Alterations of Neuromuscular Function after the World's Most Challenging Mountain Ultra-Marathon

Abstract

We investigated the physiological consequences of the most challenging mountain ultra-marathon (MUM) in the world: a 330-km trail run with 24000 m of positive and negative elevation change. Neuromuscular fatigue (NMF) was assessed before (Pre-), during (Mid-) and after (Post-) the MUM in experienced ultra-marathon runners (n = 15; finish time = 122.43 hours ±17.21 hours) and in Pre- and Post- in a control group with a similar level of sleep deprivation (n = 8). Blood markers of muscle inflammation and damage were analyzed at Pre- and Post-. Mean ± SD maximal voluntary contraction force declined significantly at Mid- (-13±17% and -10±16%, P<0.05 for knee extensor, KE, and plantar flexor muscles, PF, respectively), and further decreased at Post- (-24±13% and -26±19%, P<0.01) with alteration of the central activation ratio (-24±24% and -28±34% between Pre- and Post-, P<0.05) in runners whereas these parameters did not change in the control group. Peripheral NMF markers such as 100 Hz doublet (KE: -18±18% and PF: -20±15%, P<0.01) and peak twitch (KE: -33±12%, P<0.001 and PF: -19±14%, P<0.01) were also altered in runners but not in controls. Post-MUM blood concentrations of creatine kinase (3719±3045 Ul·(1)), lactate dehydrogenase (1145±511 UI·L(-1)), C-Reactive Protein (13.1±7.5 mg·L(-1)) and myoglobin (449.3±338.2 µg·L(-1)) were higher (P<0.001) than at Pre- in runners but not in controls. Our findings revealed less neuromuscular fatigue, muscle damage and inflammation than in shorter MUMs. In conclusion, paradoxically, such extreme exercise seems to induce a relative muscle preservation process due likely to a protective anticipatory pacing strategy during the first half of MUM and sleep deprivation in the second half.

Figure 1. Altitude profile of the entire run with the three session test locations and the distance scale in km.

Figure 2. Maximal voluntary contraction (MVC) prior to (Pre-), in the middle of (Mid-) and after (Post-) the race for knee extensors (KE, panel A) and plantar flexors (PF, panel B).

A two-way repeated measure ANOVA was used complemented by a Bonferroni post-hoc test. Values are mean ± SE.

Figure 3. Amplitude of the potentiated doublet (PS100) prior to (Pre-), in the middle of (Mid-) and after (Post-) the race for knee extensors (KE, panel A) and plantar flexors (PF, panel B).

A two-way repeated measure ANOVA was used complemented by a Bonferroni post-hoc test. Values are mean ± SE.

Figure 4. Amplitude of the potentiated peak twitch (Pt) prior to (Pre-), in the middle of (Mid-) and after (Post-) the race for knee extensors (KE, panel A) and plantar flexors (PF, panel B).

A two-way repeated measure ANOVA was used complemented by a Bonferroni post-hoc test. Values are mean ± SE.

Figure 5. Decrease in MVC force for UTMB (Ultra-Trail du Mont-Blanc), the TdG (Tor des Geants) and TdG at mid-race (Mid) for the knee extensors (KE, panel A) and the plantar flexors (PF, panel B) and decrease in peak twitch for the UTMB, the TdG and TdG Mid for the knee extensors (panel C) and the plantar flexors (panel D).

Unpaired t-tests were used. Data are given in changes from Pre- values.

Figure 6. Visual analogue scale (VAS) for the pain-foot-ankle (panel A), the knee-thigh-hip (panel B), the digestive feeling (panel C) and the general fatigue (panel D) for runners (TOR) and control group (CON) prior to (Pre-), in the middle of (Mid-) and after (Post-) the race.

A two-way repeated measure ANOVA was used complemented by a Bonferroni post-hoc test. Values are mean ± SE.