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. 2015 Aug 18;9:1179–1188. doi: 10.2147/PPA.S86465

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© 2015 Kallianos et al. This work is published by Dove Medical Press Limited, and licensed under Creative Commons Attribution – Non Commercial (unported, v3.0) License

The full terms of the License are available at http://creativecommons.org/licenses/by-nc/3.0/. Non-commercial uses of the work are permitted without any further permission from Dove Medical Press Limited, provided the work is properly attributed.

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Biplot of correlation coefficients (loading factors) of ergo/spirometric variables with PCA axes 1 and 2. The longer the arrow the greater effect is produced by the variable. Variables forming oblique angles correlate positively with each other and negatively at arrows with obtuse angles. The lower oblique or wider obtuse aperture the higher the correlation coefficient.

Abbreviations: AT, anaerobic threshold; DLCO, diffusing capacity of the lung for carbon monoxide; FEF_25–75, forced expiratory flow 25%–75%; FEV₁, forced expiratory volume in 1 second; FVC, forced vital capacity; FVC%, percent forced vital capacity; HR, heart rate; PCA, principal component analysis; RV%, percent residual volume; TLC, total lung capacity; VCO₂, carbon dioxide production; V_E, minute ventilation; VO₂, oxygen consumption; V_T, tidal volume; vom%, maximal aerobic capacity.