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Abstract

TACSM Abstract –

The Effect of Cardiovascular Drift on the Efficacy of Exercise Prescription

KATHERINE FORESTER, JIMMY SMITH, Ph.D., and SCOTT MCLEAN, Ph.D.

Kinesiology; Southwestern University; Georgetown, TX

Category: Undergraduate

ABSTRACT

Due to the difficulty in measuring metabolic cost in the field, heart rate (HR) is often used to prescribe exercise intensity. Purpose: To examine the effect of cardiovascular drift (CVdrift) on the efficacy of exercise prescription (ExRx). Methods: Eight women with a mean (sd) age 21.6(2.0) years, body mass 70.9(11.0) kg, height 163.7(6.0) cm, and VO2max of 33.7(4.2) mL/kg/min, each performed two cycling trials for 30 to 45min at work rates that elicited 50% and 70% of VO2max. HR (bpm) and VO2 (mL/kg/min) were recorded throughout each trial and values at the beginning, middle, and end of exercise across both intensities were compared using 3 x 2 two-way repeated measures ANOVAs. Repeated measures ANOVAs were used to compare responses across time within each exercise intensity. Results: Estimated work rates accurately elicited 50% and 70% of HRmax and VO2max at 5 min of exercise. For HR, there was a significant effect of both time (F (1,2) = 124.8, p < .001) and intensity (F (1,1) = 312.0, p < .001), and a significant interaction between time and intensity (F (1,2) = 6.14, p = 0.012). There was a significant effect of time on HR at both the 50% intensity (F (1,2) = 40.74, p < .001) and 70% intensity (F(1,2) = 101.9, p < .001). VO2 increased significantly due to both time (F (1,2) = 6.63, p = .009) and intensity (F (1,1) = 312.0, p < .001) but there was no interaction, and the significant effect of time was only at the 70% intensity (F (1,2) = 3.90, p = .05). Discussion: The main finding of this study was that HR and metabolic demand became increasingly dissociated across time at both intensities. This dissociation was more pronounced at an intensity of 70% of VO2max than 50% of VO2max. This finding implies that during prolonged exercise at a steady work rate, HR becomes increasingly less valid as a surrogate for metabolic demand of exercise.

Key words: Cardiovascular drift, exercise prescription, metabolic drift.

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