Endurance for Exhaustive and Moderate Work Endurance for exhaustive work depends mainly upon the ability of the body to supply and use oxygen and to endure and dispose of the rapidly mounting concentrations of lactic acid and carbon dioxide. Endurance for moderate (steady state) activity depends upon the supply and utilization of sugar, phosphocreatine and other fuels and on the functional capacity of the heart, lungs, kidneys and other organs which sustain activity. Limiting Factors in Endurance Strength The strength of the working muscles is a limiting factor in endurance. A load easily carried by strong muscles may exhaust weaker ones. Fat The amount of fat carried by the body in addition to the load is also a limiting factor in endurance. Champion athletes trained for endurance contests have reduced the fat content of the body to a minimum. A certain amount of fat is desirable, however, in the event of a debilitating illness such as typhoid fever. In such a condition, body fat is consumed to supplement the restricted food intake during the illness. The ability to endure illness as well as the ability to endure prolonged physical activity must be considered in programs of physical training. Oxygen All activities beyond those requiring single or a very few muscular contractions (shot put, javelin throw, high jump, broad jump, diving) require some endurance. If the foregoing activities are repeated endurance becomes a factor and the fall-off in performance becomes an index of the athlete's endurance. Short bouts of maximum activity such as the 100 yard dash, the 50 yard free style swim, or the rope climb are performed using only the immediate fuels of contraction and are concluded before the oxidative recovery processes are fully in action. Endurance for activities requiring violent exertion from 1 to 4 minutes is limited by the amount of oxygen debt which can be contracted and the concentration of lactic acid which can be tolerated. The runner or swimmer who appears to "tie up" near the end or the race is beset by painful concentrations of acid metabolites (chiefly lactic acid) which cannot be endured. Activities which are less vigorous can be endured for longer periods of time. A mild activity, such as walking at a moderate rate, could conceivably be continued for days. In such a marathon walk during which ample food and water are supplied, either the need for sleep or the condition of the feet usually becomes the factor limiting endurance.		Home Components of Physical Fitness Clinical Examination Differences Between Fit and Unfit Men Physiological Elements of Fitness The Step Test The Effects of Training on the Physiological Systems Work Output Physical Condition of Muscle Application of Muscular Force Maintaining Optimum Strength Tests of Muscular Strength Strength and appearance Strength as a measure of physical fitness Strength as affected by organic problems Strength as prophylaxis Role of inactivity in production of disease Lack of Sociability in Work Lactic Acid System Muscular Form Capillary Growth Heart Size Heart Rate Training produces physicochemical changes Muscular Strength Nervous Stimulation and Muscular Strength Quality of Champions Factors Which Limit Skill Kinesthesis Balance Reaction Time Muscular Tension Visual Aim Skill Center in the Brain Endurance for Exhaustive and Moderate Work Distribution of Energy