117,308 research outputs found
The energetics of cycling on Earth, Moon and Mars
No full textFrom 1885, technological improvements, such as the use of special metal alloys and the application of aerodynamics principles, have transformed the bicycle from a human powered heavy transport system to an efficient, often expensive, object used to move not only in our crowded cities, but also in leisure activities and in sports. In this paper, the concepts of mechanical work and efficiency of cycling together with the corresponding metabolic expenditure are discussed. The effects of altitude and aerodynamic improvements on sports performances are also analysed. A section is dedicated to the analysis of the maximal cycling performances. Finally, since during the next decades the return of Man on the Moon and, why not, a mission to Mars can be realistically hypothesised, a section is dedicated to cycling-based facilities, such as man powered short radius centrifuges, to be used to prevent cardiovascular and skeletal muscle deconditioning otherwise occurring during long-term exposure to microgravit
Energy balance of locomotion with pedal-driven watercraft
No full textIn this study, we examined the mechanics and energetics of locomotion with a paddle-wheel boat and a water bike. Power output (Ẇtot) was measured directly on the water bike by means of an instrumented chain-ring. The simultaneous assessment of oxygen uptake (V̇O2) allowed the computation of the "overall" efficiency of locomotion (ηo = Ẇtot/V̇O2). Mean ηo was 0.27 (s = 0.02), which was unaffected by the speed, and was assumed to be the same for the two boats as both are semi-recumbent bicycles. For the paddle-wheel boat, Ẇtot was then obtained from ηo and measures of V̇O2. The power to overcome (passive) drag was calculated as Ẇd = D · v (where D is the force measured by means of a load cell when towing the boats at given speeds). Propelling efficiency was calculated as ηp = Ẇd/Ẇtot, which was lower with the paddle-wheel boat (mean 0.35, s = 0.01) than with the water bike (mean 0.57, s = 0.01). The observed differences in ηp and Ẇd explain why at the highest speed tested (∼3 m · s-1), the energy required to cover a unit distance with the water bike is similar to that required to move the paddle-wheel boat at 1.3 m · s-1
Blood growth hormone-binding protein levels in premenopausal and postmenopausal women: roles of body weight and estrogen levels
No full textABSTRACT
A substantial proportion of GH circulates bound to high affinity
GH-binding protein (GHBP), which corresponds to the extracellular
domain of the GH receptor. Current evidence indicates that nutritional
status has an important role in regulating plasma GHBP levels
in humans. In the present study the relationship among plasma
GHBP levels, body composition [by bioelectrical impedance analysis
(BIA) and dual energy x-ray absorptiometry (DEXA)] and serum estradiol
(E2) was evaluated in premenopausal (n 5 92) and postmenopausal
(n 5 118) healthy women with different body weight [three
groups according to body mass index (BMI): normal, 18.5–24.99; overweight,
25–29.99; obese, 30–39.99 kg/m2]. Plasma GHBP levels were
measured by high pressure liquid chromatography gel filtration. GH
and insulin-like growth factor I levels were determined by immunoradiometric
assay and RIA, respectively.
GHBP levels were significantly higher in premenopausal women
with BMI above 25 kg/m2 (overweight, 3.789 6 0.306 nmol/L; obese,
4.37260.431 nmol/L) than those observed in postmenopausal women
(overweight, 1.425 6 0.09 nmol/L; obese, 1.506 6 0.177 nmol/L). No
significant differences were found between normal weight premenopausal
(1.741 6 0.104 nmol/L) and postmenopausal (1.524 6 0.202
nmol/L) women. In premenopausal women GHBP levels correlated
positively with BMI (r 5 0.675; P , 0.001), fat mass (FM; r 5 0.782;
P , 0.001; by BIA; r 5 0.776; P , 0.001; by DEXA), truncal fat (TF;
r 5 0.682; P , 0.001), waist to hip circumference ratio (WHR; r 5
0.551; P , 0.001), and E2 (r 5 0.298; P , 0.05), whereas no significant
correlation was found in postmenopausal women between GHBP levels
and BMI, FM, TF, WHR, or E2. In normal weight pre- and postmenopausal
women GHBP levels did not change between the ages of
20 and 69 yr. No statistically significant correlation was found between
GHBP and age for all groups studied. Moreover, in two distinct
subgroups of pre- and postmenopausal women, aged 40–49 yr, the
direct relationship between GHBP levels and all indexes of adiposity
were only observed in premenopausal women [BMI: r 5 0.836; P ,
0.001; FM: r 5 0.745 (BIA) and r 5 0.832 (DEXA); P , 0.001; TF: r 5
0.782; P , 0.001; WHR: r 5 0.551; P , 0.05], but not in postmenopausal
women.
In conclusion, the present data indicate a strong direct correlation
between GHBP and body fat in premenopausal, but not in postmenopausal
women, whereas they failed to detect a relationship between
GHBP and age. Therefore, these results suggest that endogenous
estrogen status may be an important determinant of the changes in
GHBP levels in women with different body weights
Blood GH-binding protein levels in premenopausal and postmenopausal women: role of body weight and estrogen levels
No full textA substantial proportion of GH circulates bound to high affinity GH-binding protein (GHBP), which corresponds to the extracellular domain of the GH receptor. Current evidence indicates that nutritional status has an important role in regulating plasma GHBP levels in humans. In the present study the relationship among plasma GHBP levels, body composition [by bioelectrical impedance analysis (BIA) and dual energy x-ray absorptiometry (DEXA)] and serum estradiol (E2) was evaluated in premenopausal (n = 92) and postmenopausal (n = 118) healthy women with different body weight [three groups according to body mass index (BMI): normal, 18.5-24.99; overweight, 25-29.99; obese, 30-39.99 kg/m2]. Plasma GHBP levels were measured by high pressure liquid chromatography gel filtration. GH and insulin-like growth factor I levels were determined by immunoradiometric assay and RIA, respectively. GHBP levels were significantly higher in premenopausal women with BMI above 25 kg/m2 (overweight, 3.789 ± 0...
Tibolone and endometrial safety in menopause
No full textObjective: Hormone replacement therapy (HRT) may increase the quality of menopausal women life. In this study we have evaluated the effects of Tibolone on the endometrium for three years and compared them to those observed in HRT patients and controls. Methods: The study was carried out on seventy post-menopausal patients; of these 32 received tibolone, 2.5 mg per day, 22 went through HRT (17 beta-estradiol, 50 microg twice a week with oral dydrogesterone, 5 mg per day) and 16 were not treated. All the patients underwent aspiration cytology in order to assess the basal conditions of the endometrium; this examination was repeated after 3 years. Results: After three years the rate of atrophic endometrium was 90% in the women who were being treated with tibolone and 60% in the patients who were receiving HRT, while the proliferative endometrium was respectively 10% and 40% (p<0.005). Conclusions: Tibolone treatment is safe for the endometrium. The use of continuous combined HRT requires a closer endometrium surveillance
Blood growth hormone-binding protein levels in premenopausal and postmenopausal women: rols of body weight and estrogen levels
No full textA substantial proportion of GH circulates bound to high affinity GH-binding protein (GHBP), which corresponds to the extracellular domain of the GH receptor. Current evidence indicates that nutritional status has an important role in regulating plasma GHBP levels in humans. In the present study the relationship among plasma GHBP levels, body composition [by bioelectrical impedance analysis (BIA) and dual energy x-ray absorptiometry (DEXA)] and serum estradiol (E(2)) was evaluated in premenopausal (n = 92) and postmenopausal (n = 118) healthy women with different body weight [three groups according to body mass index (BMI): normal, 18.5-24.99; overweight, 25-29.99; obese, 30-39.99 kg/m(2)]. Plasma GHBP levels were measured by high pressure liquid chromatography gel filtration. GH and insulin-like growth factor I levels were determined by immunoradiometric assay and RIA, respectively. GHBP levels were significantly higher in premenopausal women with BMI above 25 kg/m(2) (overweight, 3.789 +/- 0.306 nmol/L; obese, 4.372 +/- 0.431 nmol/L) than those observed in postmenopausal women (overweight, 1.425 +/- 0.09 nmol/L; obese, 1.506 +/- 0.177 nmol/L). No significant differences were found between normal weight premenopausal (1.741 +/- 0.104 nmol/L) and postmenopausal (1.524 +/- 0.202 nmol/L) women. In premenopausal women GHBP levels correlated positively with BMI (r = 0.675; P < 0.001), fat mass (FM; r = 0.782; P < 0.001; by BIA; r = 0.776; P < 0.001; by DEXA), truncal fat (TF; r = 0.682; P < 0.001), waist to hip circumference ratio (WHR; r = 0.551; P < 0.001), and E(2) (r = 0.298; P < 0.05), whereas no significant correlation was found in postmenopausal women between GHBP levels and BMI, FM, TF, WHR, or E(2). In normal weight pre- and postmenopausal women GHBP levels did not change between the ages of 20 and 69 yr. No statistically significant correlation was found between GHBP and age for all groups studied. Moreover, in two distinct subgroups of pre- and postmenopausal women, aged 40-49 yr, the direct relationship between GHBP levels and all indexes of adiposity were only observed in premenopausal women [BMI: r = 0.836; P < 0.001; FM: r = 0.745 (BIA) and r = 0.832 (DEXA); P < 0.001; TF: r = 0.782; P < 0.001; WHR: r = 0.551; P < 0.05], but not in postmenopausal women. In conclusion, the present data indicate a strong direct correlation between GHBP and body fat in premenopausal, but not in postmenopausal women, whereas they failed to detect a relationship between GHBP and age. Therefore, these results suggest that endogenous estrogen status may be an important determinant of the changes in GHBP levels in women with different body weights
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