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Article Title

REDEFINING STEADY-STATE PARAMETERS USING RESPIRATORY AND CARDIOVASCULAR VARIABLES

Abstract

Y. Wu, C. Markowski, T. Woods, C. Boyce, K. Sieler, A. Venturi, A. Nicholson, D. Terry, C. Johnson, D.E. Lankford, FACSM

Brigham Young University - Idaho, Rexburg, ID

Steady-state (SS) exercise is characterized by a physiological equilibrium between energy demand of the working muscles and aerobic metabolism, indicating that both ventilation and heart rate (HR) will remain within a range. Currently, the HR ≤ 5bpm method is a guideline for determining SS. However, little research has been done on this parameter and potential applications. PURPOSE: To redefine the determining parameters for SS exercise. METHODS: Each subject (n=31, m=21, f=10) performed four treadmill exercise tests consisting of an incremental VT/VO2 max test (day 1) and three 10-minute constant workload exercises at 2.5, 3.5, and 6.0 mph (day 2). Variables VO2, RER, and HR were recorded throughout each test. Statistical control charts were used in reverse time order to identify the earliest time point where the constant workload test variables remain in statistical control. The onset of SS was recorded as one minute after statistical control began (CC-1). Data collected after this time were used to create the Steady- State Speed Adjusted Coefficient of Variation (SAC-V): (SD/Mean) *(Speed in mph). SAC-V values less than the 95th percentile represent acceptable SS for each variable. Paired t-tests were used to compare the differences between: 1) the time at the onset of SS VO2 and HR at each speed as determined by CC-1; and 2) the time at the onset of SS HR determined by CC-1 vs. HR ≤ 5bpm method. RESULTS: SAC-V 95th percentile for VO2 = 0.39, RER = 0.15, and HR = 0.10. Time at CC-1 VO2 and HR were statistically different at 3.5 mph (2.63 ± 1.85 min, 5.23 ± 1.83 min, p < 0.05) and 6 mph (3.24 ± 1.25 min, 6.95 ± 1.31 min, p < 0.05), but not at 2.5 mph (2.83 ± 2.13 min, 3.81 ± 2.07 min, p = 0.07). HR ≤ 5bpm method prematurely determined time at SS compared to CC-1 at 3.5 mph (5.23 ± 1.83 min, 3.44 ± 0.53 min, p < 0.05) and 6 mph (6.95 ± 1.31 min, 3.67 ± 0.50 min, p < 0.05), but not at 2.5 mph (3.81 ± 2.07min, 3.46 ± 0.39 min, p = 0.38). CONCLUSION: The study showed that objective VO2, RER, and HR values can be used as independent parameters to identify and establish SS and may occur at different time points. At low work rates, the HR ≤ 5bpm method variation gave similar results as CC-1 HR for identifying time at SS, but resulted in different time at SS as intensity increased. The SAC-V values can be used to determine SS during exercise testing.

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