R. Margaria

Positive and negative work performances and their efficiencies in human locomotion

SummaryWalking at a constant speed on a steep incline, the ratio of the mechanical work performed, as calculated by the body lift, to the energy expended, as calculated by the oxygen consumption, generally referred to as “efficiency”, is independent of the incline, and it amounts to 0.25 walking uphill and to — 1.2 walking downhill. These values can be regarded as the “efficiency” values for positive (uphill) and negative (downhill) work. Walking on the level or on a mild incline, both positive and negative work are performed within the step cycle. When an equal amount of positive and negative work is performed (level walking or running) the energy level of the body at the end of the performance does not change, and the “efficiency” as calculated amounts to 0.207. This work may be consideredwasted: it reaches a maximal amount on the level of 0.044 kgm/m kg walking, and of 0.088 kgm/m kg running. For this reason a constant pull in the direction of the movement cannot replace completely the pull given by the muscles, as when other systems of progression such as cycling, skiing, skating etc. are adopted. By far the greatest amount of energy spent in walking or running at a constant speed is spent in positive work performance to counteract the deceleration (negative work) taking place at the end of each step. Very little energy is supplied for internal work, i.e. to meet the resistance to progression due to friction within the body or at the contact of the foot with the soil.

Relationship between O2 consumption, high energy phosphates and the kinetics of the O2 debt in exercise

SummaryThe oxygen consumption together with lactic acid production and concentration of ATP, ADP, and creatinephosphate was measured during exercise and recovery on an isolated dog gastrocnemius.Oxygen debt contraction and payment follow an exponential path with a half reaction time of about 20 sec. The concentration of ATP and ADP at steady state seem to be unaffected by the intensity of the exercise when this is submaximal and no appreciable production of lactic acid takes place. The concentration of creatinephosphate in muscle at steady state decreases with the intensity of the exercise. The ratio of the oxygen consumption at steady state to the alactic oxygen debt is identified with the speed constant of the resynthesis of phosphagen in muscle; the half reaction time of this process is 17–20 sec. The total alactic oxygen debt amounts to about 50 ml/kg of muscle. These figures are in good agreement with earlier data found in man.

The role played by elasticity in an exercise involving movements of small amplitude

SummaryIn an exercise consisting of repetitive small jumps on both feet at a frequency of 116/min, the mechanical work performed and the O2 consumption at steady state were measured. Of the positive work performed in the jump only 40% appears to be due to the chemical transformations taking place in the contractile component of the muscle fibres; the remaining 60% appears to be due to the elastic energy accumulated in the elastic elements of the contracted stretched muscles of the lower limbs during the falling phase of the previous jump, when the body hits the ground.

Lactic acid production in supramaximal exercise

SummaryOn 12 subjects of different muscular fitness the rate of lactic acid appearance in blood, while performing the same supramaximal exercise has been determined, together with the maximal performance time and the maximal L.A. concentration in blood. The rate of increase of lactic acid is higher in the less fit than in the athletic subjects, to compensate for the lower oxygen consumption. In all subjects the appearance of L.A. in the blood is delayed: at the onset of the exercise other anaerobic processes (alactic) supply the energy required, and only when these are exhausted L.A. formation enters into play. The energy due to lactic acid corresponds to 37±3.5 ml of O2 per g of lactic acid increase in 1 l of blood, or 50 ml of O2 (or 250 cal) per g of L.A. produced from glycogen. The maximal amount of the lactacid debt is equivalent to about the maximum oxygen consumption in 1 min. A simple relation is found between the time of performance in supramaximal exercise and the maximum oxygen consumption.

The effect of increased body temperature due to exercise on the heart rate and on the maximal aerobic power

AbstractThe effect of an increased body temperature (Tr) elicited by prolonged heavy exercise at normal ambient temperature in absence of any heat stress, on the maximal aerobic power (

Lactic Acid Production in Submaximal Work

\dot V_{O_2 \max }

Effect of alkalosis on performance and lactate formation in supramaximal exercise

) and on heart rate (HR) has been studied. The prolonged exercise consisted in running for 1 hr on a motor driven treadmill, this leading to an average increase of Tr of 1.2° C. Oxygen consumption (