Liquorice flavonoid oil increased skeletal muscle thickness as assessed by ultrasound in training football athletes

Abstract

Liquorice flavonoid oil (LFO) consisting of liquorice hydrophobic polyphenols in medium-chain triglycerides (MCT) is a new functional food ingredient effective for preventing metabolic syndrome. As it has been recently shown that LFO significantly increased skeletal muscle mass in mice, we hypothesized that it would also increase skeletal muscle mass in humans. Therefore, we carried out a randomized, double-blind, placebo-controlled study with male football athletes who ingested 300 mg per day of LFO concentrate solution for 8 weeks during the course of training at Kindai University, Osaka. Ultrasound imaging analysis revealed that the muscle thickness of the anterior thighs and anterior brachial regions in the LFO group were both significantly increased by 2.5% at week 8 in comparison to baseline, but not in the placebo group. In addition, although abdominal muscle thickness significantly increased in both the LFO and the placebo groups at week 8 in comparison to baseline, the increase in the LFO group was 1.8 times greater than that in the placebo group (p<0.05). Interestingly, stratified analysis by two team positions revealed that the offensive backs group, who require speed, gained more anterior thigh muscle, while the defensive line group, who require pushing force, gained more anterior branchial muscle with repeated intake of LFO. These results correlate well with the position-specific training of the two groups. This study indicates that LFO can contribute as a dietary supplement ingredient to increase or maintain skeletal muscle mass in humans in combination with exercise. This is the first report showing that LFO, which consists of liquorice polyphenols, increases muscle mass in humans.