Howard G. Knuttgen of Biology, Boston University, 2 Cummington Department Street, Boston, 02215 Massachusetts, USA The relationship of the formation of lactate acid to skeletal muscle energy release in exercising humans was first explored by A. V. Hill and co-workers (2l, 22). The term "oxygen debt" was suggested by them to describe the excess oxygen consumption of recovery which they felt was closely related. A combination of their work and the earlier work of Krogh and Lindhard (35) re sulted at that time in the belief that a certain amount of energy release during the transition from rest to exercise was provided by a non-aerobic source, glycolysis. The resulting accumulation of lactic acid (as lactate) in the body required an extra con sumption during recovery for its oxidative removal. Jervell (24) subsequently showed that, in exercise, the greatest accumulation in blood took place during the first few minutes. He felt that the blood lactate increase was due to a shortage of oxygen during the transition period. The observation was also made for the first time that the increased level of lac tate due to exercise could be made to fall faster if mild exercise was employed by the subjects in place of sedentary recovery. The work of Margaria, Edwards and Dill (40) appeared in 1933. They observed that exercise (treadmill running) could be carried on at low levels without significant changes in resting levels of blood lactate.

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Muscle Metabolism during Exercise in Man: A Historical Survey.- Adaptive Changes in Morphology and Enzymes of Skeletal Muscles.- Histochemical Effects of Contraction on Red and White Rat Muscle Fibres. Their Organization in the Motor Unit.- Reversal of Enzymatic Profiles and Capillary Supply of Muscle Fibers in Fast and Slow Muscles After Cross Innervation.- Metabolic Differentiation of Distinct Muscle Types at the Level of Enzymatic Organization.- Biochemical Adaptations to Endurance Exercise in Skeletal Muscle.- Influence of Exercise on Electron Transport Capacity of Heart Mitochondria.- Ultrastructural and Enzyme Changes in Muscles with Exercise.- Effects of Long-Term Exercise on Human Muscle Mitochondria.- Effect of Physical Training on Ultrastructural Features in Human Skeletal Muscle.- Energy Stores (Magnitude, Regulation and Interaction).- Release of Substrates from Extramuscular Stores During Exercise.- Metabolic Role of Muscle.- Adrenergic Neuro-Humoral Control of Lipolysis in Adipose Tissue.- Role of Circulating Noradrenaline and Adrenaline.- The Liver as an Energy Source in Man During Exercise.- Liver Glycogen in Man. Effect of Different Diets and Muscular Exercise.- Uptake and Oxidation of Energy Rich Compounds in the Muscle During Exercise.- Metabolism of Free Fatty Acids and Ketone Bodies in Skeletal Muscle.- Plasma Insulin Levels During Prolonged Exercise.- Glucose Uptake in Contracting, Isolated in Situ Dog Skeletal Muscle.- Glucose Metabolism During Exercise in Man.- Interrelationship Between Amino Acid and Carbohydrate Metabolism During Exercise: The Glucose Alanine-Cycle.- Uptake of Substrates in Isolated Contracting Slow and Fast Muscles in situ in Relation to Fatigue.- Uptake and Oxidation of Substrates in the Intact Animal During Exercise.- Fat Mobilization and Blood Lactate Concentration.- Storage and Use of Intramuscular Substrates During Exercise.- Control Mechanisms for the Synthesis of Glycogen in Striated Muscle.- Glycogen Storage in Human Skeletal Muscle.- Muscle Glycogen Utilization During Work of Different Intensities.- The Effect of Propranolol on Glycogen Metabolism During Exercise.- Local Lipid Stores and Exercise.- Influence of Intensity and Duration of Exercise on Supply and Use of Fuels.- Phosphagens and Lactate Metabolism.- Energy-Rich Phosphagens.- Energy Rich Phosphagens in Dynamic and Static Work.- Isometric Exercise - Factors Influencing Endurance and Fatigue.- Lactate and Oxygen Debt: An Introduction.- The Alactic Oxygen Debt: Its Power, Capacity, and Efficiency.- Muscle ATP, CP, and Lactate in Submaximal and Maximal Exercise.- Muscle ATP, CP, and Lactate During Exercise after Physical Conditioning.- Lactate Production During Exercise.- Turnover of 14C-L(+)-Lactate in Human Skeletal Muscle During Exercise.- Muscle Glycogen, Lactate, ATP, and CP in Intermittent Exercise.- Blood Lactate Concentrations During Intermittent and Continuous Exercise with the Same Average Power Output.- Myocardial Metabolism.- Utilization of Endogenous Lipids by the Isolated Perfused Rat Heart.- Myocardial Metabolism in Athletes.- Myocardial Metabolism in Man at Rest and During Prolonged Exercise.- Habitual Physical Activity; Aerobic Power and Blood Lipids.- Habitual Physical Activity: Aerobic Power and Blood Lipids.- Metabolic Studies in Clinical Materials.- Occlusive Artery Disease of the Heart and Skeletal Muscle.- Myocardial Metabolism in Patients with Ischemic Heart Disease.- Metabolism in Patients with Ischemic Heart Disease and Obesity After Training.- Metabolism of Free Fatty Acids During Exercise in Patientswith Occlusive Arterial Disease of the Leg.- Obesity and Diabetes.- Clinical and Metabolic Aspects on Obesity in Childhood.- Metabolism During Exercise in Patients with Diabetes.- Discussion.