Elsevier

Journal of Biomechanics

Volume 48, Issue 12, 18 September 2015, Pages 3413-3419
Journal of Biomechanics

EMG and force production of the flexor hallucis longus muscle in isometric plantarflexion and the push-off phase of walking

https://doi.org/10.1016/j.jbiomech.2015.05.033Get rights and content

Abstract

Large forces are generated under the big toe in the push-off phase of walking. The largest flexor muscle of the big toe is the flexor hallucis longus (FHL), which likely contributes substantially to these forces. This study examined FHL function at different levels of isometric plantarflexion torque and in the push-off phase at different speeds of walking. FHL and calf muscle activity were measured with surface EMG and plantar pressure was recorded with pressure insoles. FHL activity was compared to the activity of the calf muscles. Force and impulse values were calculated under the big toe, and were compared to the entire pressed area of the insole to determine the relative contribution of big toe flexion forces to the ground reaction force. FHL activity increased with increasing plantarflexion torque level (F=2.8, P=0.024) and with increasing walking speed (F=11.608, P<0.001). No differences were observed in the relative contribution of the force under the big toe to the entire sole between different plantarflexion torque levels (F=0.836, P=0.529). On the contrary, in the push-off phase of walking, peak force under the big toe increased at a higher rate than force under the other areas of the plantar surface (F=3.801, P=0.018), implying a greater relative contribution to total force at faster speeds. Moreover, substantial differences were found between isometric plantarflexion and walking concerning FHL activity relative to that of the calf muscles, highlighting the task-dependant behaviour of FHL.

Introduction

The first metatarso-phalangeal joint (MPJ) has a significant range of motion in the sagittal plane in walking (Caravaggi et al., 2010). This joint is crossed by the flexor hallucis longus muscle (FHL). The FHL originates from the distal 2/3 of the fibula and the membrana interossea, and inserts onto the distal phalanx of the big toe while also spanning the ankle (Gray, 1980). Several functions have been attributed to FHL, including flexion of the big toe, supination of the foot (Ferris et al., 1995), maintenance of the medial longitudinal arch of the foot (Thordarson et al., 1995), production of inversion torque on the rearfoot (Hintermann et al., 1994) and plantarflexion torque at the ankle (Klein et al., 1996). FHL may also play a role in accelerating the centre of mass in the push-off phase of locomotion (Goldmann et al., 2013), presumably via energy conservation (Hofmann et al., 2013, Kirane et al., 2008).

It has been estimated that during walking the forces within the foot are largest in the first ray, with 29% body weight under the first MPJ and 24% under the big toe (Jacob, 2001). FHL may make a major contribution to these large forces, since it has the largest physiological cross-sectional area of the big toe flexor muscles (Friederich and Brand, 1990). Jacob (2001) estimated that the force along the FHL tendon is around 52% of body weight at the second peak of the vertical ground reaction force in the stance phase of walking. FHL muscle activity is also maximal at the terminal stance phase of gait (Perry, 1992).

Numerous studies have shown the multifunctionality of FHL, but all of these studies used cadaver or indirect methods to estimate muscle function. Direct in vivo methods have not been used except for the study of Perry (1992), which did not examine the relationship between FHL activity and movement outcomes. The aim of this study was to examine FHL activity and the resulting force under the big toe during sustained isometric plantarflexions at different contraction levels, and in the push-off phase of walking at different speeds. This allowed us to determine differences in the use of this muscle between an isolated and a functional task, as well as changes with increasing intensity of locomotion and plantarflexion.

Section snippets

Participants

Eleven male subjects (age: 24.7±3.7 years; height: 180.6±6.6 cm; body mass: 79.2±9.1 kg) with no history of neuromuscular disorder or injury volunteered for this study. Subjects with self-reported flat foot were excluded (Angin et al., 2014). The right (dominant) leg of each subject was measured. The experimental procedures were approved by the ethics committee of the University of Jyväskylä and all subjects gave written informed consent. Testing was conducted according to the Declaration of

Results

Maximal isometric plantarflexion torque was 362.39±78.35 Nm. In isometric tasks with varying torque level, average force under the big toe generally increased with torque (F=5.41, P<0.001), but there were no significant changes in relative big toe force (F=0.836, P=0.529) (Fig. 4). For walking trials, absolute peak force under the big toe increased significantly with increasing speed (F=4.923, P=0.005), and the increase was greater than in the other regions of the foot (F=3.801, P=0.018).

Discussion

Our results show that increased isometric plantarflexion torque and increased walking speed were associated with higher FHL activity and concomitant higher forces under the big toe. It is well known that an increase in walking speed results in a decrease in stance phase duration, as well as the duration of all sub-phases (Liu et al., 2014) such as push-off (Table 1). On the contrary, force under the big toe increased at a higher rate than force in other regions of the plantar surface as walking

Conclusion

Our results show for the first time how force under the big toe and FHL EMG activity vary over different isometric plantarflexion levels and different speeds of locomotion. We found that FHL activity generally increased in parallel with the force under the big toe during isometric plantarflexion and walking. The contribution of big toe flexion to the ground reaction force also increased with increasing walking speed, indicating an increase in the relative importance of this muscle at faster

Conflict of interest statement

None of the authors have any conflict of interest to declare.

References (26)

  • P. Caravaggi et al.

    Dynamics of longitudinal arch support in relation to walking speed: contribution of the plantar aponeurosis

    J. Anat.

    (2010)
  • A. Erdemir et al.

    Dynamic loading of the plantar aponeurosis in walking

    J. Bone Jt. Surg. Am.

    (2004)
  • L. Ferris et al.

    Influence of extrinsic plantar flexors on forefoot loading during heel rise

    Foot Ankle Int.

    (1995)
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