Full length articleImmediate effects of shoes inducing ankle-destabilization around Henke's axis during challenging walking gaits: Gait kinematics and peroneal muscles activities
Introduction
According to numerous epidemiological studies, lateral ankle sprain (LAS) has been reported as a recurrent problem in athletes [1], [2]. Furthermore, 70 to 80% of the injured athletes developed residual symptoms and chronic ankle instability [3], [4]. That is why proper treatment of LAS is important.
At the muscular level, the ankle joint is protected against inversion movements by the peroneal muscles. Activity of the peroneal muscles is an essential factor for ensuring ankle stability [5]. Using surface electromyographic (EMG) activities, Santilli et al. [6] demonstrated that during walking gait, the peroneal muscles are the first to react to a sudden and unexpected ankle inversion. The EMGs in peroneal muscles are thus crucial and their significance decreases after LAS contributes to the recurrence of such injuries [7]. Hertel [8] concluded that increasing the quantity of EMG activities in peroneal muscles is of great interest for improving ankle stability.
In rehabilitation therapy, Freeman et al. [9], [10] first proposed neuromuscular control based on retroactive loops at the ankle joint. This kind of classical rehabilitation is performed using destabilization plates with multiple axes (the so-called Freeman's plate) and is most efficient when LAS has occurred for the first time [11], [12], [13]. On the contrary, other studies highlighted the weak effect of Freeman’s approach regarding ankle position sense [14]. Refshauge et al. [15] proposed that proprioceptive signal integrity was not impaired in LAS patients; In contrast to this a recent experiment clearly showed that the alert signal was impaired in chronic LAS patients [16]. Based on recent studies, it appeared that Freeman’s therapy method was efficient based on subjective evaluations of ankle instability [17]. However this technique has not been evaluated using objective measures of postural control or recurrent instability [17], [18].
During ecologic motor tasks such as walking, ankle motor control involves feedforward loops which are able to prepare the inferior limbs for heel contact, and to counteract the feet inversion imposed at the impact [19], [20]. It seems essential to state here that the multidirectional destabilization created by Freeman’s plates cannot activate peroneal muscles during ecological tasks, but solely in orthostatic postural tasks [9], [10].
Freeman’s pioneering methods thus present some limits and it seems important to investigate a more ecological approach specifically dedicated to LAS rehabilitation. It would therefore be useful to have a mechanical device which could increase the quantity of EMG activities in the peroneal muscles [5], [6], [7], [8], while stimulating the ankle joint in an ecological manner [19], [20], e.g. during voluntary locomotor tasks. Some recent studies tested the impact of mechanical devices specifically inducing subtalar joint destabilization. Their results highlighted an increase of EMG activities and anticipatory reactions in the peroneal muscles of healthy participants [21], [22] and individuals with chronic ankle instability [23] during gait. These authors concluded that their ankle destabilization device could be beneficial for rehabilitation programs during gait training.
Similarly, we tested another specific ankle destabilization device (ADD) which induced small imbalances (10 mm in amplitude) along the physiological axis of the foot that anatomically determines the unstable ankle, i.e. the Henke’s axis [3], [24]. The aim of the present study was not to measure the movements inside the foot, but to have a look at the global gait kinematics during the different locomotor tasks in order to validate the ecological stimulation allowed despite wearing the device. Compared to the previous studies, the destabilization angle used here is smaller, and with smaller amplitude of rotation angle. Consequently unlike previous studies, the present ADD allows many kinds of locomotion. This study thus investigated the modulation of the EMG activities in the peroneal muscles and the main gait kinematics parameters induced by the ADD in both legs when walking in different conditions and hence stress levels: normal (low stress) and aligned conditions (medium stress, inspired by the Sharpened Romberg Test), or walking by jumping (high stress, inspired by classical proprioceptive exercises used in sports training).
Section snippets
Subjects
Twelve healthy participants [ten men, two females, 21.3 ± 1.7 years old, 71.4 ± 8.3 kg, and 1.75 ± 0.16 m] volunteered for the experiment. None of the participants had a previous history of neuromuscular disease, severe leg injury, or ankle sprain. The experiment conformed to the Declaration of Helsinki and was specifically approved by the clinical ethic committee of the University of Burgundy (n°129.234). Written informed consent was obtained from all the participants according to the guidelines of the
No leg laterality effect
The averaged RMS of the normalized EMG during a gait cycle in every walking condition and modality is plotted in Fig. 2. The statistical analyses (ANOVA) revealed no lateralization effect (right versus left side) for the peroneus longus (F (1, 11) = 0.24, P = 0.63) and brevis (F (1, 11) = 1.9, P = 0.2).
EMG activation of the peroneal muscles corresponds to the walking condition stress level
As the experimental tasks were chosen with regards to the level of stress exerted on ankle stability, statistical analyses obviously exhibited a significant main effect of the walking conditions (NW, AW
Discussion
The main result of our study is that ADD creates significant bilateral increase of peroneus muscle activities in normal, aligned and jumping conditions. One of the functions of the peroneus muscles is to stabilize the ankle and protect it against inversion movement, especially around the Henke's axis [21], [28]. We suggest that the ADD induced mechanical imbalances which are potentially dangerous for the lateral structures of the ankle joints have been offset by the CNS with these increases of
Conclusion
This study demonstrated that inducing mechanical imbalances of 10 mm amplitudes on each side of the Henke’s axis during different walking conditions (i) first significantly increased the activities of the peroneus muscles during ecological stimulation of the ankle joints while still maintaining normal gait patterns (ii) Secondly, the increase of peroneus muscle activation was more important in the complex locomotor tasks than in the simple one.
Conflict of interest statement
There were no conflicts of interests for any of the authors of the paper.
Acknowledgements
The authors thank Cyril Sirandré, Yves Ballay and Julien Bourrelier (INSERM U1093-CAPS, University of Burgundy) for their technical help during the data collection. The authors thank Elizabeth Thomas (INSERM U1093-CAPS), Aurore Paillard, and the two reviewers for their very precise and stimulating comments that contributed to the improvement of this manuscript.
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