Background <p>Maintaining physical fitness in older adults is crucial for preventing functional decline. This study aimed to examine the effects of a 6-month medium-intensity training (MIT) programme on physical fitness components in older adults.</p> Methods <p>In this randomized controlled trial, 72 older adults aged 60–70 years in Indonesia were randomly assigned to either an exercise group (EG; <i>n</i> = 36) or a control group (CG; <i>n</i> = 36). The EG participated in MIT sessions (60 minutes, 3 times per week). Each session consisted of a warm-up with joint mobility and flexibility exercises, followed by 15–20 minutes of moderate-intensity walking performed at 55-70% of maximum heart rate, a strength training phase targeting major muscle groups with 8–10 repetitions per movement using bodyweight or light resistance, and a cooldown phase incorporating stretching for major muscle groups. Physical fitness was assessed using the Senior Fitness Test at baseline and post-intervention. Group × time interaction effects were analyzed using repeated measures ANOVA. Effect sizes were calculated using partial eta squared (partial η²), with 95% confidence intervals (CI) reported.</p> Results <p> Significant group × time interaction effects were observed for lower-limb strength (post-intervention: EG = 13.40 ± 3.22 vs. CG = 10.55 ± 2.20 reps; partial η² = 0.167, 95% CI [0.041, 0.296], <i>p</i> = 0.02, upper-body strength (15.55 ± 2.88 vs. 11.37 ± 1.71 reps; partial η² = 0.223, 95% CI [0.085, 0.352], <i>p</i>= 0.00), lower-body flexibility (3.69 ± 2.93 vs. 2.50 ± 4.04 cm; partial η² = 0.101, 95% CI [0.013, 0.229], <i>p</i>= 0.01), and aerobic endurance (468.26 ± 88.49 vs. 417.50 ± 33.72 m; partial η² = 0.325, 95% CI [0.172, 0.460], <i>p</i>&lt; 0.001). No significant interactions were found for upper-body flexibility or agility (<i>p</i>&gt;0.05). All values in parentheses represent post-intervention means ± standard deviations.</p> Conclusions <p> A structured 6-month MIT programme significantly improved key physical fitness domains in older adults, particularly muscular strength and aerobic capacity. These findings underscore the importance of implementing regular, moderate-intensity exercise as a practical strategy to support healthy aging and reduce functional limitations.</p> Trial registration <p> The trial was registered at Thai Clinical Trials Registry no TCTR20250407006 (date of registration on April 7, 2025).</p>