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.
INSERM ERM 207 Laboratory, Faculty of Sport Sciences, University of Burgundy, Dijon, France. nicolas.place@u-bourgogne.fr
Nicolas
N
Place
Romuald
R
Lepers
Gaëlle
G
Deley
Guillaume Y
GY
Millet
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