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Biomedical subjects

H Monod

Publications and source records attributed to H Monod.

18 recordsLinked to original sources
PubMed1992

Effects of endurance training at high altitude on diaphragm muscle properties.

The biochemical, histochemical, and structural changes induced by endurance training and long-term exposure to high altitude were studied in the diaphragm muscle of rats exposed to simulated altitude (HA: n = 16; Pb = 62 kPa, 463 Torr; 4000 m) and compared to animals maintained at sea-level (SL: n = 16). Half of the animals in each group were trained (T) by swimming for 12 weeks, the other half were kept sedentary (S). Except for a small decrease in type I fibres in the HA-S group (-7%, P < 0.05), in favour of type IIab and type IIb fibres, neither high-altitude exposure nor endurance training had an overall affect on fibre type distribution. The mean fibre cross-sectional area was found to be unaffected by altitude and/or chronic exercise. Capillary density was shown to be increased by both high-altitude exposure (P < 0.02) and training (P < 0.001), whereas capillary growth, estimated by the capillary/fibre ratio, was unaffected in both cases. Following endurance training, a modest increase in citrate synthase was shown to occur to the same extent in the HA-T and SL-T groups (+15% and +16% respectively, NS). Hexokinase increased following training (P < 0.05) and high-altitude exposure (P < 0.001). In normoxic and hypoxic animals, endurance training enhanced the ratio of the heart-specific lactate dehydrogenase isozyme LDH1 to total LDH activity (+59%, P < 0.01; +92%, P < 0.05 respectively). It may be hypothesized that the increased glucose phosphorylation capacity observed in diaphragm muscle contributes to the reduction of glycogen utilization during exercise.

Altitude↗
PubMed1992

Respiratory, muscular, and overall perceptions of effort: the influence of hypoxia and muscle mass.

Overall, respiratory and peripheral muscular perceptions of exercise have been examined in 16 subjects (eight men and eight women), each performing four types of exercise (two-leg, one-leg, arm + shoulder, and arm ergometry) under both normoxic and hypoxic (12% oxygen) conditions. Subjects could distinguish ratings for the three types of sensation. Both overall and peripheral muscular perceptions associated with a given oxygen intake or power output increased more than respiratory perceptions as the volume of active muscle was decreased. Hypoxia tended to increase both overall and respiratory perceptions for a given absolute oxygen consumption. Cross-modal comparisons suggested an average overall RPE of close to 13 units at 70% of a task and environment-specific peak oxygen intake, irrespective of exercise conditions, but the SD of individual responses varied by at least +/- 2 units about this average. Peripheral muscular sensations dominated small muscle tasks, but the peripheral muscular RPE became relatively consistent when related to external work rate per liter of active muscle. Respiratory perceptions provided some guide to the intensity of physical activity with a given mode of exercise and fixed environmental conditions. However, if respiratory RPE is used to "fine-tune" cross-modal exercise prescriptions, account must be taken of the distorting influence of active muscle volume and of hypoxia.

Adult↗
PubMed1991

Effects of chronic hypoxia and endurance training on muscle capillarity in rats.

Skeletal muscle capillarity expressed as capillary density (CD), and number of capillaries per fibre (C/F), as well as the mean fibre cross-sectional area (FCSA), were determined in the extensor digitorum longus (EDL), plantaris (PLA) and soleus (SOL) muscles of four groups of eight rodents trained on a swimming exercise programme (T) or maintained sedentary (S), at sea level (SL) or at simulated altitude (HA), barometric pressure 61.7 kPa (463 torr) for 12 weeks. It was shown that both HA exposure and endurance training decreased body and skeletal muscles weights (P less than 0.001). However, neither HA exposure nor endurance training induce any variation in relative importance in the skeletal muscle mass. Altitude exposure and endurance training had increasing effects on CD in all muscles studied (P less than 0.001). This study confirms the fact that altitude exposure has no direct effect on capillary development. On the other hand, the capillary supply of the several slow- and fast-twitch skeletal muscles studied is increased by endurance training. This real enhancement in capillary network is ascertained by an increase in the C/F ratio (+7%, +26%, +16%, in PLA, EDL, and SOL muscles, respectively at sea level, and +19.5%, +30%, and +14% respectively at HA). These results indicate that the effects of chronic exercise on skeletal muscle capillarity estimated by the C/F ratio, are greater in an hypobaric environment than in a SL environment.

Altitude↗
PubMed1991

Cardiovascular response to static handgrip in trained and untrained men.

The influence of aerobic capacity on the cardiovascular response to handgrip exercise, in relation to the muscle mass involved in the effort, was tested in 8 trained men (T) and 17 untrained men (U). The subjects performed handgrip exercises with the right-hand (RH), left-hand (LH) and both hands simultaneously (RLH) at an intensity of 25% of maximal voluntary contraction force. Maximal aerobic capacity was 4.3 l.min-1 in T and 3.21 l.min-1 in U (P less than 0.01). The endurance time for handgrip was longer in T than in U by 29% (P less than 0.05) for RH, 38% (P less than 0.001) for LH and 24% (P less than 0.001) for RLH. Heart rate (fc) was significantly lower in T than in U before handgrip exercise, and showed smaller increases (P less than 0.01) at the point of exhaustion: 89 vs 106 beats.min-1 for RH, 93 vs 100 beats.min-1 for LH and 92 vs 108 beats.min-1 for RLH. Stroke volume (SV) at rest was greater in T than in U and decreased significantly (P less than 0.05) during handgrip exercise in both groups of subjects. At the point of exhaustion SV was still greater in T than in U: 75 vs 57 ml for RH, 76 vs 54 ml for LH and 76 vs 56 ml for RLH. During the last seconds of handgrip exercise, the left ventricular ejection time was longer in T than in U. Increases in cardiac output (Qc) and systolic blood pressure did not differ substantially between T and U, nor between the handgrip exercise tests.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed1991

Skeletal muscle changes after endurance training at high altitude.

The effects of endurance training on the skeletal muscle of rats have been studied at sea level and simulated high altitude (4,000 m). Male Wistar rats were randomly assigned to one of four groups: exercise at sea level, exercise at simulated high altitude, sedentary at sea level, and sedentary at high altitude (n = 8 in each group). Training consisted of swimming for 1 h/day in water at 36 degrees C for 14 wk. Training and exposure to a high-altitude environment produced a decrease in body weight (P less than 0.001). There was a significant linear correlation between muscle mass and body weight in the animals of all groups (r = 0.89, P less than 0.001). High-altitude training enhanced the percentage of type IIa fibers in the extensor digitorum longus muscle (EDL, P less than 0.05) and deep portions of the plantaris muscle (dPLA, P less than 0.01). High-altitude training also increased the percentage of type IIab fibers in fast-twitch muscles. These muscles showed marked metabolic adaptations: training increased the activity levels of enzymes involved in the citric acid cycle (citrate synthase, CS) and the beta-oxidation of fatty acids (3 hydroxyacyl CoA dehydrogenase, HAD). This increase occurred mainly at high altitude (36 and 31% for HAD in EDL and PLA muscles; 24 and 31% for CS in EDL and PLA muscles). Training increased the activity of enzymes involved in glucose phosphorylation (hexokinase). High-altitude training decreased lactate dehydrogenase activity. Endurance training performed at high altitude and sea level increased the isozyme 1-to-total lactate dehydrogenase activity ratio to the same extent.(ABSTRACT TRUNCATED AT 250 WORDS)

3-Hydroxyacyl CoA Dehydrogenases↗
PubMed1991

Enzymatic adaptations to treadmill training under the influence of naftidrofuryl acid in diaphragm and limb muscles of old rats.

The effects of training and naftidrofuryl treatment were observed in 21-month-old Long-Evans rats. Rats were injected intraperitoneally twice daily for 8 weeks with 7 mg.kg-1 of naftidrofuryl acid (SN, TN), or with 7 mg.kg-1 fumaric acid (SC and TC) or used as solvent. Training groups (TC, TN) started a progressive 8-week training programme of treadmill exercise. The activities of lactate dehydrogenase (LDH), hexokinase (HK), citrate synthase (CS) and 3-hydroxyacyl-Co-A-dehydrogenase (HAD), were measured in Soleus (SOL), Extensor Digitorum Longus (EDL) and Diaphragm (DIA) muscles. The mean VO2max value was 65 ml.min-1.kg-1 for 21-month-old rats. The training protocol induced increases in the mean VO2max values in the TC and TN groups, 71.8 and 74.4 ml.min-1.kg-1. In sedentary groups (SN), naftidrofuryl increased enzymatic activities (HK, CS, HAD) in the three muscles examined. When the animals underwent 8 weeks of physical training, the enzymatic activities (HK, CS, HAD) increased in SOL, EDL and DIA. When training was combined with naftidrofuryl treatment the increases in enzymatic activities were greater than those induced by training alone. However, the total changes did not differ for the sum of the changes produced by each condition alone.

3-Hydroxyacyl CoA Dehydrogenases↗
PubMed1991

Lactate steady state velocity and distance-exhaustion time relationship in running.

The relationship between distance and exhaustion time is linear for running exercise at constant velocity lasting 5 to 45 minutes. The slope of this relationship has the dimension of a velocity (VCRIT) which can be sustained during a long time. The individual VCRIT have been studied in 8 runners by measuring exhaustion time for 4 to 5 constant-velocity running exercises performed to exhaustion. The velocity correspond to a lactate steady state (VCHASSAIN) has been estimated according to a two-step protocol proposed by Chassain for exercises on a cycle ergometer. The running velocity corresponding to maximal aerobic metabolism (VLEGER) was estimated by means of the track test proposed by Léger and Boucher. VCRIT was very well correlated (r greater than 0.97) and almost equal to VCHASSAIN. VLEGER was also very well correlated with VCHASSAIN and VCRIT.

Exercise↗
PubMed1979

Physiological effects of dynamic work on a bicycle ergometer combined with different types of static contraction.

The effects on heart rate, oxygen uptake, and pulmonary ventilation of muscular exercises, including both dynamic contractions, either simple or combined, were studied in 4 male subjects, aged 21 to 23 years. The dynamic work consisted in cycling on an ergometric bicycle at three power levels: 40, 80, and 100 W. The static work consisted in pushing against, pulling and holding with the arms a 6, 9, 12, or 18 kg load. The physiological effects are expressed as cardiac cost (delta HR), oxygen cost (delta VO2) and ventilation cost (delta V). The physiological cost of the combined work increases according to the cycling power and to the isometric load developed. A statistical analysis shows that the costs of combined work are not different from the sum of the costs of the static and dynamic contractions measured separately. Thus, the physiological responses to the combinations investigated are of an additive type.

Adult↗
PubMed1978

Quantifying fatigue in working divers.

Thirty professional divers involved in training, bounce dives, working saturations, and deep experimental saturations were observed over a 1-month period. The subjects themselves performed simple twice-daily measurements of oral temperature, heart rate, breathhold time, handgrip strength, length and quality of sleep, and a subjective estimation of fatigue. The data were analysed with respect to the type of work done by the diver, separating diving from nondiving days. The results showed that subjective estimation of fatigue corresponded to the increment of evening oral temperature and heart rate over morning values. Both inspiratory and expiratory breathhold times decreased from morning to evening in those situations deemed most tiring by the divers. Sleep was generally of average duration and quality; however, diving during the daytime was associated with a decreased amount of sleep in the 24-h period including the following night. Sleep was also of poorer quality during periods of saturation diving. In addition to such group variations, individual divers showed significant performance changes on the various tests, demonstrating the value of this approach to the practical question of deciding when a man is too tired to dive safely. Extension of this method can, we hope, aid in the definition of safe working rotations for professional divers.

Adult↗
PubMed1977

[Relationship between blood zinc level and EEG changes under the influence of hyperpnea in normal subjects].

The red blood cell and serum zinc levels have been determined by atomic absorption spectrophotometry on 27 human subjects in apparent good state of health, tested monthly for five months successively. The subjects who present a decreased frequency of the E.E.G. pattern during hyperventilation, also show a diminished red blood cell Zn level, by comparison with the other subjects. This phenomenon suggests a possible relationship between red blood cell zinc concentration and E.E.G. signs of cortical hyperexcitability. These findings are discussed in the light of the recent literature.

Adolescent↗
PubMedDate not supplied

Complementary roles of central command and muscular reflex in the regulation of heart rate during submaximal isometric contraction.

During submaximal isometric contraction, the heart rate (HR) and the electromyographic activity (EMG) increase continuously. Although activation of the muscle and the cardiovascular center is placed partly under the common control of the central command, the nature of the relationship that may exist between HR and the integrated electromyogram (iEMG) is seldom studied. Seventeen healthy men, 22.4 +/- 0.5 years of age (M +/- SE), performed isometric contractions with the right elbow flexors. Forces of 25, 40, 50 and 65% of the maximum voluntary contraction (MVC) were used, and the contractions were sustained until (isotonic isometric contraction: IIC) and beyond exhaustion (anisotonic isometric contraction: AIC). During IIC, a linear relationship exists between HR and iEMG; the slope of this relationship is independent of the relative force developed, which is in favor of a predominant role played by the central command in HR increase. The increase in the ratio iEMG/HR at the approach of local muscular exhaustion would indicate that at the end of IIC there is an increase in the relative part furnished by the information of peripheral origin in HR regulation. During AIC, the force (F) decreases in an exponential manner and stabilizes at around 25% MVC from tAIC = 70 s on. The iEMG and HR change independently: iEMG decreases like F such that iEMG/F remains constant; HR continues to increase in the first phase corresponding to the rapid decrease in F and iEMG, then in a second phase, it decreases linearly with respect to time. Our results suggest that the action of the central command is dominant during stage 1 of AIC, while during stage 2 the relative part furnished by the muscle reflexes increases. Beyond tAIC = 70 s, there seems to be a certain degree of central fatigue.

Adolescent↗