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2 Acta of Bioengineering and Biomechanics

2 2010

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The impact of changes in gait speed and step frequency on the extent of the center of mass displacements

Staszkiewicz R., Ruchlewicz T., Forczek W., Laska J.

Acta of Bioengineering and Biomechanics

2010

Vol. 12, no. 3

13-20

Center of mass (COM) trajectory plays a crucial role in the analysis of human body movements. This research aimed at studying vertical and transverse COM displacements during gait on a treadmill at a given velocity and step frequency. Locomotion study was accomplished using: Vicon 250, Cardionics Treadmill 3113 and metronome Korg Ma-30. The data achieved for 12 women and 15 men aged 21–22 revealed similarity in vertical COM oscillations in both groups. Lateral COM displacements (LCOM) were slightly higher in men than in women and they showed tendency to decrease as gait velocity increased. During natural locomotion there was an increasing trend as walking speed increased. At a given velocity of locomotion LCOM were decreasing as step frequency increased. The only astonishing thing was that the biggest changes of vertical COM oscillations (VCOM) were noticed at the fastest walking speed (6 km/h). It seems that so large decrease in VCOM during walking with high velocity and increased step cadency is a consequence of considerable shortening of the movement cycles and performing time of one step.

EMG frequency during isometric, submaximal activity : a statistical model for biceps brachii

Solnik S., De Vita P., Grzegorczyk K., Koziatek A., Bober T.

Acta of Bioengineering and Biomechanics

2010

Vol. 12, no. 3

21-28

The purpose of this study was to develop a statistical model to describe the electromyography (EMG) signal frequency changes during a submaximal isometric contraction. Thirty subjects performed a 30-second isometric contraction of the biceps brachii muscle at 80% of the maximal voluntary isometric force. Surface EMG electrodes recorded electrical activity of the biceps brachii. Zero-Crossing-Rate was calculated to identify EMG frequency shifts. The mean frequencies for every one-second period were used to calculate a linear relationship between frequency and time. A significant relationship ( p < 0.05) between slope and initial frequency value was identified. The model described EMG frequency changes during submaximal effort of biceps brachii up to 15 seconds. The prediction error was 9.8%. Modifying this equation to initial values of frequency of each participant decreased prediction error to 7.2%. These results demonstrate that despite individual differences between subjects it is possible to derive single equation that describes EMG alterations during submaximal, isometric contractions across a homogeneous group of people.