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.

Ballistic protective helmets can impair heat dissipation. A cooling device in the helmet (cooling pad, CP) could help prevent heat problems in military personnel and potentially enhance comfort. This study examined the effects of CP on rectal and skin temperatures, heart rate, percent change in plasma volume, urine specific gravity, rating of perceived exertion, and other subjective measures while performing light work in a hot environment. It was hypothesized that the CP would act as an insulator to the head, which would not positively affect any physiological variable but could positively affect wearer subjective comfort or temperature. Participants performed a work protocol for approximately 2 hr. A ballistic vest, slacks, short-sleeved button-up shirt, and a ballistic helmet (one trial with CP and one trial without) were worn. Repeated measures analysis of variance (ANOVA) showed no differences (p > 0.05) between wearing and not wearing the CP for any physiological parameter. However, participants perceived the CP as cooler (p = 0.002). Other trends in perceptual data such as thermal strain and helmet comfort indicated the CP felt cooler. However, based on forehead temperature and participant comments, the CP lost its cooling ability relatively quickly (within approximately 30 min).