J. LeBlanc

Familial Resemblance in Maximal Heart Rate, Blood Lactate and Aerobic Power

There are considerable interindividual differences in maximal oxygen uptake per kilogram of body weight (VO2 max/kg), maximal heart rate (max HR) and maximal blood lactate (max blood La) measured during a progressive exercise test. The aim of the study was to quantify the familial relationships for these variables. Parents and children of 38 families of French-Canadian descent were submitted to a modified Balke treadmill test. VO2 max/kg and max HR were the highest values reached during the test for 1 min. Max blood La was obtained from a blood sample taken 2 min after the test. The effects of age and sex were significant for max blood La and VO2 max/kg in each generation. Scores were thus adjusted through multiple regression procedures (age + sex + age X sex + age2), yielding residuals which were submitted to further analysis. Intraclass correlations (ri) were significant in pairs of sibs for max blood La and max HR, i.e. 0.28 (p less than 0.01) and 0.43 (p less than 0.05), respectively. For VO2 max/kg, pairs of spouses and sibs were about similarly correlated (ri = 0.20 and 0.15; p less than 0.05). Data suggested that children were more related to their mother than to their father for VO2 max/kg, VO2 max/kg of fat-free weight, and particularly for max HR. It was concluded that familial resemblance and heritability estimates for maximal aerobic power, max HR and max blood La were quite low and generally nonsignificant. Correlations between biological sibs were, however, consistently significant for max HR and max blood La. The suggestion of a maternal effect in maximal aerobic power should be further investigated.

Studies on the sparing effect of exercise on insulin requirements in human subjects

The reduced insulin response of trained subjects in the presence of normal glucose tolerance has been confirmed. It was also found that this beneficial effect of exercise is greatly reduced if trained subjects are inactive for 3 days while eating ad libidum. During that period excessive food intake (3291 cal/day) was noted. However, when the subjects were on a restricted diet (2076 cal/day) the reduced insulin response to a glucose load was retained. The ratio of food intake with regard to caloric utilization is possibly the important modulator of the action of exercise on insulin requirements. The effect of exercise on insulin secretion was also found to be acquired rapidly since it was observed 18 hr after 1 hr of physical activity at 70% of V02 max in non-trained subjects. For all these studies a correlation (p less than 0.01) was found between the secretion of insulin in response to glucose challenge and both basal plasma glucose and insulin.

Diminished dietary thermogenesis in exercise-trained human subjects

SummaryThe influence of exercise-training on dietary-induced thermogenesis (DIT) was investigated in humans. The resting metabolic rate was identical in trained and non-trained subjects, but the response to a meal containing 1,636 kcal (6.9 MJ) was markedly lower in trained subjects. Mean dorsal skin temperature, as measured by thermography, was not influenced by training. A significant correlation was observed between postprandial RQ and DIT, which indicates that the reduced energy expenditure noted in trained subjects is related to a greater lipid oxidation. This sparing effect of exercise-training on energy utilization in the form of carbohydrate, is interpreted as adaptive in the sense that energy is preserved for the purpose of producing work.

The effect of caffeine on food intake in rats: Involvement of corticotropin-releasing factor and the sympatho-adrenal system

The involvement of CRH and the sympatho-adrenal system in the effects of caffeine on food intake and body weight gain has been investigated in rats. Food intake and body weight gain were measured in male rats after the treatment with caffeine in combination with either an injection of the CRH antagonist alpha-helical CRH(9-41), a surgical adrenal demedullation (medullectomy), or a ganglionic blockade. Alpha-helical CRH(9-41) was injected in the lateral ventricle of the brain and hexamethonium was used to chemically block the ganglionic transmission. From 4 to 24 h following a caffeine injection, spontaneous food intake, which was cumulated from the time caffeine was injected, was significantly (p < 0.01) lower in caffeine- than in saline-treated rats. In food-deprived rats, the anorectic effect of caffeine was biphasic, being significant at 0.5 and 1 h after the caffeine administration, then vanishing for 3 h, and becoming significant again 6 h after the caffeine administration. In both the spontaneously fed and food-deprived rats, caffeine reduced the rate of weight gain, which was measured at the end of a 12- or a 24-h period following the caffeine injection. A significant (p < 0.05) interaction effect of caffeine and alpha-helical-CRH(9-41) was found on the cumulative food intake at 1, 6, and 8 h, and on the amount of food eaten between the 4-6-h interval following the injection of caffeine; the effects of caffeine on food intake and body weight gain seem largely prevented by the use of a CRH antagonist.(ABSTRACT TRUNCATED AT 250 WORDS)

Cephalic postprandial thermogenesis in human subjects

To study the role of food palatability on postprandial thermogenesis, a study was designed in which human subjects ingested palatable food while O2 consumption was measured continuously during 30 minutes before and 60 minutes after the meal. In a first experiment (normal feeding), the subjects ate a portion of sugar pie containing 1672 kJ. A rapid increase in O2 consumption was noted which reached a peak value at about 15 minutes from the beginning of the meal. In a second experiment (sham feeding), the subjects were given the same food and they were asked to chew it and to spit it out. During the first 30 minutes following the meal, sham feeding produced a significantly larger increase in O2 consumption than meal feeding, whereas in the second postprandial period the thermogenic effect of food was larger with meal feeding. The integrated elevation of O2 during one hour was the same with meal feeding as with sham feeding. These results show that sensory stimulations without food being absorbed caused an important increase in O2, and confirms in humans the presence of a cephalic postprandial thermogenesis. In the third experiment (blank feeding), the subjects mimicked the muscular activities associated with feeding such as hands, arms, jaw and throat movements. Blank feeding produced a small and transient increase in O2 consumption. An elevation of plasma norepinephrine was observed during the cephalic phase and this effect was significantly larger with sham than with meal feeding. Subjective ratings for palatability, hunger reduction and degree of fullness were higher with meal than with sham feeding.(ABSTRACT TRUNCATED AT 250 WORDS)

Influence of personality traits on plasma levels of cortisol and cholesterol.

The literature reports many organic malfunctions that are associated with elevated plasma cortisol and cholesterol levels. The present investigation was concerned with the influence of personality on plasma levels of cortisol and cholesterol. To that effect these variables were determined in a group of 20 subjects who answered the Big-Five Inventory for measurements of personality traits. It was found that: among the 5 personality traits, extraversion was positively correlated to plasma levels of cortisol and cholesterol while the correlation was negative for neuroticism. The positive correlation between extraversion and plasma cortisol and cholesterol, as well as with the responses to stress as shown in a previous study, are similar to findings previously reported on type A individuals. Further studies are needed with a larger group of subjects to conclude to a direct causal relationship between extraversion and the high levels of plasma cortisol and cholesterol, or a predisposition to some organic malfunctions as is the case for type A.

Study on the correlation of the autonomic nervous system responses to a stressor of high discomfort with personality traits

The present study investigated Eysencks predictions concerning the correlation of personality to arousal at higher levels of stress. Twenty young adults were exposed to a physical stress causing great discomfort, specifically a cold wind (4 degrees C at 60 km/h) exposure to the face for 3 min. Autonomic nervous system (ANS) responses were measured by continuous heart rate and plasma catecholamine determinations before, during and after the test. At the end of the test, the participants gave a rating of discomfort on a 0 to 10 scale. The personality traits were assessed with the Big-Five Inventory test (BFI). Results indicated that higher levels of trait extraversion were positively correlated with discomfort ratings and with the increased heart rate and the noradrenaline responses. Neuroticism was negatively correlated to discomfort and the autonomic responses. These findings tend to support Eysencks theory on the role of personality on arousal at higher levels of stress. It is also proposed that the better tolerance to this severe stress observed with neuroticism is correlated to a certain habituation process caused by light to moderate arousal frequently experienced by participants with this personality trait during their daily activities.

Plasma dopamine and noradrenaline variations in response to stress

Dopamine (DA) the precursor of noradrenaline (NA) has been shown to have many functions such as its influence on endorphins activity and its association with hedonic impact, anxiety and depression. However with regard to the sympathetic nervous system activity, the role of DA has merely been considered as being the precursor of NA. We have shown in a previous study a positive correlation between the resting plasma level of NA and those found during exposure to a physical stress. No explanation was proposed to explain this finding. Enhanced sympathetic nervous system activity has been shown to increase the secretion of NA as well as DA. It is not known however if the secretion of DA during exposure to stress parallels that of NA. What are the interactions between the two amines and also between values at rest and during exposure to stress? For that reason a test was used which consisted of blowing cold wind (4 degrees C at 60 km/h) on the face of a group of subjects and measuring plasma concentration of the two amines before, during and after the test. For a given individual, the increase of either plasma NA or DA in response to the cold wind stress parallels the resting plasma concentrations of these two amines respectively. Low level of one amine at rest coincides with low increase during the stress. Furthermore the results have shown that when the plasma level of either one of these two amines is high in response to stress, the values of the other amine are small; both amines are not high or low at the same time. The literature suggests that dopamine beta hydroxylase (DBH), the enzyme which catalyzes the synthesis of NA from DA, may provide an explanation to our findings. Lower DBH activity of this enzyme would result in a lower NA and a greater DA storage and secretion. Further investigation is needed to verify this possibility.

Response to thermal stress and personality

Tolerance to cold and heat exposure shows large variations for which there is still insufficient explanation. On the other hand the relationship between the responses to mental stress and individual personality is well documented. The aim of this study was then to find if personality traits have some influence on the responses to environmental temperature exposure. A group of 20 young adults were exposed for 90 min to cold (10 degrees C) while skin temperature (Ts), oxygen consumption and discomfort rating were recorded. In a second experiment they were exposed to heat (40 degrees C) for 90 min when the sweat rate and the discomfort rating were recorded. Prior to these tests the Big Five Personality Test was used to measure the personality traits of the subjects. The results show significant negative correlation between neuroticism and the O(2) consumed, the discomfort rating and Ts for the test in the cold, while extraversion was positively related to O(2) consumption but not to Ts and discomfort rating. In response to heat, neuroticism predominance was associated with greater discomfort, reduced tolerance and diminished sweat rate. The discomfort rating, in this case, was negatively related to extraversion. It is proposed that the reduced O(2) consumption in the cold and the lower rate of sweating in the heat observed with neuroticism, are caused by enhanced activity of the sympathetic nervous system. Further investigation is required to assess the validity of this proposal. Overall, the present investigation shows that physical environmental stresses, in common with mental stress, could be in some ways related to personality traits.

Protein meals and postprandial thermogenesis.

In North America the consumption of meat far exceeds that of fish. Because the palatability of the food has been shown to influence the thermogenic response to feeding, a study was designed to compare the metabolic response to 195-g beef steak and 250-g cod fillet containing both 43 g of proteins in a first experiment and to 250 g of both nutrients in a second experiment. The subjects who participated in this study gave a higher rating of palatability (obtained on a 10-cm visual analog scale) when the beef steak (7.4) was consumed compared to the cod fillet (3.0). Measurements of oxygen consumption during the cephalic phase (0 to 40 min) indicated a larger thermogenic response to the beef than to the fish meal. These findings suggest that the thermic response to feeding during the cephalic phase are related to the sensory stimulation of the meal. During the gastrointestinal phase (40 to >180 min) the response was not influenced by the type of food and was related instead to the amount of proteins ingested. Plasma amino acid determinations indicated differences between the beef and fish feeding. Plasma histidine and glutamine was higher after beef feeding. The meaning of these findings does not seem to be related at this time to the results obtained on postprandial thermogenesis. The increases in plasma insulin that were observed during both phases of feeding were similar for the beef and the fish meals. Despite a marked increase of insulin, plasma glucose remained unchanged after feeding either meals, suggesting an enhanced gluconeogenesis and an increased glucose utilization.