Wallace, BJ, Shapiro, R, Wallace, KL, Abel, MG, and Symons, TB. Muscular and neural contributions to postactivation potentiation. J Strength Cond Res 33(3): 615-625, 2019-This study's purpose was to explain the relationship between muscle factors (twitch potentiation [TP]) and neural factors (reflex potentiation) contributing to total postactivation potentiation (PAP) that couples these. The tibial nerve of 15 participants were stimulated intermittently for 20 minutes at supramaximal (Mmax) and submaximal (Hmax) intensities on separate days under 2 conditions: (a) rest (Control) and (b) after a 10-second plantarflexion maximum voluntary isometric contraction (MVIC). Isometric twitch torque and rate of force development (RFD) as well as soleus and gastrocnemius electromyographic values were analyzed. Torque and RFD TP were significantly greater 10 and 30 seconds after MVIC vs. Control. Postactivation potentiation of torque and RFD at Hmax were highest at 3 and 4.5 minutes after MVIC, respectively, with RFD significantly elevated. Electromyographic values were not different between conditions. Twitch potentiation significantly contributed to PAP at the following time points: 20 seconds, Hmax peak, and 20 minutes after MVIC (torque: R = 0.54, 0.76, and 0.70; RFD: R = 0.46, 0.59, and 0.53). The soleus significantly contributed to PAP torque at 20 seconds and 20 minutes after MVIC, and to PAP RFD at 20 seconds, 4.5 minutes, and 20 minutes (torque: R = 0.26 and 0.34, p ≤ 0.05; RFD: R = 0.65, 0.52, and 0.41). The gastrocnemius did not significantly contribute to PAP. Both muscle and neural factors play a significant role in PAP, and neural factors may play a more prominent role in RFD potentiation than torque potentiation.