RPE-lactate dissociation during extended cycling

This study examined the association of blood lactate concentration La] and heart rate (HR) with ratings of perceived exertion (RPE) during 60 min of steady workload cycling. Physically active college-aged subjects (n=14) completed an exhaustive cycling test to determine VO_{2 peak} and lactate threshold (2.5 mmol l^–1). Subjects then cycled for 60 min at the power output associated with 2.5 mmol l^–1 LA]. HR, LA], RPE-overall, RPE-legs and RPE-chest were recorded at 5, 10, 20, 30, 40, 50 and 60 min. The 60-min trials were below maximal lactate steady state, with peak lactate concentration occurring at 20 min after which LA] declined. The 20-min point was therefore considered pivotal, and data at other points were compared to this time point. Repeated measures ANOVA with simple contrasts (alpha=0.05) showed (a) LA] at 40, 50 and 60 min was significantly lower than at 20 min, (b) RPE-O and RPE-L were significantly greater at 30, 40, 50 and 60 min than at 20 min, (c) RPE-C was significantly greater at 40, 50 and 60 min than at 20 min, and (d) HR was significantly greater at 30, 40, 50 and 60 min than at 20 min. Significant (P<0.05) positive correlations were found between HR and RPE-O (r=0.43), RPE-L (r=0.48) and RPE-C (r=0.41) while correlations for LA]-HR (r=0.13) and LA]-RPE (RPE-O: r=–0.11, RPE-L: r=0.01, RPE-C: r=–0.06) were weak and non-significant. There is a dissociation of RPE and LA] owing to RPE drift and lactate kinetics in longer duration sub-maximal exercise. Apparently, LA] is not a strong RPE mediator during extended cycling.