C. Hausswirth et al., Evolution of electromyographic signal, running economy, and perceived exertion during different prolonged exercises, INT J SP M, 21(6), 2000, pp. 429-436
The purpose of this study was to compare the electromyographic (EMG) signal
of the vastus lateralis muscle obtained during a run section of a triathlo
n and at the end of a prolonged run performed at the same running velocity,
Seven subjects were studied on three occasions: a 2 h 15 min triathlon (30
min swimming, 60 min cycling, and 45 min treadmill running at 75% of the m
aximal aerobic speed), a 2 h 15 min run, where the last 45 min (Prolonged R
un, PR) were run at the same speed as the Triathlon Run (TR) on a motorized
treadmill, and a 45 min Isolated Run (IR) performed at the same TR and PR
velocity. The three experimental trials were randomised, Oxygen uptake ((V)
over dot O-2), heart rate (HR), and EMG data were recorded during the three
run sections. The results confirm a greater (V)over dot O-2 and HR during
PR compared with IR (P<0.01) and TR (P<0.05). Also the (V)over dot O-2 valu
es obtained during TR were significantly greater compared to IR (P<0.05). E
MG signal, obtained from the vastus lateralis muscle during 4 sec of isomet
ric contraction at 35% of maximal voluntary contraction (MVC), showed that
after PR the mean power frequency (MPF) shifted significantly to lower freq
uencies (P<0.01) compared with MPF recorded before the prolonged run. Moreo
ver, the signal amplitude (RMS) was increased significantly after PR in com
parison to pre-trial (P<0.01), Similar results were obtained for the TR at
P<0.05. The integrated EMG flow, (Q)over dot IEMG (iEMG/burst duration), re
corded during all run sections, was significantly increased near the end of
PR (i.e. 2 h 10 min of running) compared with (Q)over dot iEMG recorded af
ter 1 h 30 min of running, No significant increase in (Q)over dot iEMG was
observed with TR and IR situations. The results suggest that a long exercis
e bout of running led to a greater increase in muscle fatigue compared with
a triathlon or an isolated run performed at the same running speed. In add
ition it is suggested that the rating of perceived exertion recorded during
isometric contractions is a good indice to approach the level of fatigue d
uring prolonged exercises.