Comparative analysis of the regulation of vertical posture in athletes of different sports qualifications

The goal of study was to investigate the regulation of balance in athletes with different sports qualifications: masters of sport (MS, n=18) and candidates for master of sports (CMS, n=13). Balance examined by means of stabilographic complex ("Rhythm". Russia) in the static tests: in simple bipedal stance (BS) and squat positions (SQ), as well as in the dynamic tests: "Involute", evaluating the tracking movement and "Step input", assessing the reaction of the whole body on the visual-motor task. It was found that the MS with the same anthropometric data, PWC 170 and trunk power did not differ in linear and angular velocity of oscillations of the center of pressure (CP) in BS and SQ positions. MS had a relative dominance of low-frequency oscillations in the spectral analysis in the BS test with eyes open. In the test "Step input" MS had a lower latent period of reaction, a greater speed and an accuracy of the body motion forward and back in response to the step input signals, while they had a relative dominance of high frequency oscillations. Thus, the results showed that the masters of sport have improved postural regulation, which manifested itself mainly in the dynamic test on the speed and accuracy of the vertical body reaction to input visual signals.     

Effectiveness of vertical posture recovery after external pushing impact in athletes specialized in different sports

The ability of athletes with different training specializations to recover vertical posture after an external pushing impact was studied. Athletes engaged in cyclic exercise sports (jogging, n = 7) and complex coordinate sports (wrestling, n = 10) and nonathletes (control, n = 10) were the subjects of this study. The recovery of vertical position after a small external pushing impact on the arms extended forward was assessed using stabilography. We determined the maximum amplitude (Amp-m) of deviation from the general center of pressure, the reaction time (RT) and the velocity of reaction (V-r), as well as the variance and mean velocity of vertical posture oscillations before and after an impact. It was found that, although no differences were observed in the vertical posture stability before pushing, the Amp-m was lower in the wrestlers than in the control group (by 17.5%, p = 0.018 under the eye-open conditions; by 27.3%, p = 0.002 under the eye-closed conditions). The deprivation of visual information about the pushing moment increases the Amp-m and V-r and had no effect on the RT in all groups. Under the eye-closed conditions, an increase in Amp-m as a result of pushing was significantly lower in the wrestlers (p = 0.033) than in the control group. Under the eye-closed conditions, the accuracy of the recovery of the initial vertical position after pushing was higher in the wrestlers than in the control group (p = 0.027). The indicators of postural stability, displacement of the center of pressure, and vertical posture sway and recovery after pushing did not differ between the runners and other groups. Therefore, compared to cyclic exercises, training in complex coordinating sports more effectively improves the ability to maintain vertical posture in response to its perturbation.     

Temporal pattern of the control actions accomplishing stabilization of the vertical posture of man

The problem of determination of the temporal patterns of control actions, which accomplish the process of the vertical posture stabilization, was considered. On the basis of stabilogram analysis, it was concluded that the temporal pattern of the trajectory components of pressure center (PC) motion consists of interval sequences. Motion velocity is practically constant within each interval. Transition to the following interval is accompanied by a spasmodic change not only in the velocity magnitude but also in its sign. It was shown that velocity constancy at the linear interval is the result of linear time change in control actions. A conclusion was drawn about the presence of two separate mechanisms realizing the process of stabilization of the vertical posture. They form independent control actions oriented in the frontal and sagittal planes.     

Oxygen uptake kinetics in trained athletes differing in VO2max

Previous work has shown that when VO2 kinetics are compared for endurance trained athletes and untrained subjects, the highly trained athletes have a faster response time. However, it remains to be determined whether the more rapid adjustment of VO2 toward steady state in athletes is due to VO2max differences or training adaptation alone. One approach to this problem is to study the time course of VO2 kinetics at the onset of work in athletes who differ in VO2max but have similar training habits. Therefore, the purpose of these experiments was to compare the time course of VO2 kinetics at the onset of exercise in athletes with similar training routines but who differ in VO2max. Ten subjects (VO2max range 50-70 ml . kg-1 . min-1) performed 6-minutes of cycle ergometer exercise at approximately 50% VO2max. Ventilation and gas exchange were monitored by open circuit techniques. The data were modeled with a single component exponential function incorporating a time delay, (TD); delta VO2t = delta VO2ss (1-e-t-TD/tau), where tau is the time constant delta VO2t is the increase in VO2 at time t and delta VO2ss is the steady-rate increment above resting VO2. Kinetic analysis revealed a range of VO2 half times from 21.6 to 36.0 s across subjects with a correlation coefficient of r = -0.80 (p less than 0.05) between VO2max and VO2 half time. These data suggest that in highly trained individuals with similar training habits, those with a higher VO2max achieve a more rapid VO2 adjustment at the onset of work.     

Interaction between the vertical posture and movement control systems during a quick voluntary arm raise

The study was aimed at a deeper understanding of the interaction between the system of vertical posture control and the system of voluntary movement control based on the analysis of postural muscle activity components resulting from the action of the former or the latter system. For this purpose, a quick arm raise was performed in the standing and sitting positions with body fixation at different levels, when the task of maintaining a vertical posture was simplified or completely eliminated. Under these conditions, the muscle activity associated with posture control was supposed to change, while the activity of muscles raising the arm was supposed to remain invariable. The results showed that the simplification of the posture control resulted in a decrease or elimination of anticipatory changes in the activity of some muscles. However, most of the muscle activity variations were retained even in the sitting position, and these variations appeared simultaneously with the activity of muscles raising the arm. The so-called “anticipatory postural activity” during an arm raise in a normal standing position is supposed to consist of two components: an initial component reflecting the work of the posture control system and a later component reflecting the work of the movement control system. It is suggested that the planning of muscle activity and exchange of information between these two systems take place only before the beginning of the movement; after that, they act independently and in parallel.     

Mechanisms of reference posture correction in the system of upright posture control

It was earlier shown that ultraslow tilts of the support under quiet standing conditions evoke an unusual response reflecting the operation of compensatory mechanisms: postural sway is a superposition of postural oscillations typical of quiet standing and greater, slower inclinations of the body caused by the tilt. This may be explained by the presence of two hierarchical levels of upright posture control: real-time control compensates for small deviations of the body from the reference posture prescribed by presetting control. Mathematical simulation methods have been used to study the mechanisms of reference posture control. The results are compared with available experimental data. It is demonstrated that the reference posture can be corrected according to the gravitational vertical with the use of a kinesthetic reference alone. It is hypothesized that, when correcting the reference posture, the nervous system “assumes” the support to be immobile. The afferent input from sole pressure receptors is an important factor in reference posture correction. The advantages of the putative two-level control over control based on an explicit internal model are discussed.     

Automatic control of limb movement and posture

Studies are reviewed that address the problem of the variables controlled by the central nervous system in the maintenance of body posture and limb movement against disturbing forces. The role of global variables of control, which take into account the dynamic state of the limb, is discussed. Neural substrates that are involved in the distributed control of kinematic and dynamic parameters are also considered.     

The role of anticipatory postural adjustments in compensatory control of posture: 1. Electromyographic analysis

Anticipatory (APAs) and compensatory (CPAs) postural adjustments are the two principal mechanisms that the central nervous system uses to maintain equilibrium while standing. We studied the role of APAs in compensatory postural adjustments. Eight subjects were exposed to external predictable and unpredictable perturbations induced at the shoulder level, while standing with eyes open and closed. Electrical activity of leg and trunk muscles was recorded and analyzed during four epochs representing the time duration typical for anticipatory and compensatory postural control. No anticipatory activity of the trunk and leg muscles was seen in the case of unpredictable perturbations; instead, significant compensatory activation of muscles was observed. When the perturbations were predictable, strong anticipatory activation was seen in all the muscles: such APAs were associated with significantly smaller compensatory activity of muscles and COP displacements after the perturbations.The outcome of the study highlights the importance of APAs in control of posture and points out the existence of a relationship between the anticipatory and the compensatory components of postural control. It also suggests a possibility to enhance balance control by improving the APAs responses during external perturbations.     

The role of anticipatory postural adjustments in compensatory control of posture: 2. Biomechanical analysis

The central nervous system (CNS) utilizes anticipatory (APAs) and compensatory (CPAs) postural adjustments to maintain equilibrium while standing. It is known that these postural adjustments involve displacements of the center of mass (COM) and center of pressure (COP). The purpose of the study was to investigate the relationship between APAs and CPAs from a kinetic and kinematic perspective. Eight subjects were exposed to external predictable and unpredictable perturbations induced at the shoulder level while standing. Kinematic and kinetic data were recorded and analyzed during the time duration typical for anticipatory and compensatory postural adjustments. When the perturbations were unpredictable, the COM and COP displacements were larger compared to predictable conditions with APAs. Thus, the peak of COM displacement, after the pendulum impact, in the posterior direction reached 28 ± 9.6 mm in the unpredictable conditions with no APAs whereas it was 1.6 times smaller, reaching 17 ± 5.5 mm during predictable perturbations. Similarly, after the impact, the peak of COP displacement in the posterior direction was 60 ± 14 mm for unpredictable conditions and 28 ± 3.6 mm for predictable conditions. Finally, the times of the peak COM and COP displacements were similar in the predictable and unpredictable conditions. This outcome provides additional knowledge about how body balance is controlled in presence and in absence of information about the forthcoming perturbation. Moreover, it suggests that control of posture could be enhanced by better utilization of APAs and such an approach could be considered as a valuable modality in the rehabilitation of individuals with balance impairment.     

Compensation effect of visual biofeedback in upright posture control

The effectivity of the compensatory role of visual biofeedback in cases of decreased stability of upright posture has been analysed. The deterioration of stance was modelled by a subject standing on a soft surface and with additional weight load on the body. The influence of visual biofeedback was positive only for the compensation of decreased stability of upright posture caused by artificially increased body weight of the subject. The compensatory effectivity of visual biofeedback in stabilization of upright posture during stance on a soft surface was practically negligible. The results have shown that effective compensation of the destabilizing effect by visual biofeedback in human upright posture was possible only when the activity and efficiency of efferent-action part of the postural system remained unchanged.     

The effect of auditory image moving in vertical plane upon posture responses of humans

The influence of sound image motion on postural reactions was studied. The movement of sound source was created by successive switching of the loudspeakers situated over the arc in sagittal plane. Movement duration of sound stimulus was 1.6 s, 3.2 s and 4.8 s. The mean sway magnitudes decreased when the stimuli duration was 1.6 s and 3.2 s. Averaging of the wave-forms of center-of-pressure sway for signal with 4.8 s duration revealed that the sound image presentation induces body displacement in the direction opposite to that of sound image.     

The relationship of body segment length and vertical jump displacement in recreational athletes

The purpose of this study was to determine if segmental skeletal length contributes to vertical jump (VJ) displacement in recreational athletes. Skeletal length measurements of the trunk, femur, tibia, and foot were obtained by palpation of bony landmarks and a standard tape measure. A pilot study (n = 10) examined the intratester and intertester reliability for each skeletal measure. The pilot investigation revealed fair to excellent intratester and intertester reliability. Seventy-eight recreational athletes (55 men and 23 women) with a mean age of 21.9 +/- 2.9 years participated in the investigation. Multiple regression analysis with gender as a categorical indicator variable revealed a significant gender difference; therefore, men and women were analyzed separately. Regression analysis for men identified foot length (p < 0.033, R(2) = 0.08) as the only significant skeletal length predictor of VJ displacement. None of the skeletal length measures was predictive of VJ displacement in women. Based on the results of this investigation, intrinsic skeletal length is not a strong predictor of VJ displacement in young adult recreational athletes.