This study investigates if sorting of type Ia feedback from muscle afferents into agonistic muscle groups can be achieved through Spike Timing Dependent Plasticity (STDP). We simulate a single Degree of Freedom (DOF) joint with two antagonistic muscles groups, controlled by a Synthetic Nervous System (SNS). Simulated spiking Ia afferent responses in the model alters synaptic connections via STDP based on the temporally precise spike firing of presynaptic and postsynaptic neurons. Under randomized initial synaptic conductivity values and semi-random muscle activation, the network demonstrates capabilities to organize Ia afferent feedback into the correct groups. STDP provides a biologically plausible method by which unsupervised organization of observed connections may form in vivo. We expect, with continuing work, STDP will be able to learn muscle relationships for larger, more complex biomechanical systems, as well as provide important feedback to the SNS for muscle control and coordination.