Alterations in postural control during the world's most challenging mountain ultra-marathon.

Francis Degache,Lukas Oehen,Jérôme Van Zaen,Kenny Guex,Pietro Trabucchi,Gégoire Millet,François Hug

doi:10.1371/journal.pone.0084554

Abstract

We investigated postural control (PC) effects of a mountain ultra-marathon (MUM): a 330-km trail run with 24000 m of positive and negative change in elevation. PC was assessed prior to (PRE), during (MID) and after (POST) the MUM in experienced ultra-marathon runners (n = 18; finish time = 126±16 h) and in a control group (n = 8) with a similar level of sleep deprivation. Subjects were instructed to stand upright on a posturographic platform over a period of 51.2 seconds using a double-leg stance under two test conditions: eyes open (EO) and eyes closed (EC). Traditional measures of postural stability (center of pressure trajectory analysis) and stabilogram-diffusion analysis (SDA) parameters were analysed. For the SDA, a significantly greater short-term effective diffusion was found at POST compared with PRE in the medio-lateral (ML; Dxs) and antero-posterior (AP) directions (Dys) in runners (p<0.05) The critical time interval (Ctx) in the ML direction was significantly higher at MID (p<0.001) and POST (p<0.05) than at PRE in runners. At MID (p<0.001) and POST (p<0.05), there was a significant difference between the two groups. The critical displacement (Cdx) in the ML was significantly higher at MID and at POST (p<0.001) compared with PRE for runners. A significant difference in Cdx was observed between groups in EO at MID (p<0.05) and POST (p<0.005) in the ML direction and in EC at POST in the ML and AP directions (p<0.05).Our findings revealed significant effects of fatigue on PC in runners, including, a significant increase in Ctx (critical time in ML plan) in EO and EC conditions. Thus, runners take longer to stabilise their body at POST than at MID. It is likely that the mountainous characteristics of MUM (unstable ground, primarily uphill/downhill running, and altitude) increase this fatigue, leading to difficulty in maintaining balance.

Highlights

Postural control is a complex function that involves maintaining the projection of the centre of mass (CoM) within the base of support [1]
centre of pressure (CoP) was observed between PRE and POST sessions for both the Eyes Opened (EO) and the Eyes Closed (EC) conditions (p,0.05), and a significant change was observed between MID and POST for total and X length of CoP in the EC context (p,0.05)
In the EO context, a significant difference was found between runners and controls at POST for all parameters with interaction between group and time for total length of CoP (F = 6.159, p = 0.004), AP length of CoP (F = 5.009, p = 0.011) and for ML length of CoP (F = 5.190, p = 0.009)

Summary

Introduction

Postural control is a complex function that involves maintaining the projection of the centre of mass (CoM) within the base of support [1]. Postural control is dependent upon reflexive and voluntary muscle responses [2]. Balance is actively controlled by the central nervous system, which calls into action various relevant postural muscles when they are required [3]. Postural strategy appears to choose an equilibrium state with small-amplitude oscillations while keeping the body close to vertical alignment [4]. The bipedal control of posture in the Eyes Opened (EO) or Eyes Closed (EC) conditions has primarily been studied by analysing the trajectory of the centre of pressure (CoP), which can be recorded using posturographic platforms [5]

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