechanisms underlying muscular adaptations to occlusion training could be different from systemic hypoxia training. In addition to dynamic strength, isometric strength and isokinetic strength are other common strength tests that have long been used to assess muscular performance in exercise science research. In the present study, maximal dynamic strength as measure of 1RM squat significantly increased after short-term resistance exercise. However, maximal isometric strength and maximal isokinetic strength (at a speed of 608 per second) had no significant changes after training in both H and N groups. This agrees with a previous study showing that squat 1RM significantly increased but not peak isometric force after 13 weeks of dynamic resistance training (1). Similarly, Woo et al. (28) observed no significant increase in peak torque on knee extension/flexion after 12 weeks of resistance training at moderate intensity in adolescent males. As magnitude of strength improvement might be associated with the specificity of the strength training, this may explain the lack of significant changes in isometric and isokinetic strength after training in both groups in this study. Because systemic hypoxic exposure during resistance training did not induce greater gains in dynamic strength, it is not surprising to observe the lack of differences in isometric and isokinetic strength between H and N groups after 6 weeks of resistance training in this study. In summary, the present study investigated the effects of 6-week resistance training combining normobaric hypoxia on muscular performance and body composition. Squat 1RM improved significantly after short-term resistance training in
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both H and N groups. However, no significant changes in lean body mass were observed over 6 weeks of resistance training in both groups. The results of this study failed to demonstrate greater gains in muscular strength and hypertrophy in normobaric hypoxia than normoxia. Our data suggest that the application of systemic hypoxia during short-term resistance training may not be a promising training technique to induce greater muscular strength and enhance body composition in previously resistance-untrained men.
PRACTICAL APPLICATIONS As strength and muscle mass are key factors to improve athletic performance and the quality of life, how to maximize the strength and muscle mass effectively has always been a major area of interest to coaches, athletes, and researchers around the world. In recent years, some researchers have speculated that combining systemic hypoxia through the use of simulation altitude tents or rooms with resistance training may provide additive beneficial effects on muscular strength and body composition. Their speculations were based on the beneficial effects observed from combining occlusion training or Kaatsu training with resistance training. Despite previous studies have already reported greater anabolic hormone responses to moderate-intensity resistance exercise (above 50% of 1RM) in hypoxia, unfortunately our data suggest that short-term moderate-intensity resistance training performed under normobaric hypoxia (FiO2 = 15%) may not be a viable training method for increasing greater muscular strength and hypertrophy. In practical terms, the use of systemic hypoxia during resistance training may not be effective for enhancing greater muscular performance and body composition in previously resistance-untrained men.
ACKNOWLEDGMENTS The authors thank a dedicated group of subjects for their participation in this study and the members of the Human Performance Laboratory in National Taiwan Normal University for their assistance in data collection. This study was funded by a grant for “Aim for the Top University Plan” from National Taiwan Normal University and the Ministry of Education of Taiwan. The authors declare no conflicts of interest. Furthermore, the results of this study do not constitute endorsement by the authors or the National Strength and Conditioning Association.
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Copyright © National Strength and Conditioning Association Unauthorized reproduction of this article is prohibited.
