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Open Access Research article

Ankle dorsi- and plantar-flexion torques measured by dynamometry in healthy subjects from 5 to 80 years

Amélie Moraux, Aurélie Canal, Gwenn Ollivier, Isabelle Ledoux, Valérie Doppler, Christine Payan and Jean-Yves Hogrel*

BMC Musculoskeletal Disorders 2013, 14:104  doi:10.1186/1471-2474-14-104

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Dorsal flexion is altered with aging

Maxime Billot   (2013-10-07 09:14)  Laboratoire GRAME, Universit�� Laval email

It is with great interest that we have read the article (March 22th, 2013) `Ankle dorsi- and plantar-flexion torques measured by dynamometry in healthy subjects from 5 to 80 years�� in volume 14 of the BMC Musculoskeletal Disorders journal [1] recently published in your journal. The question was of great interest. However, we would like to revise several comments that we would make upon this article.

In this study, the authors have developed a model to establish normative data and predictive equation on torque production at the ankle joint in healthy subjects from age 5 to 80 years. For teenagers and adults (15-80 years old), the results reported no difference with aging in torque production for male (especially for left dorsi-flexion). Furthermore they found that the height of the participant was the greatest predictor of torque production in their model. The capacity of torque production in this study was assessed with resultant torque (resultant torque = agonist torque �� antagonist torque). In accordance with Moraux et al.��s study [1], when co-activation phenomenon was considered negligible, resultant torque recorded in our study indicates aging effect in plantar-flexion, while no difference was observed in dorsi-flexion [2] (Figure 1). However, in our previous works, we have showed that during dorsi-flexion, the resultant torque recorded with an ergometer (as used by Moraux et al. [1]) represents only 20 to 50% of the agonist torque produced in young adults, and thus, largely under-estimate the strength of the dorsal flexors muscles [3, 4]. The most critical point in Moraux et al. [1] study, is that the contribution of the antagonist muscles was not taken into accounted . Although the authors state that 90�� of knee flexion could decrease the muscles coactivation, Cresswell et al. [5] found that the contribution of the calf muscle between 90�� (Moraux��s study) and 120�� [2-4] was not reduced. Therefore, we suggest that the torque developed by the antagonist muscles during a dorsi-flexion is not negligible even with a knee flexion between 90-120��. We suggest that bias was introduced in Moraux��s model mostly because the mechanical impact of the antagonist torque was not taken into account when calculating the capacity of torque production.

We have previously shown that the torque developed by the dorsi-flexor muscles (i.e., agonist torque) was reduced with aging when compared with young adults. Nonetheless, and in accordance with Moraux et al. study [2], the resultant torque appeared unaffected. This finding suggests that real impairment of dorsi-flexors muscles is masked by the decrease of antagonist torque in older adults. As largely explain in the literature, the torque decrease at the ankle joint with aging can be mainly explained by sarcopenia phenomenon [6, 7]. As well, the model could not find `age�� as main predictor of torque likely because of the aged modified mechanical contribution of antagonist muscles. This has potential ramifications in terms of rehabilitation and training for elderly people. In fact, as highlighted by Moraux et al. [1], the ankle strength has a great impact in both balance and gait [8-10]. Weakness in dorsi-flexion influences motor function [11] and seems also a good predictor for reduced ambulation [12]. In the case of aging, rehabilitation program rarely include strength training for this specific muscular group if the resultant torque is considered as the maximal capacity of torque production in dorsi-flexion, despite the fact that aging significantly alters muscles. The prevention of strength loss could be provided only if the agonist torque is estimated. For instance, with Moraux et al.��s data [1], it could provide strength training for calf muscles, but not for dorsi-flexors. From our study��s data [2] where we found a 39% decrease on agonist dorsiflexion with aging (Figure 1), we would recommend a dorsal flexor muscles training program. For these reasons we believe that the estimation of agonist torque provides crucial information with regards to the aged induced alterations of neuromuscular capacity.

In conclusion, we are not agree with Moraux et al. [1] suggestion that age not mainly contribute as predictable factor to predict torque capacity of the dorsi-flexors muscles. In order to examine the maximal capacity of the neuromuscular system, we believe it is necessary to account for the torque recorded in vivo as a resultant torque, and this is not necessarily accurately indicated by the force capacity of solely the agonist muscular group.

Abbreviations
MVC: Maximal voluntary contractions

Acknowledgements
Authors express their gratitude to Pr. Alain Martin for his comments and to Dr. Grant Handrigan for the English revision.

References
1. Moraux A, Canal A, Ollivier G, Ledoux I, Doppler V, Payan C, Hogrel JY: Ankle dorsi- and plantar-flexion torques measured by dynamometry in healthy subjects from 5 to 80 years. BMC musculoskeletal disorders 2013, 14:104.
2. Simoneau EM, Billot M, Martin A, Van Hoecke J: Antagonist mechanical contribution to resultant maximal torque at the ankle joint in young and older men. Journal of electromyography and kinesiology : official journal of the International Society of Electrophysiological Kinesiology 2009, 19(2):e123-131.
3. Billot M, Simoneau E, Van Hoecke J, Martin A: Coactivation at the ankle joint is not sufficient to estimate agonist and antagonist mechanical contribution. Muscle and nerve 2010, 41(4):511-518.
4. Billot M, Simoneau EM, Ballay Y, Van Hoecke J, Martin A: How the ankle joint angle alters the antagonist and agonist torques during maximal efforts in dorsi- and plantar flexion. Scandinavian journal of medicine and science in sports 2011, 21(6):e273-281.
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8. Billot M, Simoneau EM, Van Hoecke J, Martin A: Age-related relative increases in electromyography activity and torque according to the maximal capacity during upright standing. European journal of applied physiology 2010, 109(4):669-680.
9. Guillebastre B, Calmels P, Rougier P: Effects of muscular deficiency on postural and gait capacities in patients with Charcot-Marie-Tooth disease. Journal of rehabilitation medicine : official journal of the UEMS European Board of Physical and Rehabilitation Medicine 2013, 45(3):314-317.
10. Ng SS, Hui-Chan CW: Contribution of ankle dorsiflexor strength to walking endurance in people with spastic hemiplegia after stroke. Archives of physical medicine and rehabilitation 2012, 93(6):1046-1051.
11. Burns J, Ryan MM, Ouvrier RA: Evolution of foot and ankle manifestations in children with CMT1A. Muscle and nerve 2009, 39(2):158-166.
12. Bakker JP, De Groot IJ, Beelen A, Lankhorst GJ: Predictive factors of cessation of ambulation in patients with Duchenne muscular dystrophy. American journal of physical medicine and rehabilitation / Association of Academic Physiatrists 2002, 81(12):906-912.

Competing interests

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