Intra-spinal microstimulation (ISMS) is a valuable tool for both scientists and engineers, offering mechanistic studies of the response characteristics of local spinal cord neurons and circuits in-vivo as well as potentials for high-resolution stimulation treatments of spinal cord injuries and other motor deficits. However, due to technological limitations, previous studies have mostly been conducted in anesthetized or highly constrained animals. This approach overlooks the dynamics of motor behaviors, which are integral to these applications and may influence the effect of ISMS on local spinal circuit. In this study, we investigate the effect of temporally synchronizing ISMS with natural behavioral states on the neural activation and behavioral outcome in the mouse lumbar cord. This study also contributes to understanding the spinal cord interneuron population dynamics from an electrophysiological point of view. We leverage ultraflexible intraspinal electrodes, the na- noelectronic threads (NETs), for concurrent recording and stimulation during unrestrained motor behaviors. We find that single pulse stimulation no greater than 2nC/phase elicited robust neu- ral activation. Stimulation of different channels along the dorsal-ventral axis yielded distinctive activation pattern and well-separated neuron-populational trajectories after dimensionality reduction of single-unit spiking activities, with mild day-to-day fluctua- tions and overall stability. Preliminary results suggest that the strength of modulation is dependent on the site of stimulation. Pulse-train stimulations elicited a spectrum of hind limb movements including stepping, limb flapping and muscle contraction at low currents with considerable trial-to-trial variability. In order to mitigate variability in pre-stimulation baseline neural state, we implement closed-loop stimulation using real-time behavioral markers, controlling the behavioral state for each stimulation. This paradigm will help reveal how the spinal cord neural circuitry along the dorsal-ventral axis reacts and adapts to perturbation during rhythmic activity. These ongoing efforts underscore the critical interplay between ISMS and behavior. Our study holds implications for advancing the stimulation paradigm for both basic scientific investigation and potential translational applications.