Achilles tendinopathy is one of the most common sports injuries caused by overuse syndrome (Maffulli et al., 2003; Magnussen et al., 2009). The injury rate of this condition has been reported to be approximately 7-9% in elite athletes and 6-18% in individuals who run regularly (Schepsis et al., 2002; Sorosky et al., 2004). Achilles tendinopathy is a condition that can occur in almost every sporting activity, with something along the lines of high incidences occur in activities that involve repetitive training loads (Woods et al., 2002).
The achilles tendon is a conjoint tendon composed of the insertions of the gastrocnemius and soleus muscles on the posterior calcaneus; it is approximately 15 cm in length and comprises equal proportions of the fibers of the gastrocnemius and soleus muscles. Achilles tendinopathy is accompanied by symptoms such as swelling, discoloration, changes of consistency, vascularization, and nodules (Knobloch et al., 2006), as well as an increase in the concentration of neurotransmitters such as glutamate, which causes pain and influences gait (Alfredson et al., 1999).
Two recent studies have assessed kinematic changes in gait in patients with achilles tendinopathy. Ryan et al. (2009) reported that the eversion movement of the subtalar joint increases and that the speed of dorsiflexion decreases, and Azevedo et al. (2009) reported that a decrease in knee range can be observed from initial contact to mid-stance phases and that electromyography (EMG) activation is decreased in the rectus femoris and gastrocnemius muscles.
Although running is an endurance sport that has many merits (Lee et al., 2012), such as increasing cardiopulmonary function and preventing obesity and other adult diseases, negative results from overuse, such as musculoskeletal disorders, are becoming more prevalent; therefore, means of preventing achilles tendinopathy while exercising regularly are required. Recently, as the number of individuals participating in running and other sporting activities has increased, the prevalence rate of achilles tendinopathy has also increased; when the condition occurs, it is considered a factor that hinders the participation in sports (McKean et al., 2006). A previous prospective study has shown that endurance exercises performed over a long period increase the prevalence rate of achilles tendinopathy (Cosca and Navazio, 2007). To achieve this aim, analysis of the gait movement features of runners with and without achilles tendinopathy using quantitative evaluation tools should be performed; however, studies of changes in gait or running posture in achilles tendinopathy patients are minimal.
Thus, this study was aimed at clarifying the mechanical changes in gait caused by achilles tendinopathy by comparing gait parameters and changes in hip, knee, and ankle moments between an experimental group (EG), constituting achilles tendinopathy patients with running experience of more than 1 year, and a control group (CG) of individuals of similar age and physical condition.
This study included 20 participants in the EG, which comprised 10 men and 10 women with chronic achilles tendinopathy (onset period: 7.67 [+ or -] 1.64 month) and running experience of more than 1 year, as well as 20 participants in the CG, which comprised individuals of similar age and physical condition compared with those in the EG. Subjects were recruited from the K Rehabilitation Hospital Research Center located in Seoul (Table 1). The inclusion criteria for EG patients were a diagnosis of achilles tendinopathy based on structural abnormalities found on only one side by sonography, achilles tendinopathy for at least 6 months, availability for outpatient follow-up, and ability to achieve independent gait without assistant devices.
The exclusion criteria were ankle range limitations (ankle dorsiflexion 30 degrees or less, plantar flexion 50 degrees or less), previous orthopedic surgery on the lower limb, use of foot orthoses, neurologic injuries or lesions, and other disorders such as osteoarthritis, rheumatoid arthritis, or osteoporosis in the feet in addition to achilles tendinopathy. Ample explanation was provided to the test subjects by the researcher regarding the purpose and the protocol of the study before the study was conducted, and all the subjects understood the explanation and agreed to participate. The project was approved by the University of Sahmyook Research Ethics Review Committee (SYUIRB2010-007, 27 February 2010), and the study protocol was conducted in strict accordance with the Declaration of Helsinki. Written informed consent was obtained from each subject.
The general features of the subjects, such as sex, age, weight, height, and body fat percentage, were recorded using bio-impedance body composition analyzer (Inbody 570, Biospace, Korea) before the test. For the EG, the clinical characteristics of achilles tendinopathy were also recorded, such as duration. Sixteen motion analysis markers (8 makers each side) were then attached to the subjects, who then were asked to walk in a manner suggested in a previous study, namely, repeating a distance of 13 m at their normal walking speed 5 times (Ryan et al., 2009).
Gait parameter analysis
For the gait analysis test in the EG and CG, three-dimensional movement analysis equipment was used, which comprised 9 infrared cameras, a signal control box, a computer, and the necessary software (VICON v8i motion analysis system; Vicon, Los Angeles, USA). The cameras received reflected infrared light from each marker, and location movement data were collected at 120 frames per second and an average accuracy of 0.85 mm.