M. E. Langenfeld, L. S. Hart, P. C. Kao: Plasma beta-endorphin responses to one-hour bicycling and running at 60% VO2max. Medicine and Science in Sports and Exercise, 1987-04, 19. vsk, nro 2, s. 83–86. PubMed:3574053ISSN 0195-9131Artikkelin verkkoversio.
M. E. Langenfeld, L. S. Hart, P. C. Kao: Plasma beta-endorphin responses to one-hour bicycling and running at 60% VO2max. Medicine and Science in Sports and Exercise, 1987-04, 19. vsk, nro 2, s. 83–86. PubMed:3574053ISSN 0195-9131Artikkelin verkkoversio.