Molecular and Quantum Acoustics vol. 27, (2006) 285 EXPERIMENTAL INVESTIGATIONS OF THE EFFECTS OF LOW FREQUENCY TRAINING ON VIBRATION OF SELECTED BACKBONE SECTIONS Janusz TARNOWSKI *, Marek A. KSIĄŻEK *, Zbigniew DAMIJAN ** * Institute of Applied Mechanics Cracow University of Technology, Al. Jana Pawła II 37, 31-864 Kraków, POLAND jantarno@mech.pk.edu.pl, ksiazek@mech.pk.edu.pl ** Structural Acoustics and Biomedical Engineering Laboratory AGH-University of Science and Technology Al. Mickiewicza 30, Kraków POLAND damijan@imir.agh.edu.pl The study presents the experimental data of values of selected human vertebra sections in the course of day-by-day training sections. The control group included 28 women volunteers subjected to low frequency vibration exposure. Experiments were conducted using a high speed camera and computer image processing techniques. Keywords: low frequency vibration training, high speed camera, motion analysis 1. INTRODUCTION The experiments were conducted during the low-frequency training sessions at the Laboratory of Structural Acoustics and Smart Materials AGH-University of Science and Technology in Kraków. The control group included 28 women volunteers from various age groups and with different constitution. For the subsequent 19 working days (no Saturdays or Sundays) volunteers were subjected to 20 minutes exposure to low - frequency vibrations. During the experiments they remained in the standing position. This study briefly summarises the experimental procedure and analysis and results of measurement data of vibrations of selected vertebra sections. A high speed camera was used and computer-assisted techniques of motion analysis were applied in this part of experiments The applied method of measurement and analysis were described in [2, 3]. The presented study was focused only on vibration data
286 Tarnowski J., Książek M.A., Damijan Z. for selected vertebrae sections.the remaining tests during the training included: Thayesr test, measurement of body mass and adipode tissue, thermovission images, measurement of body temperature in ear canal, monitoring and recording ECG signals. 2. EXPERIMENTAL INVESTIGATIONS Training sessions were conducted every day, at the same time of day for each woman volunteer. The sessions were continued for 19 working days (4 weeks), vertebrae vibration tests were repeated three times on Thursdays in the second, third and fourth week of training. Two participants were tested at the same time. Before acsending the platform, control points were selected and marked by a physician on the selected vertebrae (the same vertebrae sections for 28 participants). Fig 1 shows the location of control points on the volunteer s back, In figures 2 and 3 tested object and applied vibrating platforms are shown. S7 P4 P7 P10 L1 Fig.1. Location of measurement points Fig. 2. Exemplary object Fig. 3. Vibrating platforms Vibrations were generated by two vibrating platforms with a base excited shaker driven by an electric motor. Harmonic vibrations of the frequency 3,2 [Hz](near frequency of running man) and the same amplitude were applied throught the whole experimental program. Fig 4 shows the excitation system, Fig.5 amplitude spectrum of displacement of vibrating table. Each motion of chosen points of tested objects was registered by a CCD camera Pulnix 6710 at the rate 350 frames per second and stored in the memoryof the Motion Blitz 350 image recorder.
Molecular and Quantum Acoustics vol. 27, (2006) 287 3,21 [Hz] 20 40 60 80 100 120 Frequency, Hertz Fig. 4. Excitation system Fig. 5. Spectral analysis of vibrating table The camera was equipped with a remote-control lens Computar with a variable focus allowing the selection of a frame such that the CCD camera converter resolution was wholly made use of. Lighting was provided by halogen lights. Fig. 6 presents exemples of recorded frames with chosen points of analysis. Fig.6. Examples of frames of recorded images 3. NUMERICAL ANALYSIS OF EXPERIMENTAL RESULTS The sequence of recorded frames showing the participant s positions were further processed using computer-assisted techniques. Recorded images were stored in the form of films. Signal filtration and calibration was performed in the time domain and linear dimensions, applying the Mikromak package WINAnalyze (Germany) allowing automatic tracking of motion of the selected elements of an image, To find the subsequent positions of the control object, an algorithm was applied allowing to find the object s edges with subpixel accuracy. This method described in [1] allows to obtain accuracy up to 0.01 of pixel. Before the motion analysis the points, zone and method of tracking were chosen. The lines between selected by a
288 Tarnowski J., Książek M.A., Damijan Z. physician points and angles between them were marked. Fig 7 shows frame of a recorded image with marked control points, lines and angles. The analysis was performed for all objects, all weeks and allowed to obtain dynamic changes od the following: 4. vertical component of the velocity of chosen points, 5. length of lines connecting chosen points, 6. angles between these lines Fig.7. Frame with marked points, lines and angles Computer analysis of images yield the kinematic parameters of indicated control points in the function of time. Exemplary time histories of vertical component of velocity of two control points are shown in Fig 8. Fig.8. Exemplary time histories of velocity of chosen points. Thus obtained time histories were written in the matrix form, yielding 28 x 3 =84 matrices of experimental results. Each matrix contains the particular components of position, velocity and relative acceleration of the analysed 5 control points on the body of each 28 participants during 3 measurement sessions. These values were given with the step corresponding to the camera sampling period 0.00286 [s]. The package D-plot was applied for further analysis. The next part of this paper describes and presents graphically results of this analysis.
Molecular and Quantum Acoustics vol. 27, (2006) 289 3.1. RMS VALUES OF VERTICAL COMPONENT OF VELOCITY. RMS values of velocity were calculated for all selected vertebra points for three measurement sessions. Measurement data were then analysed statistically. The results are presented in Fig. 9, 10, 11 and 12. From the right hand side, we get results, starting from the lumbar vertebra right through to cervical vertebra, as shown in Fig. 7. 0.092 0.088 0.084 0.08 0.076 0.072 0.068 0.064 0.06 0.056 0.052 0.048 Median: 0.06677 Median: 0.06275 Median: 0.06427 Median: 0.06713 Median: 0.06882 Maximum Minimum 75% 25% Median Grand median (0.06713) Fig. 9. RMS vaulues of velocity of chosen points after one week Fig. 9 shows the results obtained after one week of training. The medians of the effective velocity for the selected vertebra points have different values. The highest values are registered for a control point in the lumbar vertebrae region, nearest to the excitation source, next comes the control point located in the early part of cervical vertebra. Median assumes its lowest value for control points in the thoracic vertebra. Fig. 10 presents the data computed after two weeks of training, for the same control points. The median distribution is similar, though the median of the point nearest to the excitation sources is slightly higher whilst that of the highest control point is significantly lower. Fig. 11 shows the results obtained after three weeks of training. The median distribution is similar, too; nearly the same values are obtained for the control point nearest to the shaker. All the remaining median values are lower than in the previous case.
290 Tarnowski J., Książek M.A., Damijan Z. 0.12 0.115 0.11 0.105 0.1 Median: 0.0649 Median: 0.06386 Median: 0.0655 Median: 0.06621 Median: 0.06895 Maximum Minimum 75% 25% Median Grand median (0.06571) 0.095 0.09 0.085 0.08 0.075 0.07 0.065 0.06 0.055 0.05 Fig.10. RMS vaulues of velocity of chosen points after two weeks 0.11 0.105 0.1 0.095 0.09 Median: 0.06395 Median: 0.05994 Median: 0.06035 Median: 0.06381 Median: 0.06865 Maximum Minimum 75% 25% Median Grand median (0.06346) 0.085 0.08 0.075 0.07 0.065 0.06 0.055 0.05 Fig.11. RMS vaulues of velocity of chosen points after three weeks
Molecular and Quantum Acoustics vol. 27, (2006) 291 The next Fig. 12 shows the compiled effective velocity values in the subsequent weeks Fig. 12. Compiled effective velocity values in the subsequent weeks. 3.2. VALUES OF ANGLES BETWEEN LINES CONNECTING CHOSEN VERTEBRA POINTS According to Fig. 7 the three angles were marked and chosen for analysis. If the participants have perfectly straight backbones, without any defects, these angles are about 180 [deg]. The purpose of these measurements was to find out how these angles would be affected by training. Statistical results computed for every tested group are shown in Fig. 13. It appears that training has favourable influence on the angle β. Fig.13. Influence on training for values of chosen angles.
292 Tarnowski J., Książek M.A., Damijan Z. Fig.14. Changes of distance between chosen points during training 3.3. VARIANCE OF DISTANCE BETWEEN CHOSEN POINTS OF VERTEBRA The major interest were dynamic variations of distance between the controlled vertebrae. The measured variations of these distances, taking into account the backbone shape in Fig.1 afford the means to compare the vibrations of particular backbone sections during the training to identify those parts which are subject to frequent vibrations and to determine whether vibrations parameters can be affected by training. Measurement data are presented in Fig 14. Variances reported for line sections connecting the points S-7-P4 and P10-L1 are larger than for any other section. It appears that these values are not affected by training. 3.4. FREQUENCY OF LATERAL MOVEMENTS Man maintains upright position while performing lateral movements, helping him/her to maintain balance. The experimental data allowed also for the frequency analysis concerning the lateral movements of thested persons. The influence of training on this movement was investigated. Results of the analysis for particular vertebrae are shown in Fig. 15.
Molecular and Quantum Acoustics vol. 27, (2006) 293 Fig.15. Frequency of lateral movements 4. CONCLUSIONS Measurement data proved the adequacy of the applied data recording and interpretation method. The results lead us to the following conclusions: 1. Effective velocity values for a control point in the lowest regions (i.e. in the lumbar vertebra) change very little after the following weeks of training, which evidences that training has little effect on vibration transmission by bottom body parts, e.g. legs. 2. Effective velocity values for the remaining control points tend to decrease with time, which implies that these vertebrae and the surrounding muscle systems are gradually adapting to vibration. 3. As the training sessions are continued, the lowest and progressively lowering values reach the values obtained by control points in the thoracic vertebra. 4. Effective velocity values for cervical vertebra tend to decrease with time though they remain on a higher level than for thoracic vertebra, which might be due to the effect of head mass. 5. Angles between line sections connecting the control vertebrae assume more favourable values during the training over the thoracic vertebra. 6. Variance of the distance between the vertebrae is larger for upper and lower thoracic vertebrae, where the backbone is bent. Training does not bring any significant changes. 7. During training the frequency of lateral movements does not vary in a predictable manner.
294 Tarnowski J., Książek M.A., Damijan Z. REFERENCES 1. Frischolz R., Wittenberg T., Computer Aided Visual Motion Analyzis www.winanalyze.com. 2. Książek M. A., Tarnowski J., Experiments on density energy estimation in a hand hammer drill system, 13 th Conference of European Society of Biomechanics Wrocław, Poland 1 4 September 2002. 3. Książek M. A., Tarnowski J., Measurements and modelling of hand handle system, 37 th United Kingdom Conference on Human Responses to Vibration, held at Department of Human Sciences, Loughborough University, UK, 18 20 September 2002.