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Optimum Performance: When it comes to ultra endurance races, men may fatigue before women

In this Sunday, July 12, 2015 photo released by the Brooks Running Company, Scott Jurek, of Boulder, Colo., climbs to the summit of Mount Katahdin near Millinocket, Maine, before completing the Appalachian Trail in what he claims is record time. Jurek, winner of several ultramarathon races, began at Springer Mountain in northern Georgia on May 27. (Luis Escobar/Brooks Running Company via AP) (Luis Escobar)

This week the Associated Press reported that, “Scott Jurek, 41, of Colorado overcame an injury, difficult terrain, and sleep deprivation on the final stretch of the Appalachian Trail to complete the 2,189-mile run from Georgia to Maine in a record time of 46 days, 8 hours. That beat the record held by Jennifer Pharr Davis, by three hours.” 

Not surprising that a man beat the woman’s record. Research published in the July 2015 edition of Medicine & Science in Sports & Exercise — the official journal of the American College of Sports Medicine (ACSM) — notes, “it is, however, unlikely that females will regularly outrun males because of known physiological sex differences such as greater maximal oxygen consumption and higher hemoglobin (oxygen carrying part in the blood) concentrations in males.”

Before the ladies jump my case, let me pose a question, which was asked in the same ACSM journal: “Are Females More Resistant to Extreme Neuromuscular Fatigue,” than their male counterparts — all things being equal. My money is on the women.

Neuromuscular fatigue, according to the University of Texas at Arlington (, “can be defined as a transient decrease in muscular performance usually seen as a failure to maintain or develop a certain expected force or power.”

French researchers commented in the ACSM journal that, “it is recognized that females are less fatigable than males for sustained and intermittent isometric contractions at the same relative intensity in most muscle groups,” with possible explanations being, “central nervous system functioning, muscle mass, reproductive hormones, and skeletal muscle metabolism and contractile properties.”

To find out if the women can out perform the men, these same researchers selected 20 healthy, male and female ultra-endurance trail competitors, who were matched for relative performance criteria – winning race times. They were tested pre and post competition with a maximal, incremental running test, blood testing looking for inflammatory markers – C-reactive protein and creatine phosphokinase (CPK), and EMG activity of the right knee extensors (vastus lateralis), plantar flexors (gastrocnemius lateralis, soleus) and dorsiflexors (tibialis anterior) – all of which will effect long term performance if they fatigue over time. 

Then the fun began. The competitors participated in the North Face Ultra-Trail du Mont-Blanc 2012 event – which was shortened to a total of 68.35 miles of running /walking with a total positive elevation change of 19,232 feet, under conditions of a mixture of rain, snow, and clouds in which the temperature reached a maximum of 56.6 degrees F and decreased below 32 degrees F at altitudes above 5905 feet.

In the follow up to the UTRR (ultra-trail running race), the results demonstrated that the inflammatory (blood) markers increased for both the male and female racers. It also appeared that the males experienced, “a greater MVC (maximum voluntary contraction) decrease than females in the knee extensors (thighs).” And, “males exhibited greater decreases in evoked plantar flexor (calf / soleus) torques (turning power) than females after the UTRR,” which led the researchers to, “suggest that there is a sex difference in the development of peripheral fatigue in the plantar flexors that either did not exist or was unable to be measured in the knee extensors.”

It is especially interesting to note the fatigability of the lower leg relative to when the foot makes contact to the ground. I would conclude that as the peripheral fatigue in the plantar flexors in males increases with race duration, then the ability to “push off” with the forefoot would also diminish – yielding a potential for a decrease in power and race pace.

The bottom line: the reduced level of fatigue in the thighs and lower leg of the females in extreme running races makes the female UTRR competitors a force to be reckoned with.

Guys, are we ready for some football?

Mackie Shilstone, a regular contributor to | The Times-Picayune, has been involved in the wellness sports performance industry for nearly 40 years. He is currently a fitness consultant to Serena Williams and has trained numerous other professional athletes and consulted a litany of professional sports franchises. He is St. Charles Parish Hospital’s fitness and wellness expert. Contact him at