For the longest distance runner, that tired feeling may not be due to central fatigue



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.


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 significa

Contact: Donna Krupa
American Physiological Society

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