26/04/2026
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Japanese scientists have been studying the Australian native plant lemon myrtle (LM; Backhousia citriodora) as a possible way to improve muscle mass. Their previous work demonstrated that LM extract and its key compound, the ellagitannin casuarinin, activated skeletal muscle satellite cells (SCs) both in vitro and in vivo. SCs are essential for muscle regeneration after injury or exercise, and their functional decline contributes to sarcopenia (muscle loss with ageing). In their pilot clinical study in older adults, LM leaf extract combined with typical-volume (three-set) low-load resistance training using body weight produced a greater increase in muscle size than resistance training alone, suggesting that the herb may enhance muscle growth in response to this form of exercise.
Now in two randomised controlled trials (published in a single paper), just 2.5 mg/day of casuarinin in an unspecified amount of a dried hot-water extract of lemon myrtle leaves significantly enhanced muscle hypertrophy during low-load resistance training, producing an 11.5 % vs 5.4 % increase in muscle thickness (d = 0.745) under low-volume exercise conditions (Study 2 see below). Such effects cannot be explained by nutrition or protein intake, which were unchanged, but instead suggest that even small amounts of phytochemicals from a whole-plant extract can act as biological signals that modify tissue adaptation, illustrating the network pharmacology capability of herbal medicines. A Cohen’s d of about 0.75 means the treatment produced a moderately large and clinically relevant effect, with the active group improving clearly more than the placebo group.
A total of 125 Japanese adults aged ≥65 years, with self-reported declines in muscle strength or walking ability were included. 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 randomisation into LM and placebo groups. Both studies involved low-load bodyweight resistance training twice weekly for 12 weeks. In Study 1, participants did three sets of exercise with either lemon myrtle or placebo, while in Study 2 they did only one set with either lemon myrtle or placebo.
Anterior thigh 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). Only Study 2 showed a statistically significant result for the primary outcome, although Study 1 showed a trend in the same direction, but with a much smaller effect size. No significant group-by-time interaction was found for secondary outcomes in either study.
According to the scientists only Study 2 showed a significant effect because the LM extract seemed to help more when the training stimulus was low, whereas with higher training volume the exercise itself already produced substantial muscle hypertrophy, making the added effect of the herb harder to detect. This type of benefit may be particularly useful in older people, who often cannot tolerate high-volume resistance training but still need to maintain muscle mass.
The authors concluded that 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.
Lemon myrtle is a tree native to the subtropical rainforests of eastern Australia, particularly Queensland, where it grows naturally in coastal and near-coastal regions. It belongs to the Myrtaceae family, the same family as eucalyptus and tea tree. It is striking that it is Japanese researchers who are investigating an Australian plant, given the relatively small amount of formal medical research conducted in Australia on its own native medicinal flora.
Note that these trials were conducted on a dried hot water extract, so the observed results do not reflect any impact from the essential oil, which would be lost during this process. Nonetheless, a decoction of the leaves would probably be a good approximation of what was used in the trials.
For more information see: https://pubmed.ncbi.nlm.nih.gov/41076797/
