## 1 Introduction  
Achilles tendon ruptures frequently result in long-term deficits in muscle strength and ankle functions [1, 2, 3, 4]. Clinically, it is important to identify neuromuscular deficits in individuals who are still recovering from an Achilles rupture and to design a rehabilitation plan accordingly. Studies have validated the utility of the one-legged heel-raise (OLHR) test for measuring the morphological adaptations in the myelotentious unit, such as muscle fascicle shortening in the medial gastrocnemius muscle and Achilles tendon lengthening, in the involved leg following an Achilles rupture [2; 5; 6; 7]. The OLRH test requires the plantarflexor muscles to alternate between generating concentric force to achieve a position of maximal plantar flexion and then using eccentric control to lower the heel to a position of maximum dorsiflexion in unipedal stance [1; 4]. The limb symmetry index (LSI) of average heel-rise work in the OLHR test between involved and non-involved legs one year after Achilles tendon rupture was reported to be correlated with kinetic variables during hopping, such as LSI plantarflexion power (force times velocity), six years after the injury [1]. This indicates that the musculotendinous factors that affect the performance of the OLRH test one year after a rupture may also affect common functional activities, such as hopping, later on in injured legs. Another study demonstrating electromyographic (EMG) activity in the OLHR test for all of the triceps surae muscles found that the muscles have similar EMG results during the concentric phase of the OLRH test with reduced heights of heel lifting for the involved side compared to the uninvolved side [8]. However, neither the EMG activities of individual tricep surae muscles, nor the kinetics and kinematics data for the eccentric phase, were analyzed in that study.  
The eccentric phase of the OLHR test may potentiate force production for ankle plantarflexion, which has been reported in previous studies involving stretch-shortening cycle (SSC) trials [9]. Various possible mechanisms underlying force enhancement in the eccentric phase of the SSC have been proposed, including mechanisms involving the joint angle (force-length relationship of muscle) [10], angular velocity (reflex potentiation) [11], magnitude of stored elastic energy, and the applied force that induces elongation of the myotendinous complex [9]. In previous studies that examined muscle atrophy (i.e., the side demonstrating muscle atrophy) in the medial gastrocnemius and soleus muscles of patients with an Achilles tendon rupture, the morphological findings have shown that the muscle activation of these muscles may be accompanied by atrophy that may in turn affect dynamic variables during the OLHR test [12; 13; 14]. However, this hypothesis has not been proven. The depiction of the dynamic (kinetic and kinematic) profile of the OLHR test and the muscle activation involved following an Achilles rupture can best explain the neuromechanical mechanisms leading to performance deficits in the OLHR test and, therefore, further studies are required.  
The aim of the present study was two-fold. First, the study utilized the OLHR test to assess and compare the EMG, kinematic and kinetic characteristics in the injured and non-injured legs of participants within one year of a unilateral Achilles' repair. Second, the study aimed to determine the relationship between (1) the EMG results of calf muscles (including the medial gastrocnemius and soleus) and the kinetic and kinematic characteristics and (2) those characteristics and normalized jumping distance. We hypothesized that, firstly, when compared to their contralateral non-injured legs, the repaired legs of the participants with an Achilles repair would exhibit compensatory increases of EMG activity in the leg muscles and correlated with lower values in terms of the kinematics and kinetics characteristics. Secondly, that these biomechanical characteristics would be correlated with the normalized distance of one-legged jumping.