Original researchA comparison in the muscle activity of the abductor hallucis and the medial longitudinal arch angle during toe curl and short foot exercises
Introduction
Pronation is a complicated triplanar motion of the foot. It is a critical motion that contributes to shock absorption from ground reaction forces and to the attenuation of the forces transmitted to the body during normal gait (Franco, 1987, Nack and Phillips, 1990). However, excessive pronation is associated with several overuse injuries, including plantar fasciitis (Pohl, Hamill, & Davis, 2009), hallux valgus (Easley & Trnka, 2007), Achilles tendonitis (Clement et al., 1984, Ryan et al., 2009), tibialis posterior tendon dysfunction (Tome, Nawoczenski, Flemister, & Houck, 2006), and patellofemoral pain syndrome (Powers, Maffucci, & Hampton, 1995).
The bony structures, ligamentous support, and extrinsic and intrinsic foot muscles control excessive pronation and maintain the medial longitudinal arch (MLA) during weight-bearing activities. Among the five midtarsal bones, the navicular serves as the keystone of the MLA (Franco, 1987). Various ligaments have been shown to maintain this structural integrity, including the deltoid ligament (Kitaoka, Luo, & An, 1998), plantar fascia (Cheung, Zhang, & An, 2004), and spring ligament (Borton and Saxby, 1997, Jennings and Christensen, 2008). Extrinsic muscles, including the anterior (Murley et al., 2009, O’Connor and Hamill, 2004) and posterior tibialis (Murley et al., 2009, O’Connor and Hamill, 2004) and the peroneous longus muscles (O’Connor and Hamill, 2004, Van Boerum and Sangeorzan, 2003), assist to stabilize the midtarsal joint and provide dynamic support to the MLA during stance phase. Various intrinsic foot muscles, such as the abductor hallucis, flexor digitorum brevis, and interosseous, contribute to stabilize the foot arch during propulsion (Gray and Basmajian, 1968, Mann and Inman, 1964).
The abductor hallucis (AbdH) muscle is the most medial muscle within the first layer of intrinsic muscles at the plantar surface of the foot. The AbdH muscle arises from the posteromedial calcaneus and inserts into the medial sesamoid of the hallux or proximal phalanx (Kendall, McCreary, Provance, Rodgers, & Romani, 2005). In a cadaver study, the anatomical course of the AbdH muscle contributed to its function as the abductor of hallucis, flexor and supinator of the first metatarsal, inverter of calcaneus, and external rotator of the tibia, in conjunction with the elevation of the MLA (Wong, 2007). Because the AbdH muscle passes under and is nearly perpendicular to the oblique midtarsal joint axis, this muscle contributes to stabilization and supination of the midtarsal joint against the pronating force of ground reaction during propulsion (Mann & Inman, 1964).
In previous electromyography (EMG) studies, investigators demonstrated that the AbdH muscle plays an important role to support the MLA and control pronation during static stance (Fiolkowski et al., 2003, Headlee et al., 2008). Headlee et al. (2008) found that navicular drop significantly increased after fatigue of the AbdH muscle. Fiolkowski et al. (2003) found that navicular drop significantly increased and muscle activity of the AbdH significantly decreased during great toe flexion with a tibial nerve block. Some researchers demonstrated that the AbdH muscle supports the MLA and advocated that the strengthening of foot intrinsic muscles be considered as a regimen for preventing overuse injuries in people who present with problems stemming from excessive pronation (Fiolkowski et al., 2003, Headlee et al., 2008, Wong, 2007).
Several methods are used to strengthen foot intrinsic muscles, including toe towel curls, picking up objects, shin curls, unilateral balance activities, and the short foot exercise (Anderson et al., 2004, Prentice, 2009). Toe curl (TC) and short foot (SF) exercises are prescribed in sport and rehabilitation field to strengthen the foot intrinsic muscles, for claw toe and hammer toe deformities and rheumatoid arthritis, to prevent falls in the elderly, and to improve the stability of the body during walking (Abdo and Iorio, 1994, Freiberger et al., 2007, Liebenson, 2001). TC exercise is used to strengthen the flexor digitorum longus and brevis, lumbricales, and flexor hallucis longus. Contrary to TC, SF exercise is performed to activate the foot intrinsic muscles by pulling the metatarsal heads toward the heel, while the long toe flexors are relaxed (Prentice, 2009). Although the role of strengthening the AbdH muscle has been addressed for controlling excessive pronation during walking (Fiolkowski et al., 2003, Headlee et al., 2008, Wong, 2007), no study has determined whether TC and SF exercises can activate the AbdH muscle and change the MLA angle. The purpose of this study was to compare the muscle activity of the AbdH and the MLA angle during TC and SF exercises while subjects were sitting or in one-leg standing position. We hypothesized that: (1) a difference in the muscle activity of the AbdH and the MLA angle would be observed between SF and TC exercises and (2) a difference in the muscle activity of the AbdH and the MLA angle would be observed between sitting and a one-leg standing position during both SF and TC exercises.
Section snippets
Subjects
Twenty subjects with neutral foot alignment participated in this study. Table 1 shows demographic information of the subjects. A neutral foot alignment was determined by measurement of the resting calcaneal stance position (RCSP: between 2° of inversion and 2° of eversion) and scores on the navicular drop (ND: between 5 and 9 mm) test (Cote et al., 2005, Razeghi and Batt, 2002). To measure RCSP, the examiner bisected the calcaneus of subject’s foot in the prone position. The subject was then
Results
Video motion-analysis measures of the MLA angle showed high intra-rater reliability of TC exercise (ICC (3,1) [95% CI] = 0.96 [0.91–0.99], SEM = 1.01° in sitting position; ICC (3,1) [95% CI] = 0.95 [0.89–0.98], SEM = 1.12° in one-leg standing position) and SF exercise (ICC (3,1) [95% CI] = 0.97 [0.93–0.99], SEM = 1.19° in sitting position; ICC (3,1) [95% CI] = 0.96 [0.91–0.99], SEM = 1.13° in one-leg standing position).
Significant interactions between exercise type and exercise position were
Discussion
The TC and SF exercises are commonly used to strengthen foot intrinsic muscles. The SF exercise is especially performed for balance training and enhancing the longitudinal and transverse arch (Prentice, 2009, Rothermel et al., 2004). However, no studies have investigated how much the AbdH muscle is activated during TC and SF exercises.
The AbdH muscle is the largest foot intrinsic muscle and it acts during flexion of the first MTP joint (Kura, Luo, Kitaoka, & An, 1997). In this study, the EMG
Conclusions
SF exercise is a more useful strengthening exercise than TC exercise in activating the AbdH muscle and in preventing lowering of the MLA. In addition, based on the level of the foot intrinsic muscle performance, exercise position should be considered when performing SF exercise. Further studies are needed to determine the long-term effects on the MLA of strengthening exercises for the AbdH muscle using the SF exercise in subjects with excessive pronation.
Ethical approval
The protocol for this study was approved by the Institutional Review Board of Yonsei University.
Conflict of interest
None.
Acknowledgement
This study was supported by the Korea Research Foundation Grant funded by the Korea Government (MEST, Basic Research Promotion Fund).
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2023, Journal of Foot and Ankle SurgeryCitation Excerpt :A trigno wireless mini sensor in a surface electromyography (EMG) system (DELSYS Trigno) was used to record muscle activity during the SFE. After the skin at the electrode sites was cleaned by rubbing alcohol, the surface electrode was placed on the AbH muscle (approximately 1-2 cm posterior to the navicular tuberosity) based on a previous study (11). Before attaching the surface electrodes, the participants were asked to contract the AbH, and the muscle belly was checked by the examiner.