Elliot, CA, Hamlin, MJ, and Lizamore, CA. Validity and reliability of the Hexoskin wearable biometric vest during maximal aerobic power testing in elite cyclists. J Strength Cond Res 33(5): 1437-1444, 2019-The purpose of this study was to investigate the validity and reliability of the Hexoskin vest for measuring respiration and heart rate (HR) in elite cyclists during a progressive test to exhaustion. Ten male elite cyclists (age 18-52 yrs, height 179.3 ± 6.0 cm, body mass 73.2 ± 9.1 kg, V[Combining Dot Above]O2max 60.7 ± 7.8 ml·kg·min, mean ± SD) conducted a maximal aerobic cycle ergometer test using a ramped protocol (starting at 100 W with 25 W increments each min to failure) during 2 separate occasions over a 3-4-day period. Compared with the criterion measure (MetaMax 3B) the Hexoskin vest showed mainly small typical errors (1.3-6.2%) for HR and breathing frequency (f), but larger typical errors (9.5-19.6%) for minute ventilation (V[Combining Dot Above]E) during the progressive test to exhaustion. The typical error indicating the reliability of the Hexoskin vest at moderate-intensity exercise between tests was small for HR (2.6-2.9%) and f (2.5-3.2%) but slightly larger for V[Combining Dot Above]E (5.3-7.9%). We conclude that the Hexoskin vest is sufficiently valid and reliable for measurements of HR and f in elite athletes during high-intensity cycling but the calculated V[Combining Dot Above]E value by the Hexoskin vest produced during such exercise should be used with caution because of the lower validity and reliability of this variable.