TOKYO —

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. 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.

Groundbreaking Australian Study Highlights HIIT’s Unique Benefits for Healthy Aging

A pivotal study, published in the esteemed journal Maturitas, has illuminated a significant advantage of high-intensity interval training (HIIT) for older adults seeking to improve their body composition. Researchers from the University of the Sunshine Coast (USC) in Australia conducted a comprehensive six-month trial comparing the effects of different exercise intensities on body fat and lean muscle mass in healthy older adults. The findings indicated that while all exercise intensities tested led to some degree of fat loss, only HIIT demonstrated a remarkable ability to preserve lean muscle tissue.

"We found that high, medium, and low intensity exercises all led to modest fat loss, but only HIIT retained lean muscle," stated lead author and exercise physiologist Dr. Grace Rose of the University of the Sunshine Coast. This distinction is critical, as it underscores the difference between simply losing weight and achieving a healthier, more functional body composition, particularly as individuals age.

The Six-Month Trial: A Detailed Examination of Exercise Intensity and Body Composition

The Australian research team’s investigation delved into how workout intensity impacts body composition, a crucial metric that defines the proportions of fat, muscle, and other tissues making up the body. The trial, which commenced in early 2023 and concluded in early 2024, involved 123 healthy older adults residing in the Greater Brisbane region. The average age of participants was 72 years, with an average body mass index (BMI) of approximately 26 kg/m², a range considered normal for adults over 65 by the researchers.

Over a period of six months, participants engaged in three supervised gym sessions per week, each lasting 45 minutes. These sessions were meticulously designed, with participants randomly assigned to one of three groups: a high-intensity interval training group, a moderate-intensity exercise group, or a low-intensity comparison group. To meticulously track changes in body composition, researchers employed a specialized scanning technique at three key intervals: at the commencement of the study, after three months, and finally at the six-month mark. This advanced scanning method provided precise estimations of fat and lean tissue distribution throughout the entire body.

Unveiling the Intensity Divide: Fat Loss vs. Muscle Preservation

The results of this rigorous trial revealed a clear correlation between exercise intensity and its impact on body composition. Both high- and moderate-intensity training regimens proved effective in significantly reducing fat mass, yielding greater improvements than those observed in the low-intensity group. However, a crucial divergence emerged when examining the effects on lean tissue.

"While moderate training reduced fat mass, it also caused a small decline in lean muscle," Dr. Rose explained. This finding is particularly concerning for older adults, as a loss of lean muscle can compromise strength, mobility, and overall independence. In contrast, participants who underwent HIIT sessions not only reduced their fat mass but also maintained their lean muscle mass without experiencing the same decline.

This preservation of lean muscle is exceptionally valuable later in life. Strong muscles are fundamental for maintaining physical independence, facilitating everyday activities such as climbing stairs, rising from chairs, preserving balance, and carrying out essential daily tasks. It is important to note that the study’s scans measured total lean tissue, which includes muscle, water, and other non-fat components. Therefore, while changes in lean mass are indicative, they do not directly equate to equivalent changes in muscle strength.

Beyond Fat Loss: HIIT’s Impact on Abdominal Fat

Adding to its impressive profile, HIIT also demonstrated a significant benefit in reducing abdominal fat, a particularly concerning area of fat accumulation due to its association with metabolic health risks. The researchers observed improvements in the composition of weight carried around the middle in both the high- and moderate-intensity training groups. Further analysis was ongoing for the low-intensity group’s results.

The original study specifically noted improvements in visceral adipose tissue among participants in both the high and moderate intensity groups. Visceral fat, distinct from subcutaneous fat found directly beneath the skin, accumulates deeper within the abdomen, surrounding vital internal organs such as the liver and intestines. Excessive visceral fat is a well-established risk factor for insulin resistance, cardiovascular disease, and a spectrum of other metabolic health issues.

Dr. Rose emphasized the broader implications of these findings, stating, "These findings matter because body composition can influence the development and progression of chronic diseases as people age." While general metrics like body weight and BMI offer useful insights, they fail to provide a nuanced understanding of an individual’s fat and muscle distribution. An individual who successfully reduces body fat while preserving lean muscle mass may experience a more favorable shift in body composition compared to someone who loses a similar amount of weight but sacrifices valuable lean tissue.

However, the original researchers also cautioned that the observed improvements, while statistically significant, were relatively modest. They noted that the differences, particularly when accounting for measurement uncertainties, were not clearly clinically meaningful when compared to lower-intensity exercise. This nuanced perspective is crucial for setting realistic expectations for individuals engaging in exercise programs.

The Physiological Underpinnings of HIIT’s Efficacy

The enhanced ability of HIIT to challenge the body is a likely explanation for its advantage in preserving muscle mass. Unlike steady-state cardio, HIIT involves repeated cycles of intense effort followed by periods of recovery. This dynamic approach places greater demands on the cardiovascular system and working muscles.

Associate Professor of Physiology at USC and study co-author, Mia Schaumberg, elaborated on the mechanism: "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. 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 explanation aligns with the principle of adaptation: muscles respond to the demands placed upon them. When exercise provides a sufficiently challenging stimulus, the body has a greater incentive to maintain the tissues necessary to perform that activity. Muscle preservation is particularly vital as aging is often associated with a natural decline in muscle mass and strength, a condition that can lead to sarcopenia. Sarcopenia, characterized by reduced muscle strength and quantity, can significantly impair mobility and independence in older adults.

Professor Schaumberg highlighted the practical relevance of this research, stating, "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 in 2026." The original research was a collaborative effort involving researchers from UniSC’s Healthy Ageing Research Cluster and The University of Queensland.

Emerging Research and Broader Perspectives on HIIT for Older Adults

Further research emerging in 2026 has continued to explore the multifaceted benefits of HIIT for older adults, while also emphasizing that intense workouts are not universally superior in every context.

A 2026 study published in Medicine & Science in Sports & Exercise investigated the feasibility and efficacy of home-based HIIT programs with remote supervision for older adults. This trial involved 20 participants aged 61 to 74 who utilized specialized exercise machines allowing them to work their arms and legs without bearing body weight. After an eight-week training period, participants experienced an average fat mass reduction of approximately 1.4 kilograms (about 3 pounds) and a substantial improvement in aerobic fitness. Notably, adherence to the program was high, with participants completing 96 percent of scheduled workouts and reporting no exercise-related adverse events. While this was a small trial, its findings suggest that appropriately supervised HIIT programs can offer significant benefits outside of traditional gym settings.

Another 2026 randomized trial, published in The Journals of Gerontology, Series A: Biological Sciences and Medical Sciences, compared HIIT with continuous moderate-intensity exercise in older adults living with HIV. In this study, participants engaged in 16 weeks of exercise, with both groups also incorporating resistance training. In contrast to the initial Australian study, both exercise groups in this trial achieved reductions in fat mass and increases in lean mass, with no statistically significant differences between the two groups regarding these body composition changes. These results suggest that while intensity plays a role, resistance training—which challenges muscles through weights or other forms of resistance—may also be a critical component in preserving or enhancing lean tissue. The differences in study populations and training protocols mean these findings should be viewed as complementary rather than contradictory to the Australian research.

The Nuanced Landscape of Exercise for Healthy Aging

A broader scientific review published in the Journal of Clinical Medicine in August 2026 provides further context by examining 25 reports encompassing approximately 2,818 participants to assess the impact of HIIT and other interval training modalities on older adults. The most consistently reported benefits across these studies were improvements in cardiovascular fitness, specifically in the body’s capacity to utilize oxygen during exercise. Some studies also indicated enhancements in physical function and metabolic health. However, the review did not establish HIIT as definitively superior to moderate-intensity exercise across all outcomes.

The reviewers highlighted that variations in exercise program design, participant characteristics, and study methodologies made it challenging to pinpoint a single, universally optimal training approach. Collectively, these findings suggest that HIIT can be a valuable tool for promoting healthy aging, but it is not the sole pathway to improved fitness or muscle protection.

Current recommendations from organizations such as the Centers for Disease Control and Prevention (CDC) for adults over 65 emphasize a multifaceted approach, including a combination of aerobic exercise, muscle-strengthening activities, and exercises that enhance balance. While higher-intensity workouts may be suitable for some older adults, individuals who are currently inactive or managing medical conditions may benefit from a gradual progression of fitness and professional guidance before embarking on a demanding exercise regimen.

The central message from the original Australian study remains powerfully relevant: the impact of exercise on muscle during fat loss is as significant as the amount of weight shed. HIIT has emerged as a promising strategy because of its demonstrated ability to facilitate fat reduction while simultaneously preserving lean tissue. When considered alongside newer research, this body of evidence reinforces the importance of exercise programs that support not only a lower number on the scale but also the underlying strength, fitness, and physical function essential for a vibrant and independent life in later years.