Previous literature has shown that combining lemon myrtle (LM) leaf extract with low-load resistance training may promote muscle hypertrophy. The current our studies aimed to verify the effects of LM intake combined with different training volumes on anterior thigh (AT) muscle thickness in older adults. Two independent randomized, double-blind, placebo-controlled trials. Community-based training intervention program. A total of 125 Japanese adults aged ≥65 years, with self-reported declines in muscle strength or walking ability. Study 1 (n = 47; LM group: n = 25, placebo group: n = 22) and Study 2 (n = 41; LM group: n = 22, placebo group: n = 19) were conducted independently, each with separate randomization into LM and placebo groups. Both studies involved low-load bodyweight resistance training twice weekly for 12 weeks. Study 1 compared LM + three sets of training with placebo + three sets; whereas Study 2 compared LM + one set with placebo + one set. AT muscle thickness (primary outcome) was assessed using B-mode ultrasound at baseline, 6, and 12 weeks. Secondary outcomes were normal walking speed (10-m walk test, m/s), maximum walking speed (10-m walk test, m/s), and 30-second chair stand (CS-30, repetitions). In Study 1, the LM + exercise group showed a greater increase in AT muscle thickness than the placebo + exercise group (12-week difference: 1.29 mm; 95% CI: -0.17 to 2.75 mm), although the difference was not statistically significant. In Study 2, the LM + exercise group showed a significant increase in AT muscle thickness compared with the placebo + exercise group (1.59 mm; 95% CI: 0.19-2.98 mm). No significant group-by-time interaction was found for secondary outcomes in either study. LM intake may enhance muscle hypertrophy when combined with low-load resistance training in older adults with self-reported declines in muscle strength decline, particularly under low-volume training conditions. Further studies are needed to establish its clinical relevance.