According to a new study of more than 120 healthy older adults that compared the effects of different exercise intensities on body composition, high-intensity interval training (HIIT) was the only workout to preserve muscle while supporting fat loss.
What did the study find?
During the six-month study period, participants were randomly assigned to one of three supervised exercise groups – low (which acted as the ‘active control’), moderate and high intensity. All three groups did their assigned 45-minute workout three times a week, and body composition was measured using DEXA scans at baseline, three months and six months.
The assigned workouts were as follows:
Low-intensity training Continuous treadmill exercise performed at 50-55% of maximum heart rateModerate-intensity continuous training (MICT)Continuous treadmill exercise performed at 70-75% of maximum heart rateHIIT10-minute warm-up4 intervals of 4 mins at 85-95% of maximum heart rateEach interval separated by 3 mins of active recovery at 50-70% of maximum heart rateCool-down
The researchers found that while both the moderate- and high-intensity workouts significantly reduced fat mass, HIIT was the only one to do so while preserving muscle; in the moderate-intensity group, there was a small but significant decline in lean mass.
What does this mean for us?
Preventing muscle decline as we age is crucial for overall health and longevity; our muscles support healthy movement and function, regulate blood sugar and even affect brain function.
(Peri)menopausal women are also at further risk of sarcopenia – age-related muscle loss – due to fluctuations and eventual decline in oestrogen, the sex hormone that plays a key role in supporting bone and muscle strength. So, any workout that supports muscle maintenance and a healthy body composition is useful, particularly if (sustainable) fat loss is a goal.
Why is this HIIT workout effective?
‘HIIT likely works better because it puts more stress on the muscles, giving the body a stronger signal to keep muscle tissue rather than lose it,’ explained study co-author Mia Schaumberg of the findings.
‘High-intensity training in this study involved repeated short bursts, or intervals, of very hard exercise – where breathing is heavy and conversation is difficult – alternated with easier recovery periods.’
The HIIT workout in this study actually mirrors the classic 4×4 Norwegian HIIT protocol, which, as well as being widely used in exercise physiology research and by athletes, is also a popular workout among celebs, including Elsa Pataky and Jessica Biel.
An extensive body of research has shown the method to be highly effective for improving VO2 max – how aerobically fit you are – a metric experts say is one of the most powerful single predictors of all-cause mortality.
The bottom line
Back to the new findings on muscle preservation, however, this is just one study, and the researchers highlight that the differences in lean mass between the exercise groups were small, despite being statistically significant. More studies are needed.
It’s also important not to overdo HIIT and to perform it as part of a varied exercise routine that, crucially, includes strength training and nourishing nutrition.
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Hannah Bradfield is a Senior Health and Fitness Writer for Women’s Health UK. An NCTJ-accredited journalist, Hannah graduated from Loughborough University with a BA in English and Sport Science and an MA in Media and Cultural Analysis. She has been covering sports, health and fitness for the last five years and has created content for outlets including BBC Sport, BBC Sounds, Runner’s World and Stylist. She especially enjoys interviewing those working within the community to improve access to sport, exercise and wellness. Hannah is a 2024 John Schofield Trust Fellow and was also named a 2022 Rising Star in Journalism by The Printing Charity. A keen runner, Hannah was firmly a sprinter growing up (also dabbling in long jump) but has since transitioned to longer-distance running. While 10K is her favoured race distance, she loves running or volunteering at parkrun every Saturday, followed, of course, by pastries. She’s always looking for fun new runs and races to do and brunch spots to try.