Biomedical subjects

P E Di Prampero

Publications and source records attributed to P E Di Prampero.

At least 19 recordsLinked to original sources

PubMed2005

Cardioventilatory responses during real or imagined walking at low speed.

There is increasing evidence that motor imagery involves at least in part central processes used in motor control. In order to deepen our understanding on the neural mechanisms underlying vegetative responses to real and imagined exercise, we determined cardioventilatory variables during actual or imagined treadmill walking on flat terrain at speeds of 2, 3.5 or 5 km/h, in a group of 14 healthy volunteers. During actual walking, as expected, a comparable intensity-dependent increase was found in ventilation, oxygen consumption, tidal volume and respiratory rate. Imagined walking led to a significant, albeit small (less than 10%), increase in ventilation and oxygen consumption, and to larger increases (up to 40%) in respiratory rate, which was paralleled by a non significant trend towards a decline of tidal volume. These results confirm and extend previous observations showing that motor imagery is accompanied by centrally induced changes in vegetative responses, and provide evidence for a differential control on respiratory rate and tidal volume.

Adult↗

PubMed2004

Muscle-fiber conduction velocity estimated from surface EMG signals during explosive dynamic contractions.

Muscle-fiber conduction velocity (CV) was estimated from surface electromyographic (EMG) signals during isometric contractions and during short (150-200 ms), explosive, dynamic exercises. Surface EMG signals were recorded with four linear adhesive arrays from the vastus lateralis and medialis muscles of 12 healthy subjects. Isometric contractions were at linearly increasing force from 0% to 100% of the maximum. The dynamic contractions consisted of explosive efforts of the lower limb on a sledge ergometer. For the explosive contractions, muscle-fiber CV was estimated in seven time-windows located along the ascending time interval of the force. There was a significant correlation between CV values during the isometric ramp and explosive contractions (R = 0.75). Moreover, CV estimates increased significantly from (mean +/- SD) 4.32 +/- 0.46 m/s to 4.97 +/- 0.45 m/s during the increasing-force explosive task. It was concluded that CV can be estimated reliably during dynamic tasks involving fast limb movements and that, in these contractions, it may provide important information on motor-unit control properties.

Adult↗

PubMed2002

Relationships between mechanical power, O(2) consumption, O(2) deficit and high-energy phosphates during calf exercise in humans.

Whole-body O(2) uptake ( VO(2)), O(2) deficit and the concentration of high-energy phosphates (determined by (31)P spectroscopy) in human calf muscle were measured during moderate aerobic square-wave exercise of increasing intensity in ten volunteers. Net VO(2) (above resting) increased linearly with mechanical power, yielding a delta efficiency of 13.1%. "Gross" O(2) deficit increased linearly with net VO(2). The fraction of phosphocreatine (PC) split at steady state increased linearly with the mechanical power and with the O(2) deficit. If the [PC] in resting muscle is known, the slope of the regression between PC split and O(2) deficit (in millimoles) yields the P/O(2) ratio. To calculate this, the O(2) deficit was corrected for the amount of O(2) derived from the body stores, as obtained from literature data. The value so obtained, for a resting [PC] of 30 mM was 5.9, consistent with canonical textbook values. Furthermore, the ratio of "true" O(2) deficit to steady-state VO(2) is a measure of the time constant of VO(2) kinetics at work onset at the muscle level: assuming a monoexponential time course without time delays it amounted to about 17 s, close to the value that can be expected in mammalian muscle at 37 degrees C.

Adult↗

PubMed2002

Energy expenditure during an ultra-endurance cycling race.

BACKGROUND: The energy expenditure of cycling has been investigated in great detail, mainly during trials performed for relatively short periods of time and under well established conditions. The number of investigations performed on long-lasting races, however, is very limited, probably because of practical difficulties. The aim of the present work was an attempt to estimate the energy requirements of 5 amateur cyclists who participated in an ultra-endurance long-lasting road cycling race. METHODS: A generalized equation obtained from literature was applied to calculate the energy expenditure of 26 to 137 short fractions of the competition. RESULTS: The calculated time weighted net metabolic power output ranged from 6.4 W x kg-1 to 10.8 W x kg-1; the corresponding net energy expenditure per unit distance ranging from 73.1 kJ x km-1 to 110.5 kJ x km-1. The total energy expenditure of the competition (rest included) ranged from 44.2 to 186.4 MJ, depending on the total competition duration. For all subjects, the sum total of the overall energy expenditure increased as a power function of cumulated performance time (kJ = 4872 x t0.77). However, the daily energy expenditure decreases with increasing the duration of the competition. CONCLUSIONS: It is concluded that it is possible to estimate the energy expenditure of ultra-endurance cycling performances, provided that the mechanical power output can be described by well defined equations.

Adult↗

PubMed1996

Blood pressure and heart rate responses to sudden changes of gravity during exercise.

Heart rate (HR) and blood pressure responses to sudden changes of gravity during 80- to 100-W leg exercise were studied. One group was exposed to sudden changes between 1.0 and 0 g in the head-to-foot direction (Gz+), starting upright and with repeated 30-s tilts to the supine position. Another group was exposed to sudden Gz+ changes between 1.8 and 0 g in an aircraft performing parabolic flight. Arterial blood pressure at the level of the carotid (carotid distending pressure, CDP) showed a large transient increase by 27-47 mmHg when Gz+ was suddenly decreased and a similar drop when Gz+ was suddenly increased. HR displayed a reverse pattern with larger transients (-22 to -26 min-1) in response to Gz+ decreases and more sluggish changes of lower amplitude in the other direction. Central blood volume, as estimated from the inverse of transthoracic impedance (1/TTI), varied in concert with Gz+. A model is proposed in which HR responses are described as a function of CDP and 1/TTI after a time delay of 2.3-3.0 s and including a low-pass filter function with time constants of 0.34-0.35 s for decreasing HR and time constants of 2.9-4.6 s for increasing HR. The sensitivity of the carotid component was around -0.8 to -1.0 min-1 . mmHg-1 (4-7 ms/mmHg). The cardiopulmonary baroreceptor component was an additive input but was of modest relative importance during the initial HR responses. For steady-state HR responses, however, our model suggests that inputs from carotid and cardiopulmonary receptors are of equal importance.

Adult↗

PubMed1995

Bioenergetics and biomechanics of front crawl swimming.

"Underwater torque" (T') is one of the main factors determining the energy cost of front crawl swimming per unit distance (Cs). In turn, T' is defined as the product of the force with which the swimmer's feet tend to sink times the distance between the feet and the center of volume of the lungs. The dependency of Cs on T' was further investigated by determining Cs in a group of 10 recreational swimmers (G1: 4 women and 6 men) and in a group of 8 male elite swimmers (G2) after T' was experimentally modified. This was achieved by securing around the swimmers' waist a plastic tube filled, on different occasions, with air, water, or 1 or 2 kg of lead. Thus, T' was either decreased, unchanged, or increased compared with the natural condition (tube filled with water). Cs was determined, for each T' configuration, at 0.7 m/s for G1 and at 1.0 and 1.2 m/s for G2. For T' equal to the natural value, Cs (in kJ.m-1.m body surface area-2) was 0.36 +/- 0.09 and 0.53 +/- 0.13 for G1 in women and men, respectively, and 0.45 +/- 0.05 and 0.53 +/- 0.06 for G2 at 1.0 and 1.2 m/s, respectively. In a given subject at a given speed, Cs and T' were linearly correlated. To compare different subjects and different speeds, the single values of Cs and T' were normalized by dividing them by the corresponding individual averages. These were calculated from all single values (of Cs or T') obtained from that subject at that speed.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗

PubMed1995

The concept of lactate threshold. A short review.

The anaerobic threshold (AT) is a widely used tool for investigating aerobic performance characteristics in physiological of pathological conditions. The aim of the present paper is to show that, when the lactate concentration in blood [Lab] is constant in time, regardless of its absolute level, the whole body energy sources for muscular work are entirely aerobic. In fact, [Lab] can remain constant if, and only if, La production is equal to La removal. Since this last is an entirely aerobic process, it can be shown that the net anaerobic energy yield from La production is nil, even if some muscle fibres are indeed producing La at a non trivial rate. These conditions will be defined as "unevenly aerobic" to distinguish them from: (1) the traditional "evenly aerobic" ones, in which the net La production is also zero, but because neither La production nor La removal are significantly increased, and (2) "true anaerobic" conditions wherein La production exceeds La removal and therefore [Lab] increases continuously in time. Comparison of unevenly versus evenly aerobic conditions shows that in the former case the depletion of the glycogen stores is faster in the muscles (or muscle fibres) that are producing La than in those which remove it. Hence the La producing fibres may become crucial in setting the duration (or intensity) of performance. AT, irrespective of its precise mode of assessment, is presumably a measure of the exercise intensity corresponding (or close) to the transition between evenly and unevenly aerobic conditions, thus explaining why AT is a good estimate of the subjects' training status and/or performance capacity.

Aerobiosis↗

PubMed1993

Energetics of best performances in middle-distance running.

Oxygen consumption (VO2) and blood lactate concentration were determined during constant-speed track running on 16 runners of intermediate level competing in middle distances (0.8-5.0 km). The energy cost of track running per unit distance (Cr) was then obtained from the ratio of steady-state VO2, corrected for lactate production, to speed; it was found to be independent of speed, its overall mean being 3.72 +/- 0.24 J.kg-1 x m-1 (n = 58; 1 ml O2 = 20.9 J). Maximal VO2 (VO2max) was also measured on the same subjects. Theoretical record times were then calculated for each distance and subject and compared with actual seasonal best performances as follows. The maximal metabolic power (Er max) a subject can maintain in running is a known function of VO2max and maximal anaerobic capacity and of the effort duration to exhaustion (te). Er max was then calculated as a function of te from VO2max, assuming a standard value for maximal anaerobic capacity. The metabolic power requirement (Er) necessary to cover a given distance (d) was calculated as a function of performance time (t) from the product Crdt-1 = Er. The time values that solve the equality Er max(te) = Er(t), assumed to yield the theoretical best t, were obtained by an iterative procedure for any given subject and distance and compared with actual records.(ABSTRACT TRUNCATED AT 250 WORDS)

Adolescent↗

PubMed1991

Pedalling in space as a countermeasure to microgravity deconditioning.

A system consisting of two mechanically coupled counter rotating bicycles, moving on the inner wall of a cylindrical space module, is proposed to prevent microgravity deconditioning. The two pedalling subjects generate a centrifugal acceleration vector (ac) simulating gravity. This last depends on the peripheral velocity (v) and on the radius of gyration (R): ac = v2/R. Since R is constant and equal to the inner radius of the space module, any desired value of ac can be achieved by selecting the appropriate v value. The corresponding mechanical (w) and metabolic (VO2) powers can then be calculated on the basis of the biomechanical and anthropometric characteristics of the system and subjects. It is shown that if R = 2 m, in order to attain ac = 1 g at the feet, v = 4.5 m s-1, w = 60 W and VO2 = 1.2 litres min-1. However if R = 6 m, then v = 7.8 m s-1, w = 140 W and VO2 = 3 litres min-1. The average arterial pressures prevailing at the head and feet levels in the two above conditions can also be calculated as 95, 150 and 80, 170 mmHg, respectively for a mean arterial pressure of 100 mmHg at the aortic bulbus. In conclusion, by selecting appropriately the radial dimensions of the space module in order to minimize: (1) vestibular disturbances, (2) head to feet centrifugal acceleration gradients and (3) manufacturing costs, it may be possible to combine exercise and simulated gravity, with no need for additional external power.

Aerospace Medicine↗

PubMed1987

Effects of exercise on maximal instantaneous muscular power of humans.

The maximal instantaneous anaerobic power (w), as determined during a high jump off both feet on a force platform, was measured on eight subjects starting from a resting base line; a base line of steady-state cycloergometric exercise requiring 30, 50, and 70% of individual maximum O2 consumption (VO2max); and a base line of maximal and supramaximal exercise (100 and 120% of VO2max). In addition, w was also measured during the VO2 transients from rest to each of the above work loads. Blood lactate concentration ([Lab]) was determined before and 8 min after the end of each priming load. After the onset of any priming load, w decreases with time reaching in 2 min a steady level that is lower the higher the VO2. For the three lowest work rates, the steady w level is unchanged by increasing the duration of the priming exercise up to 30 min. For low work levels, the decrease of w as a function of VO2 is essentially parallel to that of estimated muscle concentration of ATP ([ATP]). For work levels greater than 60% of VO2max involving a substantial accumulation of lactate, the decrease of w becomes smaller than the estimated drop of muscle [ATP]. This finding is tentatively attributed to an increase of either the mechanical equivalent or of the velocity constant of ATP splitting brought about by the lowering of intracellular muscle pH after lactate accumulation.(ABSTRACT TRUNCATED AT 250 WORDS)

Adenosine Triphosphate↗

PubMed1986

The role of 2,3-DPG in the oxygen transport at altitude.

A computer program is described, relating blood flow with venous PO2 for any given set of the following parameters: oxygen uptake, respiratory quotient, the 2,3-DPG/Hb molar concentration ratio (G), arterial PO2, PCO2, and pH. Two compartments (total body and one leg) and two conditions (rest and maximal exercise) are considered. Calculations are performed at five altitudes (0, 3850, 5400, 6300 and 8848 m), for which the above variables are known. The results indicate that an increased G value has a negative effect on the oxygen delivery to tissues at very high altitudes (greater than 5400 m), irrespectively of the work load, since larger blood flows (delta Q on the summit of Mt. Everest is +4 to +71/min, and +1 to +2.5 l/min, for whole body and one leg, respectively) are required for a given oxygen uptake. For submaximal work at altitudes ranging from sea level up to 5400 m, as well as for moderate work at 5400 m, high G values improve the oxygen delivery to tissues.

2,3-Diphosphoglycerate↗

PubMed1986

Physiological profile of world-class high-altitude climbers.

The functional characteristics of six world-class high-altitude mountaineers were assessed 2-12 mo after the last high-altitude climb. Each climber on one or several occasions had reached altitudes of 8,500 m or above without supplementary O2. Static and dynamic lung volumes and right and left echocardiographic measurements were found to be within normal limits of sedentary controls (SC). Muscle fiber distribution was 70% type I, 22% type IIa, and 7% type IIb. Mean muscle fiber cross-sectional area was significantly smaller than that of SC (-15%) and of long-distance runners (LDR, -51%). The number of capillaries per unit cross-sectional area was significantly greater than that of SC (+ 40%). Total mitochondrial volume was not significantly different from that of SC, but its subsarcolemmal component was equal to that of LDR. Average maximal O2 consumption was 60 +/- 6 ml X kg-1 X min-1, which is between the values of SC and LDR. Average maximal anaerobic power was 28 +/- 2.5 W X kg-1, which is equal to that of SC and 40% lower that that of competitive high jumpers. All subjects were characterized by resting hyperventilation both in normoxia and in moderate (inspired O2 partial pressure = 77 Torr) hypoxia resulting in higher oxyhemoglobin saturation levels in hypoxia. The ventilatory response to four tidal volumes of pure O2 was similar to that of SC. It is concluded that elite high-altitude climbers do not have physiological adaptations to high altitude that justify their unique performance.

Adaptation, Physiological↗

PubMed1986

Energy cost of walking and exertional dyspnea in multiple sclerosis.

Pulmonary functions at rest and cardiorespiratory responses to low speed treadmill walking were investigated in 24 patients (P), (mean age, 38 years; range, 20 to 56 yr) with multiple sclerosis and compared with a control group (C). The following parameters were significantly (p less than 0.01) different in P from those in C. At rest in P, the residual volume to TLC ratio was 21% greater, respiratory muscle strength index was 28% lower, and heart rate (HR) was 11 beats/min-1 higher. During treadmill walking at a given speed, HR, minute ventilation (VE), and O2 consumption (VO2) were all elevated (37 to 119%). In addition, the energy cost of walking, per unit distance, above resting, was 2 to 3 times greater, with mean +/- SEM values for P of 0.299 +/- 0.019 and C of 0.147 +/- 0.006 at 2 km/h and 0.275 +/- 0.042 and 0.110 +/- 0.005 (for P and C, respectively) ml O2 kg-1 m-1 at 4 km/h; the HR and VE/VO2, also when referred to a given VO2, were higher. We conclude that a high energy cost of walking may be an important contributing factor to breathlessness and leg fatigue in patients with multiple sclerosis. Poor conditioning, altered cardiovascular control, and respiratory muscle weakness may play additional roles.

Adult↗

PubMed1983

Oxygen deficit and stores at onset of muscular exercise in humans.

Single-breath O2 consumption (VO2) at the mouth and heart rate were determined in five healthy male subjects at rest, during 8 min of cycloergometric exercise (50, 100, 125, and 150 W), and in the recovery period following two experimental conditions: air breathing throughout (AA); hypoxic breathing (FIO2 = 0.11) for 6 min of preexercise rest followed by air breathing from the onset of exercise (HA). The O2 deficits and debts as well as the t 1/2 values of the VO2 on- and off-responses were determined and blood lactate concentrations measured at rest and in the recovery after 4 and 8 min of exercise. At all work loads: 1) O2 deficits were on the average 0.39 liter smaller in HA than in AA; 2) VO2 on-responses were faster in HA (t 1/2 approximately equal to 7 s) than in AA (t 1/2 = 20-30 s); and 3) O2 debts and VO2 off-responses were the same in the two conditions. Since the VO2 and heart rate levels at steady state as well as the blood lactate concentrations after 4 and 8 min of exercise were the same in AA and HA, the observed differences of O2 deficit cannot be attributed to changes of energy metabolism in the two conditions; they therefore depend on the reduction of body O2 stores at rest in HA. This, independently measured, was found to be 0.46 liters, not far from the observed O2 deficit difference (0.39 liters). Thus a decrease of O2 stores before exercise is accompanied by a reduction of the O2 deficit and faster VO2 kinetics at the onset of exercise.

Adult↗

PubMed1983

A programmable electrically braked ergometer.

Research protocols require that the actual braking power (Wb) of electrically braked ergometers (EBE) is precisely set at the chosen power level, stable, and universally programmable. No commercially available EBEs appear to meet jointly the above conditions. In fact, EBE settings were found to deviate up to 25% from the reference level (WR), their Wb to drop as a result of increased temperature as much as 30% within 1 h of continuous operation, and the programming features to be limited and rigid. To overcome the above pitfalls a procedure for building or improving EBEs is presented whereby 1) the stator of the brake used as a dynamometer is mounted on ball bearings, the torque being transmitted to a strain gauge; 2) the number of revolutions of the rotor is measured on a cogwheel by a proximity detector and an impulse counter; and 3) the torque and impulse number signals are fed into a low-priced microcomputer controlling the brake's power supply. The device has proved to be satisfactory in following any preprogrammed exercise-forcing functions. In the range approximately 10-500 W, Wb = WR +/- 1%.

Computers↗

PubMed1983

Breath-by-breath alveolar gas exchange.

A method is described for breath-by-breath measurement of alveolar gas exchange corrected for changes of lung gas stores. In practice, the subject inspires from a spirometer, and each expired tidal volume is collected into a rubber bag placed inside a rigid box connected to the same spirometer. During the inspiration following any given expiration the bag is emptied by a vacuum pump. A computer monitors inspiratory and expiratory tidal volumes, drives four solenoid valves allowing appropriate operation of the system, and memorizes end-tidal gas fractions as well as mixed expired gas composition analyzed by mass spectrometer. Thus all variables for calculating alveolar gas exchange, based on the theory developed by Auchincloss et al. (J. Appl. Physiol. 21: 810-818, 1966), are obtained on a single-breath basis. Mean resting and steady-state exercise gas exchange data are equal to those obtained by conventional open-circuit measurements. Breathing rates up to 30 X min-1 can be followed. The breath-to-breath variability of O2 uptake at the alveolar level is less (25-35%) than that measured at the mouth as the difference between the inspired and expired volumes, both at rest and during exercise up to 0.7 of maximum O2 consumption.

Humans↗

PubMed1977

Oxygen uptake transients at the onset and offset of arm and leg work.

The halftimes (t1/2) of the VO2 on-and off-responses have been determined on 4 moderately active subjects (1) in arm cranking (VO2 congruent to 1 1/min). (2) in leg pedaling at 4 graded submaximal (VO2 congruent to 0.8 to 2.51/min) work loads, and (3) when superimposing arm cranking on preexisting leg pedaling, both in the supine and in the upright position. In supine experiments the mean t1/2 of the VO2 on-response was longer for arm cranking than for leg pedaling (64 vs 44-49 sec) at equal VO2; however, at the same percentage of arm and leg VO2 max the respective t1/2 were similar. In sitting experiments all t1/2 of the VO2 on-response were shorter than when supine, but the t1/2 for the arms were still slightly longer than those for the legs. When arm cranking was superimposed on preexisting leg pedaling, the t1/4 for arms was reduced both in supine (from 64 to 35-38 sec) and in the sitting position (from 44 to 40 sec). The halftime of the VO2 off-response were much shorter (20-32 sec) than those of the on-response and similar in all experiments. In all conditions the O2 deficits at work onset were considerably larger than the fast component of the corresponding O2 debts during the first minutes of recovery. The difference was totally accounted for by anaerobic glycolysis occurring early during the VO2 on-response, particularly in arm exercise. It is concluded that at submaximal work loads the O2 deficit is accounted for the fast component of the O2 debt plus the O2 equivalent of the early lactate production.

Adult↗

PubMed1977

Quantitative analysis of the front crawl in men and women.

Body drag, D, and the overall mechanical efficiency of swimming, e, were measured from the relationship between extra oxygen consumption and extra drag loads in 42 male and 22 female competitive swimmers using the front crawl at speeds ranging from 0.4 to 1.2 m/s. D increased from 3.4 (1.9) kg at 0.5 m/s to 8.2 (7.0) kg at 1.2 m/s, with D of women (in brackets) being significantly less (P less than 0.05) than that of men. Mechanical efficiency increased from 2.9% at 0.5 m/s to 7.4% at 1.2 m/s for men, the values for women being somewhat greater than those for men. The ratio, D/e was shown to be identical to the directly measured energy cost of swimming one unit distance, V02/d, and was independent of the velocity up to 1.2 m/s. It averaged 52 and 37 l/km for men and women respectively (P less than 0.05). When corrected for body surface area the values were 27 and 22 l/km-m2 for men and women, respectively (P less than 0.05). The underwater torque, T, a measure of the tendency of the feet to sink, was 1.44 kg-m for men and 0.70 kg-m for women (P less than 0.05). VO2/d increased linearly with T for both men and women of similar competitive experience. However, the proportionality constant delta VO2/d-delta T was significantly less for competitive than noncompetitive swimmers. The analysis of the relationship VO2/d vs. T provides a valuable approach to the understanding of the energetics of swimming.

Adolescent↗