Evolution of electromyographic signal, running economy, and perceived exertion during different prolonged exercises

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.