Short-term effects of side-alternating Whole-Body Vibration on cognitive function of young adults

Abstract

Recent research in rodents and humans revealed that Whole-Body Vibration (WBV) is beneficial for cognitive functions. However, the optimal WBV conditions are not established: contrary to vertical WBV, side-alternating WBV was not investigated before. The present study investigated the short-term effects of side-alternating WBV in standing and sitting posture on specific cognitive function of young adults. We used a balanced cross-over design. Sixty healthy young adults (mean age 21.7 ± 2.0 years, 72% female) participated. They were exposed to three bouts of two-minute side-alternating WBV (frequency 27 Hz) and three control conditions in two different sessions. In one session a sitting posture was used and in the other session a standing (semi-squat) posture. After each condition selective attention and inhibition was measured with the incongruent condition of the Stroop Color-Word Interference Test. WBV significantly (p = 0.026) improved selective attention and inhibition in the sitting posture, but not in the standing posture. The sitting posture was perceived as more comfortable, joyous and less exhaustive as compared to the standing posture. This study demonstrated that side-alternating WBV in sitting posture improves selective attention and inhibition in healthy young adults. This indicates that posture moderates the cognitive effect of WBV, although the effects are still small. Future studies should focus on the working mechanisms and further optimization of settings, especially in individuals who are unable to perform active exercise.

Fig 1. Flow diagram of a balanced cross-over design assessing the effects of WBV versus control on cognition.

Participants were randomly assigned to four groups starting with different postures and conditions. Selective attention and inhibition were directly assessed after each trial. In session two, the other posture and starting condition was assigned to the participants following the same procedures.

Fig 2. Schematic example of the protocol of one participant.

Each participant underwent two sessions. The order of starting posture (standing, sitting) and condition (WBV, control) was balanced across subjects. Each condition took two minutes and after each condition the Color-Word Interference Test (CWIT) was assessed followed by a two minutes break.

Fig 3. The two postures used to examine the effects of WBV on cognition.

A: in the standing posture, participants held a static light squat while holding the handrail. B: in the sitting posture, participants were located on a stool in front of the platform with their knees bend in approximately 90 degrees while their hands were resting on the knees.

Fig 4. Feet positioning on the Galileo platform in both postures.

The medial side of the feet were located in the middle of the platform against the vertical line number 1 which is approximately 6 cm from the center of the platform.

Fig 5. Results of incongruent condition of Stroop Color-Word Interference Task after WBV and control.

Mean completion times and standard deviation of Stroop Color-Word Interference Test (CWIT) for WBV and Control conditions in standing and sitting posture. Lower mean completion times indicate less interference and a better inhibition. A significant positive effect after WBV was only found in the sitting posture. * p < 0.05 indicates statistical significance.

Fig 6. Mean rating score of the perceived joy, comfort and exertion scale in sitting and standing posture.

The sitting posture was perceived as more joyous and comfortable than the standing posture. A higher perceived exertion was found in the standing postures as compared to the sitting posture. * p < 0.05. ** p < 0.001.