The aim of the research is to (1) evaluate the potential clinical effectiveness and biological mechanisms of indoor cycling in the treatment of obesity and (2) provide-up-to-date evidence on the impact of indoor cycling in reducing cardiovascular disease (CVD) risk factors, namely, hypertension, dyslipidemia, type 2 diabetes, endothelial dysfunction. We hypothesize that IC training, can be a good stimulus to mitigate cardiovascular risk factors in women with obesity and to improve values of the examined indicators towards that occurring in women with normal body weight.

The study was designed as a prospective exercise intervention trial. The study involved women with obesity (OW) and women with normal body weight (NW). Both study groups underwent the same 3-month physical training program. Outside the implemented program, all participants were instructed to maintain their normal physical activity, diet and not to use any dietary supplements. Dietary intake was assessed using interviews conducted at baseline and after completion of the trial. The amount of nutrients in participant's daily diet was processed and evaluated using a dietetics computer program. The intake of nutrients, total caloric intake during the study were constant in both groups. Anthropometric parameters, blood pressure and physical capacity were measured and blood samples were taken at baseline and after completion of the physical training program.

The study involved 31 obese or normal weight women aged 34-62. A total of 23 women with obesity (body mass index (BMI) ≥ 30 kg/m2; waist circumference > 80 cm) registered and screened from among 163 women at the outpatient clinic of the Department of Internal Medicine, Metabolic Disorders, and Hypertension, University of Medical Sciences, Poznań, Poland were enrolled to OW group. The NW group consisted of 8 healthy women from the announcement (BMI ≤ 24.9 and ≥ 18.5 kg/m2).

Informed consent was obtained from all participants, and the study was approved by the Ethics Committee of Poznan University of Medical Sciences (case no. 1077/12; supplement no. 753/13). The study conformed to all ethical issues included in the Helsinki Declaration.

The 3-month intervention consisted of a physical exercise program involving three indoor cycling sessions per week, with a total of 36 training sessions. Subjects exercised on cycle ergometers Schwinn® Evolution® (Schwinn Bicycle Company, Boulder, Colorado, USA). Each session lasted approximately 55 minutes. Training sessions consisted of a 5-min low-intensity warm-up (cycling at 50-65% of maximum heart rate (HRmax)), 40 min of main training at an intensity of 65-95% of HRmax, 5 min of non-weight-bearing cycling, finishing with 5 min of low-intensity cool-down stretching and breathing exercises.

Main part of the training was interval. Each exercise session consisted of 3 to 4 high intensity intervals with intensity exceeding 80% of HRmax, often reaching anaerobic threshold. High intensity intervals lasted approximately 4-minutes and were interspersed by recovery periods at 65-80% of HRmax.

HR during sessions was monitored with a Suunto Fitness Solution® device (Suunto, Vantaa, Finland). To ensure that assigned exercise intensities were obtained, the average per cent of the maximum heart rate during the entire training session was obtained from the device Blood samples for biochemical analyses were taken from a basilic vein, after overnight 12-hour fasting. In the serum samples, parameters were measured using commercially available enzyme-linked immunoassays.

Both before and after the whole training programme, the following measurements were made: body weight and height, BMI, waist and hip circumference, WHR, body composition (DXA), total-body skeletal muscle mass index, graded exercise test, isokinetic muscle strength of knee flexors and extensors, exercise and resting blood pressure, and the heart rate. Vascular endothelial function indices (eNOS, VEGF, TBARS and TAS) as well as TCH, LDL-C, HDL-C, TG, oxLDL and CRP of venous blood were determined.

A sample size was determined according to changes in VO2 peak. A total of 6 subjects in OW group and 7 subjects in NW group was calculated to yield at least 80% power of detecting an intervention effect as statistically significant at the 0.05 α level.

Anthropometric measurements were conducted with the subjects wearing light clothing and no shoes. Weight was measured to the nearest 0.1 kg and height to the nearest 0.5 cm. BMI was calculated as weight divided by height squared (kg/m2 ). Obesity was defined as BMI ≥ 30 kg/m2. Waist circumference (cm) was measured at the level of the iliac crest at the end of normal expiration. Hip circumference was measured at the maximum protuberance of the buttocks. Waist and hip circumferences were measured to the nearest 0.5 cm. Waist-to-hip ratio (WHR) was calculated as waist circumference divided by hip circumference. Index of central obesity (ICO) was calculated as waist circumference (cm) divided by height (cm) (Parikh, et al., 2012).

Body composition analysis was assessed using DXA (GE Healthcare Lunar Prodigy Advance; GE Medical Systems, Milan, Italy). The subjects were instructed not to make any intense physical effort in the 24h prior to the examination. The subjects were given complete instructions on the examination procedure. They wore cotton T-shirt, shorts, and socks and lay on the DXA table supine and motionlessly during the testing procedure. They were instructed to remove all metal, rubber, and plastic objects that might affect the X-ray beam. The same well-trained laboratory technician positioned the subjects, performed the scans, and executed the analysis according to the operator's manual, using the standard analysis protocol. Total body fat mass and lean body mass were determined using standard scan mode (in case of moderately obese subjects) or thick scan mode (in case of extremely obese subjects); the absorbed dose of radiation was 0.4 μGy and 0.8 μGy, respectively.

To determine the subjects' physical capacity, a Graded Exercise Test (GXT) was performed on an electronically braked cycle ergometer (Kettler ® DX1 Pro, Kettler, Ense, Germany). GXT began at a work rate of 25 W (60 rev/min). The work rate was incremented by 25 W every 2 min until the subject could no longer maintain the required pedal cadence. Each test lasted 4-14.5 min, depending on age and aerobic fitness status. The exercise tests were conducted between 8: 00 and 12: 00 a.m. in an air-conditioned laboratory, 2 h after consuming a light breakfast. Expired gases, minute ventilations (Ve), and heart rate (HR) during GXT were monitored continuously with an automated system (Oxycon Mobile ® ; Viasys Healthcare, Hoechberg, Germany). Oxygen intake (VO 2 ) and carbon dioxide output (VCO 2 ) was measured breath-by-breath and averaged over 15-second periods. Before each trial, the system was calibrated according to the manufacturer's instructions. Peak VO2 was defined as the highest 15-second averaged VO 2 obtained during the final exercise load on the test. HR peak (bpm) was measured as the highest 15-second average value in the test. To determine ventilatory threshold (VT), the V-slope method was administered using computerized regression analysis on the slopes of the CO 2 output versus O2 uptake plot, which detects the beginning of the excess CO 2 output generated from the buffering of H +. The method involves analyzing the behavior of VCO 2 as a function of VO 2 during GXT with a consequent increase in VCO 2 . This results in a transition in the relationship between VCO 2 and VO 2 . The software supplied by Viasys Healthcare was used, supported with a visual inspection on the part of an experienced researcher. As a secondary method, the ventilatory equivalent method (VEQ method) was employed and the point at which the equivalent for oxygen (VE/VO 2 ) increased without a concomitant rise in the equivalent for carbon dioxide (VE/VCO 2 ) was detected. The VT was expressed as a heart rate (HR VT ).

Exercise blood pressure was measured during a GXT using a digital electronic tensiometer (model 705IT TM, Omron Corporation, Kyoto, Japan). The measurement was taken during maximal work rate. Exercise HR was measured as the highest 15-second average value in the GXT. Resting blood pressure was measured fasting in the morning hours, in a sitting position with the legs uncrossed and the back and arm supported. Resting HR was measured under the same conditions, using auscultation of the heart by stethoscope. Regular or large adult cuffs were used, depending on the patient's arm circumference.

Inclusion Criteria:

Initial inclusion criteria for both study groups were as follows: age: 30 to 65 years and stable body weight in the month prior to the trial (permissible deviation ± 1 kg).

For Women with Obesity Group: BMI ≥ 30 kg/m2; waist circumference > 80 cm. For Normal-weight Womeng Group: BMI ≤ 24.9 and ≥ 18.5 kg/m2

Exclusion Criteria for both study groups were as follows:

• secondary form of obesity and/or secondary form of hypertension;
• diabetes mellitus;
• history of coronary artery disease;
• stroke;
• congestive heart failure;
• clinically significant arrhythmias or conduction disorders;
• malignancy;
• poorly controlled hypertension (SBP > 140 mmHg and/or DBP > 90 mmHg), and/or modifications to antihypertensive treatment;
• lipid disorders requiring the implementation of drug treatment;
• clinically significant abnormalities in liver, kidney or thyroid gland function;
• clinically significant acute or chronic inflammatory process within the respiratory, digestive or genitourinary tracts, or the oral cavity, pharynx or paranasal sinuses; or, presence of connective tissue disease or arthritis;
• history of infection within the month prior to the study;
• nicotine, alcohol or drug abuse;
• and / or any other condition which, according to the researchers, would cause that participation would be detrimental to the participant or would prevent, limit or interfere with the results of the study.