Gathering your ‘sea legs’: Extended durations in an offshore environment increases postural sway excursions

Background: Mal de debarquement (MdD), or often called ‘sea legs’, is the perception of self-motion after exposure to passive movement such as being on a boat at sea. Previous studies highlight sensory re-organization difficulties and postural control impairments after disembarking from sea travel in experienced crew members. However, the impact of MdD in individuals with minimal offshore experience, defined as participating in less than 2 offshore excursions per year, has not been investigated. Research question: Does exposure to boat motion while at sea alter static postural control after disembarking in individuals with minimal offshore experience? Methods: Healthy adults (n = 24) with minimal offshore experience had their static balance assessed on a force platform before (PRE) and after (POST) a 7-h deep sea fishing excursion. Static balance was tested in eyes open (EO), eyes closed (EC), eyes open on a foam surface (EOF), and eyes closed on a foam surface (ECF) conditions. Sway excursions, sway velocity and sway variability in the medial-lateral (ML) and anterior-posterior (AP) directions were computed and then compared PRE/POST using a paired t-test (p < 0.05). Results: Significant increases in ML sway excursion (p = 0.004), ML sway range (p < 0.001), ML sway variability (p < 0.001), AP sway excursion (p = 0.045), AP sway range (p = 0.020), and AP sway variability (p = 0.030) were observed at POST during EOF. Significant increases in ML sway excursion (p = 0.027), AP sway excursion (p = 0.020), and AP sway variability (p = 0.014) at POST were also observed during ECF. No differences were found in the EO condition (p > 0.05). Significance: Increases in postural sway excursion and variability were observed in individuals with minimal offshore experience after disembarking. Our findings suggest sensory re-organization difficulties in order to maintain an upright posture in challenging sensory conditions are dependent on vestibular and somatosensory inputs following exposure to boat motion at sea.