1,721,187 research outputs found
Soundmyogram analysis during sustained maximal voluntary contraction in sprinters and long distance runners
No full textThe aim of this study was to describe the influence of the different fiber type composition of the vastus lateralis muscle on the soundmyogram (SMG) time and frequency domain characteristics. The SMG was recorded from the vastus lateralis belly during exhausting maximal voluntary contraction (MVC) of the leg extensors in 7 sprinters (SPR) and 7 long distance runners (LDR). Seven sedentary males (SED) were investigated in the same experimental conditions. In the SPR the effort time was shorter and the MVC was greater while the SMG root mean square and the SMG frequency. content, at the onset of contraction, were higher than in the SED and LDR, respectively. Throughout exertion the SMG RMS showed clear reduction for SPR and SED only and the SMG power spectra presented a compression towards the lower frequencies. The reported phenomena were less pronounced in the LDR than in SPR and SED. These results can be explained when the differences in the % of fast twitch fibers area, belonging to stronger and more fatiguing F motor units, in the three groups of subjects are considered and suggest that SMG characteristics reflect the muscle fiber typing
Influence of low and high dietary fat on physical performance in untrained males
No full textPurpose: Dietary manipulations have been used in athletes to enhance aerobic performance. We intended to verify whether the quality of energy substrate provided by food (percentage of total calories from fat and carbohydrates) per se has the ability to affect aerobic performance in sedentary humans. Method: Fourteen healthy sedentary males were sequentially submitted to 4-wk eucaloric diets (spontaneous diet: 30% of total calories from fat; low-fat, 15% fat; high-fat, 55% fat; and spontaneous, 30% fat). After each diet period, individual body mass, percentage body fat (plicometry), V̇O(2max) (incremental bicycle-ergometry) and endurance (pedaling time to exhaustion at 75%V̇O(2max)) were measured, V̇O2, V̇CO2, V̇(E), R, and heart rate (HR) were measured at rest and during exercise tests. Body composition and performance data (V̇O(2max) and endurance) were compared for significant differences by repeated measures ANOVA. Results: Subjects' body weight, percentage body fat, and fitness status (indicated by intercept and slope of the HR/V̇O2 linear relationship) did not change significantly during the study, thus ruling out the influence of these potential confounders. For a given workload, V̇O2, V̇(E), and R were unaffected by diet composition. V̇O(2max) and endurance time were not significantly modified by the different diets. Conclusions: Our study showed no impact, positive or negative, of diet's macronutrient composition on physical performance. It appears that the quality of energy substrate provided by food does not have the ability to affect either maximal or submaximal aerobic performance in untrained individuals
Electromyogram and mechanomyogram changes in fresh and fatigued muscle during sustained contraction in men
No full textIn surface electromyogram (EMG) and mechanomyogram (MMG) the electrical and mechanical activities of recruited motor units (MU) are summated. Muscle fatigue influences the electrical and mechanical properties of the active MU. The aim of this study was to evaluate fatigue-induced changes in the electrical and mechanical properties of MU after a short recovery period, using an analysis of force, surface EMG and MMG. In seven subjects the EMG and MMG were recorded from the biceps brachii muscle during sustained isometric effort at 80% of the maximal voluntary contraction (MVC), before (test 1) and 10 min after (test 2) a fatiguing exercise. From the time and frequency domain analysis of the signals, the root mean square (rms) and the mean frequency (f) of the power spectrum were calculated. The results were that the mean MVC was 412 (SEM 90) N and 304 (SEM 85) N in fresh and fatigued muscle, respectively; during tests 1 and 2 the mean EMG rms increased from 0.403 (SEM 0.07) mV to 0.566 (SEM 0.09) mV and from 0.476 (SEM 0.07) mV to 0.63 (SEM 0.09) mV, respectively; during test 1 the mean MMG rms decreased from 9.4 (SEM 0.8) mV to 5.7 (SEM 0.9) mV; in contrast, during test 2 constantly lower values were observed throughout contraction; during tests 1 and 2 the EMG f declined from 122 (SEM 7) Hz to 74 (SEM 7) Hz and from 106 (SEM 8) Hz to 60 (SEM 7) Hz, respectively; during test 1 the MMG f increased in the first 6 s from 19.3 (SEM 1.4) Hz to 23.9 (SEM 2.9) Hz, falling to 13.9 (SEM 1.3) Hz at the end of contraction; in contrast, during test 2 the MMG f declined continuously from 18.7 (SEM 1) Hz to 12.4 (SEM 0.8) Hz. The lower MVC after the fatiguing exercise and the changes in the EMG parameters confirmed that 10 min after the fatiguing exercise, the mechanical and electrical activities of MU were altered. In addition, the MMG results suggested that after a 10-min recovery, some highly fatigable MU might not be recruitable
Muscular sound and force relationship during isometric contraction in man
No full textThe contracting muscle generates a low frequency sound detectable at the belly surface, ranging from 11 to 40 Hz. To study the relationship between the muscular sound and the intensity of the contraction a sound myogram (SMG) was recorded by a contact sensor from the biceps brachii of seven young healthy males performing 4-s isometric contractions from 10% to 100% of the maximal voluntary contraction (MVC), in 10% steps. Simultaneously, the electromyogram (EMG) was recorded as an index of muscle activity. SMG and EMG were integrated by conventional methods (iSMG and iEMG). The relationship between iSMG and iEMG vs MVC% is described by parabolic functions up to 80% and 100% MVC respectively. Beyond 80% MVC the iSMG decreases, being about half of its maximal value at 100% MVC. Our results indicate that the motor unit recruitment and firing rate affect the iSMG and iEMG in the same way up to 80% MVC. From 80% to 100% MVC the high motor units' discharge rate and the muscular stiffness together limit the pressure waves generated by the dimensional changes of the active fibres. The muscular sound seems to reflect the intramuscular visco-elastic characteristics and the motor unit activation pattern of a contracting muscle
Ventilatory work during exercise at high altitude
No full textOxygen consumption, ventilation, and dynamic respiratory work were measured in three male subjects during cycling at 122 and 3500 mm 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 V̇(O2)max the respiratory work was predicted to reach its maximal value at 5800 m ASL where it was 30% higher than at sea level
Estimation of heart stroke volume from blood hemoglobin and heart rate at submaximal exercise
No full textMASSIMA 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
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