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.

26 February 2014

Tor des Géants effect on energy cost and running mechanics


I just read the article “Influence of the world’s most challenging mountain ultra-marathon on energy cost and running mechanics” by Gianluca Vernillo and colleagues in preprint in Eur J Appl Physiol 2014.
 
 
 
The study was performed on a group of 17 runners completing Tor des Géants (TDG) 2012 and not being so fatigued at finish so they could complete at least two out of three test protocols. The runners underwent three test protocols both before (1-2 days pre-race) and immediately after (less than 30 minutes post-race) the race. Due to the fatigue post-race only 7 runners completed all three tests and 10 two test sessions (cycling and uphill running). The test sessions consisted of in random order:

1)      A 4-minute bout on a cycle ergometer at a power of 1.5W kg-1 body mass with a pedal cadence at 80 rpm to determine whether differences in energy cost are related to mechanical or metabolic factors

2)      A 4-minute running bout at 9 km h-1 (2.5 m s-1) at 0% (level) incline on a motorized treadmill to determine differences in the energy cost and mechanics between level and uphill running

3)      A 4-minute running bout at 6 km h-1 (1.7 m s-1) at 15% (9°) incline to determine differences in the energy cost and mechanics between uphill and level running

 
The energy cost were determined using indirect calorimetry measurement and the kinematic running mechanics were recorded using two video cameras according to standardized procedures.

The runners were on average around 41 years old, were 177.5 cm tall with a body mass of 71.4 kg and BMI of 22.7. There were no statistical differences between the groups completing two or three tests and between the pre- and post-race sessions. The average race time of the study subjects was  118h 28min 26s (range 103h to 136h; rank 79th to 329th).

The energy cost of running (Cr) on level ground and the energy cost of cycling (Ccycl) did not change during the race, while the uphill energy cost of running (Cr) decreased by 13.8% (p = 0.004). The decrease in Cr during uphill running was associated with several changes several kinematic mechanical variables, among them an increase in contact time (tc) (+10.3%) and duty factor (DF) (+8.1%) and a decrease in swing time (ts)(-6.4%). There were no changes in stride frequency (SF) or stride length (SL), but the runners in the fatigued condition post-race increased the propulsive force time and used the muscles around the ankle joint differently during uphill running to compensate for a decrease in the capacity of muscle force generation following this extreme race. Interestingly, most runners had a duty factor above 50%, in particular post-race, indicating that they were running with a minimal aerial time in a gait which has been described as “grounded running” (found in ostriches and described in Rubenson et al 2004) or “Groucho running” (McMahon et al 1985). This particular from of running is expected to have been predominant in pre-modern humans (Schmitt et al 2003).

In summary, the extreme fatigue of the mountain ultramarathon TDG in this study led to a decrease in the energy cost of running uphill. This decrease was due to a change in the mechanical uphill-running pattern likely due to a need to decrease the discomfort to the lower limb muscles following this extreme endurance event. The finding of a decrease in the energy cost of running is different from previous observations in shorter running experiments over level ground where the energy cost seem to increase with distance (Nicol et al 1991; Kyröläinen et al 2000; Hunter & Smith 2007; di Prampero et al 2009; Lazzer et al 2012; Gimenez et al 2013). The difference could be explained both by the longer distance, but also by the extreme altitude changes in TDG (+24,000 m) and it is clear that level and uphill running requires different running mechanics (Padulo et al 2013). It would have been extremely interesting to study also possible changes in the energy cost of running and running mechanics following downhill running in TDG. At least I perceived this to be the greatest stress and challenge during TDG – to run downhill on endless uneven stones really did hurt and I would have expected the body to adapt even more to downhill running than to uphill walking during the race.
 
 

24 February 2014

Back in Courmayeur


I have spent the past week in Courmayeur skiing with my family. The weather was nice with several warm sunny days, there were plenty of snow in good condition, compared to Swedish ski resorts there were not many people in the lift system and in ski pistes, the views over the Mont Blanc massif in one direction and down the Aosta Valley in the other were priceless and visiting Italy is always a culinary experience. I also was able to go for short runs every day after skiing and it felt surprisingly good. In short, it was a really great vacation.
 
The Mont Blanc massif to the north of the ski piste

Courmayeur and the Aosta Valley to the south
 
It was also great to be back and be reminded of the days I spent in the town before and after last year’s Tor des Géants (TDG). The selection/inscription process TDG 2014 is underway and it looks now as there will most likely be several experienced Swedish ultrarunners, including Johan Wagner who has run UTMB several times, Jesper Fägersten, Peter Larsson and Jerry Bärnsten, who might get one of the coveted 660 places in the challenge in September. It is indeed a completely captivating adventure and not a single day passes without me thinking about some particular moment when I was out there around the Aosta valley – it truly is like animaginary running band around my wrist. I am very happy that PTL 2014 will pass the valley extensively with for instance the third life base after 170 km (just over 100 miles) located in Morgex just south of Courmayeur.

I was also reminded Tor des Géants when I read two new recently published scientific articles about the race: “Influence of the world’s most challenging mountain ultra-marathon on energy cost and running mechanics” by Vernillo and colleagues in preprint in Eur J Appl Physiol 2014 and “Alterations in postural control during the world’smost challenging mountain ultra-marathon” by Degache and colleagues in PLoS One9(1): e84554. Doi: 10.1371/journal.pone.0084554. I will describe the findings in these two very interesting studies from Grégorie Millet’s group in two separate blog posts. TDG has indeed really proved to be a great experiment for the limits of human endurance and there are now three articles based on the race including “Alterations of neuromuscular function after the world's mostchallenging mountain ultra-marathon” by Saugy and colleagues which I described in a blog post last summer.

11 February 2014

PTL 2014 Stage 5 Petit St Bernard - Chamonix

 

Col de l'Argueray 2853m


 

Col de l'Ouillon 2612m


 

Col d'Enclave 2672m


 

Col de la Fenêtre 2245m


 

Col du Mont Joly 1989m


 

Mont Joly 2525m


 

Col de Tricot 2120m


 

Bellevue 1809m



PTL 2014 Stage 4 Morgex - Petit St Bernard

 

Col d'Améran 2683m



Col Crosatie 2826m


 

Rifugio Angeli 2916m


 

Col de la Sassière 2841m


 

Pas de la Louie Blanche 2526m


 

Col de la Traversette 2383m



PTL 2014 Stage 3 Bourg St Pierre - Morgex

 

Cote 2922 (Arête du Petit Vélan) 2922m


 

Col de Proz 2779m


 

Col d'Annibal 2980m


 

Col Champillon 2709m


 

Col de Tardiva 2410m


 

Pointe Chaligné 2603m


 

Col Palletaz 2707m