François Péronnet

Aerobic fitness level and reactivity to psychosocial stress: physiological, biochemical, and subjective measures.

&NA; Aerobic fitness is associated with numerous physiological adaptations which permit physical stress to be coped with more efficiently. The present experiment examined whether aerobic fitness influences emotional response. Heart rate, biochemical measures (catecholamines, cortisol, prolactin, lactic acid), and self‐reported arousal and anxiety were monitored in 15 highly trained and 15 untrained subjects at various points before, during and following exposure to a series of psychosocial stressors. Heart rate and subjective arousal level increased markedly during the stressors in both groups. Trained subjects showed higher levels of norepinephrine and prolactin early in the stress period, more rapid heart rate recovery following the stressors, and lower levels of anxiety at the conclusion of the session. This more rapid heart rate and subjective recovery from psychosocial stress, suggests that aerobically trained individuals may be capable of faster recovery in both physiological and subjective dimensions of emotionality. The differences in reactivity profiles between the aerobically trained and untrained were discussed in light of models that have dealt with the adaptiveness of emotional response.

Lactic acid buffering, nonmetabolic CO2 and exercise hyperventilation : A critical reappraisal

It has been suggested that hyperventilation and the disproportionate increase in VCO2 versus VO2 above the ventilatory threshold (V(TH)) in ramp exercise are due to the production of nonmetabolic CO2 in muscle because of lactic acid buffering by plasma bicarbonate entering the cell in exchange with lactate [Wasserman, K., 1982. Dyspnea on exertion. Is it the heart or the lungs? JAMA 248, 2039-2043]. According to this model, plasma standard bicarbonate concentration decreases in a approximately 1:1 ratio with the increase in plasma lactate concentration, 1 mmol of CO2 is generated above that produced by aerobic metabolism for each mmol of lactic acid buffered, and nonmetabolic CO2 produced in the muscle is partly responsible for hyperventilation because of the resulting increase in the CO2 flow to the lungs. The present report shows that this model is not consistent with experimental data: (1) bicarbonate is not the main buffer in the muscle; (2) the decrease in standard bicarbonate concentration is not the mirror image of the increase in lactate concentration; (3) buffering by bicarbonate does not increase CO2 production in muscle (no nonmetabolic CO2 is produced in tissues); (4) the CO2 flow to the lungs, which should not be confused with VCO2 at the mouth, does not increase at a faster rate above than below V(TH). The disproportionate increase in VCO2 at the mouth above V(TH) is due to hyperventilation (not the reverse) and to the low plasma pH which both reduce the pool of bicarbonate readily available in the body.

Fuel selection and cycling endurance performance with ingestion of [13C]glucose: evidence for a carbohydrate dose response

Endurance performance and fuel selection while ingesting glucose (15, 30, and 60 g/h) was studied in 12 cyclists during a 2-h constant-load ride [approximately 77% peak O2 uptake] followed by a 20-km time trial. Total fat and carbohydrate (CHO) oxidation and oxidation of exogenous glucose, plasma glucose, glucose released from the liver, and muscle glycogen were computed using indirect respiratory calorimetry and tracer techniques. Relative to placebo (210+/-36 W), glucose ingestion increased the time trial mean power output (%improvement, 90% confidence limits: 7.4, 1.4 to 13.4 for 15 g/h; 8.3, 1.4 to 15.2 for 30 g/h; and 10.7, 1.8 to 19.6 for 60 g/h glucose ingested; effect size=0.46). With 60 g/h glucose, mean power was 2.3, 0.4 to 4.2% higher, and 3.1, 0.5 to 5.7% higher than with 30 and 15 g/h, respectively, suggesting a relationship between the dose of glucose ingested and improvements in endurance performance. Exogenous glucose oxidation increased with ingestion rate (0.17+/-0.04, 0.33+/-0.04, and 0.52+/-0.09 g/min for 15, 30, and 60 g/h glucose), but endogenous CHO oxidation was reduced only with 30 and 60 g/h due to the progressive inhibition of glucose released from the liver (probably related to higher plasma insulin concentration) with increasing ingestion rate without evidence for muscle glycogen sparing. Thus ingestion of glucose at low rates improved cycling time trial performance in a dose-dependent manner. This was associated with a small increase in CHO oxidation without any reduction in muscle glycogen utilization.

Oxidation of corn starch, glucose, and fructose ingested before exercise.

The purpose of this study was to compare the metabolic and endocrine responses, and the amounts of exogenous carbohydrate oxidized, during prolonged moderate cycle ergometer exercise (120 min, 60% VO2max), preceded by ingestion of 13C enriched glucose (G), fructose (F), or pure corn starch (S) (1,592 kJ ingested with 400 ml of water, 60 min before the beginning of exercise) in six healthy young male subjects. Plasma glucose and insulin concentrations significantly increased in response to G and S feeding. The high plasma insulin values resulted in a significant transient reduction in plasma glucose concentration in the first hour of exercise and blunted the response of plasma free fatty acid and glycerol concentrations, when compared to the values observed with F ingestion, which did not modify plasma glucose or insulin concentrations. Over the 2 h exercise period, the percentages of exogenous G (67 +/- 9%) and S (73 +/- 8%) oxidized were not significantly different but were significantly higher than the percentage of exogenous F oxidized (54 +/- 6%). These results confirm that 1) exogenous F is less readily available for oxidation than G or S and 2) pure corn starch does not offer any advantage over glucose as a pre-exercise meal.

Carbohydrate administration and exercise performance : what are the potential mechanisms involved ?

It is well established that carbohydrate (CHO) administration increases performance during prolonged exercise in humans and animals. The mechanism( s), which could mediate the improvement in exercise performance associated with CHO administration, however, remain(s) unclear. This review focuses on possible underlying mechanisms that could explain the increase in exercise performance observed with the administration of CHO during prolonged muscle contractions in humans and animals. The beneficial effect of CHO ingestion on performance during prolonged exercise could be due to several factors including (i) an attenuation in central fatigue; (ii) a better maintenance of CHO oxidation rates; (iii) muscle glycogen sparing; (iv) changes in muscle metabolite levels; (v) reduced exercise-induced strain; and (vi) a better maintenance of excitation-contraction coupling. In general, the literature indicates that CHO ingestion during exercise does not reduce the utilization of muscle glycogen. In addition, data from a meta-analysis suggest that a dose-dependent relationship was not shown between CHO ingestion during exercise and an increase in performance. This could support the idea that providing enough CHO to maintain CHO oxidation during exercise may not always be associated with an increase in performance. Emerging evidence from the literature shows that increasing neural drive and attenuating central fatigue may play an important role in increasing performance during exercise with CHO supplementation. In addition, CHO administration during exercise appears to provide protection from disrupted cell homeostasis/integrity, which could translate into better muscle function and an increase in performance. Finally, it appears that during prolonged exercise when the ability of metabolism to match energy demand is exceeded, adjustments seem to be made in the activity of the Na+/K+ pump. Therefore, muscle fatigue could be acting as a protective mechanism during prolonged contractions. This could be alleviated when CHO is administered resulting in the better maintenance of the electrical properties of the muscle fibre membrane. The mechanism(s) by which CHO administration increases performance during prolonged exercise is(are) complex, likely involving multiple factors acting at numerous cellular sites. In addition, due to the large variation in types of exercise, durations, intensities, feeding schedules and CHO types it is difficult to assess if the mechanism(s) that could explain the increase in performance with CHO administration during exercise is(are) similar in different situations. Experiments concerning the identification of potential mechanism(s) by which performance is increased with CHO administration during exercise will add to our understanding of the mechanism(s) of muscle/central fatigue. This knowledge could have significant implications for improving exercise performance.

Partitioning oxidative fuels during cold exposure in humans: muscle glycogen becomes dominant as shivering intensifies

The effects of changes in shivering intensity on the relative contributions of plasma glucose, muscle glycogen, lipids and proteins to total heat production are unclear in humans. The goals of this study were: (1) to determine whether plasma glucose starts playing a more prominent role as shivering intensifies, (2) to quantify overall changes in fuel use in relation to the severity of cold exposure, and (3) to establish whether the fuel selection pattern of shivering is different from the classic fuel selection pattern of exercise. Using a combination of indirect calorimetry and stable isotope methodology, fuel metabolism was monitored in non‐acclimatized adult men exposed for 90 mins to 10°C (low‐intensity shivering (L)) or 5°C (moderate‐intensity shivering (M)). Results show that plasma glucose oxidation is strongly stimulated by moderate shivering (+122% from L to M), but the relative contribution of this pathway to total heat generation always remains minor (< 15% of total heat production). Instead, muscle glycogen is responsible for most of the increase in heat production between L and M. By itself, the increase in CHO oxidation is responsible for the 100 W increase in metabolic rate observed between L and M, because rates of lipid and protein oxidation remain constant. This high reliance on CHO is not compatible with the well known fuel selection pattern of exercise, when considering the relatively low metabolic rates elicited by shivering (∼30% for M). We conclude that shivering and exercise of similar energy requirements appear to be supported by different fuel mixtures. Investigating the physiological mechanisms underlying why a muscle producing only heat (shivering), or significant movement (exercise), shows a different pattern of fuel selection at the same power output strikes us as a fascinating area for future research.

Left ventricular size following endurance, sprint, and strength training

Left ventricular size following endurance, sprint, and strength training. Med. Sci. Sports Exercise, Vol. 14, No. 5, pp. 344-347, 1982. Left ventricular dimensions in adolescent boys were determined before and after three types of training regimens: endurance (END), N = 8, means = 16.8 yr; sprint (SPR), N = 8, means = 16.3 yr; strength (STR), N = 12, means = 18.7 yr. With training the END group significantly increased VO2max in 1 X min-1 (3.71 +/- 0.27 to 4.16 +/- 0.57, P less than 0.05) and in ml X min-1 X kg-1 (58.4 +/- 5.6 to 64.2 +/- 5.5, P less than 0.05). The SPR group increased VO2max in 1 X min-1 (3.63 +/- 0.63 to 3.98 +/- 0.78, P less than 0.05) but not in ml X min-1 X kg-1 (59.5 +/- 4.1 to 63.2 +/- 5.4) because body weight increased from 61.2 +/- 10.5 to 63.1 +/- 10.7 kg (P less than 0.05) with no change in percent body fat. The STR training group significantly improved upper body strength. Despite these specific training adaptations no significant modifications were found for interventricular and left ventricular posterior wall thickness or for left ventricular internal diameter in either training group. However, calculated left ventricular mass was slightly but significantly higher by 10% and 4% in the END and STR training groups, respectively. These small increases in calculated left ventricular mass with short-term training are probably caused by small but insignificant increases in left ventricular internal diameter secondary to a training bradycardia (END group: 76 +/- 8 to 64 +/- 1 beats X min-1) and to increased diastolic filling time rather than to true cardiac hypertrophy. Significant increases in aerobic capacity and in strength can occur without modification of left ventricular dimensions.

A simple and disposable sweat collector

SummaryApart from in cystic fibrosis, where sweat analysis provides valuable diagnostic information, sweat yields remain an overlooked biological fluid. Technical problems (dilution, condensation, contamination, evaporation, etc.) linked to currently available collection procedures are of concern and thwart their use. To overcome some of these technical difficulties, an original sweat-collection technique is described. A collection capsule is created inside a flexible, adhesive and disposable anchoring membrane pasted onto the skin. A fluid-tight window is positioned in the upper part of the pocket and gives access to its content. Through the collection window, complete emptying of the sweat collector can be achieved repeatedly by suction using a vacutainer tube inserted in a tube holder equipped with a long dull needle. With prior addition of a suitable marker, fractional samplings can also be performed using a precision micropipette. This collecting method allows for kinetic studies on sweat rate and sweat content. The limited bias-inducing manipulations linked to the described technique, coupled with the ease of performing kinetic studies on sweat volume and content, make this original tool a reliable and accurate sweat-collection technique.

Echocardiographic assessment of left ventricular performance before and after marathon running

Echocardiography was used to indirectly assess the effects of marathon running on myocardial performance. Thirteen marathon runners (mean +/- SEM:30 +/- 1.6 years) were submitted to a resting echocardiographic examination before racing and during early recovery from marathon racing. Indices of left ventricular performance were computed from M-mode recordings of left ventricular dimensions and aortic valve motions. Comparison of basal and post-marathon indices of left ventricular performance showed no significant differences in either pre-ejection period (PEP), left ventricular ejection index (LVEI), fractional shortening (% delta D), ejection fraction (EF), or mean rate of circumferential fiber shortening (mVcf). Cardiac output (Qc) computed from left ventricular end-diastolic (LVEDV) and end-systolic volumes (LVESV) were significantly higher following marathon running (4.9 +/- 0.4 to 6.7 +/- 0.7 L/min) because of a marked increase in resting heart rate (HR) (58 +/- 3 to 76 +/- 3 bpm). A significant decrease in systolic blood pressure (118 +/- 4 to 108 +/- 3 mm Hg), associated with a slight reduction in calculated total peripheral resistance was also observed after the race. These circulatory adjustments probably reflect thermoregulatory activity that allows a greater blood flow to the skin for heat dissipation, as well as persistence of reactive muscle hyperemia. Echocardiographic evidence suggests that marathon running does not lead to marked impairments in left ventricular performance. However, the absence of change in the end-systolic volume, despite a marked reduction in cardiac afterload, may suggest a slight alteration in contractility that could not be detected with the use of echocardiography.

Trait anxiety, submaximal physical exercise and blood androgens

SummaryThis study evaluates the relationship between trait anxiety and both androgen and gonadotrophic hormone levels at rest and during severe physical exercise. Twelve volunteers were selected among 160 untrained male collegial students and classified as anxious (N=6) or non-anxious (N=6) subjects according to their scores on three trait-anxiety tests (STAI, IPAT, 16 PF). Serum Δ4-androgen (testosterone and Δ4-androstenedione), Δ4-androgen (DHEA and DHEA-SO4) and gonadotrophin (LH and FSH) concentrations were measured by radioimmunoassay before, during and after 20 minutes of intensive bicycle exercise (80% of maximal heart rate). Results indicate significantly lower serum Δ4-androgens in anxious subjects before exercise. However, for each subject and irrespective of his anxiety level, all measured serum androgen concentrations increased significantly during exercise, although Δ4-androstene-dione remained lower in anxious subjects than in non-anxious ones. Serum LH concentrations (but not FSH) were signicantly higher in anxious subjects throughout the observation periods. However, exercise induced in each subject a significant decrease in the serum level of both gonadotrophic hormones. The results suggest that trait anxiety level may constitute an important factor that affects both pre-exercise and exercise serum androgen concentrations in untrained subjects.