Time course of neuromuscular alterations during a prolonged running exercise.
OBJECTIVE
This study investigated the time course of contractile and neural alterations of knee extensor (KE) muscles during a long-duration running exercise.


METHODS
Nine well-trained triathletes and endurance runners sustained 55% of their maximal aerobic velocity (MAV) on a motorized treadmill for a period of 5 h. Maximal voluntary contraction (MVC), maximal voluntary activation level (%VA), and electrically evoked contractions (single and tetanic stimulations) of KE muscles were evaluated before, after each hour of exercise during short (10 min) interruptions, and at the end of the 5-h period. Oxygen uptake was also measured at regular intervals during the exercise.


RESULTS
Reductions of MVC and %VA were significant after the 4th hour of exercise and reached -28% (P < 0.001) and -16% (P < 0.01) respectively at the end of the exercise. The reduction in MVC was highly correlated with the decline of %VA (r = 0.98, P < 0.001). M-wave was also altered after the fourth hour of exercise (P < 0.05) in both vastus lateralis and rectus femoris muscles. Peak twitch was potentiated at the end of the exercise (+18%, P = 0.01); 20- and 80-Hz maximal tetanic forces were not altered by the exercise. Oxygen uptake increased linearly during the running period (+18% at 5 h, P < 0.001).


CONCLUSIONS
These findings suggest that KE maximal voluntary force generating capability is depressed in the final stages of a 5-h running exercise. Central activation failure and alterations in muscle action potential transmission were important mechanisms contributing to the impairment of the neuromuscular function during prolonged running.
Place
Nicolas
N
INSERM ERM 207 Laboratory, Faculty of Sport Sciences, University of Burgundy, Dijon, France. nicolas.place@u-bourgogne.fr
Lepers
Romuald
R
Deley
Gaëlle
G
Millet
Guillaume Y
GY
D000328:Adult; D004558:Electric Stimulation; D004576:Electromyography; D005602:France; D006339:Heart Rate; D006801:Humans; D009119:Muscle Contraction; D010100:Oxygen / Q000378:metabolism; D012420:Running / Q000502:physiology*
D010100:Oxygen