Comparison of Pathway and Center of Gravity of the Calcaneus on Non-Involved and Involved Sides According to Eccentric and Concentric Strengthening in Patients With Achilles Tendinopathy

摘要

This study compares the changes in pathway and center of gravity (COG) on the calcaneus of non-involved and involved sides according to eccentric and concentric strengthening in patients with unilateral Achilles tendinopathy. The goal was to define the biomechanical changes according to eccentric strengthening for the development of clinical guidelines. Eighteen patients with Achilles tendinopathy were recruited at the K Rehabilitation Hospital in Seoul. The subjects were instructed to perform 5 sessions of concentric strengthening. The calcaneal pathway was measured using a three-dimensional (3D) motion analyzer, and COG was measured by a force plate. Subsequently, eccentric strengthening was implemented, and identical variables were measured. Concentric and eccentric strengthening was carried out on both the involved and non-involved sides. There was no significant difference in the calcaneal pathway in patients with Achilles tendinopathy during concentric and eccentric strengthening. However, during eccentric strengthening, the calcaneal pathway significantly increased on the involved side compared to the non-involved side for all variables excluding the z-axis. COG significantly decreased on the involved side when compared to the non-involved side in patients with Achilles tendinopathy during eccentric and concentric strengthening. During concentric strengthening, all variables of the COG significantly increased on the involved side compared to the non-involved side. Compared with eccentric strengthening, concentric strengthening decreased the stability of ankle joints and increased the movement distance of the calcaneus in patients with Achilles tendinopathy. Furthermore, eccentric strengthening was verified to be an effective exercise method for prevention of Achilles tendinopathy through the reduction of forward and backward path length of foot pressure. The regular application of eccentric strengthening was found to be effective in the secondary prevention of Achilles tendinopathy in a clinical setting.Key point class="unordered" style="list-style-type:disc">Compared with eccentric strengthening, concentric strengthening decreased the stability of ankle joints, increasing movement of the calcaneus in patients with Achilles tendinopathy.Eccentric strengthening was shown to be an effective exercise method for preventing Achilles tendinopathy through the reduction of forward and backward path length of foot pressure.It was verified that regular application of eccentric strengthening is effective in secondary prevention of Achilles tendinopathy in the clinical setting. class="kwd-title">Key words: Achilles tendinopathy, concentric, eccentric, motion analyzer, center of gravity, foot pressure. class="head no_bottom_margin" id="sec1-1title">IntroductionEccentric strengthening relies on the contraction generated with increased muscle length during exercise. Although the mechanism underlying treatment of Achilles tendinopathy through eccentric strengthening remains unclear, the most reasonable hypothesis is that the stimulation generated by a specific increase is accompanied by strengthening to achieve visco-elastic change within the organ (Allison and Purdam, ). Active eccentric strengthening adjusts the threshold level for activity of the peripheral and central nervous systems, and creates an optimal increase-decrease cycle to synchronize the short-term and long-term accommodation reflexes of the exercise unit (Avela and Komi, ; Nicol et al., ). Furthermore, the eccentric load is moved to a position in which myotomes within the muscle can produce maximum contraction. This, in turn, leads to the mutual connection of a range that can display both optimal passive and active function (Brockett et al., ; Proske et al., ).Previous studies have reported that use of eccentric strengthening in patients with Achilles tendinopathy is effective in reducing pain (Knobloch et al., ; Rompe et al., ). Silbernagel et al., reported that compared with concentric strengthening, eccentric strengthening produces a significant increase in both complete recovery of damage and patient satisfaction, as well as a decrease in pain during activity. Rompe et al., used pain threshold equipment to compare an eccentric strengthening group with an external shock therapy group and a control group; they reported that eccentric strengthening produced greater reduction in pain as well as an increase in functional standard and pain threshold value. Although the pain reduction effect of eccentric strengthening is used clinically in rehabilitation settings, the mechanism underlying the efficacy of the approach remains unclear. Eccentric load can deliver greater strength to the tendon than does a concentric load, and can eventually increase the ratio of stimulation required for tendon reconstruction (Fyfe and Stanish, ; Stanish et al., ). Furthermore, although long-term eccentric strengthening gradually normalizes damaged tendon structure, no clear evidence for any relevant blood supply mechanism has been reported (Ohberg et al., ).Recent studies have attempted to uncover the mechanism underlying the effects of eccentric strengthening. Piitulainen et al., stated that compared with concentric strengthening, eccentric strengthening is more efficient in producing contraction as well as achieving a higher conduction speed in muscle fibers. In a contrasting study, Rees et al., used three-dimensional (3D) motion analysis equipment and electromyograms in an initial study on the dynamic efficiency of eccentric strengthening and concentric strengthening of the Achilles tendon. Although a significant difference was not evident in the maximum tendon contraction ability and tendon length during motion, eccentric strengthening was found to generate a higher frequency of force vibration in the tendon in comparison with that elicited with concentric strengthening. However, this investigation was performed on control subjects, and no study has directly treated patients with Achilles tendinopathy. Furthermore, to analyze the mechanism of eccentric strengthening more thoroughly, it is necessary to compare the differences in maximum muscle contraction and position variables during both eccentric and concentric strengthening. This analysis should also encompass comparison of tendinopathic and non-tendinopathic regions of the Achilles tendon and a comparison of the affected and non-affected sides.In Achilles tendonitis, calcaneal pathway may change because the Achilles tendon has an insertion into the calcaneus itself. Examination of the calcaneal pathway in patients with Achilles tendinopathy would therefore be of some importance, and should any abnormalities be noted, it would also be imperative to ascertain the direction in which the bone has moved. An increased pathway of the calcaneus in patients with Achilles tendinopathy signifies instability, functional inefficacy, and a marked limitation of function. This study compared the changes in maximal muscle contraction, calcaneal pathway, and center of gravity (COG) of involved and non-involved sides with regard to eccentric and concentric strengthening in patients with unilateral Achilles tendinopathy. Thus, this study aimed to define biomechanical changes resulting from eccentric strengthening methods and assess the superior efficacy of eccentric strengthening in order to formulate clinical guidelines.