PubMed Health⌕ Search

Biomedical subjects

H Thys

Publications and source records attributed to H Thys.

18 recordsLinked to original sources
PubMed1996

Energy cost, mechanical work and muscular efficiency in swing-through gait with elbow crutches.

Crutches are widely used to assist ambulation in disabled people. Many authors have shown that the use of crutches increases the energy cost as compared to normal walking. In this study we have measured the energy consumed and the mechanical work performed during swing-through crutch gait in order to assess if the greater energy expenditure is accompanied by an equivalent increase of the work done to move the body. Our results show that, depending upon the speed, the energy expenditure is 2-3 times higher in swing-through gait than in normal walking. On the other hand, the mechanical work increases only 1.3-1.5 times. Thus the extra cost of swing-through gait cannot be explained solely by an increase of the mechanical work, but is due at least in part to a reduction in the efficiency of positive work production.

Adolescent↗
PubMed1991

An evaluation of the maximal anaerobic capacity in man.

Maximal anaerobic capacity, i.e., the maximal amount of energy released by anaerobic processes (Ean max, J.kg-1), has been evaluated from maximal increase of plasma lactate concentration (Lâp) in eight male subjects of different physical fitness submitted to supramaximal runs of various intensity performed until volitional exhaustion (temps-limite, tlim). As previously found (2), the interindividual differences of tlim were reduced when exercise intensity was expressed by the anaerobic component of exercise defined as the difference between the overall energy requirement (E, W.kg-1) and maximal aerobic power Eox max, W.kg-1). Within the range of intensity studied, Lâp did not vary significantly as a function of E-Eox max. However, the performances achieved by the less fit subjects (group 1) remained lower than those achieved by the more athletic subjects (group 2). Mean Lâp were significantly higher in group 2 (17.2 mmol.l-1 than in group 1 (13.7 mmol.l-1. The rate of increase of Lâp, defined by the ratio Lâp/tlim, was a linear function of E-Eox max. The energy equivalent of plasma lactate accumulation (beta), given by the reciprocal of the slope of the equation describing the relationship Lâp/tlim = f(E-Eox max), amounts 56.8 J.kg-1 when Lâp is increased by 1 mmol.l-1. The energy released by anaerobic glycolysis was calculated by multiplying beta by mean Lâp measured in the two groups of subjects. Assuming that the energy yielded by the anaerobic alactic processes amounts 260 J.kg-1(1), mean Ean max values in group 1 and 2 were found to be equal to 1040 (range:910-1110) and 1240 J.kg-1 (range: 1100-1330), respectively.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed1991

[Relationship between oxygen deficit and VO2max in supramaximal running].

The maximal accumulated oxygen deficit (DO2max, ml O2/kg) has been measured in 43 healthy male subjects with different VO2max (45-70 ml O2/kg.min) during the course of supramaximal runs performed until volitional exhaustion on an inclined treadmill. It was found that DO2max and VO2max were linearly related: DG2max = 39.7 + 0.31 VO2max (r = 0.701; P less than 0.001). Mean accumulated DO2max (58 ml O2/kg) corresponds to an amount of energy equal to 1212 J/kg.

Adult↗
PubMed1988

[Relation between endurance time and maximal oxygen consumption during supramaximal running].

The relationship between speed and the maximal length of time supramaximal runs can be sustained (temps-limite, tlim) has been studied in seven male subjects (physical education students). Within the range of intensity studied, tlim strictly depends on maximal oxygen consumption (VO2max). The relationship between tlim and the relative energy cost of the exercises per unit of time (E), calculated by subtracting the maximal power of aerobic metabolism (Emaxox) from E, removes the interindividual differences of tlim. The function tlim = f(E-Emaxox) is described by an empirical equation of the form: tlim = a.exp[-b(E-Emaxox)] (r = 0.979; P less than 0.001), where the parameters a and b are respectively equal to 330.8 and 0.14 and where tlim, E and Emaxox are respectively expressed in seconds and in watts per kg of body weight.

Adult↗
PubMed1985

[Kinetics of oxygen consumption during running of supramaximal intensity in differently trained subjects].

The rate of increase of the oxygen consumption (VO2) at the onset of supramaximal exercise has been compared in trained and untrained subjects. The velocity constant of the VO2 increase up to its maximum (VO2 max) is proportional to the energy requirements of the exercise (WO2). For a given (WO2-VO2 max) value, the kinetics of VO2 is roughly the same in both types of subjects. In both cases, VO2 reaches on an average WO2 divided by 2 after 29 seconds whatever the WO2 level. The corresponding velocity constant is 1.4 min-1.

Adult↗
PubMed1985

[Calculation of record-time in the 800-meter run: predictive value of Margaria's equation].

Margaria's equation (1976)--describing the relationship between the minimum time necessary to cover a distance equal or longer than 1,000 m (record-time TR) and the maximal oxygen consumption (VO2 max)--has been modified in order to be applied to the calculation of TR in the 800 m foot race. Fifteen subjects participated in this study (VO2 max = 63 +/- 3.5 ml O2 X kg-1 X min-1, measured TR = 131 +/- 10 seconds). It has been found the TR calculated from Margaria's equation (TRc) are underestimated (TRc = 104 +/- 10 seconds). By taking into account the actual energy cost of running (0.19 ml O2 X kg-1 X m-1) and the kinetics of VO2 at the onset of exercise, TRc averaged 133 +/- 8.5 seconds. Moreover, the relationship between TRc and measured TR (TRm) is highly significant (TRc = 50.4 + 0.65 TRm; r = 0.75; P less than 0.01). These results validate Margaria's equation modifications.

Adult↗
PubMed1985

[Relation between maximal oxygen consumption and the record time in the 1500-meter run. Analysis of Lloyd's model].

Lloyd's equation (Lloyd, 1967 b) has been applied to the calculation of record time in the 1 500 meters foot race from VO2 max. Twenty-eight healthy male subjects participated in this investigation. Record times decrease with increasing VO2 max. The theoretical curve plotted from Lloyd's equation is consistent with this trend. Moreover, the relationship between calculated record times (TRc) and measured record times (TRm) is highly significant (TRc = 74.3 + 0.7 TRm; r = 0.883; P less than 0.001). These results validate Lloyd's equation and hypothesis.

Humans↗
PubMed1982

[Cardiovascular changes induced by isometric exercise in aged subjects].

Blood pressure and heart rate during static contraction of forearm muscles holding a tension of 30% maximal voluntary strength for 5 mn have been measured. Eleven young men and 11 elderly male subjects were used. Maximal voluntary strength is reduced by 19% in elderly subjects. Relative mean cardio-vascular responses were unaffected by age.

Adult↗
PubMed1979

[Effect of the modality of exercise on the VO2 max].

1. Maximum oxygen consumption has been measured by means of three different exercises: cycle ergometry, treadmill running and uphill walking with a 20 kg-load. 2. Loaded walking allowed to reach a VO2 max level in average 2% greater than running and 13% greater than bicycling. 3. This finding suggest that VO2 max may depend on peripheral factors.

Adult↗
PubMed1976

The sources of external work in level walking and running.

The work done at each step during level walking and running to lift the centre of mass of the body, Wv, and to increase its forward speed, Wf, and the total mechanical energy involved (potential + kinetic) Wext, have been measured at various 'constant' speeds (2-32 km/hr) with the technique described by Cavagna (1975). 2. At intermediate speeds of walking (about 4 km/hr) Wv = Wf and Wext/km is at a minimum, as is the energy cost. At lower speeds Wv greater than Wf whereas at higher speeds Wf greather than Wv: in both cases Wext/km increases. 3. The recovery of mechanical energy, through the pendular motion characteristic of walking, was measured as (/Wv/ + /Wf/ - Wext)/(/Wv/ + /Wf/): it attains a maximum (about 65%) at intermediate speeds. 4. A simple model, assuming that in walking the body rotates as an inverted pendulum over the foot in contact with the ground, fits the experimental data better at intermediate speeds but is no longer tenable above 7 km/hr. 5. In running the recovery defined above is minimal (0-4% independent of speed), i.e. Wext congruent to /Wv/ + /Wf/: potential and kinetic energy of the body do not interchange but are simultaneously taken up and released by the muscles with a rate increasing markedly with the speed (from about 1 to 4 h.p.). 6. Wext increases linearly with the running speed Vf from a positive y intercept owing to the fact that Wv is practically constant independent of Vf. On the contrary, Wf = aVf2/(1 + bVf), where b is the ratio between the time spent in the air and the forward distance covered while on the ground during each step.

Adult↗
PubMed1975

The role played by elasticity in an exercise involving movements of small amplitude.

In an exercise consisting of repetitive small jumps on both feet at a frequency of 116/min, the mechanical work performed and the O2 consumption at steady state were measured. Of the positive work performed in the jump only 40% appears to be due to the chemical transformations taking place in the contractile componenet of the muscle fibres; the remaining 60% appears to be due to the elastic energy accumulated in the elastic elements of the contracted stretched muscles of the lower limbs during the falling phase of the previous jump, when the body hits the ground.

Elasticity↗