For The Longest Distance Runner, That Tired Feeling May Not Be Due To Central Fatigue

Testing long-distance runners covering the equivalent of the circuit from the Lincoln Memorial to Camden Yards; results published in the Journal of Applied Physiology

(March 12, 2002) - Bethesda, MD -- An ultramarathon is any running event longer than the standard marathon distance of 42 kilometers, 195 meters (26 miles, 385 feet).  Dedicated runners from around the world take up the challenge of this long distance event.  For even the most in-shape participants, a race of this distance can last from six to nine hours.

Background

Fatigue is a natural consequence of such sustained physical activity.  Physical activity lasting one to two hours often leads to local fatigue, causing pain in a specific part of the body.  A long held belief in the scientific community is that central fatigue, resulting from alterations to the central nervous system, is the consequence of an ultra-long-duration exercise. 

Despite the purported association between central fatigue and an ultra-long-duration exercise, few studies have examined the alterations of neuromuscular function after a grueling physical endeavor.  Now, a team of French research scientists set out to examine such changes in runners' neuromuscular function after a 65 kilometer (40 mile) race, which is approximately equal to the distance between the Lincoln Memorial in Washington and Baltimore's Camden Yards, the city's baseball stadium. 

Their experiment is the first one designed to study the changes in neuromuscular functions after properties after ultra-long-fatigue.  This examination required the testing of changes in voluntary and electrically invoked evoked force of the knee extensors and plantar flexors that occur before and after an ultramarathon.

The authors of the study, "Alterations of Neuromuscular Function After an Ultramarathon," are G.Y. Millet, R. Lepers, N.A. Maffiuletti, N. Babault, V. Martin, and G. Lattier, all from the Groupe Analyse du Mouvement, Faculté des Sciences du Sport, Université de Bourgogne, Dijon Cedex, France.  Their findings are published in the February 2002 edition of the Journal of Applied Physiology.

Methodology 

Nine healthy male subjects (age 41.6 ± 5.9 years; mass 152 ± 15 lbs.; height 5 ft., 9 inches ± four inches; body fat 10.6 ± 2.6 percent), all regular competitors in running or triathlon events, were enrolled in the study.   The maximal twitches for knee extensors (KE) and plantar flexors (PF) were both examined before and after the 40-mile race using a bicycle ergometer.   This testing device uses the inertia of a flywheel to provide resistance during both shortening (concentric) and lengthening (eccentric) muscle actions. This measures isometric, concentric, and eccentric muscle actions, assessing strength and velocity of different types of muscle actions.

The first session, when subjects were in a nonfatigued state, was conducted in the week prior to the ultramarathon.  The test started with a 10 minute warm-up on the bicycle ergometer.   The second session was undertaken in a fatigued state, two minutes after the race, and required 20 minutes on the bicycle ergometer. 

During both sessions, the KE and PF were given electrical stimulation to determine muscle contractile measurements.  During the test in the nonfatigued stage, the intensity was increased until there was no further increase in the height of the muscle twitch (involuntary contraction) or the amplitude of the M wave (electrically evoked muscle potential).  The same stimulus level was used during the fatigued stage of the experiment.

Results 

Maximal voluntary contractions and maximal voluntary activation decreased significantly after the ultramarathon (a decline of 30.2 ± 18.0 percent and 27.7 ± 13.0 percent, respectively). Surprisingly, peak twitch increased after the ultramarathon from 15.8 ± 6.3 to 19.7 ± 3.3 Nm) and from 131.9 ± 21.2 to 157.1 ± 35.9 Nm for KE. Also, shorter contraction and half-relaxation times were observed for both muscles. The compound muscle action potentials (M wave) were not significantly altered by the ultramarathon with the exception of the sole of the foot, which showed a slightly higher M-wave amplitude after the running.

Conclusions 

From these results, it can be concluded that 65 km of running 1) severely depressed the maximal voluntary force capacity mainly because of a decrease in maximal voluntary activation, 2) strengthened the twitch mechanical response, and 3) did not change significantly the M-wave characteristics.

The large loss in maximal voluntary contractions induced by the 65 km (40 mile) ultramarathon was mostly due to central fatigue.  On the other hand, the strengthening twitch mechanical responses and M-wave amplitude characteristics were not altered by the extended run.

With few exceptions, neurophysiological and mechanical modifications in PF and KE were comparable.  This leads the researchers to believe that, in an ultramarathon, fatigue is task dependent, and has very specific effects on neuromuscular properties compared with a shorter duration of fatiguing exercise.

Source: February edition of the Journal of Applied Physiology.

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The American Physiological Society (APS) was founded in 1887 to foster basic and applied science, much of it relating to human health. The Bethesda, MD-based Society has more than 10,000 members and publishes 3,800 articles in its 14 peer-reviewed journals every year.

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Editor’s Note: To set up an interview with a member of the research team, please contact Donna Krupa at 703.527.7357 (direct dial), 703.967.2751 (cell) or djkrupa1@aol.com.