The Signal

Time of day may make small difference in workout results


Dear Doctors: I’m a 33-year-old woman in good health. The problem is that I got into some bad habits during the pandemic and gained weight. I’m back on track with diet, and now I am adding exercise. I remember reading that the time of day that women exercise makes a difference. Is that true?

Dear Reader: We think you’re referring to the results of a study that made headlines last spring. The findings are intriguing in that they suggest that the optimal time of day to exercise may be different for women than it is for men.

The 12-week study, which was published in the journal Frontiers in Physiology, included results from 27 women and 20 men between the ages of 25 and 55. All were in good health, had comparable body mass indexes and were already physically active when the study began. The participan­ts were randomly divided into two groups. Each group followed the same exercise regimen, which included stretching, endurance exercises, resistance training and interval sprints. They also all ate the same diet, and at the same times of day.

The only difference between the two groups was the time of day at which they were asked to exercise. The morning group worked out for an hour and ended their sessions by 8:30 a.m. The evening group also exercised for one hour, but between 6 and 8 p.m. Over the course of the study, the researcher­s took regular blood pressure readings and measured changes in body fat percentage. An assessment of each person’s strength, aerobic capacity and flexibilit­y was made at the start and the conclusion of the study.

At the end of 12 weeks, each of the participan­ts saw an increase in athletic performanc­e, as well as improvemen­ts to measures of general health, including body fat percentage and blood pressure. But the results included a surprise. It turned out that the women in the group who completed their one-hour exercise sessions before 8:30 a.m. burned more body fat, particular­ly around the abdominal region, than did those whose workouts took place in the evening. The opposite proved to be true for the men. Those whose exercise sessions took place between 6 and 8 p.m. burned more body fat than their early-morning counterpar­ts. Meanwhile, the women with the late-day exercise schedule saw greater gains in upperbody strength. They also reported improvemen­ts to mood, as well as to hunger and satiety, that were not seen in the morning group. For the men, improvemen­ts to mood occurred no matter when they exercised.

These results bolster the idea that time of day has an impact on exercise for women and men. However, this is a small study and can’t be considered conclusive.


Dear Doctors: I’m having hand surgery next year to help with carpal tunnel, and I’m not thrilled about having anesthesia. I’ve been reading about surgeons whose patients use virtual reality headsets to need less anesthesia. Does that really work?

Dear Reader: The use of anesthesia during surgical procedures dates back to antiquity. The historical record shows that the Incas used extracts of plants like datura and coca to reduce pain and induce unconsciou­sness, and early Chinese physicians offered patients opium-laced potions. Centuries later, efforts to refine and improve the process continue. And small wonder.

Anesthesia is a complex practice with multiple, and sometimes conflictin­g, objectives. The treatment must sedate the patient and suppress their pain response but not interfere with the body’s critical physiologi­cal functions, including heartbeat, breathing and maintainin­g steady blood pressure. While modern anesthesia is safer than ever before, it still carries an element of risk. That’s why research into novel drugs and new techniques continues.

For the past several years, that research has included inquiries into the use of virtual reality, or VR, as an add-on therapy. This approach is being explored in conjunctio­n with what is known as regional anesthesia. Unlike general anesthesia, where the patient is completely unconsciou­s, someone undergoing regional anesthesia is sedated, but remains conscious. Nerve blocks are used to inhibit sensation from a specific and limited part of the body.

Because the patient remains awake during regional anesthesia, managing their stress and anxiety is crucial. Many patients receive sedation so they can relax or even doze off during the procedure. With the advent of computerge­nerated virtual reality, which uses special headsets to plunge the user into an immersive 3D world, researcher­s began to wonder if it might lessen a surgical patient’s need for sedation.

The most recent study into this idea yielded intriguing results. Over the course of eight months, researcher­s at a medical center in Boston evaluated the anesthesia needs of 34 patients who were undergoing hand surgery. The patients were divided into two groups. All received drugs to completely block pain response, and all received intravenou­s sedation. But one group was also given VR headsets with a selection of programs specially designed to promote relaxation and a sense of calm.

At the end of the study, the data showed that the patients who used VR headsets during their surgery needed markedly less sedation than did the Vr-free control group. Additional­ly, the post-surgical recovery period for the VR group, during which patients wait for the effects of sedation to wear off, was significan­tly shorter.

Eve Glazier, M.D., MBA, is an internist and associate professor of medicine at UCLA Health. Elizabeth Ko, M.D., is an internist and assistant professor of medicine at UCLA Health. Send your questions to askthedoct­, or write: Ask the Doctors, c/o UCLA Health Sciences Media Relations, 10960 Wilshire Blvd., Suite 1955, Los Angeles, CA, 90024.


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