The Effect of Resistance Training in a Hypoxic Chamber on Physical Performance in Elite Rugby Athletes

Abstract

Mayo, Brad, Cory Miles, Stacy Sims, and Matthew Driller. The effect of resistance training in a hypoxic chamber on physical performance in elite rugby athletes. High Alt Med Biol 19:28–34, 2018.—Limited research suggests that muscle adaptations may be enhanced through resistance training in a hypoxic environment. Seventeen professional rugby union athletes (age [mean ± SD], 24 ± 3 years; body mass, 98.7 ± 12.8 kg; and height, 188.9 ± 7.9 cm), performed 12 resistance training sessions over a 3-week period. Participants were randomly divided into two groups: HYP (n = 8), where resistance training sessions were performed in an environmental chamber with O₂ concentration maintained at ∼14.4% (∼3000 m simulated altitude), or CON (n = 9), where identical resistance training sessions were performed without the simulated altitude (O₂ = 20.9%, at sea level). Before and after the training intervention, tests included measures of strength, power, endurance, speed, and body composition. Two-way interactions between treatment and time for any of the measured variables were not significant (p > 0.05). Small positive effect sizes for HYP were found for bench press (d = 0.24), weighted chin-up (d = 0.23), and bronco endurance tests (d = −0.21). Resistance training in a hypoxic environmental chamber may lead to small improvements in upper body strength and endurance compared to the same training performed at sea level. These findings are somewhat novel, given the short timeframe of the study and the elite population sampled.

Introduction

Resistance training plays an integral part in the physical preparation of rugby athletes (Inness et al., 2016). The development of strength and power is important for rugby athletes who are required to perform numerous high speed runs, sprints, acceleration/decelerations, and collision-based activities like tackling, static holds, scrums, rucks, and mauls (Tavares et al., 2017). Strength development involves the coordinated functioning of a number of processes with the ability to produce maximal force attributed to both neural and muscular components (Bird et al., 2005). Moreover, strength improvements are likely due to concomitant increases in muscle cross-sectional area and neural adaptations (Bird et al., 2005). Subsequent adaptations to resistance training are highly dependent on the interplay between loads and volume, with the optimal range of training stimuli being a fine balance to ensure strength and power gains without overloading the athletes (Bird et al., 2005). Because of this, practitioners working with rugby athletes are often in search of ways to add stress to the training environment, without adding unnecessary load or volume.

Stress may be added to the resistance training setting by manipulation of environmental factors such as heat, humidity and simulated altitude, or hypoxia, without adjusting the training volume or load (Scott et al., 2014b). The positive effects of resistance training under local or systemic hypoxia are becoming more evident in the research (Nishimura et al., 2010; Manimmanakorn et al., 2012; Ho et al., 2014a; Inness et al., 2016). By performing training under hypoxic conditions, it is speculated that the partial pressure of oxygen in the muscle tissue will be reduced to provide an additional training stimulus and subsequent increase in training response (Lundby et al., 2012). While the use of environmental chambers during resistance training is limited in the research literature, other strategies used during resistance training that may induce similar physiological mechanisms include the use of blood flow restriction (BFR) training, whereby a pressure cuff is applied proximally to a limb to partially limit blood flow to working muscles (Scott et al., 2014b). Some of the possible mechanisms behind increased strength through hypoxic resistance training, whether it is by BFR or intermittent hypoxic resistance training (IHRT), include increased metabolic stress accentuated by an overall reliance on nonaerobic metabolism and fatigue (Scott et al., 2017), reduced oxygenation can enhance epigenetic changes through the transcription of angiogenesis-related genes (Larkin et al., 2012), increased type II fiber recruitment (Scott et al., 2014b), accumulation of metabolites (Takarada et al., 2000), concomitant increase in the rate of PCr hydrolysis and intracellular acidosis (Ramos-Campo et al., 2017), and increases in plasma growth hormone and muscle inflammation (Kon et al., 2014). It is possible that these acute responses, when implemented in a chronic setting, may lead to long-term physiological adaptations.

The research on IHRT has resulted in conflicting findings on its effectiveness for increasing maximal strength in athletes (Scott et al., 2014a). Manimmanakorn et al. (2012) investigated the effects of low-load resistance training on muscle function and performance in 30 netball athletes, while breathing hypoxic air (equivalent to 2000–4500 m altitude). Athletes took part in a 5-week training of knee flexor and extensor muscles at an intensity of 20% of one repetition maximum (1RM). The IHRT group showed greater hypertrophy and strength improvements than the control group. More recently, Kon et al. (2014) studied 16 recreationally trained participants split into an experimental and control group, performing two sessions a week for 8 weeks. The hypoxic group was exposed to normobaric hypoxic conditions (∼3000 m) in which they performed two consecutive exercises (free weight bench press and bilateral leg press using a weight-stack machine). Both groups performed 5 sets of 10 reps at 70% of 1RM on each exercise. The authors found no additive hypertrophic or strength benefits for IHRT. Furthermore, Ho et al. (2014b), investigated whether short-term moderate-intensity resistance training performed under systemic hypoxia will lead to greater muscular strength and hypertrophy. Eighteen untrained men performed 6 weeks of squat exercise under normobaric conditions. In both groups, participants performed three sets of back squats at 10RM with a 2-minute rest between sets. The findings from this study suggest that short-term resistance training performed under normobaric hypoxia has no additive beneficial effect on muscular performance.

Given the disparate findings on IHRT, and the range of methodologies and protocols used in the literature, further research is required to determine the efficacy of such a technique. Therefore, the aim of this study was to investigate the effect of resistance training for 3 weeks in hypoxia (through a simulated altitude chamber) for developing measures of maximal strength, power, speed, and endurance in professional rugby athletes.

Materials and Methods

Participants

Seventeen elite, professional rugby union athletes (age [mean ± SD], 24 ± 3 years; body mass, 98.7 ± 12.8 kg, height; 188.9 ± 7.9 cm) were split into two groups: HYP (n = 9) and CON (n = 8). Participants were first divided into positional groups (forwards and backs) and were then randomly allocated with an even distribution of each in both groups. All athletes were from the same rugby union squad, which played in New Zealand's top provincial competition. The study took place during the preseason phase of competition, which included 4 weeks of training before this study. All athletes volunteered to take part in this study. Written informed consent was obtained from each participant, and ethical approval was obtained from the Human Research Ethics Committee of the Institution. Initially, the study included 19 participants; however, two were withdrawn from the study due to injuries sustained during activities unrelated to the study.

Study design

This study implemented a randomized, controlled, parallel-group design performed over 5 weeks. This included a week of pretesting, 3 weeks of intervention training (four sessions per week), and a week of posttesting. In addition, all participants were involved in the same team training activity outside their resistance training sessions, where training loads were monitored to ensure there were no differences between groups. Both the experimental (HYP) and control (CON) groups performed exactly the same resistance training load, volume, and intensity over the 3-week intervention period (Table 1), with the only difference between groups being the training environment:

Table 1.

Testing and Training Schedule for Both HYP and CON Groups for the Duration of the Study

Week	Monday	Tuesday	Thursday	Friday
1	Back squat 1RM		Bodyweight CMJ 10 m sprint	Bronco fitness test
	Bench press 1RM
Pretest	Weighted chin-up 1RM
	Skinfolds and body mass
2	Bilateral strength	Horizontal strength	Vertical strength	Strength and speed
	Back squat (4 × 3)	Bench press (4 × 5)	Weighted chin-up (4 × 5)	BB high pull (4 × 3)
	DL calf raise (4 × 12)	Bent over row (4 × 10)	Seated BB shoulder press (4 × 10)	KB single leg Romanian deadlift (4 × 6)
	3 minutes rest after each super set	3 minutes rest after each super set	3 minutes rest after each super set	3 minutes rest after each super set
3	Bilateral strength	Horizontal strength	Vertical strength	Strength and speed
	Back squat (3 × 2, 2 × 1)	Bench press (4 × 4)	Weighted chin-up (4 × 4)	BB high pull (4 × 3)
	DL calf raise (4 × 12)	Bent over row (4 × 8)	Seated BB shoulder press (4 × 8)	KB single leg Romanian deadlift (4 × 6)
	3 minutes rest after each super set	3 minutes rest after each super set	3 minutes rest after each super set	3 minutes rest after each super set
4	Bilateral strength	Horizontal strength	Vertical strength	Strength and speed
	Back squat (2 × 2, 3 × 1)	Bench press (4 × 3)	Weighted chin-up (4 × 4)	BB high pull (4 × 3)
	DL calf raise (4 × 12)	Bent over row (4 × 6)	Seated BB shoulder press (4 × 6)	KB single leg Romanian deadlift (4 × 6)
	3 minutes rest after each super set	3 minutes rest after each super set	3 minutes rest after each super set	3 minutes rest after each super set
5	Back squat 1RM		Bodyweight CMJ 10 m sprint	Bronco fitness test
	Bench press 1RM
Post test	Weighted chin-up 1RM
	Skinfolds and Body mass

All exercises are represented as repetitions × sets.

BB, barbell; CMJ, counter movement jump; DL, double leg; FB, full body; KB, kettle bell; 1RM, one repetition maximum.

HYP—Twelve resistance training sessions were performed in an environmental chamber, where O₂ concentration was maintained at ∼14.4% (equivalent to ∼3000 m simulated altitude).

CON—Twelve resistance training sessions were performed using the same equipment, but without the simulated altitude (O₂ = 20.9%, at sea level).

All the participants reside at sea level (O₂ = 20.9%, at sea level) and had no previous exposure to altitude in the past 6 months.

To investigate any difference in perceived intensity between groups, the level of perceived exertion was assessed at the completion of each training session using the Borg 6–20 rate of perceived exertion (RPE) scale (Borg, 1982).

Simulated altitude (hypoxia)

The altitude chamber (Synergy Fitness, Queensland, Australia) consisted of a hypoxic generator, a compressor, and an air-tight room (width × length × height: 4900 × 4600 × 2300 cm). The hypoxic environment was created by filtering compressed ambient air through a high-polymer membrane that was sent to the air-tight chamber by the compressor. The initial training session was set to 15.5% O₂ (∼2800 m equivalent), with a decrease in O₂ to 14.4% (∼3000 m equivalent) for the remaining 11 training sessions. During each of the training sessions in the HYP group, SpO₂ was monitored at 0, 15, and 30 minutes using a PureSAT GO₂ pulse oximeter (Plymouth, MN) placed on the middle finger of the dominant hand. SpO₂ measurement was used as a safety measure. Athletes were to be removed from the chamber if their SpO₂ readings dropped below 80%, fortunately, this did not occur.

Testing procedures

Testing was carried out over 1 week under controlled environmental conditions (21°C ± 1°C and 56.8% ± 8.5% relative humidity [RH] at sea level). All participants were familiar with the testing procedures and protocols, as they had been performing these as part of their regular physical testing routines. The 1RM lifts (bench press, back squat, and weighted chin-up) and body composition measures (sum of eight skinfolds and body mass) were performed on day 1, the bodyweight counter movement jump (CMJ) and 10 m sprint on day 4, and the bronco fitness test on day 5 of the first week (Table 1). All physical performance tests were preceded by a standardized warm-up specific to the test. These warm-ups included submaximal lifting repetitions in preparation to lift a 1RM, submaximal, and maximal countermovement jump, and a self-selected sprint preparation.

1RM testing

The monitoring of maximum strength was obtained from 1RM testing of the back squat, bench press, and weighted chin-up exercises before and after the training intervention. The determination of 1RM for these exercises was conducted according to the recent research (Baker and Nance, 1999; Haff and Triplett, 2015). Squat depth was visually assessed by the same researcher for all 1RM load attempts, with the athlete required to descend to a depth to which the femur was approximately parallel to the floor. The order of the 1RM exercises was as follows: back squat, bench press, and weighted chin-up, and was maintained for the two testing sessions.

Power testing

A CMJ was used to test lower-body power. Athletes started with both feet on the floor, placed a shoulder width apart and with both hands on a wooden bar placed across the upper trapezius. Athletes were instructed to perform five cyclic vertical CMJ's, aiming for maximum height with each jump (Cormack et al., 2008). The best CMJ measured by peak velocity was used for subsequent analysis. CMJ performance was measured using a linear position transducer (Gymaware, Kinetic Performance Technology, Canberra, Australia) at a sampling frequency of 50 Hz. The linear position transducer was attached to the bar laterally to the athletes left hand and to the floor directly beneath.

Speed testing

Speed was tested over 10 m from a standing start. Participants performed three trials of maximum effort, with the fastest time being recorded for subsequent analysis. Athletes were instructed to stand 50 cm behind the first timing gate before starting when they were ready. Sprint speed was measured using single beam infrared timing lights set to a height of 0.73 m (TC-Timing System; Brower, Draper, UT). The intratrial reliability of the above procedure has been established at r = 0.86 for the 10-m trained athletes (Baker and Nance, 1999).

Endurance testing

To measure the athlete's aerobic fitness, a bronco test was performed before and after training intervention. The bronco test is widely used in the rugby environment and consists of running 1200 m in a shuttle-type manner. Cones were placed at the 0, 20, 40, and 60 m lines. Athletes were asked to run from 0 to 20 m, return to the 0 m line, run again to the 40 m line and return to the 0 m line, and then, run again to the 60 m line and return to the 0 m line. Completion of the 20–40–60 m shuttles was considered one repetition, with athletes completing five repetitions as quickly as possible. Hand-held stop watches were used by trained timekeepers to record the bronco finishing times. As mentioned by Berthon et al. (1997), a 5-minute field test is easy to apply and a practical test for this setting.

Body composition

Skinfold thickness was measured on the right side of the body with Harpenden calipers to the nearest 0.5 mm at eight sites (biceps, triceps, subscapular, iliac crest, suprailiac, abdomen, thigh, and calf) by one investigator using standardized techniques (Moreno et al., 2002). Sum of skinfold thickness at these eight sites was used for analysis.

Statistical analysis

Statistical analyses were performed using the Statistical Package for Social Science (V. 22.0; SPSS, Inc., Chicago, IL). A two-way repeated measures ANOVA was performed to determine the effect of different treatments (HYP or CON) over time (pre/post) on all measured variables, with a Bonferroni adjustment if significant main effects were present. Analysis of the studentized residuals was verified visually with histograms and also by the Shapiro-Wilk test of normality. A Student's paired t-test was used to determine pre- to post-differences for each measure, and an independent t-test was used between groups for pretest values. Descriptive statistics are shown as means ± standard deviations unless stated otherwise. Standardized changes in the mean of each measure were used to assess magnitudes of effects and were calculated using Cohen's d, and interpreted using thresholds of 0.2, 0.5, and 0.8 for small, moderate, and large, respectively (Cohen, 1988). An effect size of ±0.2 was considered the smallest worthwhile effect with an effect size of <0.2 considered to be trivial. The effect was deemed unclear if its 90% confidence interval overlapped the thresholds for small positive and negative effects (Batterham and Hopkins, 2006). Statistical significance was set at p < 0.05 for all analyses.

Results

There were no statistically significant differences between groups for pretest values for any of the measured variables (p > 0.05), except for bench press, which was significantly higher in the HYP group.

The average duration for each of the 12 sessions in the HYP group was 34 ± 2 min (total altitude exposure over 3 weeks = ∼7 hours) and the mean simulated altitude was 3098 ± 68 m.

There were no significant differences between groups for mean RPE during the resistance training sessions over the intervention period (14.2 ± 0.5 and 14.1 ± 0.4 for HYP and CON, respectively).

There were no statistically significant two-way interactions between treatment and time for any of the measured variables (p > 0.05). However, there were small effect sizes in favor of the HYP group compared to CON for the bench press (d = 0.24), weighted chin-up(d = 0.23), and bronco tests (d = −0.21) (Fig. 1).

FIG. 1.

Effect sizes for measured variables between HYP and CON groups. Error bars represent 90% confidence intervals (±90% CI), with the shaded area representing a small effect (±0.2) between groups. Where 90% CI overlaps small positive and negative effects, the result was deemed unclear. ^#Small effect between groups.

Significant improvements were seen before to after testing in the HYP group for bench press, back squat, and weighted chin-up, and for back squat in the CON group (p < 0.05, Table 2).

Table 2.

Premeasure and Postmeasure (Mean ± SD) for HYP and CON Groups and P-Values and Effect Sizes for the Comparison of Change Between Groups

	HYP (mean ± SD)		CON (mean ± SD)
	Pre	Post	Pre	Post	ΔHYP–ΔCON (mean ±90% CI) Effect size
Bench press (kg)	137 ± 14	145 ± 14^a	115 ± 18	118 ± 17	5 ± 4 Small
Back squat (kg)	167 ± 28	178 ± 27^a	168 ± 20	177 ± 20^a	1 ± 8 Unclear
Weighted chin-up (kg)	145 ± 10	151 ± 9^a	130 ± 18	133 ± 17	4 ± 4 Small
Jump squat (m·s⁻¹)	3.61 ± 0.39	3.82 ± 0.44	3.63 ± 0.33	3.73 ± 0.31	0.11 ± 0.25 Unclear
Bronco (seconds)	302 ± 36	297 ± 34	299 ± 16	300 ± 19	−6 ± 9 Small
10 m sprint (seconds)	1.75 ± 0.12	1.74 ± 0.12	1.75 ± 0.06	1.73 ± 0.06	0.02 ± 0.03 Trivial
Body mass (kg)	100 ± 14	101 ± 13	95 ± 11	95 ± 10	1 ± 2 Trivial
Σ 8 Skinfolds (mm)	93 ± 38	89 ± 34	85 ± 21	85 ± 18	−3 ± 8 Trivial

Represents significant difference between premeasure and postmeasure (p < 0.05).

Discussion

Resistance training in a hypoxic chamber may lead to small changes in upper body strength (bench press and weighted chin-up) and endurance (bronco test) compared to the same training at sea level in professional rugby athletes. The hypoxic group in this study also demonstrated significant (p < 0.05) increases between pretest and posttest for bench press, back squat, and weighted chin-up, while the control group only showed significant improvements pretraining to posttraining for the back squat. Considering the participants were professional-level, strength-trained athletes, the small trends toward improved performance highlighted after just 3 weeks of hypoxic resistance training are somewhat surprising and warrant future research.

Our results would suggest that resistance training in hypoxia may show trends toward improving physical performance, particularly for improving upper-body strength. This study is the first to investigate the use of high-load resistance training combined with hypoxia, in elite athletes. Our study implemented a training program that consisted of different lifts at 85–92.5% of 1RM, whereas the majority of published IHRT studies have used low to moderate loads of 20–75% of 1RM. Given this study population included a high level of resistance trained athletes, it is unlikely that the strength increases were due to neural adaptations alone (Bird et al., 2005). Although no observable changes to body mass were found with increased 1RM, it could be that hypoxia-mediated hypertrophic changes were too small to be quantified without MRI. However, these findings are consistent with the results of the Inness et al. (2016) study, where changes in 1RM performance were evident, also without changes in body mass. This change in strength despite a lack of change in body mass is an important finding, as many athletes, including team-sport athletes, with high running demands in their sport, athletes competing in weight classes, and many endurance athletes want to increase strength without an increase in body mass.

Previous research by Nishimura et al. (2010) using moderate loads (70% 1RM) combined with moderate-level hypoxia (FiO₂ = 16%) demonstrated enhanced hypertrophic and strength responses following IHRT compared to the equivalent training in normoxia in untrained participants. The groups performed resistance training twice a week for six consecutive weeks (totaling 12 sessions), with the mean duration of each training session lasting ∼13 minutes. The authors found that 1RM had significantly increased in the hypoxic group by week 6, similar to the results found in this study. Furthermore, research by Inness et al. (2016) employed heavy-load exercises (3–6RM) at higher levels of hypoxia (Fi0₂ = 14.5%–14.1%; 3100–3400 m equivalent altitude). Participants completed 7 weeks of heavy resistance training thrice per week, with sessions performed on nonconsecutive days. During the training sessions, all participants wore a face mask connected to a hypoxic simulator. Authors noted greater improvements in relative and absolute strength compared to a placebo intervention, but no clear differences in speed or body composition. The results of this study are in agreement with these reported findings.

Historically, hypoxic research has investigated changes in aerobic responses to exercise (Hamlin et al., 2010). The results of this study demonstrated that IHRT showed small benefits to aerobic performance capacity and changes observed in the bronco test are similar to those found in previous literature (Levine and Stray-Gundersen, 2005; Morton and Cable, 2005; Dufour et al., 2006). In the aforementioned research, hypoxic exposure elicited significant improvements of maximal and submaximal running velocities and VO₂ max. In research by Levine and Stray-Gundersen (2005), an increase in endurance running performance was attributed to increases in erythrocyte volume, red cell mass, and VO₂ max following ∼3 weeks of altitude exposure. The increased “metabolic” stress on skeletal muscle tissue caused by hypoxic training (Hoppeler et al., 2008) is thought to promote muscle adaptations that surpass those triggered by normoxic exercise training. In support of this assumption, it is widely accepted that hypoxic exposure results in an increased renal release of erythropoietin, which causes a transient increase in red cell volume (Bailey and Davies, 1997). Other potential mechanisms include, but may not be limited to, mitochondrial biogenesis, mitochondrial density, and pH regulation (Bailey and Davies, 1997; Rusko et al., 2004; Hoppeler et al., 2008; Faiss et al., 2013).

A limitation of this study was the lack of placebo control. As with many hypoxic studies, it is somewhat difficult to control for the placebo effect; therefore, psychological benefits associated with the intervention cannot be discounted. Future research should examine the psychological belief in IHRT before the study, to help determine whether or not the prior belief in the efficacy of this training may have had an influence on the performance results. Future research should also incorporate longer training interventions, different levels of hypoxia, and physiological measures to determine the mechanistic changes associated with any performance benefit (e.g., blood, hormonal, and muscle cell adaptations).

In conclusion, resistance training in a hypoxic environment, by simulated altitude over a 3-week period, may lead to small improvements in upper body strength and endurance compared to the same training performed at sea level in professional rugby athletes. Thus study is the first to highlight such findings in an elite, strength-trained population, and further research incorporating longer training periods and more mechanistic measures are clearly warranted.

Footnotes

Author Disclosure Statement

No competing financial interests exist.

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