28 February 2014

Tor des Géants effect on postural control – how is balance affected while running an extreme mountain ultramarathon



Lack of balance in the Antero-Posterior (AP) plane perhaps due to fatigue and sleep deprivation. Picture from the Whatisultra website 
When I was in Courmayeur last week and looked down the beautiful alpine valley Val Ferret with the Mont Blanc massif on one side and Grande Rochère on the other I vividly remembered my desperate struggle in the early morning of Friday September 13 last year to not fall off the small mountain path I was stumbling forward on. The mountainside of the valley was much steeper than I remembered and I was suddenly reliving my fight to keep control over my mind and body watching the first rays of sun hit the Grand Jorasses and Aigulle du Géant on the Mont Blanc Massif while tripping forward the narrow path between the Bonatti and Bertone refugios. My balance was clearly affected of the fatigue and sleep deprivation at this point in the race and to not have my normal postural control was an extremely uncomfortable feeling to say the least -  one wrong step could mean a step into oblivion.

Val Ferret between Refugio Bonatti and Bertone
It was therefore of great interest when I came across the article “Alterations in postural controlduring the World’s most challenging mountain ultra-marathon” by Degache andcolleagues in PLoS ONE 2014; 9(1): e84554. doi: 10.1371/journal.pone.0084554. This is the third article from Grégorie Millet’s group regarding Tor des Géants and I have in previous blog posts described the others published by Saugy etal. 2013 and Vernillo et al. 2014.

In the study 18 male runners completing TDG with a finish time of 126 ± 16 h (rank 7th to 243rd) were compared with a control group of 8 similarly sleep deprived healthy males and tested before the race (PRE), mid-race at Donnas after 148.7 km (MID) and post-race (POST). On average the runners slept 8.6 ± 5.3 hours and the controls 12.3 ± 5.4 hours. For the tests the subjects were asked to stand upright on a posturographic platform over a period of 51.2 seconds (resulting in a 2048-point time series) using a two-leg stance under two test conditions: eyes open (EO) and eyes closed (EC) while traditional measures of postural stability/sway (center of pressure [CoP] trajectory analysis) and stabilogram-diffusion analysis (SDA) parameters were analysed. The analyses were done in the antero-posterior (AP) and medio-lateral (AL) body plane directions. The level of perceived exertion and fatigue sensations were evaluated using a 10-cm visual analogue scale (VAS).

 
The runners, not surprisingly, had a greater increase in perceived fatigue than the controls. A significant increase in the perceived level of fatigue was observed for runners between PRE and MID (54±5%; p<0.05), between MID and POST (50±37%; p<0.05) and between PRE and POST (132±29%; p<0.01). A significant difference between runners and controls was only detected at POST (78±23%; p<0.05) (F = 3.454, p = 0.009).

 
The posturographic tests revealed a similar not surprising detoriation in postural control in the runners during the race. 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).

The findings of decrease in postural control observed in runners from mid-race to post race in TDG is perhaps not surprising. More surprising is that this appears primarily due to the mountain ultramarathon-induced perhipheral afferents and the muscle fatigue rather than the sleep deprivation as the control group who had a similar level of sleep deprivation did not show any effects on postural control. This is in contrast to effects of sleep deprivation on postural control in previous studies where it has been shown in numerous studies that continuous sleep deprivation for >19 to 48 hours lead to affected postural stability (Avni et al 2006; Gribble et al 2004; Liu et al 2001; Nakano et al 2001; Morad et al 2007; Patel et al 2008). The difference might be explained by the fact that both control subjects, as did the runners, was not completely continuously sleep deprived but slept periodically during the race in periods of 30 min to 1 hour. As the authors however mention even though the sleep deprivation did not have an effect on postural control it might have led to reduced attention and this could in itself induce falls and injuries during a mountain ultramarathon. Changes in the attention level following TDG was however not part of this study and would be an interesting subject for coming studies.

An interesting finding in the study was that the postural control was mostly affected in the antero-posterior (AP) direction (36 ± 14%) compared to the medio-lateral (ML) direction (29 ± 18%). It has previously been proposed that ankle plantar- and dorsiflexors play a predominant role in the control of AP movements, whereas hip adductors and abductors primarily control ML sway (Winter et al. 1996). For a mountain ultramarathon such as TDG containing multiple uphill/downhill sections on unstable ground it is expected that there would be a greater muscle fatigue in the ankle plantar and the dorsi-flexor muscles than the hip adductors and abductors and this has also been observed in a study by Forchet et al 2012 after a 5-hour hilly run. In practice this would lead to a higher risk of falling forward or backwards rather than to the sides during the latter part of the race.  Indeed the only fall I sustained during TDG was when I in a fatigued state the last night struggling in the Merdeux valley from Saint-Rhémy-en-Bosses up to the last mountain pass of the race Col Malatra fell asleep in a step and fell forward and rolled of the trail. On the other hand I struggled more with the balance running on the relatively level track between the Bonatti and Bertone refugios a couple of hours later than when flowing down the last rather technical downhill section from the Bertone refugio to Courmayeur. Looking at the stabilogram-diffusion analysis (SDA) results it was indeed found for instance a significant difference in the ML direction in Cdx and in Ctx in both EO and EC conditions post-race  – i.e. the runners took longer to stabilize their body in the ML plane using sensory inputs from the environment. These findings were not found in the AP plane and could possibly be explained by the adaption of the dynamic balance running on very narrow mountain trails tiring also the adductor and abductor muscles of the hip.

In summary, at the end of a mountain ultramarathon such as TDG the body clearly has difficulties control motor tasks using all sensorimotor afferents and to maintain postural control. It is important to be aware of this and to adapt the pace accordingly to maintain safety. I also think it important to try to train the balance in particular by running downhill on technical paths before the race and it would be interesting to see how elite runner’s like the winner of TDG 2013 Iker Karrera or Kilian Jornet would score in postural tests as those in they study by Degache and colleagues after a strenuous mountain ultramarathon. The relationship between training of balance and postural control before a race and performance after would be interesting to study.

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