OBJECTIVE: The purpose of this study was to investigate the most effective ankle joint position for squat exercise by comparing muscle activities of lower extremity and erector spinae muscles in different ankle joint positions. METHODS: Thirty-seven normal healthy adults in their 20s participated in this study. Muscle activities of dominant vastus medialis oblique, vastus lateralis, biceps femoris, and erect spinae were measured in three ankle joint positions; dorsiflexion, neutral, and plantar flexion. RESULTS: Muscle activities of the vastus medialis oblique, vastus lateralis, and erector spinae muscles were statistically different in the three ankle joint positions during squat exercise (p< 0.05). Vastus medialis oblique muscles showed higher muscle activity in ankle plantar flexion than in the dorsiflexion or neutral positions (plantar flexion > neutral position, +3.3% of maximal voluntary isometric contraction (MVIC); plantar flexion > dorsiflexion, +12.2% of MVIC, respectively). Vastus lateralis muscles showed 7.1% of MVIC greater muscle activity in the neutral position than in dorsiflexion, and erector spinae muscles showed higher muscle activity in dorsiflexion than in plantar flexion or in the neutral position (dorsiflexion > neutral position, +4.3% of MVIC; dorsiflexion > plantar flexion, +7.1% of MVIC, respectively). CONCLUSION: In squat exercises designed to strengthen the vastus medialis oblique, ankle joint plantar flexion is probably the most effective ankle training position, and the dorsiflexion position might be the most effective exercise for strengthening the erector spinae muscle.
