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  • Author or Editor: József Tihanyi x
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Az áttekintés az izomtömeg és az izomerő növelése célzatával alkalmazott hormonok (növekedési hormon, IGF-1, anabolikus-androgén szteroidok) és az izom fejlődésében szereplő, humán használatra kerülhető egyes faktorok fizikai aktivitással kapcsolatos élettanát és klinikai alkalmazásának lehetőségeit érinti. A hatásokat illetően mítoszok, a mellékhatásokat illetően alul- és túlértesültség egyaránt jellemzi e területet. A kórállapotok sorában, s nem csak a hiányállapotok szubsztitúciójában történnek terápiás próbálkozások, amelyekben figyelembe vehetők a sportolók, testépítők tapasztalatai is.

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The objective of the study was to investigate the chronic effect of low frequency whole body vibration (WBV) on isometric and eccentric strength of knee extensors with different force exertion capacity. It was hypothesized that (1) four-week WBV intervention with the low frequency domain would enhance muscle strength and (2) the improvement would be more pronounced in the weaker muscle. To test our hypothesis twenty patients with acute stroke were recruited. Ten patients were randomly assigned to vibration and the remaining ten patients served for control.The patients in the vibration group received WBV with 20 Hz frequency three times per week standing on a vibration platform in half squat position meanwhile flexing and extending the joints and placing the weight from one leg to the other. Knee extensor strength was determined under isometric and eccentric contraction before and after WBV intervention. Myoelectrical activity (EMG) of the vastus lateralis muscle was also measured.Significant improvement was revealed in the vibration group only. The maximum isometric torque and EMG activity increased significantly for both paretic and non-paretic leg, but the improvement was threefold greater in the vibration group. No significant alteration was found in rate of torque development. Maximum eccentric torque and EMG increased significantly for the paretic leg only. Mechanical work enhanced significantly in the paretic side only.The results of our study indicate that the selection of the effective vibration frequency depends upon the physical condition of neuromuscular system. Low vibration frequency intervention can increase the strength in weak muscles due to neuromuscular impairment and restricted physical activity.

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The effect of cycling cadence and crank resistance on the activity of hamstrings and quadriceps muscles was investigated during cycling movements of able-bodied subjects on a stationary bike with slow and fast speed against different resistance conditions. The ratio of average EMG amplitudes obtained in the two speed conditions (fast/slow) was computed in each resistance condition. This ratio is higher for both muscles if cycling against higher resistance. This shows that in higher resistance condition muscle activities are not only increased but the change of muscle activities with respect to cadence change varied according to resistance condition. Average EMG amplitudes increased at a higher rate with respect to change of cadence when cycling was performed in higher resistance condition. Besides, when cycling faster, hamstrings activity increased generally at a higher rate than that of quadriceps. The correlation between cadence and EMG amplitudes were also investigated. Considering hamstrings, this correlation was low and decreased as resistance increased. The correlation between the time required to drive one cycle and EMG amplitude is negative but in absolute value it is larger than the correlation of cadence and EMG amplitude.

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Authors: G. Gyulai, L. Rácz, R. Di Giminiani and József Tihanyi

The acute residual effect of whole body vibration (WBV) on upper extremity muscles and testosterone secretion was studied. Eight highly (G1), nine moderately trained gymnasts (G2) and seven physically active persons (CG) were recruited for the investigation. The intervention occurred in push-up position with the elbow flexed at 90°. G1 and G2 received 30 s, 30 Hz and 6 mm amplitude vibration repeated five times. Subjects were tested before and after one and ten minutes intervention in push-up movement. Contact time (Tc), fly time (Tf), TF/Tc ratio and impulse was measured from the ground reaction force-time curves recorded during self-selected (SSRM) and full range of motion (FRM). Testosterone level in urine was also determined. Tf increased significantly in SSRM for G1 and decreased in SSRM and FRM for G2. Tf/Tc ratio in FRM and impulse in SSRM increased significantly for G1 only. No significant alteration in testosterone level was observed. We concluded that WBV is a reasonable training modality for influencing dynamic work of upper extremity muscle, but the reaction to WBV is training and individual dependent. It seems that WBV do not influence dynamic work through increased testosterone secretion because of the relatively low mass of the involved muscles.

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The aim of this study was to investigate the effect of fast and slow relaxation of the knee extensor muscle of the dominant leg on torque-time curve of the unilaterally contracting contralateral muscle. Eight adult male subjects were recruited without bilateral deficit. In Task 1 subjects exerted bilateral and unilateral torque and bilateral index was calculated. In Task 2 subjects relaxed the right knee extensors as slow as possible while maximum activation of the contralateral muscle had to be maintained. In Task 3 the relaxation was as fast as possible. During slow relaxation the short latency response (dM1) was 6.6% torque reduction in the left leg. On the contrary fast muscle relaxation resulted in a 7.3% increase. During long latency response the torque increased in both tasks, but did not exceed the torque measured in Task 1. Significant correlation was found between the rate of torque reduction (RTR) and dM1 (r = 0.95, P < 0.001), time to peak (t1) and dM1 (r = 0.812, P < 0.01). The regression analysis indicated that RTR greater or less than −1.0 Nm/ms results in opposite short latency response. We concluded that the different tasks for two knee extensor muscles result in transient interhemispheric effects which are time and rate of torque reduction dependent.

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