Effects of 120mg pseudoephedrine on muscle performance and fatigue
Phelps, D, Weatherby, RP & Zhou, S, 'Effects of 120mg pseudoephedrine on muscle performance and fatigue', paper presented to 6th Annual Conference of the Society of Chinese Scholars on Exercise Physiology and Fitness, Guangzhou, China, 14-16 December.
Pseudoephedrine (PSE) was recently removed from the list of prohibited substances in sports because of equivocal evidence of its effects. Following previous investigations in our laboratory, the aim of present study was to examine the potential ergogenic effects of PSE on force production capacity, muscle activation and fatigue during an incremental cycle exercise (ICE). Nine healthy male athletes, age of 18-23 years, voluntarily participated in this double-blind placebo-controlled study. Each subject undertook one familiarisation session (F) and three testing sessions (A, B and C) in a randomised order. In Session F, subjects were familiarised with the testing procedure and underwent ICE till exhaustion. In Session A, 120mg of PSE and ICE were administered. Session B was similar to Session A while the PSE was replaced by a placebo (PLA). Session C was similar to Session A while the ICE was replaced by rest as control (CON). Maximal voluntary knee extension contractions (MVC) and twitch interpolation test (TI) were performed to examine strength and muscle activation deficit (MAD) at baseline, 1hr post PSE or PLA administration, and post ICE. Electrocardiogram (ECG), Heart rate (HR), blood pressure (BP) and perceived drug effect scores (DE) were recorded before and after each performance test. Repeated measures ANOVA was used to compare the mean values of the outcome measures within and between the sessions. Results showed a significant (p<0.05) increase in MVC 1hr post PSE ingestion in Session C, a higher MVC in Session A than that in B, and a significant decrease in MAD post ICE in Session A. Although not statistically significant, a trend of increase (p=0.053) was detected in electrical stimulation evoked twitch torque (ETT) post ICE in Session A. No significant difference was found in time to fatigue during ICE or in the DE, while DE was higher during Session A than Session B. The study confirmed previous findings that PSE at doses of 120-180mg had ergogenic effects on muscle performance. The results suggest that PSE has the effects of reducing muscle activation deficit and improving muscle contractility. A case of abnormality in ECG indicated that ingestion of PSE at a dose above therapeutic level may pose an additional risk factor to the health of athletes.