Effect of Step Load Based on Time under Tension in Hypoxia on the ACL Pre-Operative Rehabilitation and Hormone Levels: A Case Study

The aim of the study was to determine the effect of step load in hypoxia on the effectiveness of preoperative rehabilitation (PR) and hormone levels based on a case study. Introduction: We assessed the impact of variables such as rate of movement and time under tension (TUT) in normobaric hypoxia on the levels of growth hormone (GH), insulin-like growth factor 1 (IGF-1), and erythropoietin (EPO). Additionally, the impact of step load on the hypertrophy and strength of knee extensors and flexors was assessed. Methods: The work uses a case study, the research subject of which was a 23-year-old female professional handball player. The tests included an isokinetic assessment of the peak torque of knee extensors and flexors as well as body composition analysis. Results: The results showed a more than (10.81-fold) increase in GH after the microcycle with time under tension (TUT). The deficit between the lower limbs was also reduced. Conclusions: Using a hypoxic environment based on an appropriate altitude, combined with changes such as a short rest break between sets and a controlled tempo of movement with an eccentric phase, TUT may offer an alternative to the PR process, especially among athletes who care about fast RTS.

Muscle Oximetry in Sports Science: An Updated Systematic Review

BACKGROUND

In the last 5 years since our last systematic review, a significant number of articles have been published on the technical aspects of muscle near-infrared spectroscopy (NIRS), the interpretation of the signals and the benefits of using the NIRS technique to measure the physiological status of muscles and to determine the workload of working muscles.

OBJECTIVES

Considering the consistent number of studies on the application of muscle oximetry in sports science published over the last 5 years, the objectives of this updated systematic review were to highlight the applications of muscle oximetry in the assessment of skeletal muscle oxidative performance in sports activities and to emphasize how this technology has been applied to exercise and training over the last 5 years. In addition, some recent instrumental developments will be briefly summarized.

METHODS

Preferred Reporting Items for Systematic Reviews guidelines were followed in a systematic fashion to search, appraise and synthesize existing literature on this topic. Electronic databases such as Scopus, MEDLINE/PubMed and SPORTDiscus were searched from March 2017 up to March 2023. Potential inclusions were screened against eligibility criteria relating to recreationally trained to elite athletes, with or without training programmes, who must have assessed physiological variables monitored by commercial oximeters or NIRS instrumentation.

RESULTS

Of the identified records, 191 studies regrouping 3435 participants, met the eligibility criteria. This systematic review highlighted a number of key findings in 37 domains of sport activities. Overall, NIRS information can be used as a meaningful marker of skeletal muscle oxidative capacity and can become one of the primary monitoring tools in practice in conjunction with, or in comparison with, heart rate or mechanical power indices in diverse exercise contexts and across different types of training and interventions.

CONCLUSIONS

Although the feasibility and success of the use of muscle oximetry in sports science is well documented, there is still a need for further instrumental development to overcome current instrumental limitations. Longitudinal studies are urgently needed to strengthen the benefits of using muscle oximetry in sports science.

Hypoxia matters: comparison of external and internal training load markers during an 8-week resistance training program in normoxia, normobaric hypoxia and hypobaric hypoxia

PURPOSE

To compare external and internal training load markers during resistance training (RT) in normoxia (N), intermittent hypobaric hypoxia (HH), and intermittent normobaric hypoxia (NH).

METHODS

Thirty-three volunteers were assigned an 8-week RT program in either N (690 m, n = 10), HH (2320 m, n = 10), or NH (inspired fraction of oxygen = 15.9%; ~ 2320 m, n = 13). The RT program (3x/week) consisted of six exercises, with three sets of six to 12 repetitions at ~ 70% of one repetition maximum (1RM) with the first session of each week used for analysis. 1RM in back squat and bench press was used to evaluate muscle strength before and after the program. External load was assessed by the volume load relative to body mass (RVL, kg·kg-1). Internal load was assessed by the ratings of perceived exertion (RPE) and heart rate (HR).

RESULTS

Smaller relative improvements were found for the back squat in the N group (11.5 ± 8.8%) when compared to the NH group (22.2 ± 8.2%, P = 0.01) and the HH group (22 ± 8.1%, P = 0.02). All groups showed similar RVL, HR responses and RPE across the program (P˃0.05). However, reduced HR recovery values, calculated as the difference between the highest HR value (HRpeak) and the resting heart rate after a two min rest, were seen in the N and NH groups across the program (P < 0.05).

CONCLUSION

It seems that 8 weeks of intermittent RT in hypoxic environments could maximize time-efficiency when aiming to improve strength levels in back squat without evoking higher levels of physiological stress. Performing RT at hypobaric hypoxia may improve the cardiorespiratory response, which in turn could speed recovery.

Hypoxia Does Not Impair Resistance Exercise Performance or Amplify Post-Exercise Fatigue

Purpose: To determine whether performing resistance exercise in hypoxia acutely reduces performance and increases markers of fatigue, and whether these responses are exaggerated if exercising at high versus low work rates (i.e., exercising to failure or volume matched non-failure). Methods: Following a within-subject design, 20 men completed two trials in hypoxia (13% oxygen) and two in normoxia (21% oxygen). The first session for hypoxic and normoxic conditions comprised six sets of bench press and shoulder press to failure (high work rate), while subsequent sessions involved the same volume distributed over 12 sets (low work rate). Physical performance (concentric velocity) and perceptual responses were measured during exercise and for 72 hr post-exercise. Neuromuscular performance (bench throw velocity) was assessed pre- and post-session. Results: Hypoxia did not affect physical performance, neuromuscular performance, and perceptual recovery when exercising at high or low work rates. Higher work rate exercise caused greater acute decrements in physical performance and post-exercise neuromuscular performance and increased perceived exertion and muscle soreness (p ≤ 0.006), irrespective of hypoxia. Conclusions: Hypoxia does not impact on resistance exercise performance or increase markers of physical and perceptual fatigue. Higher exercise work rates may impair physical performance, and exaggerate fatigue compared to low work rate exercise, irrespective of environmental condition. Practitioners can prescribe hypoxic resistance exercise without compromising physical performance or inducing greater levels of fatigue. For athletes who are required to train with high frequency, decreasing exercise work rate may reduce post-exercise markers of fatigue for the same training volume.

Mechanisms underlying the health benefits of intermittent hypoxia conditioning

Intermittent hypoxia (IH) is commonly associated with pathological conditions, particularly obstructive sleep apnoea. However, IH is also increasingly used to enhance health and performance and is emerging as a potent non-pharmacological intervention against numerous diseases. Whether IH is detrimental or beneficial for health is largely determined by the intensity, duration, number and frequency of the hypoxic exposures and by the specific responses they engender. Adaptive responses to hypoxia protect from future hypoxic or ischaemic insults, improve cellular resilience and functions, and boost mental and physical performance. The cellular and systemic mechanisms producing these benefits are highly complex, and the failure of different components can shift long-term adaptation to maladaptation and the development of pathologies. Rather than discussing in detail the well-characterized individual responses and adaptations to IH, we here aim to summarize and integrate hypoxia-activated mechanisms into a holistic picture of the body's adaptive responses to hypoxia and specifically IH, and demonstrate how these mechanisms might be mobilized for their health benefits while minimizing the risks of hypoxia exposure.

Altitude-induced effects on neuromuscular, metabolic and perceptual responses before, during and after a high-intensity resistance training session

PURPOSE

We tested if an acute ascending to 2320 m above sea level (asl) affects corticospinal excitability (CSE) and intracortical inhibition (SICI) measured with transcranial magnetic stimulation (TMS) at rest, before, during and after a traditional hypertrophy-oriented resistance training (RT) session. We also explored whether blood lactate concentration (BLa), ratings of perceived exertion (RPE), perceived muscular pain and total training volume differed when the RT session was performed at hypoxia (H) or normoxia (N).

METHODS

Twelve resistance-trained men performed eight sets of 10 repetitions at 70% of one repetition maximum of a bar biceps curl at N (SpO2 = 98.0 ± 0.9%) and H (at 2320 asl, SpO2 = 94.0 ± 1.9%) in random order. Before each session, a subjective well-being questionnaire, the resting motor threshold (rMT) and a single pulse recruitment curve were measured. Before, during and after the RT session, BLa, RPE, muscle pain, CSE and SICI were measured.

RESULTS

Before the RT session only the rMT differed between H (- 5.3%) and N (ES = 0.38). RPE, muscle pain and BLa increased through the RT session and were greater at H than N (12%, 54% and 15%, respectively) despite a similar training volume (1618 ± 468 kg vs. 1638 ± 509 kg). CSE was reduced during the RT session (~ 27%) but recovered ten minutes after, regardless of the environmental condition. SICI did not change after any RT session.

CONCLUSIONS

The data suggest that acute exposure to moderate hypoxia slightly increased the excitability of the most excitable structures of the corticospinal tract but did not influence intracortical or corticospinal responses to a single RT session.

Moderate and Severe Acute Normobaric Hypoxia and the 3-Repetition Deadlift, Hand-Release Push-Up, and Leg Tuck Events From the Army Combat Fitness Test

INTRODUCTION

The newly implemented Army Combat Fitness Test (ACFT) of the U.S. Army seeks to revolutionize the Army's fitness culture and reduce the rate of preventable injuries among soldiers. The initial rollout of the ACFT has been met with several challenges, including a gender-neutral scoring system. The ACFT has undergone several revisions to adapt to the present state of U.S. Army physical fitness; however, the test faces several more obstacles as more data become available. The ACFT was designed to measure combat readiness, a useful tool for units facing deployment or a change in duty station to a high-altitude environment. Reduced oxygen availability (hypoxia) at high altitude influences many physiological functions associated with physical fitness, such that there is an increased demand for oxygen in exercising muscle. Therefore, the purpose was to investigate the effects of normoxic and two levels of hypoxia exposure (moderate and severe; fraction of inspired oxygen [FiO2]: 16.0% and 14.3%) during the 3-repetition deadlift (MDL), hand-release push-up (HRP), and leg tuck (LTK) events of the ACFT.

MATERIALS AND METHODS

Fourteen recreationally active men (n = 10) and women (n = 4) soldier analogs (27.36 ± 1.12 years, height 1.71 ± 2.79 m, weight 80.60 ± 4.24 kg) completed the MDL, HRP, and LTK at normoxia and acute normobaric moderate (MH; FiO2 16%) and severe (SH; FiO2 14.3%) hypoxic exposure. Scores and performance were recorded for each event, and heart rate (HR) and total body oxygen saturation (SpO2) were monitored throughout. Repeated-measures analysis of variance (ANOVA) was used to assess differences in modified ACFT scores, performance, HR, and SpO2 among hypoxic conditions, with follow-up one-way ANOVA and paired t-test when appropriate.

RESULTS

Total body oxygen saturation was decreased at MH and SH conditions compared to normoxia but did not vary between ACFT events. Heart rate was not influenced by altitude but did increase in response to exercise. Scores of the modified total and individual ACFT events were not different between normoxia, MH, and SH. There was also no difference in performance based on the amount of weight lifted during the MDL and number of repetitions of the HRP and LTK events in response to hypoxic exposure.

CONCLUSIONS

Performance and scores of the modified ACFT were not influenced by acute normobaric MH and SH exposure compared to normoxia. Further investigations should examine the full testing battery of the ACFT to provide a comprehensive analysis and potential evidence for such differences.

How does multi-set high-load resistance exercise impact neuromuscular function in normoxia and hypoxia?

This study examined whether hypoxia during multi-set, high-load resistance exercise alters neuromuscular responses. Using a single-blinded (participants), randomised crossover design, eight resistance-trained males completed five sets of five repetitions of bench press at 80% of one repetition maximum in moderate normobaric hypoxia (inspiratory oxygen fraction = 0.145) and normoxia. Maximal isometric bench press trials were performed following the warm-up, after 10 min of altitude priming and 5 min post-session (outside, inside and outside the chamber, respectively). Force during pre-/post-session maximal voluntary isometric contractions and bar velocity during exercise sets were measured along with surface electromyographic (EMG) activity of the pectoralis major, anterior deltoid and lateral and medial triceps muscles. Two-way repeated measures ANOVA (condition×time) were used. A significant time effect (p = 0.048) was found for mean bar velocity, independent of condition (p = 0.423). During sets of the bench press exercise, surface EMG amplitude of all studied muscles remained unchanged (p > 0.187). During maximal isometric trials, there were no main effects of condition (p > 0.666) or time (p > 0.119), nor were there any significant condition×time interactions for peak or mean forces and surface EMG amplitudes (p > 0.297). Lower end-exercise blood oxygen saturation (90.9 ± 1.8 vs. 98.6 ± 0.6%; p < 0.001) and higher blood lactate concentration (5.8 ± 1.4 vs. 4.4 ± 1.6 mmol/L; p = 0.007) values occurred in hypoxia. Acute delivery of systemic normobaric hypoxia during multi-set, high-load resistance exercise increased metabolic stress. However, only subtle neuromuscular function adjustments occurred with and without hypoxic exposure either during maximal isometric bench press trials before versus after the session or during actual exercise sets.

Inter-set rest configuration effect on acute physiological and performance-related responses to a resistance training session in terrestrial vs simulated hypoxia

Background

Metabolic stress is considered a key factor in the activation of hypertrophy mechanisms which seems to be potentiated under hypoxic conditions.This study aimed to analyze the combined effect of the type of acute hypoxia (terrestrial vs simulated) and of the inter-set rest configuration (60 vs 120 s) during a hypertrophic resistance training (R_T) session on physiological, perceptual and muscle performance markers.

Methods

Sixteen active men were randomized into two groups based on the type of hypoxia (hypobaric hypoxia, HH: 2,320 m asl; vs normobaric hypoxia, NH: FiO₂ of 15.9%). Each participant completed in a randomly counterbalanced order the same R_T session in four separated occasions: two under normoxia and two under the corresponding hypoxia condition at each prescribed inter-set rest period. Volume-load (load × set × repetition) was calculated for each training session. Muscle oxygenation (SmO₂) of the vastus lateralis was quantified during the back squat exercise. Heart rate (HR) was monitored during training and over the ensuing 30-min post-exercise period. Maximal blood lactate concentration (maxLac) and rating of perceived exertion (RPE) were determined after the exercise and at the end of the recovery period.

Results

Volume-load achieved was similar in all environmental conditions and inter-set rest period length did not appreciably affect it. Shorter inter-set rest periods displayed moderate increases in maxLac, HR and RPE responses in all conditions. Compared to HH, NH showed a moderate reduction in the inter-set rest-HR (ES > 0.80), maxLac (ES > 1.01) and SmO₂ (ES > 0.79) at both rest intervals.

Conclusions

Results suggest that the reduction in inter-set rest intervals from 120 s to 60 s provide a more potent perceptual, cardiovascular and metabolic stimulus in all environmental conditions, which could maximize hypertrophic adaptations in longer periods of training. The abrupt exposure to a reduced FiO₂ at NH seems to reduce the inter-set recovery capacity during a traditional hypertrophy R_T session, at least during a single acute exposition. These results cannot be extrapolated to longer training periods.

Neuromuscular Adaptations in Elite Swimmers During Concurrent Strength and Endurance Training at Low and Moderate Altitudes

ABSTRACT

Tomazin, K, Strojnik, V, Feriche, B, Garcia Ramos, A, Štrumbelj, B, and Stirn, I. Neuromuscular adaptations in elite swimmers during concurrent strength and endurance training at low and moderate altitudes. J Strength Cond Res 36(4): 1111-1119, 2022-This study evaluated neuromuscular adaptations in elite swimmers during concurrent strength and endurance training (SET) at low (295 m) and moderate (2,320 m) altitudes. Sixteen elite swimmers took part in a 3-week SET during a general preparation phase. All neuromuscular tests were performed a week before and after a SET. In posttraining, maximal knee isometric torque (TMVC) and soleus H-reflex remained statistically unchanged for sea-level (SL) and for altitude (AL) training. Rate of torque development (RTD) decreased post-SL (-14.5%; p < 0.01) but not post-AL (-4.7%; p > 0.05) training. Vastus lateralis electromyographic (EMG) activity during RTD decreased post-SL (-17.0%; P = 0.05) but not post-AL (4.8%; p > 0.05) training. Quadriceps twitch torque (TTW) significantly increased post-AL (12.1%; p < 0.01) but not post-SL (-1.0%; p > 0.05; training × altitude: F1,15 = 12.4; p < 0.01) training. Quadriceps twitch contraction time and M-wave amplitude remained statistically unchanged post-SL and post-AL training. After SL training, increment in TMVC was accompanied with increment in vastus lateralis EMG (R = 0.76; p < 0.01) and TTW (R = 0.48; p < 0.06). Posttraining in AL, increment in TMVC was accompanied with increment in TTW (R = 0.54; p < 0.05). Strength and endurance training at altitude seems to prompt adaptations in twitch contractile properties. In contrast, SET performed at SL may hamper the magnitude of neural adaptations to strength training, particularly during rapid voluntary contractions. In conclusion, SET at AL might benefit muscular adaptations in swimmers compared with training at SL.

Effects of Resistance Training in Hypobaric vs. Normobaric Hypoxia on Circulating Ions and Hormones

Hypobaric hypoxia (HH) seems to lead to different responses compared to normobaric hypoxia (NH) during physical conditioning. The aim of the study was to analyze the hormonal and circulating ion responses after performing high-intensity resistance training with different inter-set rest under HH and NH condition. Sixteen male volunteers were randomly divided into two training groups. Each group completed two counterbalanced resistance training sessions (three sets × ten repetitions, remaining two repetitions in reserve), with both one- and two-minute inter-set rest, under HH and NH. Blood samples were obtained to determine hormones and circulating ions (Ca²⁺, Pi, and HCO₃⁻) at baseline and after training sessions (5, 10, and 30 min). Resistance training with one-minute rest caused greater hormonal stress than with two-minute rest in cortisol and growth hormone, although the hypoxic environmental condition did not cause any significant alterations in these hormones. The short inter-set rest also caused greater alterations in HCO₃⁻ and Pi than the longer rest. Additionally, higher levels of Ca²⁺ and Pi, and lower levels of HCO₃⁻, were observed after training in HH compared to NH. Metabolic and physiological responses after resistance training are mediated by inter-set rest intervals and hypoxic environmental condition. According to the alterations observed in the circulating ions, HH could cause greater muscular fatigue and metabolic stress than NH.

The Physiological Profile Following Two Popular Cold Interventions After Activity in Hot and Humid Environment

This research aims to describe and compare the effects of partial-body cryotherapy (PBC) and cold-water immersion (CWI) on the physiological responses of soccer players after cycling in a hot and humid environment. Sixteen elite soccer players participated in three experiments, and received CWI (13°C for 15 min), PBC (110°C−140°C for 3 min), and CON (room temperature: 21°C ± 2°C), respectively, after aerobic and anaerobic cycling in a hot and humid environment (temperature: 35°C–38°C; humidity: 60%–70%). Heart rate (HR), blood lactate (BLa-), perfusion index (PI), oxygen saturation (SaO₂), core temperature (Tc), skin temperature (Ts), and rating of perceived exertion (RPE) were assessed at baseline and through 20 min (5-min intervals). HR was lower in CWI than CON after 20 min (p < .05). SaO₂ was higher in CWI than PBC and CON between 10 and 20 min (p < .05). Tc was lower from CWI and PBC than CON between 10 and 20 min (p < .05). Ts was lower in PBC than CWI between 15 and 20 min (p < .05). RPE was lower in PBC than CON 20 min after the exercise (p < .05). No main group differences for BLa- and PI were observed. The physiological effects of PBC are generally similar to CWI. Compared with CON, both CWI and PBC could promote the recovery of physiological indexes within 20 min of exercise in a hot and humid environment. However, PBC can lead to a decrease in SaO₂ due to excessive nitrogen inhalation.

The Acute Effects of Normobaric Hypoxia on Strength, Muscular Endurance and Cognitive Function: Influence of Dose and Sex

The aim of this study was to examine the acute effects of different levels of hypoxia on maximal strength, muscular endurance, and cognitive function in males and females. In total, 13 males (mean ± SD: age, 23.6 ± 2.8 years; height, 176.6 ± 3.9 cm; body mass, 76.6 ± 2.1 kg) and 13 females (mean ± SD: age, 22.8 ± 1.4 years; height, 166.4 ± 1.9 cm; body mass, 61.6 ± 3.4 kg) volunteered for a randomized, double-blind, crossover study. Participants completed a one repetition strength and muscular endurance test (60% of one repetition maximum to failure) for squat and bench press following four conditions; (i) normoxia (900 m altitude; FiO2: 21%); (ii) low dose hypoxia (2000 m altitude; FiO2: 16%); (iii) moderate dose hypoxia (3000 m altitude; FiO2: 14%); and (iv) high dose hypoxia (4000 m altitude; FiO2: 12%). Heart rate, blood lactate, rating of perceived exertion, and cognitive function was also determined during each condition. The one repetition maximum squat (p = 0.33) and bench press (p = 0.68) did not differ between conditions or sexes. Furthermore, squat endurance did not differ between conditions (p = 0.34). There was a significant decrease in bench press endurance following moderate (p = 0.02; p = 0.04) and high (p = 0.01; p = 0.01) doses of hypoxia in both males and females compared to normoxia and low dose hypoxia, respectively. Cognitive function, ratings of perceived exertion, and lactate were also significantly different in high and moderate dose hypoxia conditions compared to normoxia (p < 0.05). Heart rate was not different between the conditions (p = 0.30). In conclusion, high and moderate doses of acute normobaric hypoxia decrease upper body muscular endurance and cognitive performance regardless of sex; however, lower body muscular endurance and maximal strength are not altered.

Acute normobaric hypoxia blunts contraction-mediated mTORC1- and JNK-signaling in human skeletal muscle

Aim

Hypoxia has been shown to reduce resistance exercise‐induced stimulation of protein synthesis and long‐term gains in muscle mass. However, the mechanism whereby hypoxia exerts its effect is not clear. Here, we examine the effect of acute hypoxia on the activity of several signalling pathways involved in the regulation of muscle growth following a bout of resistance exercise.

Methods

Eight men performed two sessions of leg resistance exercise in normoxia or hypoxia (12% O₂) in a randomized crossover fashion. Muscle biopsies were obtained at rest and 0, 90,180 minutes after exercise. Muscle analyses included levels of signalling proteins and metabolites associated with energy turnover.

Results

Exercise during normoxia induced a 5‐10‐fold increase of S6K1^Thr389 phosphorylation throughout the recovery period, but hypoxia blunted the increases by ~50%. Phosphorylation of JNK^{Thr183/Tyr185} and the JNK target SMAD2^{Ser245/250/255} was increased by 30‐ to 40‐fold immediately after the exercise in normoxia, but hypoxia blocked almost 70% of the activation. Throughout recovery, phosphorylation of JNK and SMAD2 remained elevated following the exercise in normoxia, but the effect of hypoxia was lost at 90‐180 minutes post‐exercise. Hypoxia had no effect on exercise‐induced Hippo or autophagy signalling and ubiquitin‐proteasome related protein levels. Nor did hypoxia alter the changes induced by exercise in high‐energy phosphates, glucose 6‐P, lactate or phosphorylation of AMPK or ACC.

Conclusion

We conclude that acute severe hypoxia inhibits resistance exercise‐induced mTORC1‐ and JNK signalling in human skeletal muscle, effects that do not appear to be mediated by changes in the degree of metabolic stress in the muscle.

Acute performance and physiological responses to upper-limb multi-set exercise to failure: Effects of external resistance and systemic hypoxia

This study quantified performance and physiological responses during multi-set resistance exercise to failure at light versus moderate loads in normoxia and systemic hypoxia. On separate visits, fifteen resistance-trained adults performed barbell biceps curl exercise trials (6 sets to failure, 2 min rest between sets) in four separate randomised conditions; i.e. in normoxia at 380 m above sea level or systemic hypoxia at ∼3800 m simulated altitude (inspired oxygen fraction = 20.9% and 12.9%, respectively) combined with two different intensity levels (30% and 70% of 1 repetition maximal or 1RM). Muscle activation (root mean square value calculated from surface electromyography) and oxygenation (integrated-tissue saturation index derived from near-infrared spectroscopy) were monitored for the biceps brachii muscle. The total number of repetitions before failure at 30% 1RM (122 ± 5 vs. 131 ± 5; P = 0.021), but not 70% 1RM (39 ± 1 vs. 41 ± 2; P = 0.313), was lower in hypoxia compared to normoxia. Root mean square activity of the biceps brachii muscle was higher for 70% 1RM compared to 30% 1RM (P < 0.001), while the increase in muscle activation from the first to the last set (P < 0.001) occurred independently of altitude (P > 0.158). Deoxygenation and reoxygenation responses were higher under hypoxic versus normoxic conditions at 70% 1 RM (P = 0.013 and P = 0.015) but not 30% 1RM (P = 0.528 and P = 0.384). During upper-limb multi-set resistance exercise to failure, exposure to acute normobaric hypoxia negatively impacts performance at light, but not moderate, loads. Overall, external resistance has more profound effects on physiological strain than hypoxic exposure per se.Highlights The addition of acute systemic hypoxia negatively affects work performed at low, but not moderate, loads during upper-limb resistance exercise to failure.Hypoxic exposure, however, does not fundamentally alter muscle activation and oxygenation patterns.Muscle activation and oxygenation responses in turn are more largely influenced by load lifted.

Effect of hypoxic conditioning on functional fitness, balance and fear of falling in healthy older adults: a randomized controlled trial

Background

Hypoxic conditioning has been proposed as a new tool to mitigate the sarcopenia and enhance health-related function, but decrements in standing balance have been observed during hypoxia exposure. The aim of the study was to evaluate the effect of a hypoxic conditioning training on functional fitness, balance and fear of falling in healthy older adults.

Methods

A total of 54 healthy older adults (aged 65–75 years), who voluntarily participated in the study, were randomly divided into three groups: the control group (CON), the normoxia training group (NT) that performed strength training in normoxia, and the hypoxia training group (HT) that trained under moderate hypoxic conditions at a simulated altitude of 2500 m asl. The training programme that was performed during 24 weeks was similar in both experimental groups and consisted of a full-body workout with elastic bands and kettlebells (three sets × 12–15 reps). The Senior Fitness Test (SFT), the Single Leg Stance test (SLS) and the Short Falls Efficacy Scale-International (FES-I) were assessed before and after the intervention.

Results

Results showed that after training, either in normoxia or in hypoxia, the participants increased upper and lower body strength, and the aerobic endurance, and decreased the fear of falling.

Conclusions

The moderate hypoxic conditioning seems to be a useful tool to increase the functional capacity in healthy older adults without observing a decline in balance.

Trial registration

ClinicalTrials.gov NCT04281264. Registered February 9, 2019-Retrospectively registered.

Neuromuscular responses at acute moderate and severe hypoxic exposure during fatiguing exercise of the biceps brachii

Purpose

The present study examined acute normobaric hypoxic exposure on the number of repetitions to failure, electromyographic (EMG) repetition duration (Time), EMG root mean square (RMS) and EMG mean power frequency (MPF) during biceps brachii (BB) dynamic constant external resistance (DCER) exercise.

Methods

Thirteen subjects performed two sets of fatiguing DCER arm curl repetitions to failure at 70% of their one repetition maximum under normoxic (NH), moderate hypoxia FiO₂ = 15% (MH) and severe hypoxia FiO₂ = 13% (SH). Electromyography of the BB was analyzed for EMG Time, EMG RMS, and EMG MPF. Repetitions were selected as 25%, 50%, 75%, and 100% of total repetitions (%Fail) completed. Pulse oximetry (SpO₂) was measured pre-and post-fatigue.

Results

There was no significant three-way (Condition x Set x %Fail) or two-way (Condition x Set) interaction for any variable. The number of repetitions to failure significantly decreased from (mean ± SEM) 18.2 ± 1.4 to 9.5 ± 1.0 with each Set. In addition, EMG Time increased (25% < 50%<75% < 100%), EMG RMS decreased (50% > 75%>100%), and EMG MPF decreased (75% > 100%) as a result of fatiguing exercise. SpO₂ was lower during MH (Δ5.3%) and SH (Δ9.2%) compared to NH and as a result of fatiguing exercise increased only in MH (Δ2.1%) and SH (Δ5.7%).

Conclusion

The changes in BB EMG variables indicated exercise caused myoelectric manifestations of fatigue, however, acute moderate or severe hypoxia had no additional influence on the rate of fatigue development or neuromuscular parameters.

•

Acute MH (FiO₂ 15%) and SH (FiO₂ 14%) did not alter the muscle contractile process.

•

Arm curl repetitions to failure decreased MU recruitment and conduction velocity.

•

EMG fatigue analysis, hypoxia and arm curls to failure, EMG RMS, EMG MPF and Time.

•

SpO₂ was lower at MH and SH which increased following fatiguing exercise.

Hormonal and Inflammatory Responses to Hypertrophy-Oriented Resistance Training at Acute Moderate Altitude

This study investigated the effect of a traditional hypertrophy-oriented resistance training (R_T) session at acute terrestrial hypoxia on inflammatory, hormonal, and the expression of miR-378 responses associated with muscular gains. In a counterbalanced fashion, 13 resistance trained males completed a hypertrophic R_T session at both moderate-altitude (H; 2320 m asl) and under normoxic conditions (N; <700 m asl). Venous blood samples were taken before and throughout the 30 min post-exercise period for determination of cytokines (IL6, IL10, TNFα), hormones (growth hormone [GH], cortisol [C], testosterone), and miR-378. Both exercise conditions stimulated GH and C release, while miR-378, testosterone, and inflammatory responses remained near basal conditions. At H, the R_T session produced a moderate to large but nonsignificant increase in the absolute peak values of the studied cytokines. miR-378 revealed a moderate association with GH (r = 0.65; p = 0.026 and r = −0.59; p = 0.051 in N and H, respectively) and C (r = 0.61; p = 0.035 and r = 0.75; p = 0.005 in N and H, respectively). The results suggest that a R_T session at H does not differentially affect the hormonal, inflammatory, and miR-378 responses compared to N. However, the standardized mean difference detected values in the cytokines suggest an intensification of the inflammatory response in H that should be further investigated.

Effects of Power-Oriented Resistance Training During an Altitude Camp on Strength and Technical Performance of Elite Judokas

This study investigated the effect of a 3-week power-oriented resistance training program performed at moderate altitude on leg power output variables in a countermovement jump, a related judo technique (ippon-seoi-nage) and the relationship between them. Twenty-four elite male judokas were randomly assigned to a hypobaric hypoxia or normoxia group. Mechanical outputs from an incremental loaded countermovement jump test and the kinematic variables transferred to a dummy during an ippon-seoi-nage test (time to execution and movement accelerations) were assessed before, after, 1 and 2 weeks after training. Results indicated an increase in explosive leg capacity both at moderate altitude (2320 m.a.s.l.) and sea level. The hypoxia group showed additional benefits when compared to normoxia group for peak velocities with different percentages of the body weight, maximal theoretical velocity and jump height after the training period, and these additional benefits in jump height were maintained 2 weeks after training. The hypoxia group achieved a higher peak performance in peak velocity and jump height than normoxia group (peak velocity: 8.8 vs. 5.6%, jump height: 8.2 vs. 1.4%, respectively) and was achieved earlier in hypoxia (after training) than in normoxia (1 week after training). However, there was a detrimental effect for the hypoxia group on the times of execution and acceleration of the ippon-seoi-nage compared to the normoxia group. These results suggest that altitude training may induce faster and greater improvements in explosive leg extension capacity. Specific technique-oriented training should be included at altitude to prevent technique impairment.

Resistance Training in Hypoxia as a New Therapeutic Modality for Sarcopenia-A Narrative Review

Hypoxic training is believed to be generally useful for improving exercise performance in various athletes. Nowadays, exercise intervention in hypoxia is recognized as a new therapeutic modality for health promotion and disease prevention or treatment based on the lower mortality and prevalence of people living in high-altitude environments than those living in low-altitude environments. Recently, resistance training in hypoxia (RTH), a new therapeutic modality combining hypoxia and resistance exercise, has been attempted to improve muscle hypertrophy and muscle function. RTH is known to induce greater muscle size, lean mass, increased muscle strength and endurance, bodily function, and angiogenesis of skeletal muscles than traditional resistance exercise. Therefore, we examined previous studies to understand the clinical and physiological aspects of sarcopenia and RTH for muscular function and hypertrophy. However, few investigations have examined the combined effects of hypoxic stress and resistance exercise, and as such, it is difficult to make recommendations for implementing universal RTH programs for sarcopenia based on current understanding. It should also be acknowledged that a number of mechanisms proposed to facilitate the augmented response to RTH remain poorly understood, particularly the role of metabolic, hormonal, and intracellular signaling pathways. Further RTH intervention studies considering various exercise parameters (e.g., load, recovery time between sets, hypoxic dose, and intervention period) are strongly recommended to reinforce knowledge about the adaptational processes and the effects of this type of resistance training for sarcopenia in older people.

Acute Effects of Interset Rest Duration on Physiological and Perceptual Responses to Resistance Exercise in Hypoxia

Lockhart, C, Scott, BR, Thoseby, B, and Dascombe, BJ. Acute effects of interset rest duration on physiological and perceptual responses to resistance exercise in hypoxia. J Strength Cond Res 34(8): 2241-2249, 2020-This study aimed to determine whether manipulating interset rest periods during resistance training in hypoxia impacts on physiological and perceptual responses to exercise. Twelve healthy males completed 1 repetition maximum (1RM) testing for the bilateral leg extension, before completing 4 separate randomized trials comprising 5 × 10 repetitions of leg extensions at 70% 1RM. Experimental trials were completed in both moderate hypoxia (FIO2 = 15%) and normoxia (FIO2 = 21%), using interset rest periods of both 60 and 180 seconds for each environmental condition. Near-infrared spectroscopy was used to quantify muscle oxygenation of vastus lateralis , and surface electromyography assessed the activation of vastus lateralis and medialis. Blood lactate concentration ([BLa]) and midthigh circumference were assessed before and immediately after each trial. Heart rate (HR) responses, blood oxygen saturation, and rating of perceived exertion (RPE) were also assessed after each set and the whole session RPE (sRPE). Perceived quadriceps soreness was reported before, immediately after, and at 24 and 48 hours after each trial. Muscle activation (sets 4-5), RPE (sets 3-5), and sRPE were significantly (p < 0.05) higher in the 60-second trials of the resistance exercise protocol. Significant increases (p < 0.01) were observed for [BLa] and midthigh circumference across sets within each condition. No significant main effect was observed for interset rest duration or environmental condition for muscle oxygenation, HR, or perceived quadriceps soreness. These findings indicate that performing resistance exercise in hypoxia or normoxia with shortened interset rest periods increases muscle activation and perceived exertion, without exacerbating muscle soreness.

Electromyography: A Simple and Accessible Tool to Assess Physical Performance and Health during Hypoxia Training. A Systematic Review

Hypoxia causes reduced partial pressure of oxygen in arterial blood and induces adaptations in skeletal muscle that may affect individuals’ physical performance and muscular health. These muscular changes are detectable and quantifiable by electromyography (EMG), an instrument that assesses electrical activity during active contraction at rest. EMG is a relatively simple and accessible technique for all patients, one that can show the degree of the sensory and motor functions because it provides information about the status of the peripheral nerves and muscles. The main goal of this review is to evaluate the scientific evidence of EMG as an instrument for monitoring different responses of skeletal muscles subjected to external stimuli such as hypoxia and physical activity. A structured search was conducted following the Preferred Reporting Items for Systematic Review and Meta-Analyses (PRISMA) guidelines in Medline/PubMed, Scielo, Google Scholar, Web of Science, and Cochrane Library Plus. The search included articles published in the last 25 years until May 2020 and was restricted to English- and Spanish-language publications. As such, investigators identified nine articles that met the search criteria. The results determined that EMG was able to detect muscle fatigue from changes in the frequency spectrum. When a muscle was fatigued, high frequency components decreased and low frequency components increased. In other studies, EMG determined muscle activation increased during exercise by recruiting motor units and by increasing the intensity of muscle contractions. Finally, it was also possible to calculate the mean quadriceps quadratic activity used to obtain an image of muscle activation. In conclusion, EMG offers a suitable tool for monitoring the different skeletal muscle responses and has sufficient sensitivity to detect hypoxia-induced muscle changes produced by hypoxic stimuli. Moreover, EMG enhances an extension of physical examination and tests motor-system integrity.

Neuromuscular and Mobility Responses to a Vibration Session in Hypoxia in Multiple Sclerosis

The aim of this study was to investigate the acute effects of vibration training (WBVT) under hypoxic and normoxic conditions on the voluntary rate of force development (RFD), balance and muscle oxygen saturation (SMO₂) in persons with Multiple Sclerosis (MS). 10 participants completed the study (30% males, 44.4±7.7 years, 164.3±8.9 cm, 65.2±11.1 kg, 2.5±1.3 Expanded Disability Status Scale, 24.1±4.0 kg.m^-2 BMI). Maximal force, RFD during isometric knee extension, static balance with eyes open and closed and sit-to-stand test were evaluated before and immediately after one session of WBVT (12 60-s bout of vibration; frequency 35 Hz; amplitude 4 mm; 1-min rest intervals) under both normoxic and hypoxic conditions. In addition, SMO₂ of the gastrocnemius lateralis was assessed during each condition. No changes were found in force, static balance and sit-to-stand test. Time-to-peak RFD increased in the left leg (p=0.02) and tended to increase in the right leg (p=0.06) after the hypoxic session. SMO₂ resulted in significant increases from the initial to final intervals of the WBVT under both hypoxic and normoxic conditions (p<0.05). Increases in SMO₂ during WBVT demonstrates muscle work that may contribute to the observed muscle adaptations in long-term WBVT programs without inducing decreases in neuromuscular activation, physical function and balance within a session.

Sessional work-rate does not affect the magnitude to which simulated hypoxia can augment acute physiological responses during resistance exercise

PURPOSE

To investigate whether performing resistance exercise in hypoxia augments physiological and perceptual responses, and if altering work-rate by performing repetitions to failure compared to sub-maximally increases the magnitude of these responses.

METHODS

Twenty male university students (minimum of 2 year resistance training experience) completed four sessions, two in hypoxia (fraction of inspired oxygen [F_iO₂] = 0.13), and two in normoxia (F_iO₂ = 0.21). For each condition, session one comprised three sets to failure of shoulder press and bench press (high work-rate session), while session two involved the same volume load, distributed over six sets (low work-rate session). Muscle oxygenation (triceps brachii), surface electromyographic activity (anterior deltoid, pectoralis major, and triceps brachii), heart rate (HR), and arterial blood oxygen saturation were recorded. Blood lactate concentration ([Bla^-]) was recorded pre-exercise and 2 min after each exercise. Muscle thickness was measured pre- and post-exercise via ultrasound.

RESULTS

Muscle oxygenation values during sets and inter-set rest periods were lower in hypoxia vs normoxia (p = 0.001). Hypoxia caused greater [Bla^-] during the shoulder press of failure sessions (p = 0.003) and both shoulder press (p = 0.048) and bench press (p = 0.005) of non-failure sessions. Hypoxia increased HR during non-failure sessions (p < 0.001). There was no effect of hypoxia on muscular swelling, surface electromyographic activity, perceived exertion, or number of repetitions performed.

CONCLUSIONS

Hypoxia augmented metabolite accumulation, but had no impact on any other physiological or perceptual response compared to the equivalent exercise in normoxia. Furthermore, the magnitude to which hypoxia increased the measured physiological responses was not influenced by sessional work-rate.

Effects on performance of active and passive hypoxia as a re-warm-up routine before a 100-metre swimming time trial: a randomized crossover study

Passive and active hypoxia could be used as a tool during a transitional phase to maintain the effects of warm-up and optimize athletic performance. Our purpose was to evaluate and compare the effects of four different re-warm-up strategies, i.e. rest in normoxia (RN) at FiO₂ = 20.9%, rest in hypoxia (RH) at FiO₂ = 15%, active (5 minutes dryland-based exercise circuit) in normoxia (AN) and active in hypoxia (AH), during the transitional phase, on subsequent 100 m maximal swimming performance. Thirteen competitive swimmers (n = 7 males; n = 6 females; age: 15.1±2.1 years; height: 164.7±8.8 cm; weight: 58.1±9.7 kg; 100 m season’s best time 72.0±11.8 s) completed a 20-minute standardized in-water warm-up followed by a 30-minute randomized transitional phase and 100 m freestyle time trial. Compared to AH (73.4±6.2 s), 100 m swim time trials were significantly (p = 0.002; η² = 0.766) slower in RN (75.7±6.7 s; p = 0.01), AN (75.2±6.7 s; p = 0.038) and RH (75.0±6.4 s; p = 0.009). Moreover, compared to AH (36.3±0.4ºC), tympanic temperature was significantly lower (p<0.001; η² = 0.828) at the end of the transitional phase in passive conditions (RN: 35.9±0.6; p = 0.032; RH: 36.0±0.4; p = 0.05). In addition, countermovement jump height at the end of the transitional phase was significantly higher in active than in passive conditions (p = 0.001; ^η2 = 0.728). A dryland-based circuit under hypoxia could be useful to swimmers, once it has attenuated the decline in tympanic temperature during a 30-minute transitional phase after warm-up, improving 100 m swimming performance in young amateur swimmers.

Effect of Resistance Training Under Normobaric Hypoxia on Physical Performance, Hematological Parameters, and Body Composition in Young and Older People

Background

Resistance training (RT) under hypoxic conditions has been used to increase muscular performance under normoxic conditions in young people. However, the effects of RT and thus of RT under hypoxia (RTH) could also be valuable for parameters of physical capacity and body composition across the lifespan. Therefore, we compared the effects of low- to moderate-load RTH with matched designed RT on muscular strength capacity, cardiopulmonary capacity, hematological adaptation, and body composition in young and older people.

Methods

In a pre–post randomized, blinded, and controlled experiment, 42 young (18 to 30 year) and 42 older (60 to 75 year) participants were randomly assigned to RTH or RT (RTH young, RT young, RTH old, RT old). Both groups performed eight resistance exercises (25–40% of 1RM, 3 × 15 repetitions) four times a week over 5 weeks. The intensity of hypoxic air for the RTH was administered individually in regards to the oxygen saturation of the blood (SpO₂): ∼80–85%. Changes and differences in maximal isokinetic strength, cardiopulmonary capacity, total hemoglobin mass (tHb), blood volume (BV), fat free mass (FFM), and fat mass (FM) were determined pre–post, and the acute reaction of erythropoietin (EPO) was tested during the intervention.

Results

In all parameters, no significant pre–post differences in mean changes (time × group effects p = 0.120 to 1.000) were found between RTH and RT within the age groups. However, within the four groups, isolated significant improvements (p < 0.050) of the single groups were observed regarding the muscular strength of the legs and the cardiopulmonary capacity.

Discussion

Although the hypoxic dose and the exercise variables of the resistance training in this study were based on the current recommendations of RTH, the RTH design used had no superior effect on the tested parameters in young and older people in comparison to the matched designed RT under normoxia after a 5-week intervention period. Based on previous RTH-studies as well as the knowledge about RT in general, it can be assumed that the expected higher effects of RTH can may be achieved by changing exercise variables (e.g., longer intervention period, higher loads).

Impact of Active and Passive Hypoxia as Re-Warm-Up Activities on Rugby Players' Performance

The aim of this study was to analyse the effect of four types of re-warm-up (R-WU) activity, namely rest in normoxia (RN) at FiO2 = 20.9%, rest in hypoxia (RH) at FiO2 = 15%, activity (4 × 5 jumps/15 s) in normoxia (AN) and activity in hypoxia (AH) on physical performance. Ten elite male rugby players completed a 15-min warm-up followed by one of the 15-min randomized R-WU strategies. After R-WU, countermovement jump (CMJ), 20 m sprint and repeat sprint ability (RSA) tests were assessed. Compared to passive strategies (RN and RH), tympanic temperature was higher after active R-WU (AN and AH) (p = 0.016). Higher values of CMJ height (p = 0.037) and 20 m sprint (p = 0.02) were found in AH than in RN. In addition, mean RSA was lower (p = 0.008) in AH than in RN and RH. Blood lactate concentration was higher (p = 0.007) after RN and AN strategies than after AH. Muscle O2 saturation (p = 0.021) and total Hb (p = 0.042) were higher after AH than after the other three conditions and after RN, respectively. Therefore, an active R-WU under hypoxia could be useful to elite rugby players, once it had attenuated the decline in tympanic temperature during a 15-min period after warm-up, improving jump, sprint and RSA performance.

Effects of whole-body vibration under hypoxic exposure on muscle mass and functional mobility in older adults

BACKGROUND

Ageing is accompanied by a loss of muscle mass and function, which are associated with decrease of functional capacity. Combination of WBV training with normobaric hypoxic exposure could augment the beneficial effects due to synergic effects of both treatments.

AIMS

The purpose of this study was to examine the effects of 36 sessions of the combined WBV training and normobaric hypoxic exposure on muscle mass and functional mobility in older adults.

METHODS

Nineteen elderly people were randomly assigned to a: vibration normoxic exposure group (NWBV; n = 10; 20.9% FiO₂) and vibration hypoxic exposure group (HWBV; n = 9). Participants developed 36 sessions of WBV training along 18 weeks, which included 4 bouts of 30 s (12.6 Hz in frequency and 4 mm in amplitude) with 60 s of rest between bouts, inside a hypoxic chamber for the HWBV. The "Timed Up and Go Test" evaluated functional mobility. Percentages of lean mass were obtained with dual-energy X-ray absorptiometry.

RESULTS

Neither statistically significant within group variations nor statistically significant differences between both groups were detected to any parameter.

DISCUSSION

Baseline characteristics of population, training protocol and the level of hypoxia employed could cause different adaptations on muscle mass and function.

CONCLUSIONS

The combination of WBV training and hypoxic exposure did not cause any effect on either legs lean mass or functional mobility of older adults.

Altitude-induced effects on muscular metabolic stress and hypertrophy-related factors after a resistance training session

This study examined the acute effects of exposure to moderate altitude on factors associated with muscular adaptations following whole-body hypertrophy-oriented resistance training (R _T) sessions. Thirteen resistance-trained males completed both counterbalanced standard hypertrophic R _T sessions (3 sets × 10RM, 2 min rest) at moderate-altitude (H; 2320 m asl) and under normoxic conditions (N; <700 m asl). Participants rested 72 h between training sessions. Before and after the exercise session, blood samples were obtained for determination of metabolites and ions (lactate, inorganic phosphate, liquid carbon dioxide and calcium) and hormones (testosterone and growth hormone). Session-related performance and perception of effort (s-RPE) were also monitored. Results showed no meaningful differences in performance or s-RPE (8.5 ± 1.4 vs 8.6 ± 0.8 respectively for N and H; p = 0.603). All blood variables displayed statistically significant changes throughout the recovery period compared to basal levels (p < 0.05), except for the testosterone. However, no altitude effect was observed in maximal blood lactate, calcium or anabolic hormones (p > 0.05). The reduction observed in the liquid carbon dioxide concentration in H (21.11 ± 1.46 vs 16.19 ± 1.61 mmol·l^-1) seems compatible with an increase in buffering capacity. Compared to N, inorganic phosphate displayed lower recovery values after the R _T in H (2.89 ± 0.64 vs 2.23 ± 0.60 mg dl^-1; p = 0.007). The results of this study do not support an accentuated effect of acute moderate terrestrial hypoxia on metabolic and hormonal factors linked to muscle growth during hypertrophic resistance training.

Acute effects of whole-body vibration training on neuromuscular performance and mobility in hypoxia and normoxia in persons with multiple sclerosis: A crossover study

BACKGROUND

Whole-body vibration training (WBVT) has been used in people with relapsing-remitting multiple sclerosis (pwMS), showing improvements in different neuromuscular and mobility variables. However, the acute effects of this training are still unknown. The acute effects of WBVT on neuromuscular performance, mobility and rating of perceived exertion (RPE) were evaluated in 10 pwMS.

METHODS

Maximal voluntary isometric contraction (MVIC), central activation ratio (CAR), electromyography (EMG) of the vastus lateralis during isometric knee extension, Timed Up and Go Test (TUG), walking speed and RPE were assessed before and immediately after a session of WBVT (twelve 60-s bout of vibration; frequency 35 Hz; amplitude 4 mm; 1-min rest intervals) in both hypoxic and normoxic conditions.

RESULTS

EMG 0-100, 0-200 ms and peak EMG resulted in significant differences (p < 0.05) between normoxic and hypoxic sessions. The EMG activity tended to decrease in all phases after the hypoxic session, indicating possible influence of hypoxia on neuromuscular performance. No changes were found in CAR, MVIC, TUG and walking speed in both conditions.

CONCLUSION

Based on our results, as well as those obtained by other studies that have used WBVT with other populations, more studies with a higher sample and lower dose of vibration exposure should be conducted in pwMS.

Mean Propulsive Velocity Is a Viable Method for Adjusting the Resistance-Training Load at Moderate Altitude

We examined the viability of using mean propulsive velocity (MPV) to adjust the load in the countermovement jump (CMJ) at moderate altitude. Twenty-four volunteers were assigned to a 4-week power-oriented resistance training (R_T) program in either normoxia (N, 690 m) or intermittent hypobaric hypoxia (IH, 2,320 m). The load was adjusted to maintain execution velocity of CMJ at 1m·s^-1 of MPV. Relative peak power output (P_rel), and percentage of velocity loss throughout the sets (VL) were determined for each session. The internal load was measured by the rating of perceived exertion (RPE). The absolute load lifted was higher in IH compared to N (75.6 ± 8.4 vs. 58.5 ± 12.3 kg P < 0.001). However, similar relative increases for both groups were found when comparing the final values (IH: 8.2%, P = 0.007; N: 9.8%, P = 0.03) with no changes in VL between groups (P = 0.36). Post-study P_rel improved significantly only in IH (+7% W·kg^-1, P = 0.002). Mean RPE was greater in IH vs. N (6.8 ± 1.5 vs. 5.6 ± 2, P < 0.001). The MPV seems to be a viable method for adjusting external load during R_T at moderate altitude. However, given that R_T at moderate altitude increases RPE, it is prudent to monitor internal load when using the MPV to best determine the actual physiological stress of the session.

Familiarization With Airflow-Restriction Mask During Resistance Exercise: Effect on Tolerance and Total Volume

Teodoro, CL, Gáspari, AF, Berton, R, Barbieri, JF, Silva, M, Castaño, LAA, Guimarães, P, and Moraes, AC. Familiarization with airflow-restriction mask during resistance exercise: Effect on tolerance and total volume. J Strength Cond Res 33(7): 1762-1765, 2019-This study investigated whether familiarization with the airflow-restriction mask (AIRfr) increases tolerance and avoids negative effects on performance of resistance exercise (RE). Ten resistance-trained male subjects performed a familiarization session (FAM), followed by 2 testing sessions, with the AIRfr and without airflow restriction (SHAM) in a counterbalanced and randomized cross-over design. The FAM was performed with the same number of sets, load, and level of airflow-restriction as the AIRfr experimental session. Each session consisted of 4 sets of the leg press exercise with 70% 1 repetition maximum until voluntary failure and a 90-second rest interval between sets. During the FAM, 4 of the 10 subjects expressed some intolerance to the use of airflow restriction. Total volume was lower in the FAM than in the AIRfr (p = 0.01) and the SHAM (p = 0.02), whereas no differences were observed between the AIRfr and the SHAM (p = 0.90). The first use of the AIRfr may not be well tolerated by all subjects. However, a familiarization session with the AIRfr avoids negative interferences in the total volume during RE.

Muscle Architecture and Neuromuscular Changes After High-Resistance Circuit Training in Hypoxia

Ramos-Campo, DJ, Martínez-Guardado, I, Rubio-Arias, JA, Freitas, TT, Othalawa, S, Andreu, L, Timón, R, and Alcaraz, PE. Muscle architecture and neuromuscular changes after high-resistance circuit training in hypoxia. J Strength Cond Res XX(X): 000-000, 2019-This study aimed to analyze the effect of 8 weeks of high-resistance circuit (HRC) training in hypoxia on muscle architecture, strength, and neuromuscular variables. Twenty-eight resistance-trained subjects were assigned to a hypoxia (FiO2 = 15%; HG: n = 15; age: 24.6 ± 6.8 years; height: 177.4 ± 5.9 cm; and mass: 74.9 ± 11.5 kg) or normoxia group (FiO2 = 20.9%; NG: n = 13; age: 23.2 ± 5.2 years; height: 173.4 ± 6.2 cm; and mass: 69.4 ± 7.4 kg). Each training session consisted of 2 blocks of 3 exercises (block 1: bench press, leg extension, and front lat pulldown; block 2: deadlift, elbow flexion, and ankle extension). Each exercise was performed with a 6 repetition maximum load. Subjects exercised twice weekly and, before and after the training program, vastus lateralis muscle thickness and pennation angle, knee extensors electromyographic activity, maximum voluntary contraction (MVC), and rate of force development (RFD) and H-Reflex (Hmax), M-wave of the soleus muscle were assessed. Both training groups showed similar improvements in muscle thickness (effect size [ES] = HG: 0.23; NG: 0.41), pennation angle (ES = HG: 0.86; NG: 0.15), MVC (ES HG: 0.63; NG: 0.61), Hmax (ES = HG: 0.96; NG: 0.40), RFD at 200 milliseconds (ES = HG: 0.31; NG: 0.61) and peak RFD (ES = HG: 0.21; NG: 0.66). No significant between-group differences were found. In conclusion, similar morphological and neuromuscular adaptations can be achieved after 8 weeks of HRC training under hypoxic or normoxic conditions.

Separate and combined effects of local and systemic hypoxia in resistance exercise

PURPOSES

This study quantified performance, physiological, and perceptual responses during resistance exercise to task failure with blood flow restriction (BFR), in systemic hypoxia, and with these stimuli combined.

METHODS

Fourteen young men were tested for 1-repetition maximum (1RM) in the barbell biceps curl and lying triceps extension exercises. On separate visits, subjects performed exercise trials (4 sets to failure at 70% 1RM with 90 s between sets) in six separate randomized conditions, i.e., in normoxia or hypoxia (fraction of inspired oxygen = 20.9% and 12.9%, respectively) combined with three different levels of BFR (0%, 45%, or 60% of resting arterial occlusion pressure). Muscle activation and oxygenation were monitored via surface electromyography and near-infrared spectroscopy, respectively. Arterial oxygen saturation, heart rate, and perceptual responses were assessed following each set.

RESULTS

Compared to set 1, the number of repetitions before failure decreased in sets 2, 3, and 4 for both exercises (all P < 0.001), independently of the condition (P > 0.065). Arterial oxygen saturation was lower with systemic hypoxia (P < 0.001), but not BFR, while heart rate did not differ between conditions (P > 0.341). Muscle oxygenation and activation during exercise trials remained unaffected by the different conditions (all P ≥ 0.206). A significant main effect of time, but not condition, was observed for overall perceived discomfort, difficulty breathing, and limb discomfort (all P < 0.001).

CONCLUSION

Local and systemic hypoxic stimuli, or a combination of both, did not modify the fatigue-induced change in performance, trends of muscle activation or oxygenation, nor exercise-related sensations during a multi-set resistance exercise to task failure.

Additive stress of normobaric hypoxic conditioning to improve body mass loss and cardiometabolic markers in individuals with overweight or obesity: A systematic review and meta-analysis

We performed a systematic review and meta-analysis to determine if hypoxic conditioning, compared to similar training near sea level, maximizes body mass loss and further improves cardiometabolic markers in overweight and obese individuals. A systematic search of PubMed, Web of Science and the Cochrane Library databases (up to January 2019) was performed. This analysis included randomized controlled trials with humans with overweight or obesity assessing the effects of HC on body mass loss or cardiometabolic markers. A subgroup analysis was performed to examine if HC effects differed between individuals with overweight or obesity. 13 articles (336 participants) qualified for inclusion. HC significantly decreased body mass (p = .01), fat mass (p = .04), waist/hip ratio (p < .001), waist (p < .001), LDL (p = .01), diastolic (p < .01) and systolic blood pressure (p < .01) with these effects not being larger than equivalent normoxic interventions. There were trends towards higher triglycerides decrement (p = .06) and higher muscle mass gain in hypoxic (p = .08) compared with normoxic condition. Also, the two BMI categories displayed no difference in the magnitude of the responses. Compared to normoxic equivalent, HC provides greater reductions in triglycerides and greater muscle growth, while body mass changes are similar. In addition, HC responses were essentially similar between individuals with overweight or obesity.

Evaluation of 18-Week Whole-Body Vibration Training in Normobaric Hypoxia on Lower Extremity Muscle Strength in an Elderly Population

Therapeutic benefits of hypoxic training have been suggested for clinical populations, such as elderly who could suffer loss of lower limb muscle strength and higher risk of falling. This study investigated the effects of 18 weeks of whole-body vibration (WBV) training in normobaric hypoxia on the strength parameters of an elderly population. Thirty-one healthy elderly participants were randomly assigned to a hypoxic whole-body vibration group (HWBV; n = 10), normoxic whole-body vibration group (NWBV; n = 11), or control group (n = 10). The experimental groups received the same vibration treatment in a hypoxia chamber (HWBV: 16.1% fraction of inspired oxygen [FiO₂]; NWBV: 21.0% FiO₂). Isokinetic leg muscle strength was evaluated using a Biodex System-3 isokinetic dynamometer. Body composition was obtained with dual-energy X-ray absorptiometry. There were no significant differences between groups in either strength or body composition parameters. The NWBV group showed statistically significant improvements in the maximal strength of knee extensors, with a small effect size (p = 0.004; d = 0.54). No significant differences were found in any variable of the HWBV group. The combination of WBV training and exposure to normobaric cyclic hypoxia carried out in the present study did not have an effect on strength parameters in healthy elderly subjects.

Bench press performance during an intermittent hypoxic resistance training to muscle failure

BACKGROUND

Resistance training performed under hypoxia conditions has been shown to cause major metabolic and hormonal responses. However, the influence of hypoxia on an acute session has been barely studied. The aim of this study was to evaluate the acute effects of an intermittent hypoxic resistance training (IHRT) to muscle failure on bench press performance.

METHODS

A randomized crossover design was performed, and 25 untrained men performed a resistance training under two different conditions: normoxia (FIO2=21%) and high-level hypoxia (FIO2=13%). Resistance training consisted of 3 sets of 75% 1RM to muscle failure, with a 2-minute rest between sets. Physical performance was assessed by quantifying total repetitions, concentric velocity and power variable during all sets. Arterial oxygen saturation, heart rate, rating of perceived exertion (RPE), capillary blood lactate and muscle soreness were also assessed after training.

RESULTS

Physical performance during bench press did not differ under hypoxic conditions (P>0.05). However, there were significant increases (P<0.05) of RPE (from 7.5±0.8 to 7.9±0.8) and blood lactate concentrations (from 5.5±1.2 to 6.2±1.5 mmol/L) in the hypoxia group.

CONCLUSIONS

These findings suggest that hypoxic resistance exercise does not affect exercise performance during bench press exercise. However, influence to perceived exercise intensity and blood lactate concentrations, suggesting that hypoxic resistance training may add substantially to the training dose experienced.

Intermittent Resistance Training at Moderate Altitude: Effects on the Force-Velocity Relationship, Isometric Strength and Muscle Architecture

Intermittent hypoxic resistance training (IHRT) may help to maximize the adaptations following resistance training, although conflicting evidence is available. The aim of this study was to explore the influence of moderate altitude on the functional, neural and muscle architecture responses of the quadriceps muscles following a power-oriented IHRT intervention. Twenty-four active males completed two 4-week consecutive training blocks comprising general strengthening exercises (weeks 1–4) and power-oriented resistance training (weeks 5–8). Training sessions were conducted twice a week at moderate altitude (2320 m; IHRT, n = 13) or normoxia (690 m; NT, n = 11). Training intensity during the second training block was set to the individual load corresponding to a barbell mean propulsive velocity of 1 m·s⁻¹. Pre-post assessments, performed under normoxic conditions, comprised quadriceps muscle architecture (thickness, pennation angle and fascicle length), isometric maximal (MVF) and explosive strength, and voluntary muscle activation. Dynamic strength performance was assessed through the force-velocity relationship (F₀, V₀, P₀) and a repeated CMJ test (CMJ_15MP). Region-specific muscle thickness changes were observed in both training groups (p < 0.001, ηG2 = 0.02). A small opposite trend in pennation angle changes was observed (ES [90% CI]: −0.33 [−0.65, −0.01] vs. 0.11 [−0.44, 0.6], in the IHRT and NT group, respectively; p = 0.094, ηG2 = 0.02). Both training groups showed similar improvements in MVF (ES: 0.38 [0.20, 0.56] vs. 0.55 [0.29, 0.80], in the IHRT and NT group, respectively; p = 0.645, ηG2 < 0.01), F₀ (ES: 0.41 [−0.03, 0.85] vs. 0.52 [0.04, 0.99], in the IHRT and NT group, respectively; p = 0.569, ηG2 < 0.01) and P₀ (ES: 0.53 [0.07, 0.98] vs. 0.19 [−0.06, 0.44], in the IHRT and NT group, respectively; p = 0.320, ηG2 < 0.01). No meaningful changes in explosive strength performance were observed. In conclusion, contrary to earlier adverse associations between altitude and resistance-training muscle adaptations, similar anatomical and functional muscle strength responses can be achieved in both environmental conditions. The observed region-specific muscle thickness changes may encourage further research on the potential influence of IHRT on muscle morphological changes.

Hypoxia During Resistance Exercise Does Not Affect Physical Performance, Perceptual Responses, or Neuromuscular Recovery

Scott, BR, Slattery, KM, Sculley, DV, and Dascombe, BJ. Hypoxia during resistance exercise does not affect physical performance, perceptual responses, or neuromuscular recovery. J Strength Cond Res 32(8): 2174-2182, 2018-This study aimed to determine whether performing resistance exercise in hypoxia affects markers of physical performance, perceptual responses, and neuromuscular function. Fourteen male subjects (age: 24.6 ± 2.7 years; height: 179.7 ± 5.9 cm; body mass: 84.6 ± 11.6 kg) with >2 years resistance training experience performed moderate-load resistance exercise in 2 conditions: normoxia (FIO2 = 0.21) and hypoxia (FIO2 = 0.16). Resistance exercise comprised 3 sets of 10 repetitions of back squats and deadlifts at 60% of 1 repetition maximum (1RM), with 60 seconds inter-set rest. Physical performance was assessed by quantifying velocity and power variables during all repetitions. Perceptual ratings of perceived exertion, physical fatigue, muscle soreness, and overall well-being were obtained during and after exercise. Neuromuscular performance was assessed by vertical jump and isometric mid-thigh pull (IMTP) tasks for up to 48 hours after exercise. Although physical performance declined across sets, there were no differences between conditions. Similarly, perceived exertion and fatigue scores were not different between conditions. Muscle soreness increased from baseline at 24 and 48 hours after exercise in both conditions (p ≤ 0.001). Jump height and IMTP peak force were decreased from baseline immediately after exercise (p ≤ 0.026), but returned to preexercise values after 24 hours. These findings suggest that hypoxic resistance exercise does not affect exercise performance or perceived exercise intensity. In addition, neuromuscular recovery and perceptual markers of training stress were not affected by hypoxia, suggesting that hypoxic resistance training may not add substantially to the training dose experienced.

The efficacy of resistance training in hypoxia to enhance strength and muscle growth: A systematic review and meta-analysis

Recent studies have reported that resistance training in hypoxia (RTH) may augment muscle size and strength development. However, consensus on the effects of RTH via systematic review and meta-analysis is not yet available. This work aimed to systematically review studies which have investigated using RTH versus normoxic resistance training (NRT) to improve muscular size and strength, and to perform a meta-analysis to determine the effect of RTH on these adaptive parameters. Searches were conducted in PubMed, Web of Science and the Cochrane Library from database inception until 17 June 2017 for original articles assessing the effects of RTH on muscle size and strength versus NRT. The effects on outcomes were expressed as standardized mean differences (SMD). Nine studies (158 participants) reported on the effects of RTH versus NRT for muscle cross-sectional area (CSA) (n = 4) or strength (n = 6). RTH significantly increased CSA (SMD = 0.70, 95% confidence intervals (CI) 0.05, 1.35; p = .04) and strength (SMD = 1.88; 95% CI = 1.20, 2.56; p < .00001). However, RTH did not produce significant change in CSA (SMD = 0.24, 95% CI -0.19, 0.68, p = .27) or strength (SMD = 0.20; 95% CI = -0.27, 0.78; p = .23) when compared to NRT. Although RTH improved muscle size and strength, this protocol did not provide significant benefit over resistance training in normoxia. Nevertheless, this paper identified marked differences in methodologies for implementing RTH, and future research using standardized protocols is therefore warranted.

Normobaric hypoxia increases the growth hormone response to maximal resistance exercise in trained men

This study examined the effect of hypoxia on growth hormone (GH) release during an acute bout of high-intensity, low-volume resistance exercise. Using a single-blinded, randomised crossover design, 16 resistance-trained males completed two resistance exercise sessions in normobaric hypoxia (HYP; inspiratory oxygen fraction, (FiO₂) 0.12, arterial oxygen saturation (SpO₂) 82 ± 2%) and normoxia (NOR; FiO₂ 0.21, SpO₂ 98 ± 0%). Each session consisted of five sets of three repetitions of 45° leg press and bench press at 85% of one repetition maximum. Heart rate, SpO₂, and electromyographic activity (EMG) of the vastus lateralis muscle were measured throughout the protocol. Serum lactate and GH levels were determined pre-exposure, and at 5, 15, 30 and 60 min post-exercise. Differences in mean and integrated EMG between HYP and NOR treatments were unclear. However, there was an important increase in the peak levels and area under the curve of both lactate (HYP 5.8 ± 1.8 v NOR 3.9 ± 1.1 mmol.L^-1 and HYP 138.7 ± 33.1 v NOR 105.8 ± 20.8 min.mmol.L^-1) and GH (HYP 4.4 ± 3.1 v NOR 2.1 ± 2.5 ng.mL^-1 and HYP 117.7 ± 86.9 v NOR 72.9 ± 85.3 min.ng.mL^-1) in response to HYP. These results suggest that performing high-intensity resistance exercise in a hypoxic environment may provide a beneficial endocrine response without compromising the neuromuscular activation required for maximal strength development.

Biochemical responses and physical performance during high-intensity resistance circuit training in hypoxia and normoxia

PURPOSE

The aim of this study was to analyze the effect of hypoxia on metabolic and acid-base balance, blood oxygenation, electrolyte, and half-squat performance variables during high-resistance circuit (HRC) training.

METHODS

Twelve resistance-trained subjects participated in this study. After a 6RM testing session, participants performed three randomized trials of HRC: normoxia (NORM: FiO₂ = 0.21), moderate hypoxia (MH: FiO₂ = 0.16), or high hypoxia (HH: FiO₂ = 0.13), separated by 72 h of recovery in normoxic conditions. HRC consisted of two blocks of three exercises (Block 1: bench press, deadlift and elbow flexion; Block 2: half-squat, triceps extension, and ankle extension). Each exercise was performed at 6RM. Rest periods lasted for 35 s between exercises, 3 min between sets, and 5 min between blocks. Peak and mean force and power were determined during half-squat. Metabolic, acid-base balance, blood oxygenation and electrolyte variables, arterial oxygen saturation (SaO₂), and rating of perceived exertion (RPE) were measured following each block.

RESULTS

During the first set, peak force and power were significantly lower in HH than MH and NORM; whereas in the second set, mean and peak force and power were significantly lower in HH than NORM. At the end of the HRC training session, blood lactate and RPE in HH were significantly higher than in MH and NORM. SaO₂, pH, HCO₃^-, and pO₂ values were significantly lower in all hypoxic conditions than in NORM.

CONCLUSION

These results indicate that simulated hypoxia during HRC exercise reduce blood oxygenation, pH, and HCO₃^-, and increased blood lactate ultimately decreasing muscular performance.