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.

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