Accumulated HIIT Leads to Improvement of Fitness Level, Cognition, Anxiety and Depression-Like Behaviors in Aged Rats

This study aimed to compare the effects of High-Intensity Interval Training (HIIT) performed in a single session (1xHIIT) versus three daily sessions (3xHIIT) on fitness level, cognition, anxiety, and depressive-like behaviors in aged rats. Eighteen-month-old Wistar rats were assigned to Untrained (UN), 1xHIIT, or 3xHIIT (n=12/group). Both groups, 1xHIIT and 3xHIIT, performed 15 min of a treadmill running HIIT protocol during 8 weeks. The 1xHIIT group protocol consisted of a single daily session of 15 min, while the 3xHIIT performed three daily sessions of 5 min with a 4-hour interval between the sessions. Morris Water Maze (MWM) task was used to evaluate spatial learning and memory. Splash test, Forced Swim test, and Elevated Plus Maze task (EPM) were used to evaluate anhedonic, depressive-like, and anxious behaviors, respectively. Rats were euthanized, and the hippocampus was harvested for western blot analyses (AKT; CaMKII; and BDNF). Both HIIT protocols improved VO2max and spatial learning and memory. Notably, only the 3xHIIT protocol reduced anxious and depressive-like behaviors. Western blot analyses of the hippocampus revealed that both HIIT protocols increased AKT and BDNF levels. The BDNF levels were higher in the 3xHIIT when compared with 1xHIIT group, and we observed increasement of the CamKII levels just in the 3x HIIT group. In conclusion, this study reveals the positive impact of single and accumulated daily sessions of HIIT on cognition, behavior and neuroplasticity in aged rats. We also showed a superior effect of 3xHIIT over 1xHIIT on improvement of the anxious and depressive-like behaviors.