Distinct from the feed-forward gait generation method, which mainly depends on the estimation of CoM and CoP, only muscle reflexes presented by [PERSON] and [PERSON] (feedbacks from proprioception of different joints and positive force self-excitation) are implemented to generate the locomotion pattern. By using optimized parameters, the walking controller proposed by [PERSON] and [PERSON] has shown the potential to achieve human-like walking and self-stability against disturbances in a simulation study. [PERSON] and [PERSON] [29], in the following study, applied a similar neuromuscular model with muscle reflex control on leg prostheses, to fulfill balance recovery. This muscle reflex-based controller is also capable of controlling a bipedal robot [30]. The human ankle joint contacts the ground directly and plays an important role in upright standing. A simple spring-like model was assumed by [PERSON] et al. [PERSON] et al. (2018) for ankle muscle control during quiet standing. In their model, the human body was presumed to be an inverted pendulum (IP), swaying around the ankle joint. The ankle joint acted like a torsional spring to maintain body quiet standing balance. This type of spring-like behavior was considered to be due to the controlling results from Central Nervous System (CNS). To investigate the internal quiet standing control mechanism, based on a similar IP model to that suggested by [PERSON], [PERSON] et al. [PERSON] et al. (2018) applied a PD controller to yield the preceding motor commands. However, there are few studies evaluating the reflex mechanism in dynamic push-recovery upright standing, in which a disturbance is imposed. Although many ankle joint robots have been designed to enhance human locomotion ability, little attention has been paid to assisting upright standing balance with ankle joint exoskeletons ([PERSON], 1999). To achieve this goal, understanding the human ankle joint-level internal control mechanisms such as reflex control under push-recovery situations is important. Although a considerable amount of effort has been made in investigating upright standing, much of the research has been focused on the role of central control, i.e., examining the relation between CoM and human response. Further details from the point of view of the joint level are still needed to provide more direct guidelines for robot controller design. This paper evaluates the local reflex response of calf muscles and the corresponding ankle joint torque production during upright standing feet-in-place push-recovery. The aim of this study is twofold: (a) to investigating the human ankle joint reflex control mechanism facing sudden limited external disturbance, (b) to provide a fast method of using sEMG signals to calculate reflex control parameters and ankle joint torque. To explore reflex control, a time-increasing search method is applied to find a feasible time interval for reflex control. A two-piecewise response is revealed by the experimental results, and different gains seem to be adopted by subjects in the two-piecewise intervals. The remainder of this paper is organized as follows. The muscle reflex, musculoskeletal system modeling and experimental setup are stated in Section 2. The experimental results are shown in Section 3. Section 4 ends this paper by the analysis and discussion of the experimental results, as well as showing several related issues.