The application of maximal heart rate predictive equations in hypoxic conditions.

Gallagher, Carla; Willems, Mark; Lewis, Mark; Myers, Stephen

Purpose: Peak heart rate (HR) is a common tool used in exercise prescription for groups in which maximal exercise intensity is contraindicated; however, the application of this method in normobaric hypoxia is unknown. Therefore, this study investigated the response of HR and the application of predictive HR equations to prescribe exercise intensity in acute normobaric hypoxia. Results were used to examine whether age-derived HR predictive equations are valid in hypoxic conditions. Methods: Fifteen untrained (eight men) volunteers (age 22 ± 2 years; peak rate of oxygen consumption 46.3 ± 7.0 ml kg min) completed incremental cycle ergometer tests (randomised order) to measure HR at sea-level (SL (ambient inspiratory oxygen fraction (FO) 0.209)) and four normobaric hypoxic conditions FO: 0.185, 0.165, 0.142, 0.125 (≈1,000-4,000 m). Results: HR was similar across all conditions (SL, 182 ± 13; 0.185, 178 ± 11; 0.165, 177 ± 9; 0.142, 178 ± 9; 0.125, 175 ± 10 b min) despite a reduction in oxygen saturation with increasing hypoxia (SL, 95 ± 5; 0.185, 95 ± 2; 0.165, 92 ± 2; 0.142, 88 ± 3; 0.125, 82 ± 4 %; P ≤ 0.05). The HR was overestimated by all equations compared to the measured value ( P < 0.05). Four equations overestimated HR in all conditions ( P < 0.01); two in four conditions (0.185, 0.165, 0.142, 0.125; P < 0.01); and two in three conditions (0.165, 0.142, 0.125; P < 0.01). Conclusion: The overestimation of HR by commonly used age-derived predictive equations in normobaric hypoxic conditions suggests that despite possible contraindications researchers should directly measure HR whenever possible if it is to be used to prescribe exercise intensities.

HEART beat measurement; EXERCISE physiology; HYPOXEMIA; ERGOMETRY; PHYSIOLOGICAL effects of oxygen

European Journal of Applied Physiology, 2015, Vol 115, Issue 2, p277

1439-6319

Academic Journal

10.1007/s00421-014-3007-6