1. Osler W: The Principles and Practice of Medicine. New York City, D Appleton, 1892
2. Deutsch F, Kauf E: Heart and Athletics. Warfield LM, trans. St Louis, CV Mosby, 1927, pp 17–103
3. Astrand P, Rodohl K: Textbook of Work Physiology. New York City, McGraw-Hill, 1977, p 176
4. The velocity factor in cardiac work