CONDITIONING AND SPRINTING TECHNIQUE

The purpose of this paper was to show relationship between muscle strength and sprinting technique. Stride length and frequency correspond to different kinetic chains and by changing their characteristics the stride pattern will change as well. Ground reaction force parameters of squat jump may be used for functional assessment of kinetic chain due to its proximal-distal pattern of muscle activation. The first part of squat jump is dominated by hip extensors (proximal part) while final take-off velocity is related to knee extensors (distal part). Since grabbing is performed by hip extensors, stride frequency is expected to be related to the first part of the squat jump. Pushing is mainly performed by knee extensors and thus provides rationale for relation between stride length and take-off velocity

EFFECT OF ADDITIONAL ELECTRICAL STIMULATION OF MUSCLES ON MAXIMAL FORCE PRODUCTION

The effect of additional electrical stimulation (ES) of quadriceps femuris muscle on muscle force production was investigated during maximal voluntary isometric contraction (MVC). Eight sport students, all in good condition, participated in the study. ES consisted from the trains of impulses of different length (single impulse, 0.05 s, 0.10 s, 0.15 s, and 0.20 s) with the frequency of 100 Hz. After reaching the maximal voluntary force level, the ES was applied directly to the muscle. Results show the growing muscle force over the MVC level in all stimulating conditions reaching its plateau at 0.10 s of ES (24 % over the MVC). This suggests that the certain minimum time of the additional activation is needed to elicit the whole muscle force capacity. Results may help to elucidate the possible mechanical effects of the reflex activation of the muscles

ABSOLUTE MUSCLE FORCE DETERMINATION

An absolute muscle force is applied when the muscle is activated to its fully extent, what normally doesn't happen in voluntary actions. It is believed that interpolated electrical stimulation (ES) during maximum voluntary contraction (MVC) is capable to fully activate the muscle. Six sport students volunteered the study. They were asked to perform isometric knee extensions at different activation levels (go%, 90%, and 100% of MVC) and were then transcutaneously electrically stimulated (quadriceps muscle) with equal ES amplitude, set to the individual tolerance threshold. Four volunteers additionally performed 100% MVC knee extensions with different ES amplitudes (80%,100%, and 120% of the tolerance threshold). In all subjects the interpolated ES elicited an additional force growth, over the actual voluntary level. Results showed that in the first experiment the force was growing according to the voluntary activation level almost linear. In the second experiment different ES amplitudes exhibited no statistically significant differences in force levels. It is concluded that interpolated ES enables, already at the submaximal ES amplitude, to achieve a stable force level, which can not be further elevated with a rising of ES amplitude and which might correspond to the absolute force of the agonists. A comparison to the MVC force would reveal an activation deficit. Because of the substantial force improvements in comparison to the MVC, interpolated ES can be used to study a single muscle andlor muscle group sensitiveness to the joint acceleration

[Iskanje najkrajšega režima: frakcionacija biološko enakovredne kombinacije hiper- in hipofrakcioniranega zdravljenja]

Purpose. To analyze the possibility of reducing the number of fractions but maintaining the full biological effect of radiotherapy by varying the dose perfraction. Methods. An arbitrary treatment with a constant dose per fractionis substituted for a fully isoeffective combination of a hyperfractionated and hypofractionated treatment. The number of fractions of the combined treatment is derived. All calculations are based on the linear-quadratic model. Conclusions. Standard uniform fractionation requires the fewest fractions. Any variation in dose per fraction increases the number of fractions of a fully isoeffective treatment

RELIABLE MEASUREMENT OF THE TRICEPS SURAE STRETCH REFLEX

INTRODUCTION: Reflex occurrence and its modulation play an important role in motor control. A special platform with a leverage system to induce foot movement was constructed to research the triceps surae stretch reflex. The aim of this research was to establish the reliability of reflex measurements with this measurement device. METHODS: Six adult males (age 30.5 ± 5.1 years, height 180.3 ± 4.4 cm, and body mass 71.3 ± 4.6 kg) participated in the study. Each was asked to sit on a rigid chair with their right foot clamped to a pedal. The ankle and knee angles of the right leg were respectively 90 and 120 degrees. Angular displacement of the foot was measured with an electronic goniometer (Penny and Giles, G35, Blackwood Gwent, GB). Electromyograms (EMG) were recorded from the soleus (SO), using surface electrodes placed over the belly of the muscle. The EMG signal was recorded with Biotel 88 (Glonner, München, Germany). A displacement (10 deg) of the pedal was performed at 57 deg/s. Pedal displacement was induced by a weight lowered with a constant velocity on a leverage system to move the pedal. Two measurements were made. Between the first and second measurements, the subjects stood up and took their foot from the pedal. Nine stimuli were recorded each time. Data were acquired at 1000 Hz. A statistical significance of the differences between the first and second measurements was tested with the paired-samples t-test (two-way). RESULTS: [Table...] CONCLUSIONS: There were no statistical differences between the first and the second measurements. It was possible to conclude that the special platform with a leverage system is relevant for the measurement of the short-latency stretch reflex

TORQUE-JOINT ANGLE RELATIONSHIP FOR VASTUS LATERALIS MUSCLE

The aim of this work was to study a single muscle torque contribution during a knsee extension in different knee angles. Six subjects performed three tasks: maximum voluntary knee extension (MVC), supramaximal twitch of relaxed quadriceps femoris muscle, and contraction of relaxed vastus lateralis muscle, activated with a train of submaximal electrical impulses.~A ll contractions were performed at angles of 450, 600, 750, and 900 at the knee joint and in a supine position (hips extended). In both tasks with the electrical stimulation (ES) the same stimulation parameters were used in all angles. Results showed that relative torques (100% at 450) for MVC and the twitch were merely the same, exhibited a maximum (143.6% and 153.1%, respectively) at 750 and fell to 133.3% and 137.4% at 900. Vastus lateralis muscle attain its maximum (1 16.8%) at 600 and fell continuously to its minimum of 602 % at 900. It is possible to see that a single head of the quadriceps muscle behaves in a much different way as the whole quadriceps muscle. Establishing a torque joint angle relationship for single muscles or muscle groups may be interesting for muscles' dynamics modelling, used in a professional work

RECOVERY OF ELECTRICAL STIMULATION FORCE AFTER ONE-MINUTE OF MAXIMAL HOPPING AND CYCLING

INTRODUCTION Recovery of electrical stimulation force depends on a type of peripheral muscular fatigue. Low frequency force, designated to a low frequency fatigue, may recover in a few hours after the workout, while a recovery of a high frequency force, designated to a high frequency fatigue, ends in a few minutes after the workout (Cooper et aJ., 1988). The aim of the present study was to examine a recovery of electrical stim01ation force at 20 Hz and 100 Hz after one-minute of a 'maximal hopping on a force plate and cycling on a Monark ergometer. Eleven students of physical education (age 22. 9± 3.9 yrs, height 176.1 ± 4.1 cm, mass 71.8 ± 3.7 kg) performed both tests on separate weeks. Relaxed vastus lateralis museie (VL) was electrically stimulated before and 1., 2.,3.,4.,5.,6.,7., and 10. minute after the end of the workout and the isometric knee torque during stimulation was measured. Statistically significant changes to the pre-workout result were tested with a two-way student-test. Post-workout results were afterwards normalised to the preworkout torque. Asterisks denote a statistically significant change according to pre-test state (* -