1. Figure 2. Turning Point Core Trainer.
RELIABILITY OF THE TURNING POINT CORE TRAINER AS A MEASURE OF PEAK PELVIC TORSO SEPARATION ANGLE, PEAK
UPPER TORSO ROTATIONAL VELCOITY, AND PEAK PELVIC ROTATION VELOCITY DURING THE VOLLEYBALL SPIKE
Bader J. Alsarraf1, Justin R. Brown2, Mike Waller4, Patricia Eisenman2, Charlie A. Hicks-Little3
1Department of Physical Education and Sport, College of Basic Education in Kuwait, Adailiya, Kuwait;
2Department of Exercise and Sport Science, University of Utah, Salt Lake City, Utah;
3Sports Medicine Research Laboratory, Department of Exercise and Sport Science, University of Utah, Salt Lake City, Utah; and
4Department of Human Performance and Physical Education, Adams State University, Alamosa, Colorado
ABSTRACT
INTRODUCTION: Pelvic and upper torso y-axis rotational velocities are important contributors to the velocity that is imparted to balls during the volleyball spike, golf drive, and baseball batting, but the sequencing of pelvic and upper y-axis torso rotation is even more important for imparting high velocity to a ball. Therefore, being able to readily assess pelvic and upper y-axis torso rotational velocities as well as the sequencing of pelvic and upper torso rotation would be helpful for evaluating athlete performance and the efficacy of core strength training programs. The Turning Point Core Trainer (TP), is a devise designed to quantify y-axis rotational velocities and the sequencing of pelvic and upper torso rotation; however, reliability data are yet to be published. The purpose of the current study was to establish preliminary evidence for the internal-consistency reliability of the TP as a measure of select rotational actions (RA). METHODS: Fourteen Division I female collegiate volleyball players from the University of Utah volunteered for this study (age 20.9±2.8 years, height 181.6±7.7 cm, weight 72.9±12.5 kg, BMI 22.0±3.0 kg/m2, body fat 22.0±6.3 %, playing experience 3.2±1.4 years). This study was approved by the Institutional Review Board at the University of Utah. Each player, after a 10 minute self-selected warm-up, completed 3 practice trials, and then executed a total of 10 RA in the TP at zero resistance. A 30 second rest period separated trials. The TP was used to assess Peak Upper Torso Rotational Velocity (PUTRV) and Peak Pelvic Rotational Velocity (PPRV) in ˚-sˉˡ for each TRA. All rotational velocities were recorded around the y-axis. Peak difference in the rotation angle of the pelvis and upper torso about the body’s y-axis was recorded in degrees and termed the Peak Pelvic torso Separation Angle (PPTSA). STATISTICAL ANALYSIS: Internal consistency reliability of the TP was assessed by Cronbach’s alpha Coefficients (α), measurement precision was determined by coefficient of variation (CV), and standard error of measurement (SEM) was used to determine between subject variations. The stability was determined by using a two-way factor mixed (participants random and trials fixed) repeated measures factorial ANOVA. Statistical significance set at p < All data analyzed using PASW Statistical software18.0 (IBM Inc., Chicago, IL). RESULTS: The results of statistical analysis are reported in Table 1. DISCUSSION: The results support the hypothesis that the TP has excellent internal consistency reliability. These findings support the use of the TP for assessing rotational variables as part of a sports conditioning program. ACKNOWLEDGEMENTS We would like to express our gratitude to BioTechnology for use of the Turning Point.
INTRODUCTION
Sport skills such as the golf swing, baseball pitch, and volleyball spike, are similar in that high velocity must be transferred to the ball for successful skill execution. Sports scientists have identified rotational variables as significant contributors to ball velocity in golf, baseball, and volleyball (1,2,4). Myers et al. (2) investigated the roles of pelvic and upper torso rotation during the golf swing. Their findings indicate that the difference between the sequencing of pelvic and upper torso rotation, also known as the x-factor, (Figure 1), is a more important contributor to ball velocity than the magnitudes of the pelvic and upper torso rotational velocities. Understanding the importance of pelvic-torso separation (PTSA), pelvic and upper torso rotational velocities has been possible due to the use of three-dimensional (3-D) motion capture analysis to examine the kinematic and kinetic aspects of rotational sport skills (3,5). Recent development of the Turning Point Core Trainer (TP) has prompted research regarding its ability to measure the variables used in determining the X-factor. Alsarraf et al. (1) suggested that the TP is capable of quantifying Peak Pelvic Torso Separation Angle (PPTSA), Peak Upper Torso Rotational Velocity (PUTRV) and Peak Pelvic Rotational Velocity (PPRV). Furthermore, the TP measurement values are available to athletes in real time, and do not require lengthy time periods for cinematographic analysis. Because the TP is a new measurement tool, its reliability must be established.
PURPOSE
The purpose of the current study was to establish preliminary evidence for the internal-consistency reliability of the TP as a measure of select rotational actions. We hypothesized high internal consistency reliability coefficients would result from using the TP as a measure of PPTSA, PUTRV, and PPRV during Y-axis rotational actions.
Figure 1. Definition of the upper torso rotation, pelvic rotation and pelvic- torso separation angles (Also known as the x-factor).
METHODS
Fourteen Division I female volleyball players (age 20.9±2.8 yrs, height 181.6±7.7 cm, weight 72.9±12.5 kg, BMI 22.0±3.0 kg/m2, body fat 22.0±6.3 percent, playing experience 3.2±1.4 years) volunteered for the study. Body composition was assessed using Air Displacement Plethysmography. Horizontal arm bars were adjusted to the height just above the shoulders and the hip pads were raised to the levels of the anterior superior iliac spine. Prior to entering the Turning Point Core Trainer, players performed a 10 minute self selected warm up. Players were then given three trial periods which were followed by 10 repetitions with maximal effort. Movement began in the neutral position and players initiated a rotational movement similar to the backswing followed by forward rotation similar to the spiking action. Players were given 30 seconds recover y between each repetition with zero resistance.
RESULTS
Peak pelvic separation angle, peak upper torso rotational velocity, and peak pelvic rotational velocity were ±13.23º, ±41.51, and 249±57.44 respectively (Table 1). Cronbach’s alpha indicates high levels of internal consistency reliability for PPTSA (a=.98), PUTRV (a=.91), and PPRV (a=.94). Furthermore, repeated measures factorial ANOVA (participant's random and trials fixed) indicated stability between trials.
Figure 2. Turning Point Core Trainer.
Table 1. Mean (SD) and Cronbach’s Alpha of Measurement for Peak Pelvic Torso Separation Angle, Peak Upper Torso Rotational Velocity, and Peak Pelvic Rotational Velocity During the Volleyball Spike.
CONCLUSIONS
These data indicate a high level of evidence in support of the reliability of the TP as a tool for assessing rotational variables about the Y-axis, including velocity of both the torso and the pelvis as well as the separation angle between the torso and pelvis. The reliable assessment of such rotational actions support the use of the TP in evaluating the efficacy of conditioning programs on Y-axis rotation of athletes.
REFERENCES
Alsarraf, B.J. (2011) The validity of the “Turning Point – Core Trainer” in volleyball players. Unpublished doctoral dissertation, University of Utah, Salt Lake City, UT.
Myers, J, Lephart, SM, Tsai, YS, Sell, TC, Smoliga, JM, and Jolly, JT. The role of upper torso and pelvis rotation in driving performance during the golf swing. Journal of Sports Sciences 26(2): 181–188, 2008.
Shahbazi, M. M., Sanders, H. R., & Coleman, S. G. S. (2002). Initial ball speed and force estimation at impact in volleyball and football. 20 International Symposium on Biomechanics in Sports, 318–321.
Szymanski DJ, McIntyre JS, Szymanski JM, Bradford TJ, Schade RL, et al. (2007) Effect of torso rotational strength on angular hip, angular shoulder, and linear bat velocities of high school baseball players. Journal of Strength and Conditioning Research 21(4): 1117–1125.
Zhang, Y., & Hsiang, S. M. (2008). A new methodology for three-dimensional dynamic analysis of whole body movements. International Journal of Sports Science and Engineering, 2(2), 87–93.