Scientists have assessed the effect of one intense workout per week on obesity

One interval training session per week helped sedentary adults with abdominal obesity reduce their body fat in 16 weeks. A decrease was also observed in those who divided the same workload into three classes. In terms of endurance, the advantage of three workouts was shown in an additional analysis. The information about how long the lesson took and what results were preserved after the completion of the program is in the Izvestia material.

How the experiment was set up

The University of Hong Kong team enrolled 315 overweight and abdominal obese adults in the trial. This is the name given to the excessive accumulation of adipose tissue in the abdominal area. Prior to the start of the experiment, the participants led a sedentary lifestyle. Their average age was 48 years, and their average body mass index was 28.7 kg/m. The volunteers were randomly assigned to three equal groups.

Two groups worked out on a treadmill under the supervision of trainers. The program included four weeks of gradual adjustment to the workload. The participants then completed three 25-minute blocks per week. In each block, periods of intensive work alternated with active recovery. Some completed all three blocks in one visit with breaks, while others distributed them over three days. For each participant, the intensity was selected based on the results of a stress test. The control group attended health classes.

In both training groups, 75 minutes per week were allocated for interval blocks. These minutes included periods of active recovery within the block. During one visit, the participants also took two breaks of 15-30 minutes each. The blocks and pauses themselves took from 105 to 135 minutes, with a warm-up and a hitch.

According to the authors' calculations, taking into account the road and classes, participants spent an average of about 4.5 hours per week with one visit and 8.2 hours with three. The main savings were provided by reducing the number of trips to the center.

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What has changed in four months

The main indicator was the total mass of adipose tissue. It was determined by the method of dual-energy X-ray absorptiometry. This scan allows you to assess body composition, including fat and fat-free mass. After 16 weeks, the adjusted difference with the control group was about 0.8 kg of fat in those who exercised once a week and 1 kg in those who exercised three times. Waist circumference also decreased in both groups.

The difference in fat mass between the training groups themselves turned out to be statistically insignificant. The sample size was calculated primarily to identify the effect of classes compared with the control group. To determine whether the two modes can be considered equivalent or whether one of them provides a slight advantage, an experiment designed specifically for such a comparison is needed.

Weight and body mass index were also measured. A statistically significant difference with the control group in both indicators was found only in those who exercised three times a week. This is a separate result. The scales show the total body weight, while the scan allows you to estimate how much fat is in it. The authors also checked blood pressure, fasting glucose, and blood lipids. There were no significant differences between the groups.

Why was endurance assessed separately

The researchers tested how the heart, lungs and muscles cope with physical exertion. To do this, we measured how much oxygen the body is able to use during a stress test. By the end of the program, cardiorespiratory endurance increased by an average of about 6% for those who exercised once a week and 11% for those who exercised three times.

Both groups improved this indicator compared to the control group. In the main analysis, there was no statistically significant difference between the training modes. The advantage of the three classes appeared after additional adjustments, including age, baseline activity, and attendance. According to Columbia University physiologist Keith Diaz, who commented on the work for Popular Science, more frequent exercise can give the heart, blood vessels and muscles more opportunities to adapt.

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What remained after the end of classes

After another 16 weeks, when the organized program had already ended, both training groups had a smaller waist than the control group. The group with three sessions retained an advantage in endurance relative to control. There was no statistically significant difference in total body fat between the groups at this point. A separate question for further work is whether people manage to maintain the selected schedule on their own and save changes for years.

The participants of the Hong Kong test were pre-selected, mastered the load gradually and studied under supervision. The researchers did not register any undesirable phenomena related to the program. On average, the participants' glucose and blood pressure levels were relatively good at the start. The effect of this regimen on complications of obesity, including type 2 diabetes, still needs to be tested.

What is known about the load in one or two days

In another paper published in JAMA in 2023, scientists examined data from almost 90,000 participants in the British biobank. People who gained the bulk of their weekly workload in one or two days were less likely to experience a heart attack and stroke than participants who gained less than 150 minutes of moderate or intense activity per week. A similar relationship was observed in those who distributed the load more evenly. The researchers tracked people's habitual activity, so separate data is needed to assess the impact of a specific interval training regimen on the risk of heart attack and stroke.

The World Health Organization recommends that adults gain 150-300 minutes of moderate-intensity or 75-150 minutes of high-intensity aerobic activity per week. Additionally, the recommendations provide exercises for the main muscle groups at least two days a week. The Hong Kong experiment provides an answer to a narrower question. With the same interval training time and the support of a trainer, even those who came to the gym one day a week managed to notice a moderate decrease in body fat.