L.J. Miller, L.J. D’Acquisto, D. D’Acquisto, K. Roemer, M. Fisher

Central Washington University, Ellensburg, WA

PURPOSE: The primary aim of this study was to examine physiological and perceived exertion responses to a high intensity, shallow water exercise interval workout (HISWE). It was hypothesized that HISWE would result in cardiometabolic (oxygen uptake (V̇O2) & heart rate (HR)) and rating of perceived exertion (RPE, Borg 6-20 scale) responses that would be classified as “vigorous” according to the American College of Sports Medicine (ACSM) intensity guidelines. METHODS: Volunteers (n=9, females, 26±6 yrs) completed the following three testing sessions (TS): TS1, familiarization; TS2, head-out, shallow water incremental exercise to exhaustion to determine peak V̇O2 (indirect calorimetry) and HR (telemetry); and, TS3, performed HISWE while being monitored for V̇O2, HR, and blood lactate responses. HISWE consisted of a warmup followed by 4 x 4 minute (min) bouts. Each bout consisted of 20 seconds (s) exercise followed by 10 s of rest (8 x 20 s exercise effort per 4 min bout) with a 1-min rest between bouts. Participants were instructed to perform each 20 s effort all-out. Exercise bouts were performed with participants immersed in water (~28-290 celcius) to axillary level. RESULTS: Peak V̇O2 and HR, 2.7±0.3 l.min-1 and 181±8 bpm, respectively. Overall, V̇O2, HR, and RPE for HISWE was 2.0±0.2 l.min-1 (73±5% V̇O2 peak), 156±8 bpm (86±2% HR peak), and 18.5±1.1 (~extremely hard), respectively. Percent V̇O2 and %HR peak increased in a step-wise fashion from bout 1 (71±6 and 84±4%) to bout 4 (85±6 and 94±2%, respectively) (P<0.05). Despite participants being asked a-priori to perform each 20 s exercise interval all-out, there was a gain in physiological strain (end-spurt) during the final 4 min bout (greater %V̇O2, %HR, and blood lactate for bout 4 versus 1, 2, & 3; P<0.05). Peak blood lactate was 9.2±1.7 mM following the last 4 min HISWE bout. CONCLUSION: Cardiometabolic and RPE responses indicated a vigorous to near-maximal effort according to ACSM’s guidelines for exercise intensity. The presence of a cardiometabolic end-spurt noted in bout 4 suggests that participants, overall, did not fully tax their physiological reserve during the shallow water interval workout, possibly to avoid overextending themselves in order to prevent premature fatigue.

Supported by CWU-Ellensburg Master's Research or Creative Activity Fellowship.

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