Study design
A randomized study, with a control group, two parallel experimental groups, and a single-blind design (the laboratory expert was blind), was performed on sedentary adults. The goal of the study was to investigate the effects of 18 sessions of EMS training on the physical and some adipokines serum of overweight individuals. At first, the participants were introduced to the research implementation process. They were informed about the benefits and potential risks of the study, signed a consent form, and pre-tests including anthropometric and performance tests were taken. By using the block randomization way (size 6), the participants were allocated to three groups. Subsequently, the subjects were engaged in 18 training sessions and the post-tests were repeated.
Participants
Sedentary and overweight adults (25-40 years) who were eligible to participate in this study were recruited by distributing leaflets in two areas of Tehran, Iran. The inclusion criteria were overweight individuals aged 25-40 years, having no acute and chronic cardiovascular or orthopedic diseases; and having not received drugs or medication. The exclusion criteria were the absence in more than three consecutive sessions, the unwillingness to continue training, and not taking post-tests. A sample size calculation was conducted using G*Power Software version 3.1.9.6 (15) for analysis of covariance (ANCOVA), using a rejection criterion of 0.05 and 0.8 (1-beta) power, and large effect (f=0.5), 42 participants needed. Forty-four eligible adults volunteered to attend this study, but the data of 38 individuals (age: 31.7 ±4.7 years; height: 171.1 ± 9.2 cm, body mass: 86.1 ± 14.9 kg) was analyzed finally. Using the block randomization method, a third person who was not in the research team, randomly assigned participants into three groups, including the EMS group (EMS, n=13), the traditional exercise group (TE, n=13), and the control group (C, n=12). Six participants were excluded due to not being interested in continuing the intervention and did not complete the post-test.
Training protocol
The training protocol lasted six weeks, three sessions per week (18 workouts). Each session was around 30 minutes, including 5 minutes of warm-up with dynamic movements, 20 minutes of main exercises, and five minutes for cool down with stretching movements. The EMS group performed dynamic exercises while receiving electrical stimulation with endurance and resistance frequencies (XBody PRO, Hungary). They received 10 minutes of resistance stimulation (30 Hz, 350 μs, 4 s of strain 6 s rest) and 10 minutes of endurance stimulation (85 Hz, 350 μs, 6 s of strain, 4 s of rest) (16). At first, the subjects were instructed to wear an ensemble that included a black T-shirt and shorts. Then, they wore the special vest, which contained electrodes in the areas of the arms, backs, chests, abdomens, thighs, and gluteal. The electrodes were previously wet with water to facilitate the conduction of the electric current. The electrodes are capable of simultaneously activating 18 regions or 10 muscle groups. The intensity level was adjusted for specific muscle groups and gradually increased throughout the intervention, which was recorded on a device for the next session. The EMS protocol was carried out without external loads, performing dynamic exercises (such as squats, trunk flexion, lunges, lateral raises, arm curls, isometric abdominal contractions, and …). All movements were performed at low intensity in the standing position to allow a voluntary contraction simultaneously with the electrical stimulation.
The TE group also performed traditional exercises for 20 minutes (plus 10 minutes for warming up and cooling down). Ten minutes of traditional resistance training was performed in two sets, 10 repetitions, with 50-60% of one maximum repetition with 20 seconds of rest between sets. The movements for large muscle groups were chest press, leg press, shoulder press, leg curl, lat down, and crunches. Then, they ran on the treadmill for 10 minutes at a speed of 7-7.5 and 10-11 km/h alternately, based on their fitness. The training intensity was monitored using the Borg scale, a 10-point scale. The C group did not attend any exercise training and continued their routine life; they participated in the pre and post-tests.
Measurements
Anthropometric indices
Anthropometric and performance indices were taken before and after the training protocol. Height and body mass were measured using a standard stadiometer (Seca 213, Germany) and a calibrated digital scale (Seca 769, Germany). Body mass index (BMI) was determined by the body mass divided by the square of the body height and is expressed in units of kg/m2. Abdominal and arm subcutaneous fat was measured using a caliper (Harpenden, USA) according to the standard protocol on the right side.
Aerobic test
Subjects performed a researcher-designed aerobic incremental test on a treadmill. They started at a speed of 5 km/h and every 2 minutes, one kilometer was added to the speed until the subjects were exhausted. The running time was recorded and used to perform statistical tasks.
Muscle endurance
The push-up is a test for the assessment of upper body endurance. The starting position was with the hands and toes touching the floor, the body and legs in a straight line, feet slightly apart, and the arms at shoulder-width apart. In this position, by keeping the back and knees straight, the subject lowers the body to make a 90-degree angle at the elbows, then returns to the starting position with the arms extended. The number of complete movements during one minute was counted.
The endurance of the abdominal muscles was measured by a sit-up test. Subjects lay on a mattress while their knees bent at approximately right angles. The hands touched the shoulders crosswise. Then, with the contraction of the abdominal muscles, they raised to touch their elbows to their knees and returned to the starting position. The number of correct movements during one minute was recorded.
Blood sampling
Blood samples were collected from the antecubital venous after a night of fasting at 8-8:30 am before and after the interventions. Blood samples were centrifuged at 3000 rpm for 15 minutes, and serum was separated from the blood samples using a suspension technique and stored at a –20 °C freezer. Serum resistin and adiponectin were measured using an enzyme-linked immunosorbent assay (ELISA) kit (RK00139, ZwllBio, Germany). The enzyme colorimetric method using an automatic analyzer (Abbott, Model Alcyon 300, and USA) with Pars-Azmoon Kit was used to measure fat profile (HDL, and triglyceride). Total cholesterol (TC) levels were determined by the enzymatic spectrophotometric method using an auto-analyzer with Pars-Azmoon Kit (Tehran, Iran). LDL was calculated by the Friedewald formula (LDL=TC− (TG/5 + HDL).
Statistical analysis
Data presented in mean ± standard deviation (SD). The post-intervention values between groups were compared using a one-way analysis of covariance (ANCOVA) with pre-test values included as covariates. First, the assumptions of the normal distribution of data using Shapiro-Wilk’s test, homogeneity of variance by box plot test, and homogeneity of regression slopes were confirmed. When significant differences were found in the intergroup, Bonferroni posthoc tests were performed. The effect size (ES) was calculated by partial Eta Squared (ηp²). ES was considered as a small <0.20; a moderate ES was between 0.21-0.50; a large ES was 0.51-0.8 and a very large ES was >0.80. The significance level was set at p≤0.05 for all statistical analyses and we used the Statistical Package of Social Sciences (SPSS, IBM, v19) to analyze data.