JOURNAL OF SPORTS SCIENCE & MEDICINE |
Research article |
THE INFLUENCE OF VELOCITY OVERSHOOT MOVEMENT ARTIFACT ON ISOKINETIC KNEE EXTENSION TESTS | |||||||||
Fabiano Peruzzo Schwartz1, Martim Bottaro2, Rodrigo Souza Celes2, Lee E. Brown3 and Francisco Assis de Oliveira Nascimento1 | |||||||||
1Department of Electrical Engineering, University of Brasilia, Brasilia, DF, Brazil, 2Department of Physical Education, University of Brasilia, Brasilia, DF, Brazil, 3Department of Kinesiology, California State University, Fullerton, CA, USA. | |||||||||
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© Journal of Sports Science and Medicine (2010) 9, 140 - 146 | |||||||||
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ABSTRACT | |||||||||||||
Exercise on an isokinetic device involves three distinct movement phases: acceleration, constant velocity, and deceleration. Inherent in these phases are unique occurrences that may confound test data and, thereby, test interpretation. Standard methods of data reduction like windowing and other techniques consist of removing the acceleration and deceleration phases in order to assure analysis under constant velocity conditions. However, none of these techniques adequately quantify the velocity overshoot (VO) movement artifact which is a result of the devices resistance imposed to the limb. This study tested the influence of VO on isokinetic data interpretation. A computational algorithm was developed to accurately identify each movement phase and to delineate the VO segment. Therefore, the VO was then treated as a fourth and independent phase. A total of sixteen healthy men (26.8 ± 4.7 yrs, 1.76 ± 0.05 m, and 79.2 ± 9.4 kg) performed two sets of ten maximal concentric extension repetitions of their dominant knee (at 60º·s-1 and 180º·s-1), on separate days and in a counterbalanced order, on a Biodex System 3 Pro dynamometer. All the phases of the isokinetic exercise were measured in terms of their biomechanical descriptors and according to the developed algorithm, the windowing method, and a data reduction technique that eliminates the first and last 10º of the total range of motion. Results showed significant differences (p < 0.05) between the constant velocity phases found by each method: the largest segment was obtained with the windowing method; the second one, with the algorithm; and the smallest, with data reduction technique. The point of peak torque was not affected by none of the techniques, but significant differences (p < 0.05) were found between the data including and not including the VO phase, concerning total work, time interval, and average length of load range: VO represents more than 10% of the amount calculated in constant velocity phase. As a consequence, the correct removal of VO was suggested as a required procedure to adequately interpret isokinetic tests. Therefore, the use of the proposed algorithm is advisable in order to perform analysis according to the isokinetic definition. Key words: biomechanics, dynamometry, constant velocity, phases of movement. |
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INTRODUCTION | |||||||||||||
Muscular strength is a valuable attribute to perform many sports and simple day-to-day activities. Thus, the assessment of muscular strength is essential for understanding the performance capacity of an individual (Bottaro et al., 2005). Commercially available isokinetic machines have created lots of clinical application for injury rehabilitation, measurements of muscular torque, work, power, or endurance. However, many internal and external factors in the isokinetic testing procedures can have an undesirable effect on the test results. |
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METHODS | |||||||||||||||
Sixteen normal healthy adult males (age 26.8 ± 4.7 years) of height 1.76 ± 0.05 m and body mass 79.2 ± 9.4 kg with no history of orthopedic disease participated in this study. They voluntarily read and signed a written consent form before participating in the experiment that was approved by the University Institutional Review Board.
Percent relation is a measure of how much each IRP contributes with the whole value of the descriptor inside a repetition. |
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RESULTS | |||||||||||||
The first set of descriptor values was calculated for the four IRPs identified by the proposed algorithm (see Table 1). A comparison between the two angular velocities (60º·s-1 and 180º·s-1), for each IRP, and for all of the studied descriptors revealed significant differences (p < 0.05), except for PRPTBW (percent relation of peak torque to body weight) in ILR phase where the means are visibly equal. The results from the windowing (Table 3) and data reduction (Table 4) techniques concerning LR phase were compared between them and with the results of ILR phase delineated by the proposed algorithm. Significant differences (p < 0.05) showed that the largest segments for LR were found with the windowing method, followed by the ILR segments obtained with the algorithm, and finally by the segments found with data reduction technique. The average length descriptor gives a good notion of this finding. From Tables 1, 3, and 4, LR (or ILR) contributes to the following percentage of AL at 60º·s-1 (180º·s-1): 95.67% (86.46%) for the windowing method, 82.97% (76.87%) for the proposed algorithm, and 75.60% (75.63%) for the data reduction technique. Table 5 summarizes these relations for TW, TI, and AL. There are no differences for the PTBW descriptor in none of the studied methods. Lastly, the LR segment found by windowing was not significantly different from the VO+ILR segment obtained with the algorithm. Figure 2 illustrates the variation of the time length segments according to the angular velocity and the identification technique used. |
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DISCUSSION | |||||||||||||
The most widely used technique for data adjustment in isokinetic exercises is the windowing technique which treats VO and LR as one isokinetic phase (Bottaro et al., 2005; Brown et al., 1995a; 1995b; Findley et al., 2006; Kurdak et al., 2005; Wilk et al., 1992; 1994). In this study, velocity overshoot was seen as a separate phase. Table 1 shows that VO has an important contribution to the descriptor values. Figure 1c illustrates how the velocity variation is accentuated in the VO phase when compared with the ILR phase. Table 2 reveals that the velocity variation in the VO is approximately 7 times larger than the variation in ILR at both velocities (60º·s-1 and 180º·s-1) when the least peak torque case is observed. For the greater peak torque case, the relation increases to approximately 9 times (60º·s-1) and 13 times (180º·s-1) respectively. It means that even for individuals with low peak torque production, the VO phase has a large fluctuation when compared with ILR. Therefore, it is reasonable to consider that the ILR phase is the only part where velocity could be constant. |
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AUTHORS BIOGRAPHY | |
Fabiano Peruzzo SCHWARTZ Employment: Doctorate Student, Department of Electrical Engineering, University of Brasilia, Brasilia/DF, Brazil. Degree: Electrical Engineer, MSc in Computer Science. Research interests: Processing of biological signals and their physiological causes. E-mail: fabiano.schwartz@camara.gov.br | |
Martim BOTTARO Employment: Professor, College of Physical Education, University of Brasilia, Brasilia/DF, Brazil. Degree: PhD in Exercise Physiology. Research interests: Exercise physiology, neuromuscular physiology, and resistance exercise. E-mail: martim@unb.br | |
Rodrigo Souza CELES Employment: Researcher, College of Physical Education, University of Brasilia, Brasilia/DF, Brazil. Degree: MSc in Physical Education. Research interests: Resistance training and physical evaluation on isokinetic device. E-mail: rodrigoceles@terra.com.br | |
Lee E. BROWN Employment: Professor, Strength and Conditioning, California State University, Fullerton/CA, USA. Degree: EdD. Research interests: Sport performance, anaerobic assessment and high velocity neuromuscular adaptations. E-mail: leebrown@fullerton.edu | |
Francisco Assis de Oliveira NASCIMENTO Employment: Professor, Department of Electrical Engineering, University of Brasilia, Brasilia/DF, Brazil. Degree: PhD in Electrical Engineering. Research interests: Digital signal processing, scientific instrumentation and automation. E-mail: assis@unb.br | |