Dynamic equilibrium is an integral aspect of human locomotion and the ability to react and maintain equilibrium during an unexpected perturbation is critical in prevention of injury. Few studies have been conducted that quantify reactive gait alterations due to unexpected forward perturbations (FP) and of those performed, only electromyographic and kinematic information has been presented. Therefore, the purpose of this study was to determine the joint moments (M), powers (P), and kinematics associated with unexpected FP during gait. Ten healthy young adults participated in study in which an unexpected FP was applied at heel strike (HS) by the forward displacement of a force plate on which they walked. Video and ground reaction force (GRF) data were collected and combined with inverse dynamics calculations to estimate the ankle (A), knee (K), and hip (H) joint angles, M, and P during the stance phase of gait. Data were recorded from 44 trials on both limbs in which the first 12 were blocked control trials followed by 32 trials consisting of perturbations and non-perturbations (NP) randomly ordered to prevent anticipation. Data were analyzed according to 5 phases of stance determined from GRF data and two-way repeated measure ANOVAs performed to indicate differences, if any, between conditions. Compared to normal walking patterns, results indicate an overall 40% and 14% reduction in support M and combined joint extensor angular impulse (EAI) respectively during the FP (P < 0.01). The FP also resulted in the K and H demonstrating 144% and 62% more positive EAI respectively throughout stance possibly to compensate for a 31% decrease in observed A EAI (P < 0.01). During the FP condition, the A demonstrated 51% less plantarflexor M and 21% less negative and 70% less positive P production from early stance until toe-off (TO) compared to NP (P < 0.01). In response to the FP, the K was initially 23% less flexed demonstrating an opposite flexor M compared to the K extensor M exhibited during NP gait. After midstance (MS), K angle was 30% more flexed than in NP and exhibited an extensor M after MS returning to a 58% reduced flexor M in preparation for TO (P < 0.01). During the FP, the H demonstrated 124% greater extensor M and 52% more positive P production from HS to MS than in NP, possibly to compensate for the K flexor M. These results indicate that subjects, in response to an unexpected FP, demonstrate distinct joint M, P and kinematic patterns to maintain dynamic equilibrium during locomotion.