|Year : 2021 | Volume
| Issue : 1 | Page : 141
The effect of all extremity high intensity interval training on athero-protective factors and endothelial function in overweight and obese women
Volga Hovsepian1, Sayad M Marandi1, Fahimeh Esfarjani1, Reihaneh Zavar2, Masoumeh Sadeghi3
1 Department of Exercise Physiology, Faculty of Physical Education and Sport Sciences, University of Isfahan, Isfahan, Iran
2 Heart Failure Research Centre, Cardiovascular Research Institute Isfahan University of Medical Sciences, Isfahan, Iran
3 Cardiac Rehabilitation Research Center, Cardiovascular Research Institute, Isfahan Iran, University of Medical Sciences, Isfahan, Iran
|Date of Submission||10-Jul-2019|
|Date of Acceptance||23-Jan-2020|
|Date of Web Publication||26-Oct-2021|
Sayad M Marandi
Department of Exercise Physiology, Faculty of Physical Education and Sport Sciences, University of Isfahan, Isfahan
Source of Support: None, Conflict of Interest: None
Context: Obesity is associated with endothelial dysfunction and cardiovascular diseases. Adiponectin and fibroblast growth factor 21 (FGF21) as hormones are highly contributive in cardiovascular system, while they are disrupted through obesity. Weight-bearing high intensity interval training (HIIT) as an effective procedure in preventing obesity-related complications in adults with obesity may be limited due to the subjects' muscular weakness and complications interfering walking. Aims: The purpose of this study was to assess the effectiveness of non-weight bearing all extremity HIIT (all ex. HIIT) on FGF21, adiponectin, nitric oxide (NO), and flow mediated dilation (FMD) in overweight and obese women. Methods: Thirty healthy overweight and obese sedentary university female students within 20.53 ± 1.50 age range and BMI ≥27 kg.m-2 were assigned in two experimental and control groups. All ex. HIIT consisted of 4 × 4 min at 85–90% max HR with an interspersed with 3 × 3 min recovery per round at 70% max HR by upper and lower ergometers in a simultaneous manner on 10 weeks of four sessions of 40 min each. FGF21, adiponectin, NO, FMD, weight, waist and maximal oxygen uptake (VO2max) were measured in pre and post-tests. Paired sample t-test and analysis of covariance are applied for statistical analysis. Results: Results indicated a significant increase in adiponectin (P ≤ 0.01) and FMD (P ≤ 0.001), while there existed no changes in FGF21 at (P ≥ 0.10) and NO (P ≥ 0.84). The weight and waist decreased at (P ≤ 0.001), and the VO2max increased at (P ≤ 0.001). Conclusions: All ex. HIIT may be a safe alternative for overweigh and obese women who have complications with weight-bearing exercises, and may increase adiponectin, and improve the FMD, aerobic fitness, and body composition.
Keywords: Adiponectin, atherosclerosis, fibroblast growth factor 21, high intensity interval training
|How to cite this article:|
Hovsepian V, Marandi SM, Esfarjani F, Zavar R, Sadeghi M. The effect of all extremity high intensity interval training on athero-protective factors and endothelial function in overweight and obese women. Int J Prev Med 2021;12:141
|How to cite this URL:|
Hovsepian V, Marandi SM, Esfarjani F, Zavar R, Sadeghi M. The effect of all extremity high intensity interval training on athero-protective factors and endothelial function in overweight and obese women. Int J Prev Med [serial online] 2021 [cited 2022 May 24];12:141. Available from: https://www.ijpvmjournal.net/text.asp?2021/12/1/141/329344
| Introduction|| |
Obesity constitutes one of the major risk factors for non-communicable metabolic diseases. Metabolic disorders like diabetes, insulin resistance, and cardiovascular disease are not a simple dysfunction of the local organs, instead they are uncoordinated among hormones productions in different organs. Adipose tissue and liver are the highly active endocrine organs that secrete bioactive molecules which are highly contributive in regulating body energy metabolism and cardiovascular tone. Adiponectin and FGF21 constitute the two major hormones secreted from adipose tissue and liver respectively., In spite of their production sources and structures, both the hormones are contributive in decreasing lipid and glucose,, and protecting cardiovascular system.
Assessment of adiponectin/FGF21 by administration or genetic manipulation has revealed an increase in energy expenditure, a decrease in the insulin resistance and atherosclerosis., The FGF21 decreased atherosclerosis through adiponectin induction,, while adiponectin alleviated endothelial function by an increase in NO production through adenosine monophosphate-activated protein kinase (AMPK) pathway. There exist studies on presence of FGF21–adiponectin axis in regulating vascular and metabolic homeostasis, while as to this axis in obesity they revealed some distortion., FGF21 is high, and adiponectin is low in obese than normal weight people.,
According to the meta-analyses run by, the traditional exercise training including resistance, continues or circuit trainings improved FMD by 2.3%, while it is revealed in many studies that weight-bearing HIIT had impressive effect of cardiovascular function in relation to traditional moderate intensity trainings in obesity.,, On the other hand slow walking, dyspnoea, foot and ankle pain and lower muscular weakness due to obesity make weight-bearing HIIT exercise difficult. Non-weight bearing all ex. HIIT may be an appealing modality to compensate the lower extremity fatigue and activates many muscles. To the best knowledge of the author here, as the obesity, there exist no assessment on this type of training. The objective of this study was to assess the effect of non-weight bearing all ex. HIIT on FGF21, adiponectin, NO and the athero-protective effect thereof, in overweight and obese women.
| Methods|| |
This study was extracted from a dissertation and was a cross-sectional semi-experimental study approved by the Research Committee of the University of Isfahan, Iran according to the policy of the Ethics Committee of University of Isfahan code: 1396.041. The statistical population here consisted of 30 female university students within 18–23 age range, selected in experimental and control groups equally. All were of sedentary (exercise ≤2 times/week), overweight or obesity, with body mass index (BMI) ≥27 kg.m-2, free of CVD, diabetes, hormonal complications, medication consumption, smoking, with no restricted diet. Participants responded to a medical history questionnaire and signed a written consent for participating in this experiment prior to data collection. The following procedures were applied to materialize the objective here.
The baseline measurements were made after 12 h fasting. The post-test measurements were made 48 h after last session of training at the fasting state to eliminate acute effect of the exercise. In day 1 the weight and height were measured with the least cloths on, on Seca scale and stadiometer (model 220, Germany). Waist (level of iliac crest) was measured by standard tape. After 20 min rest in sitting position the pulse meter (Polar F4, Finland) was applied to register resting heart rate (HR). To estimate the body composition, calliper (Lange, Korea) was applied to measure skin fold in three sides abdomen, ilium, and triceps. To assess VO2max, Young Men's Christian Association's (YMCA) submaximal test was run with ergometer (Monark 839 Sweden). In day 2, after 12 h fasting, 10cc of venues blood was collected and centrifuged 4,000 rpm for 20 min. The serum was gathered and stored in -80°C. The FGF21 [R&D systems, Quanticine, “enzyme-linked immunosorbent assay (ELISA), USA], adiponectin (Bio legend, ELISA MAX Deluxe Set, USA), and NO (abcam, colorimetric, UK) kits are applied in this analysis according to manufacture instructions.
Measurement of FMD
FMD was measured after 72 h during which no medication, and vitamin supplement were consumed. A 12 h restriction was assigned in consuming alcohol, caffeine, high fat, and high carbohydrate diet and vigorous exercise. The FMD was measured at phase one of menstruation days 1–7, with high resolution ultrasound machine (Vivid 3, GE Health care, USA) and a linear array probe (10 MHZ). The measurement was made at the end of diastolic phase identified by R wave on electrocardiography. The initial measurement of brachial artery diameter was made after 20 min resting in supine position at 22–24°C in about 3 cm above antecubittal fossa. Following this, one cuff fixed at 8 cm of brachial artery distal was inflated to 250–300 mmHg for 5 min. The arterial baseline diameter was measured before cuff inflation and 2 min after cuff deflation in the same point. FMD% was calculated through the following equation:
Recorded daily physical activity and diet
All subjects were instructed to maintain their normal daily physical activity and diet during the study period. Their daily physical activities except all ex. HIIT program was measured through pedometer (iHealth Edge, USA) at base line, 5th and 10th weeks for three times: two weekday and one weekend day. The mean of three daily activities in each series was calculated and compared between and within both the groups. To calculate the calorie intake, the subjects were asked to report volume of food and drink intake according to the above interval, in a 3-day diet record. Energy intake was determined by applying the diet analyzer software NUT-4 modified by inserting the Iranian Food Table. The mean of three daily calorie intake in each series was calculated and compared between the between and within the both groups.
The peak HR was determined by 220-age. All ex. HIIT group were exposed to 4 × 4 min at 85–90% max HR interspersed with 3 × 3 min recovery per round at 70% max HR. The upper body ergometer (Monark 831E) and lower body ergometer (Monark 839E) were applied in a simultaneous manner on 10 weeks of four sessions of 40 min each. The first week was considered as the familiarization and preconditioning phase, after which the intensity and duration of training were increased to reach the target peak HR and total time of 40 min.
All statistical analyses were run in IBM SPSS Statistics version 22 software. Shapiro–Wilk test was applied to assess the normality of data distribution. Non-normally data was subjected to logarithmic transformation. Levine's test was run to indicate homogeneity of variances. The Pair sample t-test was run to compare pre- and post-interventions within the groups. Analysis of covariance (ANCOVA) with pre-test score as covariate and Mann–Whitney U test were run to assess differences in parametric and non-parametric data, respectively. Repeated measure ANOVA was applied for calorie intake and Krouskal–Wallis test was run for daily physical activity analyses. Quantitative variables was expressed as the mean ± SD. Power calculation was based on primary outcome of FMD%. According to statistical power 0.8 and level of significance (α = 0.05) for detection of effect size 15% introduced by, to determine the FMD% from pre- to post-HIIT, at least eight individuals in each group are needed.
| Results|| |
Of the 30 participating subjects, 4 (13%) did not complete the intervention. The reasons of withdrawal consisted of: schedule conflict (3 subject) and exercise induced asthma in high intensities of HIIT (1 subject). At first sessions it was hard to coordinate the arms and legs during upper and lower ergometers operation in a simultaneous manner, which was resolved over time. There was no significant differences in all variables at baseline [Table 1]. There were no changes in daily physical activity (P = 0.95) and daily calorie intake (P = 0.88) between the groups. No significant changes were observed in both the groups as to FGF21 and NO. The observed increase in the adiponectin was 6.9%, FMD was 15.6% and VO2max was 19.7%. The observed decrease in the weight was 2.4%, body fat percent (BF%) was 7.2%, and waist was 3.3% after training and all variables remained unchanged in control group, [Table 2].
|Table 1: General characteristics, anthropometric and blood analyses of groups at baseline|
Click here to view
|Table 2: Effect of all ex. HIIT on blood variables, endothelial function, aerobic power and body composition|
Click here to view
| Discussion|| |
This study demonstrated that all ex. HIIT would be feasible and well tolerated for overweight and obese women who have complication with weight bearing exercise. This was based on 86% completion rate for this training mode. The daily physical activity and daily calorie intake of the subjects remained unchanged, therefore, it was speculated that changes in variables were only related to exercise training.
In this study the effect of all ex. HIIT on the athero-protective effect of FGF21, adiponectin, FMD, NO, aerobic fitness, and weight management of women with overweight and obesity were assessed. The observation of experiment period revealed that serum FGF21 and NO remained unchanged, adiponectin level increased, FMD and Vo2max improved and weight, BF% and waist decreased. As mentioned this was the first study run in assessing the effect of all ex. HIIT on overweight and obese women. Due to uniquenessof this study where the focus was on all ex. HIIT on overweight obese women, there existed no study to which this article could be compared with, while because of necessity the studies run on HIIT were mentioned here.
Despite to assessment run on metabolic effects of FGF21 in human, there existed few studies run on this hepatocyte in cardiovascular disease. No significant changes in FGF21 was observed in this study. In only one available study, it was reported that 3 months combined exercise program decreased FGF21 in young obese women. An increase in FGF21 after exercise in young women was found in. These discrepancies between this and the available studies may be explained by the obesity status, age of subjects, or differences in exercise training programs and duration.
Here a significant increase in adiponectin was observed after intervention with respect to weight, waist, and BF% reduction. According to available studies weight decreased and adiponectin level increased after weight bearing HIIT or aerobic training in obese women.,,, On the other hand six months of aerobic exercise had no changes in weight and subsequently adiponectin level in obese patients. It is deduced that any loss in weight and body fat to a certain degree is necessary in affecting adiponectin level in obesity. In this study a reduction in weight, BF%, and waist circumferences were significant with non-weight bearing all ex. HIIT and these were probably the reasons of increasing adiponectin. Recently such findings are reported as well. Adiponectin has an anti-atherogenic and anti-inflammatory effect by activation AMPK that lead to endothelial NO production and alleviate endothelial dysfunction and prevent atherosclerosis.
In this study all ex. HIIT improved endothelial function assessed by FMD in a significant manner, while the plasma NO level remained unchanged. Improvement of FMD due to all ex. HIIT could be an important result in preventing atherosclerosis and CVD in obesity. The claim by Ramos JS et al. stated that HIIT was an affective program for FMD and the findings by Sawyer BJ et al. were in correspondence with this study. Some studies revealed no changes on FMD after HIIT. These differences might be due to the age of the subjects or the type and duration of the exercise programs. One of the most important mechanisms of exercise-induced FMD improvement is the shear stress and NO production. It is possible that exercise subject to another mechanisms independent of NO could improve the endothelial function which could be related to weight loss. In this study weight and BF% and waist decreased significantly. It was deduced that all ex. HIIT could decrease both the subcutaneous and visceral fat, where the latter is more important factor in preventing CVD risk. One of the reasons in weight and fat reduction in this study was the involvement of large muscle mass due to activation of upper and lower body in obese women. This might be due to both the exercise and post-exercise fat oxidation increase caused by resynthesized adenosine three phosphate (ATP) from Phosphocreatine (PCr) and triacylglycerol in muscles.
Here it was observed that VO2max had a significant improvement after all ex. HIIT. Although there existed studies where due to sub-maximal aerobic test which an underestimation of VO2max was evident. The result observed here revealed an improvement of about 5.6 ml.kg/min in response to all ex. HIIT. This was a good result because according to the available data every 3.5 ml.kg/min improvement in aerobic power is related to 12–22% lower risk of CVD mortality. The fact that VO2max improved significantly due to all ex. HIIT corresponded to the findings by Hwang C-L et al. Mechanisms underlying all ex. HIIT in increasing VO2max are undetermined, but is assumed that a decrease in total peripheral resistance in vessels and constitute the reason to improve VO2max.,
In this study, it was observed that the changes in VO2max percentage was higher than changes in weight and body fat percentage. This revealed that implementing exercise protocol in overweight and obese subjects should not be only emphasized on weight reduction, because even at low weight reduction, the appropriate exercise by increasing VO2max could be an essential factor in increasing FMD and preventing atherosclerosis and CVD.
The strength of this study consisted of: (1) being the first in assessing the non-weight bearing all ex. HIIT by upper and lower ergometers simultaneously, in overweight and obese women; (2) each exercise session was supervised by monitoring heart rate to assure the accuracy of exercise intensity; and (3) it was prescription of exercise rather than increased habitual physical activity.
The limitation of this study is consisted of: (1) The adaptation observed in this study were limited to length of this intervention which could have needed longer interventions to observe greater adaptations. (2) This intervention included only young women, and assessing the gender-specific effects were not of concern. (3) The sample size of this study was small, while larger cohorts would have produced better findings.
| Conclusions|| |
It was concluded that non-weight bearing all ex. HIIT could be appropriate for overweight and obese women having problem with weight bearing or running exercises. Although all ex. HIIT could not change FGF21 and NO, but it decreased weight, BF %, and waist, subsequently, increased adiponectin and improved FMD. The percentage of changes in VO2max was greater than the same in weight and BF%, indicating that the focus of the exercise protocols for these subjects should not be only on weight loss. More studies need to clarify and assure the beneficial effect of all ex. HIIT on overweight and obese women. It is obvious that the findings here and studies alike would contribute to the prevention of the issue at hand.
We would like to thank Dr. Nafiseh Esmail, Dr. Hossain Khanahmad, the and laboratory personnel of Department of Immunology of Medical University of Isfahan, and the Cardiology Research Centre of Isfahan for their cooperation. Also we would thank to participants of this study for their time and effort.
Financial support and sponsorship
Conflicts of interest
There are no conflicts of interest.
| References|| |
Khosravi ZS, Kafeshani M, Tavasoli P, Zadeh AH, Entezari MH. Effect of vitamin D supplementation on weight loss, glycemic indices, and lipid profile in obese and overweight women: A clinical trial study. Int J Prev Med 2018;9.
Romacho T, Elsen M, Röhrborn D, Eckel J. Adipose tissue and its role in organ crosstalk. Acta physiologica 2014;210:733-53.
Scherer PE. Adipose tissue: From lipid storage compartment to endocrine organ. Diabetes 2006;55:1537-45.
Szmitko PE, Teoh H, Stewart DJ, Verma S. Adiponectin and cardiovascular disease: State of the art? Am J Physiol Heart Circ Physiol 2007;292:H1655-H63.
Kliewer SA, Mangelsdorf DJ. Fibroblast growth factor 21: From pharmacology to physiology. Am J Clin Nutr 2010;91:254S-7S.
Geng L, Liao B, Jin L, Huang Z, Triggle CR, Ding H, et al
. Exercise alleviates obesity-induced metabolic dysfunction via enhancing FGF21 sensitivity in adipose tissues. Cell Rep 2019;26:2738-52. e4.
Iwabu M, Okada-Iwabu M, Yamauchi T, Kadowaki T. Adiponectin/AdipoR research and its implications for lifestyle-related diseases. Front Cardiovasc Med 2019;6:116.
Katsiki N, Mantzoros C. Fibroblast growth factor 21: A role in cardiometabolic disorders and cardiovascular risk prediction? Metabolism 2019;93:iii-v.
Berg AH, Combs TP, Du X, Brownlee M, Scherer PE. The adipocyte-secreted protein Acrp30 enhances hepatic insulin action. Nat Med 2001;7:947.
Kokkinos J, Tang S, Rye KA, Ong KL. The role of fibroblast growth factor 21 in atherosclerosis. Atherosclerosis 2017;257:259-65.
Lin Z, Pan X, Wu F, Ye D, Zhang Y, Wang Y, et al
. Fibroblast growth factor 21 prevents atherosclerosis by suppression of hepatic sterol regulatory element-binding protein-2 and induction of adiponectin in mice. Circulation 2015;131:1861-31.
Ouchi N, Walsh K. Adiponectin as an anti-inflammatory factor. Clinica Chimica Acta 2007;380:24-30.
Hui X, Feng T, Liu Q, Gao Y, Xu A. The FGF21–adiponectin axis in controlling energy and vascular homeostasis. J Mol Cell Biol 2016;8:110-9.
Yang W, Liu L, Wei Y, Fang C, Zhou F, Chen J, et al
. Exercise ameliorates the FGF21–adiponectin axis impairment in diet-induced obese mice. Endocr Connect 2019;8:596-604.
Mikołajczak A, Oświęcimska J, Świętochowska E, Roczniak W, Ziora K. Serum FGF21 in girls with anorexia nervosa–comparison to normal weight and obese female adolescents. Neuro Endocrinol Lett 2017;38:173-81.
Montero D, Walther G, Benamo E, Perez-Martin A, Vinet A. Effects of exercise training on arterial function in type 2 diabetes mellitus. Sports Med 2013;43:1191-9.
Hollekim-Strand SM, Bjørgaas MR, Albrektsen G, Tjønna AE, Wisløff U, Ingul CB. High-intensity interval exercise effectively improves cardiac function in patients with type 2 diabetes mellitus and diastolic dysfunction: A randomized controlled trial. J Am Coll Cardiol 2014;64:1758-60.
Molmen-Hansen HE, Stolen T, Tjonna AE, Aamot IL, Ekeberg IS, Tyldum GA, et al
. Aerobic interval training reduces blood pressure and improves myocardial function in hypertensive patients. Eur J Prev Cardiol 2012;19:151-60.
Ramos JS, Dalleck LC, Tjonna AE, Beetham KS, Coombes JS. The impact of high-intensity interval training versus moderate-intensity continuous training on vascular function: A systematic review and meta-analysis. Sports Med 2015;45:679-92.
Hills A, Hennig E, Byrne N, Steele J. The biomechanics of adiposity–structural and functional limitations of obesity and implications for movement. Obes Rev 2002;3:35-43.
Kim HK, Hwang Cl, Yoo JK, Hwang MH, Handberg EM, Petersen JW, et al
. All-extremity exercise training improves arterial stiffness in older adults. Med Sci Sports Exerc 2017;49:1404-11.
Golding L. YMCA Fitness Testing and Assessment Manual. Champaign, IL: Human Kinetics; 2000.
Wilbur J, Naftzger-Kang L, Miller AM, Chandler P, Montgomery A. Women's occupations, energy expenditure, and cardiovascular risk factors. J Women's Health 1999;8:377-87.
Hashemi SM, Mokhtari SM, Sadeghi M, Foroozan R, Safari M. Effect of vitamin D therapy on endothelial function in ischemic heart disease female patients with vitamin D deficiency or insufficiency: A primary report. ARYA Atheroscler 2015;11:54-9.
Ahmadi A, Akbarzadeh M, Mohammadi F, Akbari M, Jafari B, Tolide-Ie HR. Anthropometric characteristics and dietary pattern of women with polycystic ovary syndrome. Indian J Endocrinol Metabol 2013;17:672-6.
Hwang CL, Yoo JK, Kim HK, Hwang MH, Handberg EM, Petersen JW, et al
. Novel all-extremity high-intensity interval training improves aerobic fitness, cardiac function and insulin resistance in healthy older adults. Exp Gerontol 2016;82:112-9.
Madsen SM, Thorup AC, Overgaard K, Bjerre M, Jeppesen PB. Functional and structural vascular adaptations following 8 weeks of low volume high intensity interval training in lower leg of type 2 diabetes patients and individuals at high risk of metabolic syndrome. Arch Physiol Biochem 2015;121:178-86.
Yang SJ, Hong HC, Choi HY, Yoo HJ, Cho GJ, Hwang TG, et al
. Effects of a three-month combined exercise programme on fibroblast growth factor 21 and fetuin-A levels and arterial stiffness in obese women. Clin Endocrinol 2011;75:464-9.
Cuevas-Ramos D, Almeda-Valdés P, Meza-Arana CE, Brito-Córdova G, Gómez-Pérez FJ, Mehta R, et al
. Exercise increases serum fibroblast growth factor 21 (FGF21) levels. PLoS One 2012;7:e38022.
Racil G, Ounis OB, Hammouda O, Kallel A, Zouhal H, Chamari K, et al
. Effects of high vs. moderate exercise intensity during interval training on lipids and adiponectin levels in obese young females. Eur J Appl Physiol 2013;113:2531-40.
Kim ES, Im JA, Kim KC, Park JH, Suh SH, Kang ES, et al
. Improved insulin sensitivity and adiponectin level after exercise training in obese Korean youth. Obesity 2007;15:3023-30.
Lim S, Choi SH, Jeong IK, Kim JH, Moon MK, Park KS, et al
. Insulin-sensitizing effects of exercise on adiponectin and retinol-binding protein-4 concentrations in young and middle-aged women. J Clin Endocrinol Metab 2008;93:2263-8.
Corbi G, Polito R, Monaco ML, Cacciatore F, Scioli M, Ferrara N, et al
. Adiponectin expression and genotypes in Italian people with severe obesity undergone a hypocaloric diet and physical exercise program. Nutrients 2019;11:2195.
Hulver MW, Zheng D, Tanner CJ, Houmard JA, Kraus WE, Slentz CA, et al
. Adiponectin is not altered with exercise training despite enhanced insulin action. Am J Physiol Endocrinol Metab 2002;283:E861-E5.
Hwang CL, Lim J, Yoo JK, Kim HK, Hwang MH, Handberg EM, et al
. Effect of all-extremity high-intensity interval training vs. moderate-intensity continuous training on aerobic fitness in middle-aged and older adults with type 2 diabetes: A randomized controlled trial. Exp Gerontol 2019;116:46-53.
Sawyer BJ, Tucker WJ, Bhammar DM, Ryder JR, Sweazea KL, Gaesser GA. Effects of high-intensity interval training and moderate-intensity continuous training on endothelial function and cardiometabolic risk markers in obese adults. J Appl Physiol 2016;121:279-88.
Klonizakis M, Moss J, Gilbert S, Broom D, Foster J, Tew GA. Low-volume high-intensity interval training rapidly improves cardiopulmonary function in postmenopausal women. Menopause 2014;21:1099-105.
Green DJ, Maiorana A, O'driscoll G, Taylor R. Effect of exercise training on endothelium-derived nitric oxide function in humans. J Physiol 2004;561:1-25.
Gaitanos GC, Williams C, Boobis LH, Brooks S. Human muscle metabolism during intermittent maximal exercise. J Appl Physiol 1993;75:712-9.
Carter JG, Brooks KA, Sparks JR, editors. Comparison of the YMCA cycle sub-maximal VO2 max test to a treadmill VO2 max test. Int J Exerc Sci 2011;5:40.
[Table 1], [Table 2]