Losing body fat is one thing. Losing fat while keeping the muscle that helps you stay strong and active is another, especially as you get older. Research suggests that one particular type of exercise may have an advantage when it comes to achieving both goals, shifting the focus of healthy aging away from simple weight loss toward the preservation of vital lean tissue.
High-intensity interval training (HIIT), which involves alternating short bursts of demanding exercise with easier recovery periods, may be especially helpful for older adults who want to reduce fat without sacrificing lean muscle. While many forms of physical activity can help shed pounds, preserving the underlying musculoskeletal framework remains a critical challenge in gerontology and physical health.
In a study published in Maturitas, researchers from the University of the Sunshine Coast compared three different exercise intensities to determine their physiological impacts. Although participants across all groups experienced modest fat loss over the course of the trial, HIIT stood out for its unique ability to reduce fat while maintaining lean tissue intact.
"We found that high, medium and low intensity exercises all led to modest fat loss but only HIIT retained lean muscle," said lead author and exercise physiologist Dr. Grace Rose of the University of the Sunshine Coast.
The results highlight an important distinction in healthy aging: losing weight is not necessarily the same as improving body composition. While bathroom scales measure total mass, they fail to differentiate between a loss of stubborn fat and a depletion of functional muscle tissue.
Six Months of Exercise Revealed a Key Difference
The Australian research team investigated how workout intensity affects body composition, meaning the proportions of fat, muscle, and other tissues that make up the human body. Understanding these shifts is vital for designing effective fitness interventions for older populations.
A total of 123 healthy older adults from the Greater Brisbane region participated in the trial. Their average age was 72, and their average body mass index was approximately 26kg/m2, which the researchers described as normal for adults over the age of 65.
Participants completed three supervised gym sessions each week for six months. Each session lasted 45 minutes, and participants were assigned to high-intensity intervals, moderate-intensity exercise, or a low-intensity comparison group to evaluate comparative outcomes.
To track changes accurately, researchers measured body composition at the beginning of the study, after three months, and again at the six-month mark. They used a specialized scanning technique that estimates fat and lean tissue throughout the body with a high degree of precision.
The findings revealed that exercise intensity made a significant difference in how the body responded to the physical demands. Both high- and moderate-intensity training significantly reduced fat mass, producing larger improvements than those seen in the low-intensity group. However, the two more demanding approaches differed notably in their effects on lean tissue.
"While moderate training reduced fat mass, it also caused a small decline in lean muscle," Dr. Rose noted.
Participants performing HIIT, meanwhile, reduced fat without experiencing the same decline in lean mass. This preservation could be particularly valuable later in life, when maintaining muscle becomes increasingly important for preserving physical independence. Strong muscles help people climb stairs, get out of chairs, maintain balance, and carry out everyday activities safely and effectively.
One important distinction to keep in mind is that the scans measured lean tissue rather than muscle strength directly. Lean mass includes muscle but also other tissues and water, so changes in these measurements do not necessarily translate into equivalent changes in strength.
High-Intensity Exercise Also Reduced Abdominal Fat
The researchers found another potentially important benefit involving fat stored around the middle of the body, a region particularly vulnerable to metabolic complications with age.
"Both high and moderate intensities improved the composition of weight carried around the middle. Further analysis is needed of the low intensity results," Dr. Rose explained.
The original study found improvements in visceral adipose tissue among both the high and moderate intensity groups. Visceral fat is fundamentally different from the subcutaneous fat that sits directly beneath the skin. It accumulates deeper in the abdomen, surrounding internal organs such as the liver and intestines.
Excessive amounts of this visceral fat have been linked to insulin resistance, cardiovascular disease, and other metabolic problems that pose serious health risks for aging populations. According to Dr. Rose, these findings matter because body composition can influence the development and progression of chronic diseases as people age.
While overall body weight and body mass index provide useful general information, they do not reveal how much fat or muscle a person actually carries, or where that fat is stored anatomically. Someone who loses fat while maintaining muscle may experience a more favorable change in body composition than someone who loses a similar amount of weight along with valuable lean tissue.
Still, the original researchers emphasized that the improvements observed were relatively small. They cautioned that the differences were not clearly clinically meaningful when compared with lower intensity exercise, particularly after accounting for measurement uncertainty and individual biological variation.
Why HIIT May Help Aging Muscles Stay Strong
One possible explanation for HIIT’s advantage lies in the unique way it challenges the physiological systems of the body. Rather than exercising at the same steady pace throughout a workout, HIIT repeatedly pushes the cardiovascular system and working muscles through periods of intense effort, followed by easier recovery activity.
University of the Sunshine Coast Associate Professor of Physiology and study co-author Mia Schaumberg explained how the training protocol worked in practice.
"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," Professor Schaumberg said. "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."
This physiological explanation is consistent with the established scientific principle that muscles adapt specifically to the demands placed upon them. When exercise provides a sufficiently challenging stimulus, the body has a stronger evolutionary and biological reason to maintain the tissues needed to perform that demanding activity.
Muscle preservation is especially important because aging is often accompanied by a gradual, natural decline in muscle mass and strength. In more advanced cases, this degenerative process can contribute to sarcopenia, a condition characterized by reduced muscle strength and quantity that can severely interfere with mobility and long-term independence.
Professor Schaumberg said the original research could help people make more informed decisions about exercise and healthy aging strategies. When the university publicized the findings, she also highlighted their broader relevance to people setting fitness and wellness goals.
"With the festive season now behind most of us and New Year’s resolutions in full swing, this research can help inform people’s plans for healthy aging," she said. The research involved collaborators from UniSC’s Healthy Ageing Research Cluster and The University of Queensland.
More Recent Studies Reveal Additional Benefits of HIIT
Subsequent research has provided further insight into how HIIT affects older adults, although it also suggests that intense workouts are not necessarily superior in every physiological situation or demographic group.
One study investigated whether older adults could benefit from completing HIIT at home with remote supervision. The study involved 20 adults aged 61 to 74 who exercised using a specialized machine that let them work their arms and legs without bearing their full body weight. After eight weeks of targeted training, participants had lost an average of approximately 1.4 kilograms, or about 3 pounds, of fat mass, while their overall aerobic fitness improved substantially.
Participants completed 96 percent of their scheduled workouts during the trial, and the researchers reported no exercise-related adverse events. Although the trial was relatively small, its findings suggest that appropriately supervised HIIT programs may offer substantial benefits outside of a conventional gym setting.
Another randomized trial compared HIIT with continuous moderate-intensity exercise in older adults living with HIV. In that study, participants completed 16 weeks of exercise, with both groups also performing supplementary resistance training. Unlike the original Australian study, both exercise groups experienced reductions in fat and increases in lean mass, and researchers found no statistically significant difference between the two groups in those body composition changes.
These contrasting results suggest that workout intensity is not the only factor that matters in physical conditioning. Resistance training, which challenges muscles through weights or other forms of external resistance, may also play a crucial role in helping to preserve or increase lean tissue regardless of aerobic interval intensity. Because the populations and training programs differed across these investigations, the findings should not be treated as a direct contradiction of the Australian results.
Is HIIT Really the Best Exercise for Older Adults?
A broader scientific review published in the Journal of Clinical Medicine offers additional perspective on the matter. Researchers examined 25 reports involving approximately 2,818 participants to assess how HIIT and other forms of interval training affect older adults across various metrics.
The most consistent benefits identified in the review involved cardiovascular fitness, including significant improvements in the body’s ability to utilize oxygen efficiently during sustained exercise. Some studies also reported notable improvements in physical function and metabolic health. However, the review did not establish that HIIT was consistently superior to moderate-intensity exercise across every measured health indicator.
The researchers noted that differences between exercise programs, participant characteristics, and study methods made it difficult to identify a single optimal training approach for every individual. Taken together, the findings suggest that HIIT can be a useful tool for healthy aging, but it is not the only way to improve fitness or protect vulnerable muscle mass.
For adults over the age of 65, public health guidelines from organizations like the Centers for Disease Control and Prevention recommend a balanced combination of aerobic exercise, muscle-strengthening activities, and exercises that improve balance and stability. Higher intensity workouts may be entirely appropriate for some older adults, but individuals who are currently inactive or managing underlying medical conditions may benefit from gradually building up their fitness levels and seeking professional medical guidance before beginning a demanding exercise program.
The central message from the Australian study remains compelling for those navigating physical fitness later in life: what happens to muscle during fat loss may be just as important as the absolute amount of weight someone manages to lose. HIIT showed notable promise because it helped participants reduce body fat while actively maintaining lean tissue. Combined with newer findings, the research reinforces the value of exercise programs that support not just a lower number on the scale, but also the strength, fitness, and physical function essential for healthy aging.
