O2 transport during exercise after cardiac transplantation.
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Adult↗
Biomedical subjects
P Cerretelli
Publications and source records attributed to P Cerretelli.
Effects of temperature on the maximal instantaneous muscle power of humans.
The maximal instantaneous muscle power (wi,max) probably reflects the maximal rate of adenosine 5'-triphosphate (ATP) hydrolysis (ATPmax), a temperature-dependent variable, which gives rise to the hypothesis that temperature, by affecting ATPmax, may also influence wi,max. This hypothesis was tested on six subjects, whose vastus lateralis muscle temperature (Tmuscle) was monitored by a thermocouple inserted approximately 3 cm below the skin surface. The Wi,max was determined during a series of high jumps off both feet on a force platform before and after immersion up to the abdomen for 90 min in a temperature controlled (T = 20 +/- 0.1 degrees C) water bath. Control Tmuscle was 35.8 +/- 0.7 degrees C, with control Wi,max being 51.6 (SD 8.7) W.kg-1. After cold exposure, Tmuscle decreased by about 8 degrees C, whereas wi,max 27% lower. The temperature dependence of Wi,max was found to be less (Q10 less than 1.5, where Q10 is the temperature coefficient as calculated in other studies) than reported in the literature for ATPmax. Such a low Q10 may reflect an increase in the mechanical equivalent of ATP splitting, as a consequence of the reduced velocity of muscle contraction occurring at low Tmuscle.
Adenosine Triphosphate↗
Effects of muscle temperature on the VO2 kinetics at the onset of exercise in man.
The kinetics (i.e. the rate of readjustment) of O2 uptake (VO2) at the mouth of muscle blood flow in the vastus lateralis muscle (Qm), and the net accumulation of lactate in the rest-to-exercise transient (early lactate) were assessed in 6 untrained men (age 31 +/- 8 (SD) yrs) during constant-load 5-min duration exercises on the cyclo ergometer of 75 and 125 W, performed at muscle temperatures (Tm) of 35.5 +/- 0.9 degrees C (N) and of 28.0 +/- 1.65 degrees C (C). VO2 was measured breath-by-breath; Qm was assessed from 133Xe clearance; early lactate was calculated as the difference between the venous lactate concentrations observed after and before exercise. At both work loads, steady-state VO2 was slightly higher in N than in C (P less than 0.05 at 75 W; NS at 125 W). The half-times of VO2 kinetics were: in N, 36.2 +/- 6.7 s at 75 W and 41.6 +/- 8.6 s at 125 W; in C, 41.4 +/- 10.0 at 75 W and 43.8 +/- 14.0 at 125 W (NS). Mean steady state Qm was 8.5 ml.min-1.100 g-1 in C, and 13.4 in N at 75 W (NS); at 125 W, Qm was 18.3 ml.min-1.100 g-1 in C vs. 25.0 in N (NS). The half-times of the Qm kinetics tended to be slower in C than in N (NS). At both work loads, early lactate was slightly greater in C than in N (NS). It is concluded that, at submaximal exercise, (a) steady state VO2 and the VO2 kinetics are not affected by Tm, and (b) at the onset of exercise Qm does not affect VO2 kinetics.
Adult↗
Energy sources for muscular exercise.
The basic energy yielding mechanisms of muscle contraction are reviewed and the main structural and functional features of human muscle are compared with those of some common athletic animal species. Sex and age related muscle power (alactic) characteristics are examined in both sedentary and athletic subjects. Recent measurements of the kinetics of contraction of the O2 debt by NMR spectroscopy by the human plantar flexors are shown. The main features of anaerobic (lactic) exercise in untrained and trained subjects, as a function of sex, age and environmental conditions (high altitude), are described with particular emphasis on the so-called lactic anaerobic threshold. With regard to aerobic exercise, the main determinants of O2 transport to the tissues are reviewed and an update of the factors limiting human performance is made. The possible causes of arterial O2 desaturation in athletes, both at sea level and at altitude, are discussed. A comparative analysis between man and woman of the progress of the records of some typical competitions is made and possible implications are discussed. The potential role of some commonly used physiological and/or paraphysiological procedures for improving the performance is analyzed.
Age Factors↗
Metabolic transient studies by NMR.
The time course of phosphocreatine (PC) hydrolysis in humans was measured by 31P-NMR spectroscopy (31P-NMRS) with a time resolution of 10.8 s in the gastrocnemius muscle and a relationship between muscle O2 consumption (VO2) and [PC] was derived from a bioenergetic model. This allowed a direct estimate of the half-time of the intracellular VO2 kinetics (t1/2 VO2) of the contracting human gastrocnemius in aerobic conditions. t1/2 VO2 was found to be approximately 16 s and independent of the work load. This value corresponds to the shortest t1/2 VO2 determined at the mouth of the subject in the absence of lactate accumulation in the rest to work transient. t1/2 VO2 may now be assessed in man at low muscle temperatures. To this aim a procedure was developed allowing corrections of the 31P-NMR spectra based on the muscle temperature profiles obtained by a simultaneously acquired proton image.
Adenosine Triphosphate↗
Muscle carnitine after strenuous endurance exercise.
The effect of very long endurance exercise on muscle carnitine was studied. Eighteen cross-country skiers took part in a race in the Alps (average inspired partial pressure of O2 100-110 Torr) that lasted on average 13 h 26 min. Carnitine intake, evaluated for 2 wk before the event, was 50 +/- 4 (SE) mg/day. Muscle (vastus lateralis) total carnitine concentration, measured twice with a 2-yr interval on eight rested subjects, did not change with time (17 vs. 16 mumol/g dry wt, NS) but showed consistent interindividual differences (range 12-22, P = 0.001) with no correlation with intake. After exercise, total muscle carnitine was unaltered (from 17.9 +/- 1.0 at rest to 18.3 +/- 0.8 mumol/g dry wt postexercise in the 15 subjects who completed the race, NS), but muscle free carnitine decreased 20% (from 14.9 +/- 0.8 mumol/g, P = 0.01) and short-chain acylcarnitine increased 108% (from 3.5 +/- 0.4 mumol/g, P = 0.01). These results suggest that carnitine deficiency will probably not result from strenuous aerobic exercise in trained subjects who consume a moderate amount of carnitine in their food.
Adult↗
Phosphocreatine hydrolysis by 31P-NMR at the onset of constant-load exercise in humans.
The kinetics of phosphocreatine (PC) breakdown in human plantar flexors at the onset of constant-load aerobic exercise was determined by high-resolution 31P-nuclear magnetic resonance spectroscopy (NMRS). The half time of the process (t1/2PC) was obtained by fitting curves (n = 13) from five subjects at various aerobic work loads for which muscle pH was not different from that at rest. Steady-state PC concentration ([PC]) was not < 70% of the resting value and was linearly related to the work load (w) ([PC] = -3.01 +/- 0.08 w + 1 (r = 0.48, 2P < 0.1)). The average t1/2PC was 16.2 s and was independent of work load. Because the half time of the muscle PC kinetics reflects the half time of the O2 uptake (MO2) kinetics (t1/2MO2), the latter is equal to that found earlier in the isolated perfused dog gastrocnemius. Whereas in the dog the above t1/2MO2 compares well with the homologous half time of the O2 uptake at the alveolar level, in humans such equivalence is found only at extremely low work loads, when the transient contribution by anaerobic glycolysis is negligible.
Adult↗
Protein absorption and energy digestibility at high altitude.
To test the hypothesis that malabsorption of dietary protein is partly responsible for the weight loss observed during prolonged altitude exposure, six healthy male subjects [31.8 +/- 4.5 (SD) yr] received 15N-labeled soya protein by mouth and [15N]glycine intravenously at 122 and 5,000 m. From the subsequent 4-day total urine and fecal pools, the different fractions of the administered 15N were determined by mass spectrometry. Weight and skinfold thickness were measured at the beginning and end of the altitude exposure. In addition, the overall digestible energy of the diet at altitude was assessed by a 3-day diet control and adiabatic bomb calorimetric assessment of the energy content of the corresponding fecal pool. The average decrease of the subjects' weight during altitude exposure was 3%. Loss of fat mass at altitude estimated from the skinfold measurements was 9%. Protein absorption, calculated as 100--[fecal excretion of 15N after ingestion of 15N soya protein (% of dose given)--fecal excretion of 15N after injection of 15N glycine (% of dose given)], was not significantly impaired at altitude compared with sea level (96 vs. 97%, respectively), and overall digestible energy at altitude, calculated as 100--percent undigested gross energy in the feces, amounted to 96%. It is concluded that, at least up to an altitude of 5,000 m, malabsorption does not play a role in altitude-related weight loss.
Adult↗
Muscle energetics and ultrastructure in chronic hypoxia.
High-altitude exposure impairs both maximal aerobic and anaerobic (lactic and alactic) performances. The maximal aerobic power (VO2max) decreases exponentially with increasing altitude. At 5,350 m, a sudden rise in inspired O2 pressure (PIO2) was found to raise the VO2max of acclimatized lowlanders from 70 to only 92% of the control sea-level value. Since the hemoglobin concentration was about 35% higher than that of the controls, hemoglobin O2 saturation was restored to about 100%, and maximal cardiac output was only 10-20% lower than at sea level, the above result can only be the consequence: (1) of a reduced muscle mass and/or of muscle deterioration, and (2) of impaired muscle perfusion. In muscle biopsies taken from the vastus lateralis muscles of mountaineers after a 6- to 8-week sojourn at high altitude, a reduction in the fiber cross-sectional area was found which was accompanied by a decrease in the volume density of the mitochondria and by a lower tissue oxidative capacity. In acclimatized lowlanders, the maximal blood lactate concentration after exhausting exercise was halved compared to sea-level conditions. On the other hand, the peak anaerobic power was not affected by severe hypoxia within the first 3 weeks of exposure; thereafter, it decreased by about 25%, probably as a consequence of muscle deterioration. It is concluded that, whereas in acute hypoxia VO2max is primarily reduced by a lack of O2, in chronic hypoxia muscle deterioration may become an important factor contributing to the limitation of the maximal aerobic performance.
Acclimatization↗
Gas exchange kinetics in heart transplant recipients.
Submaximal and/or peak levels of oxygen consumption (VO2), pulmonary ventilation (VE), heart rate (HR), stroke volume of heart (SV), cardiac output (Q), muscle blood flow (qm), as well as the kinetics of readjustment of gas exchange, Q and qm (t1/2 VO2on-, t1/2 Qon-, t1/2 qmon-) were determined in 44 heart transplant recipients (HTRs) and in a group of age-, sex-, and physical activity-matched control subjects (CTL) when carrying out rectangular loads (25 to 125 W) on a bicycle ergometer. The increase of SV occurring at work onset appears to compensate in HTRs for the sluggish readjustment of HR so that the rate of readjustment of Q is kept within normal limits. As a consequence, qm, t1/2 q mon-, and t1/2 VO2on- appear to be similar or only moderately delayed in HTRs compared with CTLs. It is concluded that in HTRs, because of constrained maximum HR, only work loads up to 60% of the VO2max of CTLs may be attained; also, owing to the fast readjustment of Q, up to work loads of 75 to 100 W, the rest to work transition phase is not impaired.
Electrocardiography↗
Neurotransmitter amino acid variations in striatum of rats exposed to 50 Hz electric fields.
Concentration of neurotransmitter amino acids (Tau, Gly, Asp, Glu, Gln, Ala, GABA) were measured in rat striatum following varying exposure (320 to 1408 h) to high intensity (50 Hz) electric fields. Tissue extracts in methanol, after drying, were derivatized with dansyl chloride and the amino acids quantitated by high-pressure liquid chromatography with ultraviolet detection. Short exposures (320 h) to 100 kV/m field induced a decrease in almost all tested amino acids. Longer exposure times (640 h) to 25 and 100 kV/m were only associated with a decrease in Tau. A further increase of the exposure time (1240 and 1408 h) both at 25 and 180 kV/m were mainly associated with a reduction of the amino acid levels. It is concluded that electric fields in the range 20-180 kV/m generate bimodal variations in neurotransmitter amino acids with troughs at very short and longer exposure times, independent from the field strength.
Amino Acids↗
Peak anaerobic power in master athletes.
The age-related decline in maximal physical performance of healthy subjects may be attributed both to the aging process per se and/or to a progressive reduction in physical activity. In two groups of master athletes, power (P) or endurance (E) trained (n = 115; aged 40-78 years), the degree and rate of the age-related deterioration of the maximal instantaneous muscle power (peak power, Wpeak), and the relative contribution of quantitative (muscle mass) and qualitative factors possibly underlying such deterioration were determined. Two groups of young athletes (n = 20; 17-26 years) and healthy untrained subjects (U, n = 37; 22-67 years) were also tested for comparison. The following two variables were assessed, firstly the lower limb muscle plus bone volume (LMV) by anthropometry, and secondly Wpeak, by means of a standardized vertical jump off both feet, performed on a force platform. The results obtained were that LMV of E and P, as well as of U, was about the same between age 20 and 45 years, whereas at older ages a progressive reduction was observed; the LMV values were higher in P than in E and U.(ABSTRACT TRUNCATED AT 250 WORDS)
Adolescent↗
Energetics of locomotion in African pygmies.
The energy cost of walking (Cw) and running (Cr), and the maximal O2 consumption (VO2max) were determined in a field study on 17 Pygmies (age 24 years, SD 6; height 160 cm, SD 5; body mass 57.2 kg, SD 4.8) living in the region of Bipindi, Cameroon. The Cw varied from 112 ml.kg-1.km-1, SD 25 [velocity (v), 4 km.h-1] to 143 ml.kg-1.km-1, SD 16 (v, 7 km.h-1). Optimal walking v was 5 km.h-1. The Cr was 156 ml.kg-1.km-1, SD 14 (v, 10 km.h-1) and was constant in the 8-11 km.h-1 speed range. The VO2max was 33.7 ml.kg-1.min-1, i.e. lower than in other African populations of the same age. The Cr and Cw were lower than in taller Caucasian endurance runners. These findings, which challenge the theory of physical similarity as applied to animal locomotion, may depend either on the mechanics of locomotion which in Pygmies may be different from that observed in Caucasians, or on a greater mechanical efficiency in Pygmies than in Caucasians. The low Cr values observed enable Pygmies to reach higher running speeds than would be expected on the basis of their VO2max.
Africa↗
Alveolar gas composition and exchange during deep breath-hold diving and dry breath holds in elite divers.
End tidal O2 and CO2 (PETCO2) pressures, expired volume, blood lactate concentration ([Lab]), and arterial blood O2 saturation [dry breath holds (BHs) only] were assessed in three elite breath-hold divers (ED) before and after deep dives and BH and in nine control subjects (C; BH only). After the dives (depth 40-70 m, duration 88-151 s), end-tidal O2 pressure decreased from approximately 140 Torr to a minimum of 30.6 Torr, PETCO2 increased from approximately 25 Torr to a maximum of 47.0 Torr, and expired volume (BTPS) ranged from 1.32 to 2.86 liters. Pulmonary O2 exchange was 455-1,006 ml. CO2 output approached zero. [Lab] increased from approximately 1.2 mM to at most 6.46 mM. Estimated power output during dives was 513-929 ml O2/min, i.e. approximately 20-30% of maximal O2 consumption. During BH, alveolar PO2 decreased from approximately 130 to less than 30 Torr in ED and from 125 to 45 Torr in C. PETCO2 increased from approximately 30 to approximately 50 Torr in both ED and C. Contrary to C, pulmonary O2 exchange in ED was less than resting O2 consumption, whereas CO2 output approached zero in both groups. [Lab] was unchanged. Arterial blood O2 saturation decreased more in ED than in C. ED are characterized by increased anaerobic metabolism likely due to the existence of a diving reflex.
Adult↗
Ventilatory and gas exchange kinetics in a human recipient of a Jarvik-7 total artificial heart.
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Adult↗
Muscle structure and performance capacity of Himalayan Sherpas.
The ultrastructure of the vastus lateralis muscle of Sherpas from Nepal [5 males; age 28 +/- 2.8 (SD) yr, indirect maximal O2 consumption 48.5 +/- 5.4 ml.kg(-1).min(-1)] was assessed and compared with those of sedentary lowlanders and of Caucasian climbers before and after high-altitude exposure. The mean cross-sectional area of the fibers was 3,186 +/- 521 microns2, i.e., similar to those of Caucasian elite high-altitude climbers (3,108 +/- 303 microns2) and a group of climbers after a 6- to 8-wk sojourn at 5,000-8,600 m (3,360 +/- 580 microns2) but significantly (P less than 0.05) smaller than that of unacclimatized climbers (4,170 +/- 710 microns2) and slightly, although not significantly, lower than that of sedentary lowlanders (3,640 +/- 260 microns2). The number of capillaries per square millimeter of muscle cross section was 467 +/- 22, not significantly smaller than those of climbers on return from a Himalayan expedition (538 +/- 89) and elite high-altitude climbers (542 +/- 127) but significantly (P less than 0.05) greater than that of sedentary lowlanders (387 +/- 25). The volume density of mitochondria was 3.96 +/- 0.54%, significantly (P less than 0.05) less than the values found for any other investigated group, including sedentary subjects at sea level (4.74 +/- 0.30%). It is concluded that Sherpas, like acclimatized Caucasian climbers, are characterized by 1) facilitated convective and diffusive muscle O2 flow conditions and 2) a higher maximal O2 consumption-to-mitochondrial volume ratio than lowlanders despite a reduced mitochondrial volume density.
Acclimatization↗
Effect of aging on human adductor pollicis muscle function.
The effect of aging on the voluntary and electrically evoked contractile properties of the human adductor pollicis muscle was investigated in 70 healthy male subjects aged 20-91 yr, 10 subjects for each decade. Maximum isometric voluntary force declined significantly (range of P values less than 0.001-0.05) after the age of 59 yr, dropping by the eighth decade to 57.6% of the level recorded in the second decade. A significant shift (P range less than 0.001-0.05) to the left of the frequency-force curve after ulnar nerve supramaximal stimulation at 1, 10, 20, 30, and 50 Hz was observed in the most elderly group (greater than 80 yr) compared with the youngest group (20-29 yr). Maximum relaxation rate dropped by 48.7% from the second to the eighth decade. The decrease became significant (P range less than 0.05-0.001) with the sixth decade. Isometric endurance, evaluated during 30 s of stimulation at 30 Hz, showed a linear (P less than 0.001) increase with age. Aged muscle is thus weaker, slower, and tetanized at lower fusion frequencies but, paradoxically, more resistant to static fatigue.
Adult↗
Muscle 31P-NMR in humans: estimate of bias and qualitative assessment of ATPase activity.
A mathematical model is developed whereby the longitudinal magnetization of phosphocreatine (PC), ATP, Pi, and total phosphate (PT) can be calculated on the basis of assumed chemical rate constants (kappa i) and spin lattice relaxation times of the muscle PC in equilibrium ATP in equilibrium Pi exchange system. By means of this model, some unexplained 31P nuclear magnetic resonance (NMR) spectroscopy results from the literature (e.g., a decrease of PT in a closed system) could be explained simply on the basis of the physiological variability of kappa i. Moreover, appropriate model simulations indicate that 1) 31P-NMR spectra obtained with short relaxation delays may be influenced to various extents by the metabolic and physicochemical status of the muscle; 2) the assessment of kappa i by standard NMR spectroscopy techniques may be extremely critical; 3) delta PC/delta Pi, as obtained from conventional 31P-NMR spectra, may represent a sensible index of kappa 2 (the pseudo first-order chemical exchange rate constant of the adenosinetriphosphatase reaction); 4) delta PC/delta Pi changes as detected from sequential (short relaxation delays) 31P-NMR spectra obtained in humans during metabolic transients (e.g., during transition from rest to work and vice versa) may represent an index of transient changes of kappa 2.
Adenosine Triphosphatases↗