Frank I. Katch


Santorio experiments breakthrough
in energy metabolism

August Krogh (1874-1949) 

The inaugural profile features August Krogh, one of the most accomplished scientists. His career strongly influenced basic and applied research in the biological sciences, including the emerging field of exercise physiology.

Krogh began his career in the laboratory of the noted Christian Bohr (1855-1911), who himself had been trained by physiologist Carl Ludwig in Leipzig, Germany. Bohr had already clarified the dynamics of muscle contraction and solubility of oxygen in different fluids including blood. His studies of oxygen influenced Krogh's early experiments of tissue respiration in animals. Krogh devised equipment to measure respiratory gas exchange in snails, frogs, and fishes. Krogh's An Account of the Structure and Function of the Lungs and Air Sacks of Birds, the equivalent of a master's thesis (1899), proved oxygen diffused rapidly through the thin pulmonary membranes, while the skin eliminated carbon dioxide. Subsequent experiments in gas transport corrected the prevailing view that lungs were gland-type structure that secreted oxygen and carbon dioxide. Krogh's highly accurate equipment analyzed respiratory gases, and established that pulmonary gas was exchanged by the mechanism of diffusion, not secretion. Krogh stated:

The cutaneous absorption of oxygen cannot be regulated at all by the organism, hence I am of the opinion that with a probability almost amounting to certainty it is affected by plain physical powers--diffusion.

 Krogh determined to win the prestigious Seegan Prize* by solving the problem of whether or not free nitrogen or nitrogenous gases were released from the body as a normal by-product of metabolism. In 1906, he proved that gaseous nitrogen remained constant and won the prize. His original approach using respiratory methods to quantify nitrogen dynamics also won fame. It succeeded without using the traditional German method of Liebig, Rubner, and their students who measured nitrogen in ingested food and fluid and excreted nitrogen in feces and urine.

Example of early respiratory apparatus used by August Krogh to analyze respiratory gas. Krogh constructed his own equipment, perfecting the art of glassblowing and other laboratory skills. The Krogh respiratory gas analysis equipment was the most accurate of any developed; this enabled Krogh to conduct crucial experiments that eventually led to decisive experiments and the Nobel Prize. 

In 1905, Krogh married Marie Jorgensen, a promising medical student and scientist in her own right.** The husband-wife team researched transport of carbon dioxide in the lungs, metabolism of Eskimos (with Benedict), and insulin's role in the body. Together, they published seven important papers known as the "seven little devils." Their experiments disproved the oxygen secretion hypothesis championed by Krogh's early mentor, Christian Bohr. Krogh invented the microtonometer, indispensable for quantifying gas transport in blood. Krogh earned enough money from selling equipment to support his laboratory.

Marie Krogh sits next to the respiration chamber constructed in Greenland in July, 1908. Two Eskimos remained inside the chamber for up to four days. Food consumption was monitored, respiratory gas was analyzed using Krogh's hand-made but precise equipment, and daily urine samples analyzed for nitrogen content. The experiments were conducted with the expert callaboration of Professor Francis Gano Benedict, director of the Carnegie Nutrition Laboratory in Boston.

Krogh published nearly 300 research papers (1), many of which we consider "classics" in exercise physiology. For example, he and Johannes Lindhard (1870-1947) studied regulation of respiration and circulation during exercise and recovery. Krogh devised a bicycle ergometer with magnets and weights to quantify exercise intensity. He perfected a method that used nitrous oxide gas to estimate exercise cardiac output. He found that tissues extracted more oxygen during exercise; concurrently, circulation and ventilation increased. Interested in how a muscle receives oxygen, he studied capillary blood flow, as well as oxygen's pressure and diffusing capacity through tissues (1).

Krogh (left); Lindhard (right) on board a ship. Lindhard was instrumental with Krogh in developing the nitrous oxide method to determine minute ventilation of the lungs (1912). Lindhard established his mark in exercise physiology for pioneering studies concerning the physiology of circulation, muscular contraction (action potentials), and respiration. Lindhard worked with Krogh in the Zoophysiological Laboratory in Copenhagen.

Krogh won the 1920 Nobel Prize in Physiology or Medicine for discovering the mechanism that controlled capillary blood flow in resting and active muscle (in frogs; 2,3,4). He chronicled his research in 1922 (5).

August Krogh the day after winning the Nobel Prize

Although there are brief reviews of his career (6,7), a biography by August Krogh's daughter (Bodil Schmidt-Nielsen) furnishes the most "up-close and personal" information about the lives of both August and Marie Krogh (1). This Nielsen book is a "must" read; the content provides numerous insights about famous scientists in Europe and the United States with whom the Kroghs collaborated.

Published for the American Physiological Society by Oxford University Press. New York. 1995. ISBN 0-19-509099-3

August Krogh's research linked exercise physiology with nutrition and metabolism. Experiments in comparative zoology (zoophysiology) and cardiovascular physiology inspired experiments in exercise physiology. Krogh interacted with distinguished physiologists A. Keys, Abbey H. Turner, E. M. Landis, E. H. Christensen, F. G. Kovian, A. M Hemmingsen, H. H. Ussing, and T. W. Fogh. He influenced the next generation of scientists in exercise physiology, particularly those in Nordic countries and the United States. They in turn taught others to investigate human nutrition during acute and chronic physical activity.

© Frank I. Katch, William D. McArdle, Victor L. Katch. 1997.

*Established by the Imperial Academy of Sciences in Vienna with a cash award of four thousand kroner.

**In 1914, she became the fourth Danish woman to earn a scientific doctoral degree in medicine (Dr Med.).


1. Schmidt-Nielsen, B., August & Marie Krogh. Lives in Science. New York, American Physiological Society, Oxford University Press, 1995.

2. Krogh, A. The rate of diffusion of gases through animal tissues with some remarks on the coefficient of invasion, J. Physiol., 52, 1919.

3. Krogh, A. The number and distribution of capillaries in muscles with calculations of the oxygen pressure head necessary for supplying the tissue, J. Physiol., 52, 1919.

4. Krogh, A. The supply of oxygen to the tissues and the regulation of the capillary circulation, J. Physiol. (London), 52, 457, 1919.

5. Krogh, A. The Anatomy and Physiology of Capillaries, Yale University Press, New York, 1922.

6. Liljestrand, G., and Krogh, A. Acta Physiol. Scand, 20, 109, 1950.

7. Snorrason, E., Krogh, Shack August Steenberg, Dictionary Scientific Bibliography, Vol VII: 501, Scribner's and Sons, New York, 1973.

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