In this work, the anterior-posterior displacement of the center of pressure was modeled as a fractional Brownian motion to analyze the effect of fatigue of plantar flexor muscles by isometric contraction. A sample of 17 young, healthy adults was evaluated by stabilometric test, 2 min before and after a plantar flexion, sustained until exhaustion. For each test, the model was applied to four consecutive periods of 30 s and then averaged to estimate the parameters. The fatigue increased the stochastic activity in both persistent and antipersistent controls, and also increased the Hurst exponent of the long-term mechanism. As a conclusion, the used model suggests that peripheral fatigue increases the body sway and reduces the gain of the antipersistent mechanism. However, these changes are detectable only when more than one 30 s data segment is considered for analysis.