Introduction
locomotor behaviors
“If you want to find the secrets of the universe, think in terms of energy, frequency, and vibration” by Nikola Tesla (Two common types of vibrations, sub-, and supra-threshold vibration, have been widely used to enhance postural control in standing and walking (Gait characteristics and their respective variabilities have been widely agreed on as indicators of dynamic balance control. For instance, while applying sub-threshold vibration on the sole, the stride time variability significantly decreases in recurrent fallers and non-fallers, and no significant difference in stride length and step width variabilities is observed (When considering the activities of daily living, walking up/downhill is inevitable. With the change in locomotor tasks and environmental demands, the body adjusts the gait strategy to keep balance and avoid falling while completing the inclination (Previous studies have shown that young and older adults may employ a cautious gait pattern with shorter step time (higher cadence), shorter step length, and broader step width during downhill walking to mitigate the risk of falling than walking on level ground (The findings from the abovementioned studies led to an important research question: whether different types of plantar vibration affected the gait characteristics and respective variabilities differently when performing other daily locomotor behaviors, such as walking on different inclines, including uphill and downhill. Therefore, this study aimed to answer the abovementioned question. To our best knowledge, this is the first study to investigate the effect of different types of plantar vibration on different gait characteristics during walking on different inclines. Understanding the alternations in these gait characteristics under the abovementioned sensory-conflicted combined inclined conditions could identify the priorities of these gait characteristics for future use in clinical applications. Importantly, this study may provide new ideas for the clinical application of vibrations and inclined treadmill training as rehabilitation protocols. We hypothesized that the interaction between different types of vibration and levels of inclines on gait characteristics and respective variabilities could be observed. Specifically, the supra-threshold vibration might have a stronger effect than sub-threshold/no vibrations during downhill (challenging tasks) walking.