05/05/2023
Plantar intrinsic foot muscle 🦶 💪 activation during functional exercises compared to isolated foot exercises
🦶Training the plantar intrinsic foot muscles (PIFMs) has the potential to benefit patients with lower extremity musculoskeletal conditions (plantar heel pain, Achilles tendinopathy, chronic ankle instability, hallux valgus, symptomatic pronated feet, diabetic neuropathy) as well as the aged population. https://pubmed.ncbi.nlm.nih.gov/27780109/, https://pubmed.ncbi.nlm.nih.gov/22166747/, https://pubmed.ncbi.nlm.nih.gov/31593918/, https://pubmed.ncbi.nlm.nih.gov/27570782/, https://pubmed.ncbi.nlm.nih.gov/23356426/, https://pubmed.ncbi.nlm.nih.gov/31278774/, https://pubmed.ncbi.nlm.nih.gov/32258170/
👉Isolated foot exercises, often standard in clinical practice, are difficult to perform, whereas functional exercises are much easier to accomplish. Functional exercises as opposed to isolated foot exercises (i.e. both traditional and PIFM exercises, i.e. short foot exercise, toe spread exercise) are habitual movements and challenge the PIFMs the way these muscles act in usual daily activities or sports activities. However, it is unclear whether functional exercises are comparable to isolated foot exercises in activating the PIFMs.
👉 Therefore, Willemse et al. (2023) examined the surface EMG activation of three PIFMs (m. abductor hallucis (AbH); m. flexor digitorum brevis (FDB); and m. flexor hallucis brevis (FHB)) in four functional exercises (i.e. normal/unstable toe stance, toe walking, and hopping, s. picture) versus a muscle-specific isolated foot exercise (s. picture) in 29 younger adults, resulting in 12 comparisons of 29 participants (21 women, 8 men). https://pubmed.ncbi.nlm.nih.gov/37126537/
👉 For the comparison with the functional exercises, one muscle-specific isolated foot exercise was selected. This was the exercise that provoked the largest mean EMG amplitude for that specific PIFM. The muscle-specific isolated foot exercise was the hallux grip for the FHB, toe curl for the FDB, and toe spread-out for the AbH.
📊 Results: Functional exercises showed larger mean EMG amplitudes than the isolated foot exercises in 25% of the 12 comparisons, while there was no difference in the remaining 75%.
📊 Of the 12 comparisons, 3 showed a significantly greater mean EMG amplitude for the functional exercises and 9 comparisons showed similar activation between the muscle-specific isolated foot exercise and each of the functional exercises.
📊 During hopping, FHB and AbH exhibited a significantly larger mean EMG amplitude than during the muscle-specific isolated foot exercise (FHB – median difference: 48%, IQR: 4% to 80%, p < .05; AbH – median difference: 108%, IQR: 79% to 153%, p < .05). In addition, toe stance on a compliant surface showed a larger mean EMG amplitude for FHB compared to the muscle- specific isolated foot exercise (median difference: 29%, IQR: −9% to 54%, p < .05).
🦶 As all functional exercises were performed in a toe stance position, this position seems to activate the PIFMs substantially. Toe stance requires the calf muscles to generate ankle plantar flexor force, which needs to be transmitted to the ground distal to the MTP joints. Therefore, the foot must serve as a rigid lever and the MTP joints must stiffen to resist the external toe extension moment generated by the ground reaction force.
📣 Conclusion: Functional exercises provoked comparable or even more activation of the PIFMs than isolated foot exercises. Given that functional exercises are easier to perform, this finding indicates the need to further investigate the effectiveness of functional exercises in physical therapy to improve muscle function and functional task performance in populations that suffer from PIFM weakness or dysfunction.
