Assessment of stress response and its interrelationship with external load in female soccer players.

INTRODUCTION AND OBJECTIVE: The study aimed to evaluate the physiological stress response, i.e. internal load to intermittent and continuous exercise performed during the treadmill running in professional female soccer players, and additionally to determine the most appropriate method for assessing load in the athletes. MATERIAL AND METHODS: Six professional female athletes (age 25.3±1.8 years, height 168.4±2.7 cm, weight 64.8±5.8 kg, maximal oxygen consumption (V˙ O2max) 64±4.1 mlÛ°kg-1Û°min-1, and heart rate (HRmax) 195±1.8 b.p.m.) performed a series of preseason treadmill tests. HR and V˙ O2max were measured in the athletes during intermittent load (increase and decrease of running time and treadmill speed) and an incremental load (gradual increases running time, treadmill speed and a treadmill incline angle). Banister's, Edwards', Stagno's and Lucia's training impulse (TRIMP) quantification methods were used to assess internal load. The relationships between V˙ O2max and above-mentioned TRIMPs load indicators were calculated using Pearson's correlation coefficient. RESULTS: Large, very large and near perfect correlations between TRIMP and V˙ O2max were observed during intermittent and incremental load (range r = 0.712 - 0.852 and r =563 - 930; p < 0.05, respectively). Correlations between other TRIMPs and V˙ O2max demonstrated moderate, small and negative small relationships. CONCLUSIONS: Changes in HR and oxygen consumption registered during intermittent or gradually increasing load conditions could be evaluated using the TRIMP method for both types of activities, and this method could potentially be useful for the testing of high-intensity intermittent physical fitness of players before the soccer season.

Hysteresis and Synergy of the Central Commands to Muscles Participating in Parafrontal Upper Limb Movements.

The averaged electromyograms (EMGs) were registered from the arm muscles of ten subjects in movements of the right hand performed under visual guidance on the horizontal plane along linear trajectories going parallel to the frontal plane at various distances from the trunk. The tests consisted of the steady movements (speed 4 cm/s) between two points symmetrical about the shoulder axis; the hand moved firstly from left to right, then in the opposite direction. The tests repeated ten times for each of two equal loads (10.2 N) applied to the hand along movement trajectory in the right- (F r ) or leftward (F l ) directions. The elbow and shoulder flexors reacted predominantly on F r loads; the extensors were mostly activated by F l loads. Positional changes of the averaged EMGs in both flexor and extensor muscles belonging to different joints demonstrated hysteresis properties; the respective hysteresis loops had counterclockwise direction in flexors and clockwise in extensors. The muscles predominantly opposing the loading forces of a given direction participate in a cocontraction mode as antagonists when the direction of load is changed; in this case, together with a decrease in the amplitude of the hysteresis loops, their direction is also reversed. The multiplication index of synergy (MIS), which is based on multiplication of the respective normalized averaged EMG records, has been proposed to evaluate quantitatively changes in the synergy effects between various muscle groups. For distal shifts of the movement traces, the synergy effects are shown to be changed in different directions, increasing in flexors and decreasing in extensors. The obtained results demonstrate that the muscle hysteresis leads to strong modification of the central commands during movements.

The Movement- and Load-Dependent Differences in the EMG Patterns of the Human Arm Muscles during Two-Joint Movements (A Preliminary Study).

Slow circular movements of the hand with a fixed wrist joint that were produced in a horizontal plane under visual guidance during conditions of action of the elastic load directed tangentially to the movement trajectory were studied. The positional dependencies of the averaged surface EMGs in the muscles of the elbow and shoulder joints were compared for four possible combinations in the directions of load and movements. The EMG intensities were largely correlated with the waves of the force moment computed for a corresponding joint in the framework of a simple geometrical model of the system: arm - experimental setup. At the same time, in some cases the averaged EMGs exit from the segments of the trajectory restricted by the force moment singular points (FMSPs), in which the moments exhibited altered signs. The EMG activities display clear differences for the eccentric and concentric zones of contraction that are separated by the joint angle singular points (JASPs), which present extreme at the joint angle traces. We assumed that the modeled patterns of FMSPs and JASPs may be applied for an analysis of the synergic interaction between the motor commands arriving at different muscles in arbitrary two-joint movements.