The Effect of 12-week Circuit Training on Insulin Sensitivity and Endothelial Function in Women With Insulin Resistance

During the last 10 years many studies concerning the impact of physical training on whole-body insulin sensitivity have been published, but there is a lack of an extended investigation on the potential clinical benefits of novel circuit training-based on strength and endurance exercises-relating to the optimization of insulin sensitivity and vascular endothelial function. It is of interest to precisely determine the physiological and biochemical effects of circuit training. An important aspect of the planned research will be the analysis of the effects of physical training on the released during muscle contraction myokines capable of modulating various metabolic processes. We hypothesized that in studied participants 12 weeks of the novel form of training would result in improving insulin sensitivity and vascular endothelial function mainly via myokines released by contracting skeletal muscles.

The following questions will be asked: (1) whether the 12-week circuit training (combined strength and endurance exercises) performed by women with insulin resistance, improves insulin sensitivity, carbohydrate and lipid metabolism and promotes the efficiency of endothelial defense mechanisms? (2) whether the 12-week circuit training (combined of strength and endurance exercises) changes the concentrations of transcription factors regulating lipid and carbohydrate metabolism or the synthesis and/or secretion of myokines and adipokines in women with insulin resistance? (3) whether the 12-week strength training, interspersed with bouts of endurance exercise has a positive effect on cytokine profile? (4) whether there is a relationship between changes in body composition, HOMA-IR, and the level of myokines caused by physical training? (5) whether the 12-week circuit training reduces low back pain symptoms, plantar stifness and improve functioning of the patient in everyday life? A group of 80 women, aged 25 to 45 years, with diagnosed insulin resistance will participate in the planned study. Participants will be enrolled in the research program based on medical qualification. Before the intervention all women will have venous blood collected to determine fasting glucose, hemoglobin glycosylated (HbA1C) and insulin levels and insulin resistance by the homeostasis model assessment of insulin resistance (HOMA-IR) will be calculated. The inclusion criteria will be as follows: (1) women, age: 25-45 years, menstruating, (2) BMI 18,5-29,9 kg/m2, (3) insulin resistance based on HOMA-IR (cut-off point 2.5), (4) HbA1C ≤ 6.5%, (5) not contraindicated to physical activity. Participants meeting the inclusion criteria will be randomly divided into two groups. The first group of women will undergo circuit training, consisting of exercises performed on 7 machines arranged in a circuit. Thanks to the use of adequate software the machines will automatically adjust their parameters, such as seat height or resistance to the exercising person, and the training progress will be individually monitored. The planned training will last for 3 months, during which the patients will exercise 3 times a week for 30 minutes (2 circuits will be done during each session). The planned duration of the training session will be controlled (one minute for strength exercises, four minutes for endurance exercises and a 30-second break between each exercise). In the training group, one-repetition maximum exercise test (1RM) will be performed to determine the appropriate training load and later after the program to verify the increase in muscle strength. The range of maximum heart rate (HRmax) will also be determined in all exercising women. The second group of women, who will be asked to maintain their current level of physical activity and their diet for a period of 3 months will serve as a control group. Before and after the training program in all participants of the study pulse wave velocity, anthropometric parameters and body composition will be assessed. Concurrently venous blood will be taken to determine biochemical indicators related to carbohydrate and lipid metabolism, insulin resistance, vascular endothelium function, inflammation and adipocytokines and myokines. In both groups of women, the questioners concerning dietary intake and the level of daily physical activity will be administered.

Results will be subjected to analysis involving descriptive, and advanced statistic method among them analysis of correlations, regression, variance and cluster analysis. All calculations and statistics will be performed using TIBCO Statistica 13.3 software (TIBCO).

The training program will be performed on 7 machinesin a circuit. The devices will be controlled by a pre-programmed chip card, so that they will automatically adjust their parameters, such as seat height or resistance to the patient, and it will be possible to monitor the training progress of exercising women and their presence during training. Only two people will be allowed in the room during the training. The planned duration of the exercises will be controlled (one minute for strength exercises, four minutes for endurance exercisesand a 30-second break between each exercise) and for each trainee the load will be dosed using the electronic resistance motor system. Exercises in the training program are planned in such a way that the different muscle groups of women exercising are loaded alternately, which will ensure comprehensive training of the whole body. The range of movement, exercise duration and breaks will be controlled automatically by the system and the software of the devices and will not require additional training attention.

In the training group, one-repetition maximum exercise test (1RM) will be performed to determine the appropriate training load and later after the program to verify the increase in muscle strength.

The HR max range will be determined for exercising women by the indirect method using the formula: training HR = 220 -subject age.

The characteristics of exercises in the circuit:

1. The training circuit starts with an exercise on a cycloergometer -"bike", which lasts 4 minutes.
2. The second exercise -"abdominal crunch", shapes the strength of the abdominal muscles and together with exercise number six, it not only improves muscle strength parameters, but also shapes balance and maintains the correct position of the body.
3. The third exercisein a circuit-"leg curl", shapes the muscular strength of the back of the thigh (biceps femoris muscleand muscles adjacent to it).
4. The fourth exercise -"lat pulldown", trains the strength of the latissimus dorsi muscle, shoulder girdle muscles and upper chest. In addition to improving the strength and function of the muscles mentioned above, the exercise also perfectly stimulates the auxiliary respiratory muscles.
5. Fifth exercise -"crosswalker".This exercise trainsmost of the body's muscles, itlasts 4 minutes and, like training on a cycloergometer, primarily shapes thephysical capacity.
6. The sixth exercise -"back extension"trains the strength of the abdominal muscles, erector spinae and other muscles of a back.
7. The seventh exercise -"legabductor", the last in the series, is an exercise that shapes the gluteal muscles, as well as hip adductor and abductor muscles. This exercise fulfills the function of shaping strength and securing the hip joint, by training the muscle parts less frequently used in everyday life, the more difficult to be kept fit as the years go by and the level of physical activity decreases.

Eligibility Criteria:
Inclusion Criteria:

* women,
* age: 25-45years,
* menstruating,
* BMI 18,5-29,9 kg/m2,
* insulin resistance based on HOMA -IR (cut-off point 2.5),
* not contraindicated to physical activity.

Exclusion Criteria:

* type 1 and 2 diabetes,
* poorly controlled hypertension (mean SBP \>140mmHg and/or mean DBP \>90mmHg) over the last month and/or need to modify the pharmacological treatment,
* obesity: BMI \> 30 kg/m2,
* lipid disorders requiring implementation of pharmacological treatment in the last 3 months before or during observation,
* a positive history of ischemic heart disease, carotid atherosclerosis and / or lower limb atherosclerosis,
* clinically significant arrhythmias or conduction disorders,
* chronickidney disease,
* clinically significant liver dysfunction,
* acute or chronic, clinically manifest inflammatory process,
* an acute infection in the last month,
* cancer,
* taking dietary supplements within a month before inclusion and during observation,
* taking medication that could interfere with the results of the tests,
* other conditions that may pose any risk to the patient during the observation.