## 4 Discussion
This assumption could be supported by the observation that when the plantarflexion angle is increasing with extra loading during eccentric contractions, the soleus muscle is more affected than the gastrocnemius muscle in terms of increases in EMG activity [24]. Collectively, these correlations support the possible contributions of the above muscles during the OLHR test and suggest that the enhancement of soleus muscle activation may be effective in terms of energy storage and enhancing movement efficiency, and the eccentric strengthening of the soleus could prevent excessive mechanical energy from being dissipated by the Achilles tendon and, thereby, reduce the risk of re-rupture. Our findings in this regard underscore the need to carry out eccentric exercises for late-stage rehabilitation. It is suggested, relatedly, that future studies be conducted to assess the training effects of soleus eccentric exercises on the maximal and explosive ankle performances in participants soon after an Achilles rupture in order to verify the role of the soleus muscle in functional recovery. The kinematics and kinetics data in this study showed that, in a repaired leg, there are reduced amplitudes in the ankle joint angle, angular velocity, ground reaction force and mechanical work of the heel during the concentric and/or eccentric phases in the OLHR exercise (Figure 2a-d). These parameters in the concentric and eccentric phases respectively represent various aspects of performance, including force and movement generation, as well as factors of force potentiation induced by the SSC, including muscle length (ankle joint), rate of length change or reflex potentiation (angular velocity), force applied and induced joint angular movement or tissue deformation (ground reaction force), and stored elastic energy (negative works) [10; 11]. Throughout the concentric and eccentric phases, the kinematics data, respectively, demonstrated that the repaired legs exhibited less angular movement generation and velocity, and that a poor length-force relationship and reflex potentiation reduced ankle joint angles (Figure 2a,b). Since the fascicle of the medial gastrocnemius muscle is respectively shortened and stretched as the foot is perform ing concentric and eccentric plantarflexion contractions [6; 32; 33], our kinematics results indicated that fascicle contraction or the contributions of the fascicles and aponeurosis to the muscle-tendon unit shortening velocity in the repaired legs were reduced within the end range of plantarflexion motion. Furthermore, the Achilles tendon lengthening that occurs after a rupture may adversely affect the tendon elongation magnitude within the end range of plantarflexion motion [8] and, therefore, decrease the operating range or velocity of the fascicle simultaneously. Our results regarding the reduced ground reaction force and mechanical work done during the concentric and eccentric phases in the repaired legs could also be illustrated by the above-assumed mechanism (Figure 2c,d). However, the kinetic data only showed significant differences in either the beginning or end of the phases, unlike the kinematic data, which showed differences throughout the phases. Our correlation data also showed that there were correlations of the kinematic (ankle angular velocity) and kinetic (mechanical work) results in the eccentric phase with the normalized distance results of the one-legged jumping test (r= 0.575, and \(-\)0.471, respectively). These findings are comparable to those of a previous study using a linear encoder that showed that the heel position-derived parameters during heel-raise exercises correlated with ankle kinematics during walking [1]. This study with three-dimensional kinematic and kinetic analyses further pointed out that, during the OLHR test, the mechanical work done by the plantarflexor muscles could be a predictor of jumping performance. Clinicians and therapists may enroll this parameter without actually measuring jumping performance with risks from high-magnitude impact forces or falls.