0.8 kg: the once-a-week workout headline, checked

A study from January made headlines again this month, focusing on whether one workout per week can help reduce belly fat. It’s worth taking a closer look than most coverage did.

What?

Researchers led by Parco Siu in Hong Kong assigned 315 inactive adults with central obesity to 3 groups: one group performed one workout a week, another performed 3, and the third attended health education classes. After 16 weeks, the once-a-week group lost 0.8 kg of fat compared to the control, while the 3-times-a-week group lost 1.0 kg. The difference between the 2 exercise groups was too small to be significant. Both groups reduced their waist size by about 2 cm. The study was published in Nature Communications.

There are two important details that most reports missed. The exercise involved supervised treadmill sessions: 4 intervals of 4 minutes each at 85-95% of peak heart rate, with 3 minutes of easy walking between intervals. For the once-a-week group, the session meant doing 3 of these blocks in a row with rest breaks, making it almost 2 hours at the gym, not just a long walk.

So what?

The main difference between the groups was in fitness. The once-a-week group improved their VO2 peak by 1.5 ml/kg/min, while the 3-times-a-week group improved by 2.6. 16 weeks after the training ended, only the 3-times-a-week group still had better fitness than the control group. By then, the fat loss was gone, but both groups kept their smaller waists.

I’ve said before that VO2 max is the best measure of how long you’ll live and how well you’ll function. From that perspective, the headline is only partly true. The once-a-week plan matched the others for fat loss, but it didn’t keep up in fitness; fitness was the lasting benefit at week 32.

The other side is important too. For living longer, how you spread out your workouts might not matter much. A 2025 review of 21 studies found that people who exercise only on weekends and those who exercise more regularly both experienced similar reductions in death rates. If you can only fit in one session a week, it’s still worth doing.

The real difference came from working at 85-95% of your peak heart rate.

Now what?

Try the workout as it was tested: start with 5 minutes of easy effort, then do 4 rounds of 4 minutes hard and 3 minutes easy, and finish with another 5 minutes of easy effort. The whole session takes about 35 minutes.
‘Hard’ means you shouldn’t be able to finish a sentence. If you can talk easily during the 4-minute intervals, you’re not pushing hard enough. You don’t need a heart rate monitor for this.
Aim for 3 sessions a week if you can, since that group kept their fitness gains. The study didn’t test 2 sessions a week, so I can’t speak to that.
If your week gets busy, still try to fit in at least one session. Even one workout was better than just attending the education class.
Don’t let the scale be your only measure. Choose a set route or stairwell, time yourself today, and check your progress again in 8 weeks.

8 weeks from today is October 7. Mark your calendar for your retest.

Stay healthy.

Andre

Editor's note

Editorial clarification and evidence update

The Upward ARC is an educational newsletter for a general audience, not a medical publication. It may use ordinary-language metaphors and simplifications to make complex evidence readable. Those phrases are not clinical terminology. The editorial standard remains unchanged: do not fabricate, cite falsely, hide important uncertainty, or simplify a point so far that it changes the practical meaning.

Updated August 13, 2026. The historical edition above remains unchanged.

The 35-minute protocol: The 35-minute session in the action list was the study's three-times-weekly session. The once-weekly group completed three 25-minute HIIT bouts, separated by 15 to 30 minute breaks, in one supervised visit. Participants had a maximal cardiopulmonary exercise test, progressed over 4 weeks, trained with certified instructors and wore continuous heart-rate monitors. The study did not test an unsupervised 35-minute once-weekly plan without a monitor. [1]

What the frequency comparison can show: The primary fat-mass difference between the once- and three-times-weekly groups was not statistically significant. The trial was not powered to establish that the schedules were equivalent. At week 32, fat mass was no longer different from control, waist circumference remained lower in both exercise groups and only the three-times-weekly group remained fitter than control. [1]

The weekend-warrior mortality evidence: The 21-study review pooled observational studies in which activity was concentrated into 1 or 2 days. The result supports similar mortality associations for weekend-warrior and regularly active patterns compared with inactivity. It does not show that one 35-minute session reduces mortality, and the observational evidence cannot prove that the schedule caused the lower death rate. [2]

The intensity claim: The trial compared one versus three weekly sessions while holding the weekly HIIT dose at 75 minutes. It did not compare 85 to 95 percent of peak heart rate with moderate-intensity exercise. The study therefore cannot establish that high intensity was the reason for the outcomes. [3]

What VO2 peak predicts: Cardiorespiratory fitness, often measured through VO2 max or VO2 peak, is a strong predictor of mortality and future disease across cohort research. It is not a direct measure of how long an individual will live or function. The certainty of the 2024 overview ranged from very low to moderate across outcomes. [4]

References

For informational and educational purposes only. This page does not provide individual medical advice, diagnosis, or treatment. Read the full medical disclaimer.