Background and Purpose: The purpose was to investigate the effects of fatigue on balance in individuals with Parkinson’s disease (PD). Because falls in this population can have deleterious consequences, it is important to understand the influence of fatigue and PD medications on balance. Additionally, since brain-derived neurotrophic factor (BDNF) has been shown to be related to motor performance, we explored its role in balance fatigue. Participants: 27 individuals (age= 65.4±8.1; males= 14, females= 13) with neurologist-diagnosed PD. Of the 27, 13 were genotyped for BDNF as Val/Val, 11 as Val/Met, 2 as Met/Met, and one refused genotyping. Methods: Participants were tested twice, first on medication and second off medication, one week apart. On both days, participants completed the following tests before and after a fatiguing condition: mini-Balance Evaluation Systems Test (mini-BESTest), computerized dynamic posturography (sensory orientation and motor control), functional reach, and gait spatial-temporal parameters at preferred gait speed across an instrumented walking mat. To address the primary aim of the study, a 2 (condition: pre and post) X 2 (medication: on and off) factorial ANOVA was performed for each outcome variable in each of the following domains: 1. anticipatory postural response; 2. adaptive postural responses; 3. Dynamic balance; 4. sensory orientation; and, 5. gait characteristics. For the exploratory aim, independent t-tests were conducted to compare both pre- and post-fatigue states, and on and of medication states for all of the aforementioned balance domains. Results: There were no statistically significant interactions between time (pre and post) and medication (on and off) for anticipatory postural responses, adaptive postural responses, dynamic balance, sensory orientation, or gait characteristics (ps≥.187). Participants with BDNF Met alleles were not significantly different from Val/Val participants in balance or gait (ps≥.111) and response to a fatiguing condition (ps≥.070). Discussion: The results of this study suggest that fatigue does not have a detrimental effect on balance and gait in individuals with PD. Likewise, our results were also in line with other studies that suggest that PD medications are not effective for decreasing risk of falls due to postural instability. Lastly, these results also indicate that individuals with a BDNF Met allele are not at an increased fall risk after a fatiguing condition compared to those with the Val/Val genotype
