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ACUTE PHYSIOLOGICAL RESPONSES TO “RECOVERY INTERMITTENT HYPOXIA” IN HIIT

RESPUESTAS AGUDAS A LA “HIPOXIA INTERMITENTE DE RECUPERACIÓN” EN EL HIIT

ABSTRACT

Introduction:

Traditional intermittent hypoxia training improves sport performance after short periods of exposure, but acute exposure to intermittent hypoxia leads to decreased training intensity and technical quality. The solution to overcome these negative effects may be to perform efforts in normoxia and the intervals between efforts in hypoxia, maintaining the quality of training and the benefits of hypoxia.

Objective:

This study aimed to evaluate the acute physiological responses to hypoxia exposure during recovery between high intensity efforts.

Materials and methods:

Randomized, one-blind, placebo-controlled study. Sixteen men performed a graded exercise test to determine their maximal intensity and two sessions of high-intensity interval training. The training intervals could be in hypoxia (HRT), FIO2: 0.136 or normoxia (NRT), FIO2: 0.209. During the two-minute interval between the ten one-minute efforts, peripheral oxygen saturation (SpO2), heart rate (HR), blood lactate ([La]), blood glucose ([Glu]) were constantly measured.

Results:

There were differences in HR (TRN = 120 ± 14 bpm; TRH = 129 ± 13 bpm, p < 0.01) and SpO2 (TRN = 96.9 ± 1.0%; TRH = 86.2 ± 3.5%, p < 0.01). No differences in [La] and [Glu] TRN (4.4 ± 1.7 mmol.l-1; 3.9 ± 0.5 mmol.l-1) and TRH (5.2 ± 2.0 mmol.l-1; 4.0 ± 0.8 mmol.l-1, p = 0.17).

Conclusion:

The possibility of including hypoxia only in the recovery intervals as an additional stimulus to the training, without decreasing the quality of the training, was evidenced. Level of Evidence II; Randomized Clinical Trial of Minor Quality.

Keywords:
Oxygen Saturation; Lactate; High-Intensity Interval Training; Hypoxia

RESUMEN

Introducción:

El entrenamiento tradicional en hipoxia intermitente mejora el rendimiento deportivo tras cortos periodos de exposición, sin embargo, la exposición aguda a la hipoxia intermitente conduce a una disminución de la intensidad del entrenamiento y de la calidad técnica. La solución para superar estos efectos negativos puede ser realizar los esfuerzos en normoxia y los intervalos entre esfuerzos en hipoxia, manteniendo la calidad del entrenamiento y los beneficios de la hipoxia.

Objetivo:

Este estudio pretendía evaluar las respuestas fisiológicas agudas a la exposición a la hipoxia durante la recuperación entre esfuerzos de alta intensidad.

Materiales y métodos:

Estudio aleatorizado, a ciegas y controlado con placebo. Dieciséis hombres realizaron una prueba de ejercicio graduado para determinar su intensidad máxima y dos sesiones de entrenamiento por intervalos de alta intensidad. Los intervalos de entrenamiento podían ser en hipoxia (HRT), FIO2: 0,136 o normoxia (NRT), FIO2: 0,209. Durante el intervalo de dos minutos entre los diez esfuerzos de un minuto, se midieron constantemente la saturación periférica de oxígeno (SpO2), la frecuencia cardiaca (FC), el lactato en sangre ([La]) y la glucemia ([Glu]).

Resultados:

Hubo diferencias en la FC (TRN = 120 ± 14 lpm; TRH = 129 ± 13 lpm, p < 0,01) y la SpO2 (TRN = 96,9 ± 1,0%; TRH = 86,2 ± 3,5%, p < 0,01). No hubo diferencias en [La] y [Glu] TRN (4,4 ± 1,7 mmol.l-1; 3,9 ± 0,5 mmol.l-1) y TRH (5,2 ± 2,0 mmol.l-1; 4,0 ± 0,8 mmol.l-1, p = 0,17).

Conclusión:

Se evidenció la posibilidad de incluir hipoxia sólo en los intervalos de recuperación como estímulo adicional al entrenamiento sin disminuir la calidad del mismo. Nivel de Evidencia II; Ensayo Clínico Aleatorizado de Baja Calidad.

Descriptores:
Saturación de Oxígeno; Lactato; Entrenamiento de Intervalos de Alta Intensidad; Hipoxia

RESUMO

Introdução:

O treinamento de hipóxia intermitente tradicional melhora o desempenho esportivo após curtos períodos de exposição, porém a exposição aguda à hipóxia intermitente leva à diminuição da intensidade do treinamento e da qualidade técnica. A solução para superar esses efeitos negativos pode ser realizar esforços em normóxia e os intervalos entre os esforços em hipóxia, mantendo a qualidade do treinamento e os benefícios da hipóxia.

Objetivo:

Este estudo teve como objetivo avaliar as respostas fisiológicas agudas à exposição de hipóxia durante a recuperação entre esforços de alta intensidade.

Materiais e métodos:

Estudo aleatório e one-blinded, com efeito placebo controlado. Dezesseis homens realizaram um teste de exercício graduado para determinar sua intensidade máxima e duas sessões de treinamento intervalado de alta intensidade. Os intervalos de treinamento podem ser em hipóxia (TRH), FIO2: 0,136 ou normóxia (TRN), FIO2: 0,209. Durante os dois minutos de intervalo entre os dez esforços de um minuto, foram medidos constantemente a saturação periférica de oxigênio (SpO2), frequência cardíaca (FC), lactato sanguíneo ([La]), glicemia ([Glu]).

Resultados:

Houve diferenças na FC (TRN = 120 ± 14 bpm; TRH = 129 ± 13 bpm, p <0,01) e SpO2 (TRN = 96,9 ± 1,0%; TRH = 86,2 ± 3,5%, p <0,01). Sem diferenças em [La] e [Glu] TRN (4,4 ± 1,7 mmol.l-1; 3,9 ± 0,5 mmol.l-1) e TRH (5,2 ± 2,0 mmol.l-1; 4,0 ± 0,8 mmol.l-1, p = 0,17).

Conclusão:

Evidenciou-se a possibilidade de incluir a hipóxia apenas nos intervalos de recuperação como um estímulo adicional ao treinamento, sem diminuir a qualidade do treinamento. Nível de Evidência II; Estudo Clínico Randomizado de Menor Qualidade.

Descritores:
Saturação de Oxigênio; Lactato; Treinamento Intervalado de Alta Intensidade; Hipóxia

INTRODUCTION

Intermittent hypoxia training (IHT) consists of performing continuous or repeated efforts generally in hypoxia and spending intermittent periods of the day in hypoxia.11 Sinex JA, Chapman RFJJoS, Science H. Hypoxic training methods for improving endurance exercise performance. J Sport Health Sci. 2015;4(4):325-32.

2 Millet GP, Roels B, Schmitt L, Woorons X, Richalet JJSm. Combining hypoxic methods for peak performance. Sports Med. 2010;40(1):1-25.
-33 Faiss R, Girard O, Millet GP. Advancing hypoxic training in team sports: from intermittent hypoxic training to repeated sprint training in hypoxia. Br J Sports Med. 2013;47(Suppl 1):i45-i50. The use of IHT as an additional stimulus for training has been a common practice in sports training in different cyclic modalities.33 Faiss R, Girard O, Millet GP. Advancing hypoxic training in team sports: from intermittent hypoxic training to repeated sprint training in hypoxia. Br J Sports Med. 2013;47(Suppl 1):i45-i50.

Studies show the efficacy of IHT in improving sports performance in short periods (i.e. 3-5 weeks of training), providing evidence of anaerobic improvements,44 Czuba M, Wilk R, Karpiński J, Chalimoniuk M, Zajac A, Langfort J. Intermittent hypoxic training improves anaerobic performance in competitive swimmers when implemented into a direct competition mesocycle. PloS One. 2017;12(8):e0180380. changes in pH, greater carbonic anhydrase, glucose transport, and HIF1α activity into muscle.33 Faiss R, Girard O, Millet GP. Advancing hypoxic training in team sports: from intermittent hypoxic training to repeated sprint training in hypoxia. Br J Sports Med. 2013;47(Suppl 1):i45-i50. Furthermore, IHT is effective for improving movement economy, maximum oxygen uptake, and repeated sprint ability.44 Czuba M, Wilk R, Karpiński J, Chalimoniuk M, Zajac A, Langfort J. Intermittent hypoxic training improves anaerobic performance in competitive swimmers when implemented into a direct competition mesocycle. PloS One. 2017;12(8):e0180380.

5 Czuba M, Waskiewicz Z, Zajac A, Poprzecki S, Cholewa J, Roczniok R. The effects of intermittent hypoxic training on aerobic capacity and endurance performance in cyclists. J Sports Sci Med. 2011;10(1):175-83.

6 Galvin HM, Cooke K, Sumners DP, Mileva KN, Bowtell JLJBJSM. Repeated sprint training in normobaric hypoxia. Br J Sports Med. 2013;47(Suppl 1):i74-i9.
-77 Katayama K, Sato K, Matsuo H, Ishida K, Iwasaki K-i, Miyamura MJEjoap. Effect of intermittent hypoxia on oxygen uptake during submaximal exercise in endurance athletes. Eur J Appl Physiol. 2004;92(1-2):75-83.

Despite IHT being efficient in promoting positive adaptations, performing training in hypoxia cause a reduction in training intensity and loss of movement quality, reducing the capacity to generate power and decrease the number of efforts performed. The decrease in exercise intensity caused by hypoxic over time could explain the absence of positive results or even reduced performance in some research.88 Billaut F, Buchheit M. Repeated-sprint performance and vastus lateralis oxygenation: Effect of limited O 2 availability. Scand J Med Sci Sports. 2013;23(3):e185-e93.

9 Brocherie F, Millet GP, Morin J-B, Girard O. Mechanical alterations to repeated treadmill sprints in normobaric hypoxia. Med Sci Sports Exerc. 2016;48(8):1570-9.
-1010 Deb SK, Brown DR, Gough LA, Mclellan CP, Swinton PA, Andy Sparks S, et al. Quantifying the effects of acute hypoxic exposure on exercise performance and capacity: a systematic review and meta-regression. Eur J Sport Sci. 2018;18(2):243-56.

IHT results in a paradoxical effect, it can promote additional adaptations due to hypoxia exposure; on other hand, the exposure may decrease the training intensity. The negative effects can “dilute” the possible positive effects on performance.11 Sinex JA, Chapman RFJJoS, Science H. Hypoxic training methods for improving endurance exercise performance. J Sport Health Sci. 2015;4(4):325-32.

Because of this, performing IHT with efforts at normoxia and pauses between efforts in hypoxia may be an alternative to maintain intensity and technical/mechanical quality during training. This strategy would probably generate positive adaptations from both regular training and hypoxia exposure, avoiding the harmful effects of hypoxia during exercise. However, to the best of our knowledge, no study to date has investigated this possibility under real training conditions. Thus, the present study aimed to assess the acute physiological responses to hypoxic during intervals between high-intensity efforts and compare with normoxia. Our hypothesis was that method could generate physiological alterations on traditional exercise markers as [La], HR and rate of perceived efforts (RPE) great than in normoxia training without decrease the number of efforts performed.

MATERIALS AND METHODS

Participants

Sixteen men participated in this study (age= 23±4 years, height= 180±10 cm, weight= 78.4±11.9 kg). The participants signed a consent form agreeing to participate in the study. All procedures adopted by the study comply with the university's human research ethics committee (CAAE: 32220020.0.0000.5659) and the Helsinki declaration.

Experimental Design

The participants came to the laboratory on 3 different days, with a minimum 48-hour interval. They were advised to maintain the same diet, to eat regular meals at least two hours before the interventions, and to avoid caffeine/alcohol. All procedures were performed at the same time of day. The laboratory was located at an altitude of 531 meters above sea level, with a controlled temperature of 22 °C. None of the participants had traveled to altitudes above 1,500 m in the previous 6 months. All experiments were performed on a treadmill (Super ATL, Imbrahmed, Brazil).

On the first day, height and body weight were measured, the participants were familiarized with the treadmill and the unidirectional face mask used during the study. Before each intervention, a 5-minute treadmill warm-up was performed at an intensity of 7 km.h−1. The subjects performed a graded exercise test (GXT) until exhaustion, to estimate the peak speed achieved (VPEAK). On the other two days, the participants realized a repeated high-intensity effort training session, with recovery between stimuli being performed in normoxia (TRN) or hypoxia (TRH). These executions were carried out at random, with the participants unaware of the situation they were being exposed to.

Graded Exercise Test (GXT)

The GXT started at 8 km.h−1, increments of 1 km.h−1 every 3 minutes, until voluntary exhaustion. Between each stage, there was a 30-second interval to collect blood samples and record HR and RPE. The following exhaustion criteria was adopted: a) [La] > 8.0 mmol.l−1; b) maximum HR predicted by age (HRpred = 208 – (0.7 * age); c) RPE > 9 on an RPE scale from 0-10 points.1111 Foster C, Florhaug JA, Franklin J, Gottschall L, Hrovatin LA, Parker S, et al. A new approach to monitoring exercise training. J Strength Cond Res. 2001;15(1):109-15.

The VPEAK was the highest velocity achieved in the GXT; when exhaustion occurred before completing the stage. VPEAK was adjusted using the equation:1212 Kuipers H, Verstappen F, Keizer H, Geurten P, Van Kranenburg GJIjosm. Variability of aerobic performance in the laboratory and its physiologic correlates. Int J Sports Med. 1985;6(4):197-201.

V PEAK = SLC + ( TI/TE ) * I

Where SLC is the last complete stage speed; TI is the time performed in the last stage; TE is the stipulated time per stage; I was the increase in intensity.

Hypoxia Instrumentation

An Air San unidirectional mask (Air Safety, Brazil) was connected to a 3-meter flexible hose (IVPU, air vacuum PU 1.1/2), the opposite end was connected to a tent (CAT, TentTM, USA) with air capacity of 12,000 liters, connected to a hypoxia generator (CAT-430TM, Altitude Control Technologies, USA). The system remained online throughout the experiment. The FIO2 selected to hypoxia was of 0.135. The FIO2 was monitored using an O2 sensor (Oxygen Senor R-17MED, Teledyne Analytical Instruments, USA). The participants performed the same procedures for the normoxic, however received ambient air (FIO2: 0.209).

Training Session

Both training sessions with recovery in normoxia (TRN) and hypoxia (TRH) consisted of ten 1-minute efforts at 100% VPEAK, with 2-minute of passive pauses. In both sessions, the participants carried out their efforts exclusively in normoxia. However, during the intervals, the participants breathed air with either 0.209 or 0.136 FIO2. RPE, [La], [Glu] were measured after the end of each effort, the HR, and SpO2, were collected each ten seconds, until 120 seconds of interval. (Figure 1)

Figure 1
Representation of the dynamics of the high-intensity intermittent training session with recovery intervals in hypoxia or normoxia. VPEAK - maximum speed reached in the incremental test; E - effort period; R- the interval between efforts; RPE- the subjective perception of effort; SpO2- partial pressure of oxygen, represents a measurement of heart rate; represents a measurement of blood lactate concentration.

Hypoxic Dose Calculation (HD)

The HD was estimated as the exposure time in hours (t) multiplied by the reduction in SpO2, assuming a resting SpO2 value of 98%. Thus, HD = (98 - SpO2) x t.1313 Millet GP, Brocherie F, Girard O, Wehrlin JP, Troesch S, Hauser A, et al. Commentaries on Viewpoint: Time for a new metric for hypoxic dose?. J Appl Physiol (1985). 2016;121(1):356-8.

Calculation of the Arterial Partial Pressure of Oxygen (PaO2)

The SpO2 values were converted to PaO2 values using the equation:1414 Gadrey SM, Lau CE, Clay R, Rhodes GT, Lake DE, Moore CC, et al. Imputation of partial pressures of arterial oxygen using oximetry and its impact on sepsis diagnosis. Physiol Meas. 2019;40(11):115008.

P a O 2 = 23400 1 S p O 2 0.99 1 3

Blood Sample Analysis

The blood samples were collected using heparinized and calibrated capillary tubes to collect 25μl of blood from the earlobe. The samples were dropped into Eppendorf tubes containing 50μl of 1% sodium fluoride. These tubes were frozen at −20°C for posterior analysis in a blood analyzer to determine [La] and [Glu] (YLS, model 2700, Ohio, USA).

Statistical Analysis

Data normality, homogeneity, sphericity were checked using the Shapiro-Wilk test, Levene test, and Mauchy test, respectively. The Greenhouse-Gesser correction was applied when necessary. The data were expressed in mean ± SD. To compare two means the Student t-test was used for dependent samples. To compare normoxia and hypoxia in different periods the repeated measures ANOVA was used. In the case of significant F values, the Sidak post-hoc test was used. The effect size (ES) and its 95% confidence interval (C.I.) was interpreted following: trivial <0.2, small 0.2–0.6, moderate 0.6–1.2, large 1.2–2.0, and very large >2.0. Only the RPE variable was analyzed using the Wilcoxon signed rank non-parametric f test, considering the value of the rank-biserial correlation (rb) as the ES. A p-value of 0.05 was used for all tests. The JASP software (version 0.13.1.0, Amsterdam, Netherlands) was employed.

RESULTS

Figure 2, panel (A) shows the SpO2 values in intervals, panel (B) shows the SpO2 responses during an interval. The SpO2 values of all the sessions were TRN (96.9 ± 1.0%) and TRH (86.2 ± 3.5%, p < 0.01, ES = 3.04 C.I. = 1.85, 4.22). The decrease in SpO2 was 1.1 ± 1.0% for TRN and 11.8 ± 3.5% for TRH (p < 0.01, ES= 3.04 C.I. = 1.85, 4.22).

Figure 2
Comparison of the average blood oxygen saturation behavior during the recovery intervals, in the different training sessions; panel A - The comparison between the SpO2 average from each series, panel B - SpO2 behavior during the 120 seconds interval. ▄ represents training performed with intervals in hypoxia; ○ represents training performed with intervals in normoxia. * means the statistical difference from normoxia with hypoxia situations (p < 0.05).

As expected, the HD for TRN (0.35 ± 0.34%.h) was lower than the one for TRH (3.89 ± 1.17%.h, p < 0.01, ES= 3.04, C.I.= 1.85, 4.22). The SpO2 transformed into PaO2 are presented in Figure 3. TRN presented a higher PaO2 value compared to TRH (p<0.01, ES= 3.991, C.I= 2.488, 5.479).

Figure 3
Comparison between arterial oxygen pressure (PaO2) in interval training performed with intervals in hypoxia (TRH) and interval training performed in normoxia (TRN) situation of exposure to hypoxia at rest and situation of hypoxia with high-intensity interval training. * represents statistical difference (p<0.05).

The HR responses during the recovery are presented in Figure 4. The mean HR of TRN (120 ± 14 bpm) was lower than that of TRH (129.1 ± 12.7 bpm, p < 0.01, ES= 1.35, C.I.= 0.65, 2.02).

Figure 4
Panel A- Comparison between the average frequency during the intervals between efforts. Panel B- Comparison of heart rate behavior during recovery time. Represents training session in normoxia with recovery between intervals in hypoxia; □ represents the training session held in normoxia at maximum intensity. * represents the statistical difference between situations (p<0.05). ▄ represents training performed with intervals in hypoxia; ○ represents training performed with intervals in normoxia.

No statistical differences were observed in the [Glu] between groups (TRH= 4.0 ± 0.8 mmol.l−1; TRN= 3.9 ± 0.5 mmol.l−1), although no statistical differences were observed in the [La] was slightly higher in TRH (5.2 ± 2.0 mmol.l−1) than in TRN (4.4 ± 1.7 mmol.l−1). (Figure 5)

Figure 5
Comparison between blood lactate and glucose concentrations during the ten 1min efforts in the different training sessions. White symbols represent normoxia situation; black symbols represent hypoxia situation.

The RPE showed no difference between TRN (5.68 ± 2.12 pts.) and TRH (6.06 ± 2.35 pts, p= 0.54, ES= 0.24, C.I = −0.451, 0.775).

DISCUSSION

The main finding was that training session with hypoxia during the intervals between high-intensity efforts was efficient in causing acute physiological changes in SpO2 and HR levels compared to normoxia. Thus, the inclusion of hypoxia represents an additional training stimulus, confirming our hypothesis. It is important to highlight that this intervention did not alter the physical efforts, which were all performed in normoxia. The manipulation of the PaO2 conditions only occurred in the intervals between the maximum 1-minute stimuli, thus not impairing the evaluated individual's motor gestures.

We are unaware of any other studies that investigate the effect of intermittent hypoxia only in the intervals. There is only one study that verifies the effect of hypoxia exposure during recovery after a training session.1515 Moon H-W, Shin S-H, Lee C-H, Park H-Y, Sunoo S, Nam S-S. Effects of various acute hypoxic conditions on the hemorheological response during exercise and recovery 1. Clinical hemorheology and microcirculation. Clin Hemorheol Microcirc. 2016;63(4):451-60. The aforementioned authors applied a continuous submaximal training and used a 30-minute recovery after the end of the exercise.1515 Moon H-W, Shin S-H, Lee C-H, Park H-Y, Sunoo S, Nam S-S. Effects of various acute hypoxic conditions on the hemorheological response during exercise and recovery 1. Clinical hemorheology and microcirculation. Clin Hemorheol Microcirc. 2016;63(4):451-60. Thus, we consider the data original.

Hypoxia decreases body oxygen supply, causing acute changes such as decrease in alveolar pressure, PaO2, capillary pressure, intramuscular oxygen pressure (PiO2).1616 Richardson RS, Duteil S, Wary C, Wray DW, Hoff J, Carlier PGJTJop. Human skeletal muscle intracellular oxygenation: the impact of ambient oxygen availability. J Physiol. 2006;571(2):415-24.,1717 Richardson RS, Noyszewski EA, Kendrick KF, Leigh JS, Wagner PDJTJoci. Myoglobin O2 desaturation during exercise. Evidence of limited O2 transport. J Clin Invest. 1995;96(4):1916-26.

A reduction in PiO2 below to 8.00 mmHg is sufficient to stabilize HIF1α.1818 Flueck M. Plasticity of the muscle proteome to exercise at altitude. High Alt Med Biol. 2009;10(2):183-93. In normoxic, the PHD hydroxylates HIF1α, enabling coupling with the von Hippel-Lindau protein and marking the E3 ubiquitin ligase complex, for degradation of HIF1α in the 265 proteasomes. With the decrease in PHD due to the decrease in PiO2, HIF1α stabilizes, increasing its concentration inside the cell's cytosol, causing the MAPK protein to phosphorylate HIF1α. This protein translocates to the cell nucleus, connecting with HIF1β, forming the HIF1α/HIF1β complex. This complex connects to the HRE domain, increasing the transcription of several other proteins that are responsible for the positive adaptations resulting from exposure to hypoxia.1919 Graham AM, McCracken KG. Convergent evolution on the hypoxia-inducible factor (HIF) pathway genes EGLN1 and EPAS1 in high-altitude ducks. Heredity (Edinb). 2019;122(6):819-32.

20 Fernández-Torres J, Martínez-Nava GA, Gutiérrez-Ruíz MC, Gomez-Quiroz LE, Gutiérrez MJRBdR. Papel da via de sinalização do HIF-1α na osteoartrite: revisão sistemática. Rev Bras Reumatol. 2017;57(2):162-73.
-2121 Lindholm ME, Rundqvist HJEp. Skeletal muscle hypoxia-inducible factor-1 and exercise. Exp Physiol. 2016;101(1):28-32.

A study using 0.100 FIO2, which is lower than the level used in this study (FIO2: 0.136), the PaO2 values at rest were 46 ± mmHg, with respective PiO2 values of 23 ± 6 mmHg.1616 Richardson RS, Duteil S, Wary C, Wray DW, Hoff J, Carlier PGJTJop. Human skeletal muscle intracellular oxygenation: the impact of ambient oxygen availability. J Physiol. 2006;571(2):415-24. These values were above what was necessary for HIF1α stabilization, indicating that passive hypoxia does not leads to adaptations in the HIF-1α pathway. In corroboration, a review showed that only passive hypoxia was not efficient in causing aerobic or anaerobic changes.2222 Bärtsch P, Dehnert C, Friedmann-Bette B, Tadibi VJSJoM, Sports Si. Intermittent hypoxia at rest for improvement of athletic performance. Scand J Med Sci Sports. 2008;18(Suppl):50-6.

Other studies show that physical exercise in normoxia performed at high-intensity can decrease PiO2 values from 35 mmHg to 3.1 mmHg, thus exercise at high-intensity seems to be enough to stabilize this pathway.1616 Richardson RS, Duteil S, Wary C, Wray DW, Hoff J, Carlier PGJTJop. Human skeletal muscle intracellular oxygenation: the impact of ambient oxygen availability. J Physiol. 2006;571(2):415-24.,1717 Richardson RS, Noyszewski EA, Kendrick KF, Leigh JS, Wagner PDJTJoci. Myoglobin O2 desaturation during exercise. Evidence of limited O2 transport. J Clin Invest. 1995;96(4):1916-26.,2323 Richardson RS, Knight DR, Poole DC, Kurdak SS, Hogan MC, Grassi B, et al. Determinants of maximal exercise VO2 during single leg knee-extensor exercise in humans. Am J Physiol. 1995;268(4):H1453-H61.

Studies report PaO2 values of 46 mmHg and PiO2 values of 2.3 mmHg when high-intensity exercises are combined with hypoxia, being enough for HIF1α stabilization.1717 Richardson RS, Noyszewski EA, Kendrick KF, Leigh JS, Wagner PDJTJoci. Myoglobin O2 desaturation during exercise. Evidence of limited O2 transport. J Clin Invest. 1995;96(4):1916-26.,1818 Flueck M. Plasticity of the muscle proteome to exercise at altitude. High Alt Med Biol. 2009;10(2):183-93. In the present study, when hypoxia was added during the recovery intervals, we found PaO2 values of 50.26 ± 4.57 mmHg.

We are unable to say whether the decrease in oxygen supply in the proposed session was sufficient to stabilize HIFα, since we did not perform muscle biopsies to determine its concentration or expression. The mean SpO2 value during the intervals was similar to or lower than observed in studies that have demonstrated improved performance with IHT, compared to training performed in normoxia.33 Faiss R, Girard O, Millet GP. Advancing hypoxic training in team sports: from intermittent hypoxic training to repeated sprint training in hypoxia. Br J Sports Med. 2013;47(Suppl 1):i45-i50.,66 Galvin HM, Cooke K, Sumners DP, Mileva KN, Bowtell JLJBJSM. Repeated sprint training in normobaric hypoxia. Br J Sports Med. 2013;47(Suppl 1):i74-i9.,2424 Millet G, Bentley DJ, Roels B, Mc Naughton LR, Mercier J, Cameron-Smith DJPo. Effects of intermittent training on anaerobic performance and MCT transporters in athletes. PLoS One. 2014;9(5):e95092. Based on the aforementioned information, it can be speculated that the hypoxia addition during interval is an additional stimulus to optimize physiological gains, with the advantage of maintaining the “quality of effort,” since the efforts can be performed in normoxia.

The HD was higher in the recovery periods in hypoxia, however, literature provides limited information concerning the HD required to trigger positive adaptations.2525 Garvican-Lewis LA, Sharpe K, Gore CJ. Time for a new metric for hypoxic dose?. J Appl Physiol. 2016;121(1):352-5. The HD for a given activity seems to be dependent on both exposure time and the variation in SpO2 values. This variation seems to be influenced by several factors, such as age, training level, and ability to maintain oxygen uptake at altitude and during the ventilatory response to hypoxia. The ventilatory response can alter the entire oxygen consumption cascade from alveoli to muscle PiO2.1616 Richardson RS, Duteil S, Wary C, Wray DW, Hoff J, Carlier PGJTJop. Human skeletal muscle intracellular oxygenation: the impact of ambient oxygen availability. J Physiol. 2006;571(2):415-24.,2626 Chapman RF. The individual response to training and competition at altitude. Br J Sports Med. 2013;47(Suppl 1):i40-i44.

There was a tendency for [La] to increase in TRH compared to TRN, however no differences were found. This was similar to observed in IHT.55 Czuba M, Waskiewicz Z, Zajac A, Poprzecki S, Cholewa J, Roczniok R. The effects of intermittent hypoxic training on aerobic capacity and endurance performance in cyclists. J Sports Sci Med. 2011;10(1):175-83. The increase in [La] due to hypoxia can be explained in part, by the greater use of anaerobic pathways to generate energy, since the aerobic pathway is compromised when less oxygen is transported to cells.2727 Girard O, Brocherie F, Millet GP. Effects of altitude/hypoxia on single-and multiple-sprint performance: a comprehensive review. Sports Med. 2017;47(10):1931-49. In this study, the [Glu] maintained stable during training, suggesting that hypoxia only in the recovery was not enough to increase the lactic demand to generate energy. However, some authors have reported no changes in [La] after hypoxia, a phenomenon known as the “lactate paradox”.2828 Hochachka P, Beatty C, Burelle Y, Trump M, McKenzie D, Matheson G. The lactate paradox in human high-altitude physiological performance. News Physiol Sci. 2002;17:122-6.

Hypoxia can cause reduction in [Glu] accelerating the fatigue and decreasing performance.2929 Paris HL, Sinai EC, Shei R-J, Keller AM, Mickleborough TDJEJoSS. The influence of carbohydrate ingestion on peripheral and central fatigue during exercise in hypoxia: a narrative review. Eur J Sport Sci. 2021;21(10):1423-35. During this study, the participants performed efforts without any decrease in intensity or increase other parameters associated to fatigue.

The HR was frequently used to determine internal training load, it is noted that TRH was effective in changing HR during recovery, showing a greater internal load for TRN, Internal load manipulation was associated with improved performance.3030 Manzi V, Iellamo F, Impellizzeri F, D'ottavio S, Castagna CJMSSE. Relation between individualized training impulses and performance in distance runners. Med Sci Sports Exerc. 2009;41(11):2090-6. Thus, add hypoxia in training seems to be alternative to raise internal load, without increase the external load. This hypothesis still needs to be confirmed in future chronic studies. Besides, studies that manipulate training loads during hypoxia have consistently reported additional benefits in performance-related parameters.44 Czuba M, Wilk R, Karpiński J, Chalimoniuk M, Zajac A, Langfort J. Intermittent hypoxic training improves anaerobic performance in competitive swimmers when implemented into a direct competition mesocycle. PloS One. 2017;12(8):e0180380.,55 Czuba M, Waskiewicz Z, Zajac A, Poprzecki S, Cholewa J, Roczniok R. The effects of intermittent hypoxic training on aerobic capacity and endurance performance in cyclists. J Sports Sci Med. 2011;10(1):175-83.

The present study has limitations: the subjects did not carry out a training session entirely in hypoxia or other combinations, although our objective was to prevent the entire session from being performed with low O2 availability for the reasons previously reported. No muscle biopsy was performed to determine biomolecular parameters.

CONCLUSION

We conclude that hypoxia during the intervals between efforts can be an additional and innovative stimulus for high-intensity interval training, without hindering the execution of physical efforts and external training load, maintaining the intensity of efforts, furthermore, this acute model proved to be effective in promoting substantial acute physiological alterations.

ACKNOWLEDGE

We would like to thank all the participants in this study and the School of Physical Education and Sport of Ribeirão Preto (EEFERP / USP).

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Edited by

Associate Editor responsible for the review process: Paulo Zogaib

Publication Dates

  • Publication in this collection
    18 Sept 2023
  • Date of issue
    2024

History

  • Received
    20 Apr 2022
  • Accepted
    15 Dec 2022
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