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Biomedical subjects

F Saibene

Publications and source records attributed to F Saibene.

At least 37 records · Page 2Linked to original sources
PubMed1990

The mechanisms for minimizing energy expenditure in human locomotion.

In walking and in running the progression of the body involves at each step changes in kinetic energy, Ek, due to acceleration and deceleration, and changes of potential energy, Ep, due to vertical displacement. The energy costs of walking and running are minimized by two different mechanisms. In walking an alternate exchange of Ek and Ep takes place at each step, so that the muscles have only to restore the small part of the energy that is not recovered. The most economical speed of walking is that at which this recovery is maximal. In addition, at each speed there is an optimal frequency at which the total (external plus internal) mechanical power, and hence the metabolic cost, is minimal. In running the changes of Ek and Ep are almost completely in phase, implying a greater energy dissipation than in walking: part of this energy is stored by stretching the elastic elements of the previously contracted muscles and recovered during the following cycle, increasing the overall efficiency of the progression. The energy cost of walking with a load increases proportionally with the load. However, walking at low speed with a load not exceeding 5-10 per cent of the body weight is not more expensive than unloaded walking. Moreover, it has been observed that African women walking at their optimal speed can carry on their heads loads of up to 20 per cent of their body weight without any extra cost. A possible explanation of this finding could be that a different distribution of the body mass, with a higher position of the centre of gravity of the body, further increases the recovery of energy at each step.

Biomechanical Phenomena↗
PubMed1989

The energy cost of level cross-country skiing and the effect of the friction of the ski.

Oxygen consumption [(VO2) in ml.kg-1.min-1], blood lactate concentration ([La] in mM) and dynamic friction of the skis on snow [(F) in N] were measured in six athletes skiing on a level track at different speeds [(v) in m.min-1] and using different methods of propulsion. The VO2 increased with v and F, the latter depending mostly on snow temperature, as did [La]. The VO2 was very much affected by the skiing technique. Multiple regression equations gave the following results: with diagonal stride (DS), VO2 = -23.09 + 0.189 v + 0.62 N; with double pole (DP), VO2 = -30.95 + 0.192 v + 0.51 N; and with the new skating technique (S), VO2 = -32.63 + 0.171 + 0.68 N. In terms of VO2 DS is the most expensive technique, while S is the least expensive; however, as F increases, S, at the highest speed, tends to cost as much as DP. At speeds from 18 to 22 km.h-1, the speeds measured in the competitions, the F for DS and DP can represent from 10% to 50% of the energy expenditure, with F ranging from 10 to 60 N; with S this range increases to 20%-70%. This seems to depend on the interface between the skis and the snow and on the different ways the poles are used.

Energy Metabolism↗
PubMed1985

Energy sources in alpine skiing (giant slalom).

The energy cost of a giant slalom event was measured in eight skiers of national level. The lap lasted on average 82 s. VO2 was measured during the first, the second and the last third of the lap in different trials and also during recovery from a complete lap. Blood lactate was measured at the end of a lap. From the data obtained it was possible to calculate that: a) VO2, as measured during the lap, would correspond at steady state to 80% of the VO2max of the subjects; b) the total metabolic power delivered during the lap should be equal to about 72 ml O2 X kg-1 X min-1, corresponding to 120% of VO2max of the subjects. Considering the short duration of the trial and the power output delivered during maximal efforts on a bicycle ergometer, it appears that the giant slalom is not a very high energy demanding event.

Adult↗
PubMed1985

Maximal anaerobic (lactic) capacity and power of the horse.

Blood lactate concentrations were determined in 16 horses (three Thoroughbreds, seven Standardbreds and six polo ponies) before and 5 mins after they galloped over distances of 200, 300 and 400 m at maximal speed. The highest net lactate concentration (delta Lamax) of 14 to 15 mmol/litre was attained by the polo ponies and the highest speed by the Thoroughbreds. The maximal rate of lactate production (delta Låmax) was about 35 mmol/litre X min for the polo ponies and 20 to 25 mmol/litre X min for the Standardbreds and the Thoroughbreds. Values for delta Lamax and delta Låmax were similar to those measured in human athletes after exhaustive work. delta Låmax increases with the speed (v) and can be described by the equation delta Lå = a (v-v1), where a is a proportionality constant representing the amount of lactate needed to cover a unit distance and v1 the theoretical speed at which delta Lå = 0 X v1 was highest for the Thoroughbreds and lowest for the polo ponies; this difference could be caused by the effect of training and/or to genetic differences among the different breeds of horses X v1 could be a useful index of the fitness of a horse following a training programme.

Anaerobiosis↗
PubMed1982

Ventilatory work during exercise at high altitude.

Oxygen consumption, ventilation, and dynamic respiratory work were measured in three male subjects during cycling at 122 and 3500 m above sea level (ASL). At a given ventilation the dynamic respiratory work was 20% less at 3500 m ASL; this change was due to a decrease of airway resistance. At a given submaximal exercise intensity, the respiratory work was significantly higher at 3500 m ASL (+ 140%-180%); hence, the increase of ventilation was not compensated for by the decrease of airway resistance. At VO2max the respiratory work was predicted to reach its maximal value at 5800 m ASL where it was 30% higher than at sea level.

Airway Resistance↗
PubMed1981

Work of breathing in dog during exercise.

In six dogs trained to wear a mask and to swallow an esophageal balloon, the dynamic work of breathing (Wdyn) was measured while the animals ran on a treadmill at different intensities (7-13 km.h-1,+10%). Wydn (kg.m.min-1) increased with ventilation (VE, 1.min-1) according to Wdyn = 0.308.10(-2) VE2 + 0.0098.10(-2).VE3. However, if the exercise was prolonged so that the body temperature rose above approximately 39 degrees C, Wdyn, for a given ventilation, decreased; and hence Wdyn = 0.253.10(-2).VE2 -- 0.0011.10(-2).VE3. Similar observations have been made on another dog heated from an external source. From this finding it seems that during exercise, when the temperature rises and the ventilation increases to dissipate heat, the airway size, at least in some portion of the respiratory tract, increases markedly and therefore the cost of breathing is greatly diminished. This mechanism would save oxygen for the exercising limb muscles when exercise has to be continued for an extended time.

Airway Resistance↗
PubMed1979

Equation of motion of a cyclist.

Tractional resistance (RT, N) was determined by towing two cyclists on a racing bike in "fully dropped" posture in calm air on a flat track at constant speed (5--16.5 m/s). RT increased with the air velocity (v, m/s): RT = 3.2 + 0.19 V2. The constant 3.2 N is interpreted as the rolling resistance and the term increasing with v2 as the air resistance. For a given posture this is a function of the body surface (SA, m2), the air temperature (T, degree K), and barometric pressure (PB, Torr). The mechanical power output (W, W) can then be described as a function of the air (v) and ground (s) speed: W = 4.5.10(-2) Ps + 4.1.10(-2) SA (PB/T)v2 s, where P is the overall weight in kg. With a mechanical efficiency of 0.25, the energy expenditure rate (VO2, ml/s) is given by: VO2 = 8.6.10(-3) Ps + 7.8.10(-3) SA (PB/T)v2 s (1 ml O2 = 20.9 J). As the decrease of VO2max with altitude is known from the literature, this last equation allows the calculation of the optimal altitude for top aerobic performance. The prediction derived from this equation is consistent with the present 1-h world record.

Air↗
PubMed1978

Oronasal breathing during exercise.

The shift from nasal to oronasal breathing (ONBS) has been observed on 73 subjects with two independent methods. A first group of 63 subjects exercising on a bicycle ergometer at increasing work load (98--196 W) has been observed. On 35 subjects the highest value of ventilation attained with nasal breathing was 40.2 +/- 9.41 . min-1 S.D. Ten subjects breathed through the mouth at all loads, while 5 never opened the mouth. On 13 subjects it was not possible to make reliable measurements. On a second group of 10 subjects utilizing a different techniques which did not need a face mask, the ventilation at which one changes the pattern of breathing was found to be 44.2 +/- 13.51 . min-1 S.D. On the same subjects nasal resistance did not show any correlation with ONBS. It is concluded that ONBS is not solely determined by nasal resistance, though an indirect effect due to hypoventilation and hence to changes in alveolar air composition cannot be ruled out. It is likely that ONBS is also influenced by psychological factors.

Adult↗
PubMed1976

Energy cost of speec skating and efficiency of work against air resistance.

The energy expenditure during speed ice skating (PB=650 mmHg; T=-5 degrees C) was measured on 13 athletes (speed range: 4-12 m/s) from VO2 and (for speeds greater than 10 m/s) from blood lactic acid concentration. The energy spent (O2 equivalents) per unit body wt and unit distance (Etot/V, ml/kg-min) increases with the speed (v, m/s): Etot/v=0.049 + 0.44 X 10(-3) V2. At 10 m/s, Vtot/v amounts then to 0.093 ml/kg-m: about half the value of running. The constant 0.049 ml/kg-m is interpreted as the energy spent against gravitational and inertial forces. The term 0.44 X 10(-3) v2 indicates the energy spent against the wind, the constant 0.44 X 10(-3) ml-s2-kg-1-m-3 being a measure of k/e, where k is the coefficient relating drag to v2, and e the efficiency of work against the wind. From a direct estimate of k in a wind tunnel, e was calculated as 0.11. In running, skating, and cycling k/e is similar (approximately 0.020 ml-s2-m-3 per m2 body area), hence at a given speed the energy spent against the wind is equal. On the contrary, the energy spent against other forces decreases in the above order: 0.19, 0.05, 0.018 ml-m-1 per kg body wt. This explains the different speeds attained in these exercises with the same power output.

Adult↗
PubMed1969

Contribution of the diaphragm and the other inspiratory muscles to different levels of tidal volume and static inspiratory effort in the rabbit.

1. The contribution of the diaphragm and that of the other inspiratory muscles at different levels of tidal volume and during static inspiratory efforts of various strength has been studied in supine rabbits by blocking phrenic conduction with an electrotonic current. The rabbits were lightly anaesthetized with urethane and pentobarbitone.2. The volume displaced by the extradiaphragmatic muscles (V(tEDM)) in vagotomized rabbits increases linearly with the tidal volume (V(t)), according to the function V(tEDM) = - 3.27 + 0.32 V(t). The relative contribution of extradiaphragmatic muscles (V(tEDM)/V(t) x 100) for resting ventilation is 12% and becomes ca. 25% for the maximum V(t) value attained during re-breathing.3. When the vagi are left intact, the V(tEDM) is always higher because of the compensatory hyperactivity of the extradiaphragmatic muscles due to Hering-Breuer reflexes during the phrenic block.4. The pressure exerted by the extradiaphragmatic muscles, during inspiratory efforts with closed airways, increases linearly with the strength of the effort, without any difference between intact and vagotomized rabbits. The relationship between the pressure exerted by the extradiaphragmatic muscles (P(EDM)) and the pressure exerted by all the inspiratory muscles (P) is expressed by the function P(EDM) = - 3.29 + 0.38P.5. These results indicate that the diaphragm is the main inspiratory muscle at all levels of inspiratory activity.

Action Potentials↗