Functional exercises provoked comparable or even more activation of the intrinsic foot muscles than isolated foot exercises
By integrating some functional exercises into your daily routine, you can train the intrinsic muscles of the plantar foot in a time-efficient manner
Isometric exercises produced more muscle activation of the intrinsic foot muscles than concentric exercises, except for the FDB muscle
The foot is our base of support for everyday and athletic activities. A good base of support is therefore important to prevent and overcome injuries of the foot and ankle and even higher up the kinetic chain. In this light, the intrinsic foot muscles are especially important in controlling the medial longitudinal arch of the foot and acting as dynamic stabilizers. We previously reviewed a study on this topic, which you can read here. To strengthen the intrinsic foot muscles, the use of isolated foot exercises has widely been used. A disadvantage of this type of exercise is that for many, contracting these foot muscles is difficult or impossible. Despite your encouragement and demonstration, a lot of individuals won’t be able to contract these muscles. It is known that, as functional exercises create unstable positions, the foot muscles will react and try to provide a stable base of support. In this light, this study aimed to compare the muscle activation of the plantar intrinsic muscles of the foot during the execution of functional exercises compared to the more difficult isolated foot exercises.
To compare the muscle activation of the plantar intrinsic foot muscles, surface EMG was used to measure the activity of the following muscles:
The M. flexor hallucis longus (FHL) was selected to represent the extrinsic toe flexor muscle.
One reference exercise was done at the start of the experiment to normalize the EMG amplitude. Following this, 5 static foot exercises were performed:
These exercises were compared to five functional exercises for their activation of the intrinsic foot muscles:
To make the comparison with the functional exercise, one muscle-specific isolated foot exercise was selected. This was the exercise that provoked the largest mean EMG amplitude for that specific intrinsic foot muscle. 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.
Comparisons were made between concentric and isometric exercises. The concentric toe curl exercise was compared to the isometric toe grip, hallux grip and lesser toe grip. The influence of body weight on the activation of the intrinsic foot muscles was studied by comparing a single-leg toe stance to a single-leg toe stance with forward lean.
Moreover, the EMG amplitude integrated over time was measured. That is, the muscle activity is measured with the contraction time in mind to determine the total activity in the muscle. For example, a hop is a very brief moment but this may produce a lot of muscle activity in that short time. With measuring the iEMG, the duration of the movement is taken into account.
Twenty-nine healthy and asymptomatic participants were included in the trial. They were on average 23 years old.
The difference in muscle activation between the muscle-specific isolated foot exercises and the functional exercises is shown in the picture hereunder.
The isometric exercises produced significantly larger mean muscle activation than the concentric exercises for the FHB and the AbH. On the other hand, the concentric exercises produced more muscle activity in the FDB and FHL muscles.
Increasing body weight on the foot during toe stance with forward lean did not influence muscle activation, compared to the normal stance.
Where did this idea of isolating the intrinsic foot muscles come from in the first place? This was probably to avoid compensation from extrinsic foot muscles. Probably, this was a way to study the actions of the intrinsic foot muscles, but apart from studying this, I don’t see the benefit of it for rehab. You will need more than to just activate the plantar muscles of the foot in daily life, and you’ll probably compensate with other muscles higher up the chain, so why would we want to avoid that? You don’t target the vastus medialis obliquus muscle alone for increasing stability around the knee joint, do you?
This study may have a promising impact on the rehabilitation of foot and ankle problems in children. Potentially, it may be helpful in increasing a good foot posture for efficient load transmission and shock absorption. As the isolated foot exercises may be difficult to explain, and even more difficult to teach young children and adolescents, this study gives us a wide array of other potentially useful movements. It can even be more playful to give hopping exercises and tip-toeing than to just let them spread out their toes.
This study compared the activation of the intrinsic foot muscles between isolated foot exercises and functional exercises. The results showed that it is not necessary to perform isolated foot exercises to get the intrinsic foot muscles working. Instead, by standing on your toes, walking on your toes, or hopping, you can generate the same amount or even more muscle activity in the plantar muscles. For many, these exercises are potentially easier to perform and can easily be integrated into daily routines, making the training more time-efficient.
Willemse L, Wouters EJM, Pisters MF, Vanwanseele B. Plantar intrinsic foot muscle activation during functional exercises compared to isolated foot exercises in younger adults. Physiother Theory Pract. 2023 Apr 26:1-13. doi: 10.1080/09593985.2023.2204947. Epub ahead of print. PMID: 37126537.
Kurihara T, Yamauchi J, Otsuka M, Tottori N, Hashimoto T, Isaka T. Maximum toe flexor muscle strength and quantitative analysis of human plantar intrinsic and extrinsic muscles by a magnetic resonance imaging technique. J Foot Ankle Res. 2014 May 5;7:26. doi: 10.1186/1757-1146-7-26. PMID: 24955128; PMCID: PMC4049512.
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