TOKYO —

Losing body fat is a common health goal, but for many, especially as they age, the challenge intensifies when it comes to retaining the muscle mass crucial for strength and an active lifestyle. Emerging research suggests that a specific form of exercise, high-intensity interval training (HIIT), may offer a distinct advantage in achieving this dual objective, proving to be more effective than moderate or low-intensity workouts for older adults looking to improve their body composition.

Unpacking the Benefits of HIIT for Healthy Aging

A pivotal study conducted by researchers at the University of the Sunshine Coast (UniSC) in Australia, published in the journal Maturitas, directly addressed this concern. The investigation compared the effects of three distinct exercise intensities on healthy older adults over a six-month period. The findings were significant: while all exercise groups achieved modest fat loss, only those engaging in HIIT demonstrated the ability to reduce fat mass without compromising 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 UniSC. This distinction is critical, as it highlights that simply losing weight does not equate to improving overall body composition, a far more nuanced indicator of health, particularly in later life.

A Six-Month Trial Reveals Intensity’s Crucial Role

The Australian research team meticulously examined how workout intensity influences body composition—the relative proportions of fat, muscle, and other tissues that constitute the body. The trial involved 123 healthy older adults, with an average age of 72, residing in the Greater Brisbane region. Their average body mass index (BMI) was approximately 26 kg/m², a figure considered normal for adults over 65.

Over six months, participants attended three supervised gym sessions per week, each lasting 45 minutes. They were strategically assigned to one of three groups: high-intensity intervals, moderate-intensity exercise, or a low-intensity comparison group. To meticulously track changes, researchers employed specialized scanning techniques to estimate fat and lean tissue distribution throughout the body, taking measurements at the study’s outset, after three months, and again at the six-month mark.

The data collected painted a clear picture: exercise intensity demonstrably influenced outcomes. Both high- and moderate-intensity training significantly reduced fat mass, yielding greater improvements than the low-intensity group. However, a divergence emerged concerning their impact on lean tissue. Dr. Rose elaborated, "While moderate training reduced fat mass, it also caused a small decline in lean muscle." In stark contrast, participants in the HIIT group managed to reduce fat without experiencing a similar decline in lean mass.

This preservation of lean tissue is particularly vital as individuals age. Maintaining muscle mass is intrinsically linked to physical independence, enabling essential daily activities such as climbing stairs, rising from chairs, maintaining balance, and executing everyday tasks with ease. It’s important to note that the scans measured lean tissue, which encompasses muscle, water, and other non-fat components, rather than muscle strength directly. Therefore, changes in lean mass do not necessarily translate one-to-one with changes in strength.

HIIT Targets Abdominal Fat with Added Benefits

Beyond preserving overall lean tissue, the UniSC study also uncovered another significant benefit associated with HIIT: its impact on abdominal fat. Both high- and moderate-intensity training demonstrated improvements in the composition of weight carried around the midsection. Further analysis of the low-intensity group’s results was pending at the time of the initial reporting.

The original study indicated improvements in visceral adipose tissue among both the high and moderate intensity groups. Visceral fat, distinct from subcutaneous fat, accumulates deep within the abdomen, surrounding vital organs like the liver and intestines. Excessive visceral fat is a known precursor to serious health issues, including insulin resistance, cardiovascular disease, and other metabolic disorders.

Dr. Rose underscored the broader implications of these findings, emphasizing that body composition plays a crucial role in the development and progression of chronic diseases with age. While general metrics like body weight and BMI offer a broad overview, they fail to capture the intricate details of fat and muscle distribution. An individual who reduces body fat while preserving muscle may experience a more favorable health outcome than someone who loses a similar amount of weight but also sacrifices valuable lean tissue.

However, the original researchers themselves cautioned that the observed improvements, while statistically significant, were relatively modest. They noted that the differences were not definitively "clinically meaningful" when compared to lower-intensity exercise, particularly after accounting for measurement uncertainties.

Understanding the Biological Mechanism: Why HIIT Challenges Muscles

The apparent advantage of HIIT in preserving muscle likely stems from its unique physiological challenge. Unlike steady-state exercise, HIIT involves alternating short, intense bursts of activity with brief recovery periods. This cyclical demand repeatedly taxes the cardiovascular system and working muscles.

Associate Professor of Physiology at UniSC and study co-author, Mia Schaumberg, explained the training protocol: "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."

Schaumberg theorized, "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 aligns with the principle that muscles adapt to the demands placed upon them. A sufficiently challenging stimulus from exercise provides the body with a compelling reason to maintain the tissues necessary for performing such demanding activities.

Muscle preservation is particularly vital in the face of aging, a process often accompanied by a gradual decline in muscle mass and strength. In severe cases, this can lead to sarcopenia, a condition characterized by reduced muscle strength and quantity, significantly impacting mobility and independence.

Broader Context and Recent Developments

The UniSC research aimed to empower individuals, especially older adults, to make more informed decisions about exercise and healthy aging. As the findings gained traction in early 2026, Schaumberg highlighted their relevance for New Year’s resolutions and long-term fitness planning. "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," she remarked. The study was a collaborative effort involving researchers from UniSC’s Healthy Ageing Research Cluster and The University of Queensland.

Subsequent research has continued to explore the benefits of HIIT for older adults, though it also underscores that intense workouts are not universally superior in all contexts. A 2026 study published in Medicine & Science in Sports & Exercise investigated the feasibility and effectiveness of home-based HIIT with remote supervision for older adults. This trial, involving 20 participants aged 61 to 74 who used specialized exercise machines, resulted in an average fat mass reduction of approximately 1.4 kilograms (about 3 pounds) and substantial improvements in aerobic fitness. Participants reported high adherence rates with no exercise-related adverse events, suggesting that supervised home-based HIIT programs can be a viable option.

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 instance, after 16 weeks of training, which also included resistance training for both groups, both exercise regimens led to reductions in fat and increases in lean mass, with no statistically significant difference between the groups in these body composition changes. This finding suggests that resistance training plays a crucial role in preserving or increasing lean tissue, and workout intensity is not the sole determinant of success. Researchers acknowledge that differences in populations and training protocols prevent direct contradictions of the earlier Australian study.

A Balanced Perspective: Is HIIT the Ultimate Solution?

A comprehensive scientific review published in the Journal of Clinical Medicine in August 2026, encompassing 25 reports and nearly 2,818 participants, offered a broader perspective on HIIT’s impact on older adults. The review confirmed consistent benefits in cardiovascular fitness, including enhanced oxygen utilization during exercise. While some studies indicated improvements in physical function and metabolic health, the review did not definitively establish HIIT’s consistent superiority over moderate-intensity exercise. The authors noted that variations in exercise programs, participant characteristics, and study methodologies made it challenging to pinpoint a single optimal training approach.

Collectively, the evidence suggests that HIIT is a valuable tool for healthy aging, but it is not the only pathway to improved fitness or muscle preservation. The Centers for Disease Control and Prevention (CDC) recommends that adults over 65 incorporate a combination of aerobic exercise, muscle-strengthening activities, and balance exercises into their routine.

While higher-intensity workouts may be suitable for some older adults, individuals who are currently inactive or have underlying medical conditions may benefit from a gradual approach to fitness, seeking professional guidance before embarking on demanding exercise programs.

The enduring takeaway from the foundational Australian study remains profound: what happens to muscle mass during fat loss may be as significant as the amount of weight shed. HIIT’s demonstrated ability to help participants reduce body fat while maintaining lean tissue, when viewed alongside newer findings, reinforces the importance of exercise programs that prioritize not just a lower number on the scale, but also the strength, fitness, and functional capacity essential for a healthy and independent aging process.