However, the physiological response derived from HIIT at different durations is not yet well established. Studying HIIT in laboratory rats enables to investigate precisely the biomarkers adaptations due to better methodological control i.

Thus, the present study was designed to investigate the physiological and performance adaptations after 6 weeks short-term and 12 weeks long-term of HIIT in rats. Specifically, to analyze metabolites creatinine, uric acid, urea , muscle injury markers creatine kinase, lactate dehydrogenase , antioxidant enzymes catalase, superoxide dismutase , hormones testosterone and corticosterone , glycogen concentrations liver, soleus and gastrocnemius , and immune system white blood cells at baseline, after 6 and 12 weeks.

It was hypothesized that HIIT short term: 1 increases aerobic and anaerobic performance similarly HIIT long term and 2 causes lower physiological stress in comparison to HIIT long term. All experiments involving animals were performed in accordance to the principles of laboratory animal care NIH publication No.

The experimental protocol was approved by specific resolutions on Bioethics in Experiments with Animals no. Fifty male Rattus norvegicus albinus Wistar rats, 60 days old, were selected for this study.

The animals received water and commercial chow Louis, MO ad libitum and were housed at 22 ± 2°C with an inverted h light—dark cycle — lights on. The purpose of adaptation to the water was to reduce water stress without promoting physiological adaptations to physical training. The adaptation to the water environment consisted of a 5-min 31 ± 1°C exposure daily, in tanks 80 × 80 × 80 cm subdivided into four cylindrical compartments of 30 cm diameter × 60 cm depth for individual jumps.

The training session was subdivided in 4 series of 10 jumps in water depth of approximately 30 cm with 30 s of passive recovery Marqueti et al. The rats of HIIT short term were euthanized after 6 weeks;. The rats of HIIT long term were euthanized after 12 weeks;.

Ten rats were euthanized before the experimental period baseline , after 6 and 12 weeks. To determine the aerobic and anaerobic performances during the experimental period, we utilized the lactate minimum test LM in accordance with the methods of de Araujo et al.

The LM enables the determination of the aerobic and anaerobic parameters in a single protocol. This test consists in a hyperlactatemia induction phase followed by incremental swimming intensity. The effort until exhaustion s of second exercise bout was used to evaluate the anaerobic performance.

Exhaustion was assumed when the animal was unable to stay on the water surface for 10 s. After hyperlactatemia induction, blood samples of tail were collected at 7 and 9 min for lactate peak determination. The incremental phase involved swimming with tethered loads backpack lead equivalent to 3.

The stages in each load lasted for 5 min and were separated by 30 s for blood collection and lactatemia determination. This represents a balance between production and clearance of lactate and as consequence the aerobic capacity.

The aerobic capacity was used as an aerobic performance index. The LM was applied in all groups after adaptation to the water baseline and after 6 and 12 weeks of the experimental period.

Blood and tissues were collected after adaptation to the water baseline and 24 h after the last session in weeks 6 and 12 of the experimental period. The antioxidants enzymes levels, hormones concentrations, metabolites levels and glycogen concentrations analyses are described below.

Blood was collected via cardiac puncture after thoracotomy into EDTA tubes plasma or dry tubes serum in accordance with the analyses.

After this, the soleus, liver and the white gastrocnemius muscles were carefully dissected and then placed on filter paper to remove excess fat and connective tissues.

The glycogen concentration of the tissue samples was immediately analyzed according to the methods of Dubois et al. Muscle — mg samples and liver mg were immediately digested in 0. After 15 min of boiling, the absorbance was determined at nm For the lactate concentration measurement, the blood samples 25 μL were collected from the animals tail and placed in microtubes 1.

The homogenized sample and reagent were incubated at 37°C for 20 min, and absorbance was determined at nm. Uric acid concentration was determined using an enzymatic method containing liquid stable mono-reagent: buffer pH 7.

The uric acid sample was analyzed 2 h after euthanasia of rats. The radioactivity was measured in a gamma counter 1 min following the instructions provided with the commercial Kit-Coat-A-Count from Diagnostic Products Corporation ®.

To measure the sulfhydryl groups, plasma 50 μL was mixed in 1 mL of Tris—EDTA buffer for the first spectrophotometric FS analysis nm. Then, 20 μL of 5.

A sample containing DTNB and buffer Tris—EDTA was analyzed in a spectrophotometer as a blank. Catalase CAT and superoxide dismutase SOD activity were measured using commercial kits.

SOD activity was determined using an EIA Cayman Chemical Assay Kit ® by the xanthin and xanthin oxidase method absorbance was nm. CAT activity was measured using an EIA Cayman Chemical Assay Kit ®.

The sample was mixed in the kit reagents Buffer, formaldehyde standard, KOH, methanol, hydrogen peroxide and potassium periodate , and the absorbance was measured at nm. The sample was obtained using a specific pipette and diluted in Turk solution 3 min.

After mix, the solution was pipette in Chamber Neubauer for leukocytes count in microscope. All of the dependent variables were subjected to the normality test using the Shapiro-Wilk W-test. All analyses were conducted with a statistical software package Statistica ® , version 7.

The analysis of variance ANOVA two-way with Ducan's multiple range test was used to examine changes over time 0, 6, and 12 weeks within aerobic and anaerobic performances, glycogen stores soleus, liver and gastrocnemius and biochemical analyses lactate, creatine kinase, lactate dehydrogenase, uric acid, urea, creatinine, catalase, superoxide dismutase, testosterone, and corticosterone between the groups CT and HIIT.

For non-parametric samples, the Kruskal-Wallis method was used, followed by Dunn's method. The aerobic performance in HIIT short term did not enhance in comparison to baseline and CT after 6 weeks. CT 12 weeks reduced the aerobic capacity in relation to baseline Figure 1.

Figure 1. Aerobic capacity measured by Lactate minimum test in each period of training 0 week—baseline, 6 weeks—HIIT short term and 12 weeks—HIIT long term.

The anaerobic performance measured by exhaustion time was not different in HIIT long and short term in relation to baseline, but both groups showed higher values than CT at 6 and 12 weeks Figure 2. Furthermore, the anaerobic index decreased in CT group after 6 and 12 weeks when compared to baseline Figure 2.

Figure 2. No differences were found between short and long term of HIIT. No differences were found between HIIT short and long term for soleus. Figure 3. Percentage differences in soleus, liver, and gastronemius tissues when compared to 0 week baseline.

No differences were found in creatine kinase and lactate dehydrogenase concentration intra-groups. The cortiscosterone concentration in HIIT short term was higher than CT 6 weeks and baseline. HIIT long term 12 weeks reduced the corticosterone concentration in relation to CT 12 weeks and baseline Table 1.

No differences were found in testosterone, catalase and sulfhydryl groups concentration during experimental period in both HIIT groups Table 1. Figure 4.

Percentage differences in creatinine, uric acid, and urea when compared to respective CT group. Figure 5. Values of white blood cells in baseline, HIIT short term, and HIIT long term.

This is the first study to investigate the effects of HIIT duration on aerobic and anaerobic performances, blood biomarkers and glycogen stores. Our results contradict our hypothesis and showed a higher aerobic capacity, glycogen concentration and lower physiological stress after HIIT long term in comparison to short term.

HIIT has been an important protocol of signaling to a multitude of target cells allowing aerobic adaptations during short term further than traditional endurance training de Araujo et al. Some studies reported that endurance training in rats may attenuate the natural loss, but not increase the aerobic capacity in comparison to baseline de Araujo et al.

The difficulty to develop the aerobic capacity has been assigned to high volume of exercise, training monotony and overtraining symptoms Foster, Our data showed that aerobic performance after HIIT long term was higher than those observed in endurance protocols de Araujo et al.

While the endurance protocols attenuated the natural loss of aerobic capacity, the HIIT long term increased significantly. Scariot et al. This result was attributed to small cages of confinement of laboratory rats. However, our results showed that HIIT induces increases in aerobic performance despite negative interferences of confinement during experimental period.

Furthermore, the aerobic performance was accompanied with glycogen supercompensation in gastrocnemius, liver as well as reduced corticosterone and white blood cells. Thus, the effects of overtraining were not caused by HIIT long term. Overtraining state increases the blood stress biomarkers and reduces performance Lehmann et al.

The corticosterone is a catabolic hormone and its concentration increases after overload period, as for example, after HIIT short term.

The HIIT short term may be considered a transitory stress period and an important stimulus to lead a positive adaptation in the training sequence. These authors speculated that HIIT may lead an overtraining state.

However, an overtraining diagnosis was unaccomplished in the present study due to similar values of performance and stress biomarkers in comparison to baseline and CT. Perhaps, a HIIT short term promotes an immediate high stress and insufficient period of positive adaptations.

Thus, a long term may be more indicate to complete the organic adaptation to stress, as example, our data showed that aerobic performance enhanced after 12 weeks, but not after 6 weeks of HIIT. Studies have shown a complex molecular interaction activated by HIIT in skeletal muscle in order to increase: angiogenesis, mitochondrial biogenesis, oxidative enzymes and other Jensen et al.

Laursen showed that cellular stimulus to aerobic adaptations is predominantly dependent of AMPK-PGC1α pathway activation or CAMK- PGC1α activation, and HIIT activates more AMPK- PGC1α than CAMK- PGC1α. However, the anaerobic index not increased after HIIT short and long term. This may have been a limitation of the study.

On the other hand, HIIT stimulated glycogen synthesis, but the moderate values of peak lactate may to indicate a breakdown of glycogenolysis Vandenberghe et al. Possibly, with variations in overload and series of lactate production, the exhaustion time and peak lactate would have increased.

Martinez-Valdes, E. Differential motor unit changes after endurance or high-intensity interval training. Matsuo, T. An exercise protocol designed to control energy expenditure for long-term space missions. Space Environ.

Effects of a low-volume aerobic-type interval exercise on VO 2max and cardiac mass. McRae, G. Extremely low volume, whole-body aerobic—resistance training improves aerobic fitness and muscular endurance in females.

Metcalfe, R. Towards the minimal amount of exercise for improving metabolic health: beneficial effects of reduced-exertion high-intensity interval training.

Changes in aerobic capacity and glycaemic control in response to reduced-exertion high-intensity interval training REHIT are not different between sedentary men and women.

Milanovic, Z. Effectiveness of high-intensity interval training HIT and continuous endurance training for VO 2max improvements: a systematic review and meta-analysis of controlled trials. Moore, A. Peak exercise oxygen uptake during and following long-duration spaceflight.

Maximal exercise as a countermeasure to orthostatic intolerance after spaceflight. National Aeronautics and Space Administration [NASA] Exercise device for Orion to pack powerful punch. Integrated resistance and aerobic training study Sprint. Nederveen, J. The effect of exercise mode on the acute response of satellite cells in old men.

Acta Physiol. Nybo, L. High-intensity training versus traditional exercise interventions for promoting health. Ortega, H. Barrat and S. Pool New York, NY: Springer , — Osawa, Y. Effects of week high-intensity interval training using upper and lower body ergometers on aerobic fitness and morphological changes in healthy men: a preliminary study.

OAJSM 5, — Robinson, M. Enhanced protein translation underlies improved metabolic and physical adaptations to different exercise training modes in young and old humans.

Cell Metab. Rodas, G. A short training programme for the rapid improvement of both aerobic and anaerobic metabolism. Rognmo, O. Cardiovascular risk of high- versus moderate-intensity aerobic exercise in coronary heart disease patients.

Circulation , — Rønnestad, B. Short intervals induce superior training adaptations compared with long intervals in cyclists - an effort-matched approach. Sports 25, — Sale, D. Influence of exercise and training on motor unit activation. Sport Sci. Scott, J. Introduction to the Frontiers research topic: optimization of exercise countermeasures for human space flight—lessons from terrestrial physiology and operational considerations.

Scribbans, T. Fibre-specific responses to endurance and low volume high intensity interval training: striking similarities in acute and chronic adaptation.

Sculthorpe, N. One session of high-intensity interval training HIIT every 5 days, improves muscle power but not static balance in lifelong sedentary ageing men. Medicine 96, e—e Shephard, R. Intensity, duration and frequency of exercise as determinants of the response to a training regime. Sloth, M.

Effects of sprint interval training on VO 2max and aerobic exercise performance: a systematic review and meta-analysis. Sports 23, e—e Sperlich, B. Functional high-intensity circuit training improves body composition, peak oxygen uptake, strength, and alters certain dimensions of quality of life in overweight women.

Taylor, J. The effects of repeated-Sprint training on field-based fitness measures: a meta-analysis of controlled and non-controlled trials. The Danish Aerospace Company [Internet]. DAC to build multi-function exercise equipment; [cited Jan 8]. Vollaard, N. Effect of number of sprints in a SIT session on change in VO 2max : a meta-analysis.

Weston, K. High-intensity interval training in patients with lifestyle-induced cardiometabolic disease: a systematic review and meta-analysis. Weston, M. Effects of low-volume high-intensity interval training HIT on fitness in adults: a meta-analysis of controlled and non-controlled trials.

Wisloff, U. Superior cardiovascular effect of aerobic interval training versus moderate continuous training in heart failure patients: a randomized study.

Wright, M. Contrasting effects of a mixed-methods high-intensity interval training intervention in girl football players. Sports Sci.

Zelt, J. Reducing the volume of sprint interval training does not diminish maximal and submaximal performance gains in healthy men.

Keywords: high-intensity interval training, cardiorespiratory fitness, neuromuscular fitness, human spaceflight, microgravity, physical performance, exercise countermeasure.

Citation: Hurst C, Scott JPR, Weston KL and Weston M High-Intensity Interval Training: A Potential Exercise Countermeasure During Human Spaceflight.

Received: 01 February ; Accepted: 25 April ; Published: 22 May Copyright © Hurst, Scott, Weston and Weston. This is an open-access article distributed under the terms of the Creative Commons Attribution License CC BY. The use, distribution or reproduction in other forums is permitted, provided the original author s and the copyright owner s are credited and that the original publication in this journal is cited, in accordance with accepted academic practice.

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Sections Sections. About journal About journal. Article types Author guidelines Editor guidelines Publishing fees Submission checklist Contact editorial office. MINI REVIEW article Front. Effects of low-volume high-intensity interval training HIT on fitness in adults: a meta-analysis of controlled and non-controlled trials.

Gist NH, Fedewa MV, Dishman RK, Cureton KJ. Sprint interval training effects on aerobic capacity: a systematic review and meta-analysis. Wewege M, van den Berg R, Ward RE, Keech A. The effects of high-intensity interval training vs.

moderate-intensity continuous training on body composition in overweight and obese adults: a systematic review and meta-analysis. Girard J, Feng B, Chapman C. The effects of high-intensity interval training on athletic performance measures: a systematic review.

Physic Therap Rev. Engel FA, Ackermann A, Chtourou H, Sperlich B. High-intensity interval training performed by young athletes: a systematic review and meta-analysis. Front Physiol. Hansen EA, Rønnestad BR.

Effects of cycling training at imposed low cadences: a systematic review. Rosenblat MA, Perrotta AS, Thomas SG. Effect of high-intensity interval training versus sprint interval training on time-trial performance: a systematic review and meta-analysis.

de Oliveira-Nunes SG, Castro A, Sardeli AV, Cavaglieri CR, Chacon-Mikahil MPT. HIIT vs. SIT: what is the better to improve VO2max? A systematic review and meta-analysis. Rosenblat MA, Granata C, Thomas SG. Effect of interval training on the factors influencing maximal oxygen consumption: a systematic review and meta-analysis.

Moher D, Shamseer L, Clarke M, Ghersi D, Liberati A, Petticrew M, et al. Preferred reporting items for systematic review and meta-analysis protocols PRISMA-P statement. Syst Rev. Skinner JS, Jaskólski A, Jaskólska A, Krasnoff J, Gagnon J, Leon AS, et al. Age, sex, race, initial fitness, and response to training: the HERITAGE Family Study.

Quesada JI, Kerr ZY, Bertucci WM, Carpes FP. The categorization of amateur cyclists as research participants: findings from an observational study. De Pauw K, Roelands B, Cheung SS, de Geus B, Rietjens G, Meeusen R. Guidelines to classify subject groups in sport-science research.

Podlogar T, Leo P, Spragg J. Using VO2max as a marker of training status in athletes — can we do better? Jeukendrup AE, Craig NP, Hawley JA. The bioenergetics of world class cycling.

Jones AM, Burnley M, Black MI, Poole DC, Vanhatalo A. Physiol Rep. Poole DC, Rossiter HB, Brooks GA, Gladden LB. Faude O, Kindermann W, Meyer T. Lactate threshold concepts: how valid are they?

Forbes SC, Candow DG, Smith-Ryan AE, Hirsch KR, Roberts MD, VanDusseldorp TA, et al. Supplements and nutritional interventions to augment high-intensity interval training physiological and performance adaptations - a narrative review. Stepto NK, Hawley JA, Dennis SC, Hopkins WG. Effects of different interval-training programs on cycling time-trial performance.

Higgins JPT, Savović J, Page MJ, Elbers RG, Sterne JAC. Chapter 8: Assessing risk of bias in a randomized trial. In: Higgins JPT, Thomas J, Chandler J, Cumpston M, Li T, Page MJ, Welch VA, editors.

Cochrane Handbook for Systematic Reviews of Interventions version 6. Available from www. Guyatt GH, Oxman AD, Vist GE, Kunz R, Falck-Ytter Y, Alonso-Coello P, et al. GRADE: an emerging consensus on rating quality of evidence and strength of recommendations.

Schünemann HJ, Higgins JPT, Vist GE, Glasziou P, Akl EA, Skoetz N, Guyatt GH. Creer AR, Ricard MD, Conlee RK, Hoyt GL, Parcell AC. Neural, metabolic, and performance adaptations to four weeks of high-intensity sprint-interval training in trained cyclists.

Int J Sports Med. Interval training program optimization in highly trained endurance cyclists. Turnes T, de Aguiar RA, de Oliveira Cruz RS, Pereira K, Salvador AF, Caputo F. High-intensity interval training in the boundaries of the severe domain: effects on sprint and endurance performance.

Viechtbauer W. Conducting meta-analyses in R with the metafor package. J Stat Software. Morris SB. Estimating effect sizes from pretest-posttest-control group designs. Org Res Methods. Caputo F, Denadai BS. The highest intensity and the shortest duration permitting attainment of maximal oxygen uptake during cycling: effects of different methods and aerobic fitness level.

Amrhein V, Greenland S, McShane B. Scientists rise up against statistical significance. McShane BB, Gal D, Gelman A, Robert C, Tackett JL. Abandon statistical significance. Am Stat. Higgins JP, Thompson SG, Deeks JJ, Altman DG. Measuring inconsistency in meta-analyses. Higgins JP, Altman DG, Gøtzsche PC, Jüni P, Moher D, Oxman AD, et al.

The Cochrane Collaboration's tool for assessing risk of bias in randomised trials. Vollaard NBJ, Metcalfe RS, Williams S. Effect of number of sprints in an SIT session on change in VO2max: a meta-analysis.

Bacon AP, Carter RE, Ogle EA, Joyner MJ. VO2max trainability and high-intensity interval training in humans: a meta-analysis. Coyle EF, Feltner ME, Kautz SA, Hamilton MT, Montain SJ, Baylor AM, et al. Physiological and biomechanical factors associated with elite endurance cycling performance. Edge J, Bishop D, Goodman C, Dawson B.

Effects of high- and moderate-intensity training on metabolism and repeated sprints. Gormley SE, Swain DP, High R, Spina RJ, Dowling EA, Kotipalli US, et al. Effect of intensity of aerobic training on VO2max.

Zapico AG, Calderón FJ, Benito PJ, González CB, Parisi A, Pigozzi F, et al. Evolution of physiological and haematological parameters with training load in elite male road cyclists: a longitudinal study.

J Sports Med Phys Fitness. Rønnestad BR, Hansen J. Optimizing interval training at power output associated with peak oxygen uptake in well-trained cyclists. Rozenek R, Funato K, Kubo J, Hoshikawa M, Matsuo A.

Physiological responses to interval training sessions at velocities associated with VO2max.