Effect of daily versus intermittent exposure on heat acclimation

In order to compare the effectiveness of a daily to an intermittent acclima tion protocol, 14 competitive rowers (mean +/- SD (V) over dot (O2peak) = 4 8 +/- 7 ml(.)kg(-1.)min(-1)) were randomly assigned to either a consecutive (10 consecutive days) or intermittent acclimation group (10 sessions over 3 weeks). For every heat exposure, subjects in each group exercised for 30 min at 70% (V) over dot (O2peak) in an environmental chamber set at 38 degr eesC and 70% relative humidity. Acclimation state was monitored by measurin g heart rate (HR), rectal and skin temperature (Tre and Trk), ratings of pe rceived exertion (RPE) and whole body sweat rate (SR) during each heat expo sure. Final exercise Tre decreased significantly by 0.6 +/- 0.7 degreesC wi th intermittent heat exposure but the decrease was significantly larger (p < 0.05) with consecutive day heat exposure (1.0 <plus/minus> 0.1 degreesC). Final exercise HR also decreased significantly by 13 +/- 12 bpm (p < 0.05) in the consecutive group, and non-significantly by 5 <plus/minus> 13 bpm i n the intermittent group. RPE decreased with daily (5 +/- 1, p < 0.05) but did not significantly decrease with intermittent heat exposure (1 <plus/min us> 3). Similarly, Tsk significantly decreased with consecutive (0.4 +/- 0. 2 degreesC, p < 0.05) but not intermittent exposure (0.2 <plus/minus> 0.3 d egreesC) and SR did not change in either group. Minimal adaptation occurs w ith intermittent heat exposure and it appears that daily heat exposure is t he most effective acclimation strategy.