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MASSIMA POTENZA ANAEROBICA ALATTACIDA E MASSE MUSCOLARI IN SCIATORI DI LIVELLO NAZIONALE
No full textThe role of muscle mass of the lower limbs in developing explosive leg strength (extensor muscles) has been investigated in 79 male athletes of the Italian national alpine skiing team. Muscle mass was assessed as thigh and calf cross section area and explosive strength was measured as: a) maximal anaerobic power according to Margaria (running at top speed up a staircase) and Davies and Rennie tests (standing vertical jump of both feet from force platform) and b) displacement of the center of gravity (vertical jump, Sargent test). The muscle mass as well as explosive leg strength was about 10% higher in down-hill and special and giant slalom than in other groups. A linear correlation between thigh or calf muscle mass and explosive leg strength was not observed. However, multiple correlations between both thigh and calf cross section areas were statistically correlated with the explosive leg strength
Cardiac output and cardiac load during isometric exercise in man
No full textCardiac output, heart rate, arterial pressure and indirect left ventricular oxygen consumption have been measured in three subjects during isometric contractions (50 - 170 kg) of the plantar flexors until fatigue was reached and during walking on a treadmill. Cardiac output was linearly related to V(O2) for both exercises. However, for the same V(O2) Q was four times higher during isometric effort than during walking. In the last 15 s of static tasks, HR was linearly increasing to V(O2) and AP reached values of 160 and 125 Torr (systolic and diastolic, respectively) independently of V(O2). For comparable V(O2) in static and isotonic exercises myocardial O2 uptake was doubled during isometric rather than during the isotonic exercise
Energy cost and energy sources for alpine skiing in top athletes
No full textO2 uptake (V̇(O2)) during exercise and at 2 min of the recovery along with blood lactate concentration 5 min after exercise were measured in an all-out special slalom (SS) and giant slalom (GS) performed by eight top male athletes and five controls in a field study. Heart rate (HR) was continuously monitored before, during, and after each task. On the basis of an energy equivalent of 3.15 ml O2.kg body wt-1 for 1 mmol.l-1 lactate accumulation and the assumption that the amount of O2 consumed in recovery is used to reconstitute ~ phosphates used during the exercise, the total energy cost (ΔV(O2tot)) could be calculated and subdivided into aerobic, lactic, and alactic fractions. In top atheletes, ΔV(O2tot) was equal during SS and GS [7.28 ± 1.14 (SD) and 7.47 ± 0.89 liters for about 55- and 70-s performances, respectively]. When referred to time, the O2 expenditure rate was 2 and 1.6 times V̇(O2max) in SS and GS, respectively. In SS and GS, the energy sources were about 40% aerobic, 20% alactic, and 40% lactic metabolism. In control skiers, ΔV(O2tot) of GS was 6.12 ± 1.45 liters for 77 s, amounting to about 1.3 V̇(O2max), with the contribution of the different energy sources being roughly the same as in top skiers. HR reached maximal values in 30-40 s in all subjects for all conditions
Kinetics of heart rate increase with exercise in different athletes
No full textThe kinetics of heart rate (HR) increase in man at the beginning of muscular exercise follow a biexponential function whose fast and slow components seem to depend on neurogenic (0-2 min) and/or chemical stimuli (1-5 min of exercise). The feasibility of this model and the different roles played by the two components have been analyzed in endurance (EA) and sprinter (SA) athletes and in sedentary controls (SC) during bicycle exercise of different intensities at 0.15-0.90 of the maximal aerobic power, V̇(O2) max, range. It appears that: 1) in EA group, characterized by both high V̇(O2) max and fraction of slow twitch muscle fibers, the fast component alone is responsible for the HR increase up to a work load of about 0.6 V̇(O2) max. In SA and SC the corresponding value is 0.5 and 0.3 V̇(O2) max respectively; 2) the half-time values of the fast and slow exponential functions are in the range of 3-15 sec and, if any, of 35-100 sec respectively, independent of work intensity and athletic characteristics. The different training history seems therefore to affect differently the mode of the heart control elicited by muscular exercise
Energy cost of walking with hip joint impairment
Full text linkThe energy cost of walking was measured in 12 patients (age 39-73 years) with hip joint impairment and 10 healthy controls during unassisted walking (2-6 km·h -1) on a level treadmill surface and on a 5% incline. The energy cost of locomotion in most patients increased up to 50% and 70% during level-surface and uphill walking, respectively. This difference between patients and controls was probably due to the increased external mechanical work. The energy cost of walking, although related to pain experienced during walking but not hip joint range of motion or to joint status evaluated radiographically, provides an additional variable when defining the conditions of disability and functional impairment individuals with this pathological condition
Effects of stretching on maximal anaerobic power : the roles of active and passive warm-ups
No full textThe purpose of the study was to provide practical suggestions on the effect of stretching on the maximal anaerobic power preceded by active or passive warm-up. To this aim, 15 relatively fit male subjects (age 23 +/- 0.2 years, height 177 +/- 2 cm, body mass 74 +/- 2 kg; [mean +/- SE]) randomly performed a series of squat jumps (SJ) and countermovement jumps (CMJ). Jumps were preceded alternatively by: i) passive stretching of lower limbs muscles; ii) active warm-up (AWU); iii) passive warm up (PWU); and iv) the joining of stretching with either active warm-up (AWU+S) or passive warm-up (PWU+S). In control conditions (C) only jumps were required. For the 2 jumps the flight time (Ft), the peak force (Pf), and the maximal power (Wpmax) were calculated. It resulted that Ft, Pf, and Wmax values were significantly higher: i) after AWU than after PWU and PWU+S in CMJ; and ii) in AWU as compared to those of other protocols of SJ. Stretching did not negatively affect the maximal anaerobic power, per se, but seems to inhibit the effect of AWU.The results suggested that AWU seemed to increase vertical jump performance when compared to PWU, presumably due to an increase in metabolic activity as a consequence of AWU, which did not occur in PWU, despite the same skin temperature. Passive stretching alone seemed not to negatively influence vertical jump performance, whereas, if added after AWU, could reduce the power output
Acute effects of passive stretching active and passive warm up of leg extensor muscles during vertical jump
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Biologic effects of prolonged exposure to ELF electromagnetic fields in rats. I. 50 Hz electric fields
No full textA three-year investigation was conducted on the biological effects of high-intensity electric field exposures of rats for up to 18% of their life span. Two hundred and forty adult male rats, divided into groups of 20 animals each, were exposed at ground potential for 8 h/day at 25-kV/m and 100-kV/m 50-Hz electric fields or were sham exposed for 280, 440, and 1240 h. The corresponding ages at sacrifice were 140, 164, and 315 days. An additional group of 40 rats was investigated under similar experimental conditions after 440 h of exposure at floating potential. Independent of exposure duration, mode of grounding, and field strength, no statistical differences in body weight, morphology, and histology of the liver, heart, mesenteric lymph nodes, and blood variables (hematology and serum chemistry) were found in comparison with sham-exposed animals. Plasma levels of luteinizing hormone (LH), follicle-stimulating hormone (FSH), and testosterone (TS) at sacrifice varied widely among experimental animals in the same group but did not differ in exposed compared with sham-exposed rats. A nonsignificant tendency toward a decrease in the testes/body weight ratio was found after 1240 h of exposure. Microscopic examination of a large number of specimens showed no quantitative or qualitative statistical differences in testes alterations either among exposed animals or between exposed and their corresponding sham-exposed groups. We conclude that 50-Hz electric field exposure, even of long duration at very high field strengths, does not induce harmful effects on tissues with high cellular turnover rates and does not impair the reproductive function of rats. Moreover, after exposure, all variables investigated were well within the normal physiological range
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