Critical analysis of the "anaerobic threshold" during exercise at constant workloads.

The method described by Wasserman for anaerobic threshold (AT) determination, based on the recording of ventilatory parameters, was supported by the simultaneous appearance of hyperlactacidemia and hyperventilation during a standardized incremental work test. Our study aimed at testing the AT in another profile of exercise, viz., during exercises at constant workloads. A homogenous population of 66 healthy subjects performed on a treadmill a total of 100 exercises of 20 min duration at constant workloads (43, 48, 52, 57, 63, and 71% VO2 max). The VO2, V, and venous plasma lactic acid (LA) were determined every minute. LA showed an initial transient increase at 43% VO2 max and a steady-state elevated level above 48% VO2 max. In contrast, the hyperventilation threshold (HVT) was only observed above 57% VO2 max, simultaneously with a delayed steady-state VO2 and with a sustained increase of lactate until the end of exercise. The meaning of the simultaneity of these three events must still be studied. However, the dissociation between both early and steady-state lactate thresholds and HVT is not in keeping with the concept of AT. In these conditions, there is no evidence that HVT necessarily represents an AT, viz., a critical intensity of exercise inducing an insufficient oxygen delivery to the muscles. This conclusion does not imply that the measurement of HVT should be rejected as an empirical test of physical fitness

Effect of protein-supplemented fasting on metabolic and hormonal responses to epinephrine infusion in obese subjects.

The present study aimed at investigating the effects of an epinephrine (EPI) intravenous infusion (10 micrograms/min for 30 min) in normal subjects and in obese patients before and after 13 days of protein-supplemented fasting (PSF, 70 g protein/day). Blood glucose, plasma free fatty acids (FFA), lactate, insulin (IRI) and glucagon were determined before, during (15, 30 min) and after (+30 and +60 min) the EPI infusion. 1. When compared to lean control subjects, obese patients exhibited a less marked rise in blood glucose and a more important increase in plasma FFA, EPI infusion decreased IRI plasma levels in normals but not in the obese. Plasma glucagon was lower in the obese under basal conditions and their A cell reactivity to EPI was clearly reduced. 2. Comparison of the results obtained in obese patients before and after PSF revealed that EPI-induced blood glucose rise was not altered despite lower basal values after PSF. Plasma lactate response was impaired, probably because of the depletion in muscle glycogen. Reduction in basal plasma IRI was associated with a significantly higher FFA mobilization. Abnormally low basal EPI-stimulated glucagon concentrations persisted after PSF despite concomitant reductions in blood glucose and plasma IRI

Reduction of exercise inudced hyperventilation by blocking beta adrenergic receptors

In normal subjects, beta-adrenergic blockage by propranolol or pindolol reduces exercise hyperventilation (40 to 60% VO2 max)

Decreased secretion of epinephrine during protein-supplemented fasting in obese subjects (author's transl)

peer reviewedThe protein-supplemented fasting induces a progressive but moderate decrease in blood glucose (-26%) and a marked rise in plasma free fatty acids levels (+ 43%). Nevertheless the secretion of epinephrine by the adrenal medulla, as indirectly estimated by the ratio of the basal urinary elimination to the recovery percentage from the urine of an epinephrine infusion, shows a significant decrease (- 36%) during the protein diet. Thus the enhanced lipolysis does not result from an adrenergic overactivity but merely depends upon the marked reduction in the plasma insulin level (- 38%)

The cause of slow increase of heart rate during muscular exercise in man

The slow increase in heart rate which is observed in normal man submitted to heavy muscular exercise is due for a part to an activation of orthosympathetic cardiac activity which is blocked by beta antagonists. It is also explained by direct action of hyperthermia on the heart

Intravenous perfusion of adrenaline and adaptation to muscular exercise in man

Eleven normal subjects underwent epinephrine perfusions (1.9; 6.1; 11.8 ng/min) during a short (20 min) and mild (50% VO2 max) exercise. VO2 was not modified by epinephrine perfusion, while heart rate ventrilation and plasmatic lactate were increased proportionally to epinephrine doses

Influence of the nutritional state on exercise induced hyperlactacidemia

In normal man, food ingested two hours before the beginning of physical exercise increases the lactacidemia (+ 27%)