Only HIIT preserved muscle while burning fat in older adults, 6-month study finds
A six-month randomized trial from the University of the Sunshine Coast (UniSC) and the University of Queensland has found that high-intensity interval training (HIIT) was the only exercise mode that helped older adults lose body fat while preserving lean muscle mass. Moderate-intensity continuous training (MICT) produced a similar degree of fat loss but was accompanied by a small but statistically significant decline in muscle mass.
The study, published in Maturitas and registered as ACTRN12618000700235, enrolled 123 apparently healthy adults with an average age of 72 years (51% female, mean BMI 25.8 kg/m²) from the Greater Brisbane region. Participants were randomized to one of three treadmill-based, supervised exercise groups, each training three times per week for 45 minutes over six months.
The three protocols
The HIIT group performed a 10-minute warm-up, then four 4-minute intervals at 85–95% of peak heart rate, described as “very hard exercise where breathing is heavy and conversation is difficult”, separated by 3-minute active recovery periods at 60–70% HRpeak, followed by a cool-down.
The moderate-intensity (MICT) group walked continuously at 60–70% HRpeak, steady, moderate effort throughout.
The low-intensity (LIT) control group performed balance, stretching, and toning exercises at 45–55% HRpeak.
Body composition was measured by dual-energy X-ray absorptiometry (DXA) at baseline, three months, and six months.
What the data showed
The HIIT group lost an average of 0.54 kg of fat mass (p = 0.026 from baseline) and showed a 1.10 percentage-point reduction in body fat percentage (p = 0.017), the only group with a net improvement in body composition. Lean muscle mass was maintained with no significant loss.
The MICT group lost a comparable amount of fat (0.50 kg, p = 0.035) but also experienced a significant decline in lean mass of 0.69 kg over the first three months (p = 0.005), which approached but did not reach significance at six months (p = 0.050). The between-group difference in lean mass at six months, HIIT superior to MICT by 0.69 kg (95% CI 0.02–1.35, p = 0.042), was the key finding distinguishing the two approaches.
Both HIIT and MICT reduced visceral adipose tissue (the fat stored around internal organs), with MICT showing a significant reduction of 41.21 g versus control (95% CI −76.73 to −5.69, p = 0.009) and HIIT trending similarly (p = 0.023 within-group).
Lead author Grace Rose (UniSC and UQ) noted that the headline captures a real and important difference, but it comes with caveats. The changes were small in absolute terms; the paper itself describes them as “not clinically meaningful on average.” Only 44% of HIIT participants achieved a clinically meaningful improvement in body fat percentage, compared with 27% in MICT and 33% in controls (p = 0.197, not statistically significant between groups).
Why muscle mass matters for older adults
The preservation of lean mass during weight loss is a critical concern for older populations. Sarcopenia, age-related muscle loss, is associated with frailty, falls, loss of independence, and higher all-cause mortality. Any weight-loss intervention that also reduces muscle mass can do net harm, particularly in adults over 70 who already face declining muscle reserves.
The moderate-intensity group’s loss of 0.69 kg of lean mass over the first three months, even while losing fat, is precisely the pattern clinicians want to avoid. HIIT appears to provide a metabolic stimulus that preserves muscle protein synthesis even under conditions of caloric deficit, possibly through its greater activation of fast-twitch motor units and the associated anabolic signaling pathways.
Corresponding author Dr Mia Schaumberg (UniSC and UQ) said the findings suggest that for older adults seeking body composition improvements, the intensity of exercise matters as much as the duration. “Not all exercise is created equal for this population,” she said. “The prescription needs to match the goal, and if the goal is fat loss without muscle loss, HIIT appears to be the superior choice.”
Limitations
The study had several limitations. DXA scans were not performed under fasted conditions, which can affect precision. The actual intensity overlap between groups was smaller than intended; the low-intensity group averaged 59% HRpeak, the moderate group 74%, and the HIIT group 79% (where the target was 85–95%). The sample size did not allow sex-specific analyses, an important gap given known sex differences in body composition and exercise response. The authors also noted that no direct breath-by-breath gas analysis was used for intensity verification, and that a 4-compartment body composition model would have provided greater accuracy.
The findings add to a growing body of evidence that exercise prescription for older adults needs to be specific and goal-directed, and that moderate-intensity walking, while beneficial for cardiovascular health and visceral fat reduction, may not be sufficient to preserve muscle mass during weight loss.
Sources:
1. Rose, G., Hume, E., Blackmore, D. et al. “The effects of six months of high-intensity interval training versus moderate-intensity continuous training on body composition in older adults.” Maturitas 203, 108763 (2025). DOI: 10.1016/j.maturitas.2025.108763
2. University of the Sunshine Coast. Press release via ScienceDaily, June 22, 2026.
3. Australian New Zealand Clinical Trials Registry. ACTRN12618000700235.