The effect of selective β1-blockade on EMG signal characteristics during progressive endurance exercise

Abstract.

This study analysed the effect of selective β₁-blockade on neuromuscular recruitment characteristics during progressive endurance exercise. Ten healthy subjects ingested a selective β₁-blocker, acebutolol (200 mg b.d.), for 7 days (for one of two cycling trials), with a 10-day wash-out period between trials. On the last day of acebutolol ingestion subjects performed three successive 15-min rides at 30%, 50% and 70% of their peak power output and then cycled at increasing (15 W min^–1) work rates to exhaustion. Force output, heart rate, submaximal V˙O₂, rate of perceived exertion (RPE), electromyographic (EMG) data and blood lactate were captured during the cycling activity. Peak work rate [270 (111) W vs 197 (75) W, CON vs BETA, P <0.01], time to exhaustion [49.7 (23.2) min vs 40.3 (23.7) min, CON vs BETA, P <0.05] and heart rate [mean, for the full ride 135.5 (38.3) beats min^–1 vs 111.5 (30.0) beats min^–1 CON vs BETA, P <0.05] were significantly lower for the group who ingested β₁-blockade (BETA) compared to the control group (CON). Although not significant, submaximal V˙O₂ was reduced in BETA during the ride, while RPE was significantly higher during the ride for BETA (P <0.01). Mean integrated electromyography was higher in the BETA group although these differences were not significant. Mean power frequency values of the BETA group showed a significant (P <0.05) shift to the upper end of the spectrum in comparison to the control group. Lactate values [11.7 (3.5) mmol.l^–1 vs 7.1 (4.1) mmol.l^–1 CON vs BETA] were significantly lower (P <0.05) at exhaustion in BETA. Significant reductions in cycling performance were found when subjects ingested β₁-blockers. This study has shown significant shifts to the upper end of the EMG frequency spectrum after β₁-blocker ingestion, which could be caused by a change in neuromuscular recruitment strategy to compensate for the impaired submaximal exercise performance.