ORIGINAL RESEARCH
RELIABILITY OF THE TURNING POINT CORE TRAINER AS A MEASURE OF ROTATIONAL ANGLES AND VELOCITIES Justin R. Brown, Ryan Bennion, Charlie A. Hicks-Little Department of Exercise and Sport Science, University of Utah
Corresponding Author: Justin R. Brown ParvoMedics, Inc. 6526 S. State Street Suite #202, Murray, UT 84107 Email:
[email protected];
[email protected]
ABSTRACT Introduction: The x-factor is considered an important measure in rotational sports such as golf and is typically assessed using three-dimensional motion capture analysis. Due to equipment costs and lengthy time periods to analyse measurements it is not practical for coaches. Although three-dimensional motion capture analysis is recognised as the gold standard, a cheaper and quicker tool is needed to evaluate such measurements. The Turning Point Core Trainer (TP) is a device designed to measure the x-factor and angular velocities of the upper torso and hips; however, data regarding reliability of the TP is lacking. The purpose of this study was to examine between session reliability of the TP as a measure of the x-factor and angular velocity of the upper torso (SAV) and hips (HAV). Methods: Sixty two college adults volunteered for this study (male = 35, female = 27, age 24.85 ± 4.54 years, height 1.72 ± 0.09 m, weight 71.09 ± 12.81 kg, BMI 23.78 ± 2.89 kg/m2). Participants completed three 30 second trials on two separate testing days using the TP with zero resistance in the upright position with no forward incline. A one minute rest period separated each trial. Participants were asked to return to the lab 3 to 14 days following the initial testing. The TP measured SAV and HAV about the body’s y-axis and was recorded in (°/s). Intraclass correlations (ICC) were used to examine reliability between testing sessions. Paired t-tests were used to examine differences between testing sessions. Statistical significance was set at p < 0.05. All data was analysed using PASW Statistical software 18.0 (IBM Inc., Chicago, IL). Results: ICC’s were very strong for both the right and left directions for x-factor (0.86 vs. 0.80), SAV (0.96 vs. 0.95), and HAV (0.91 vs. 0.91), respectively. Only HAVR reached statistical significance between testing days (72.85±29.22°/s vs. 76.82±26.06°/s, p=0.04). Discussion and Conclusion: These results suggest excellent test-retest reliability using the TP and support its use for assessing the x-factor, SAV, and HAV. Keywords: Angular velocity, rotational sports, x-factor, reliability
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INTRODUCTION The core musculature plays an important role in trunk stabilisation as well as athletic performance. In sports with a rotational component the x-factor (Figure 1), which is the separation between the upper torso and pelvis in the global y-axis 1, have demonstrated a significant contribution to sports performance 1, 2, 3, 4, 5, 6, 7, 8. By increasing the x-factor athletes maximise the elastic energy released during the downswing resulting in a greater activation of the core muscles and ultimately imparting a higher force on the ball thereby increasing ball velocity 1 In golf, researchers have investigated ball velocity and the x-factor 1, 5, 6, 8. Those results demonstrated greater ball velocity for higher skilled golfers with a greater x-factor. In volleyball, Brown et al. (2014) used a laboratory setting to examine spiked ball velocity and the x-factor in female collegiate volleyball players. That study found a greater x-factor for diagonal across court spikes versus down the line spikes (-12.56±5.36° vs. -9.16±5.32°). In addition, significant positive correlations were observed between spiked ball velocity and DAC spikes suggesting a positive relationship between a greater x-factor and increased spiked ball velocity.
Figure 1. Illustration of the x-factor. The difference in angle between the upper torso and the pelvis is known as the x-factor or upper-torso pelvic separation angle. At the initiation of the forward swing, the pelvis moves in a counterclockwise direction for the right handed person while the upper torso remains fixed for a brief period of time. The figure has been modified from Brown et al. (2014).
In baseball, pitchers with a greater x-factor had faster pitching velocities 2, 7, 9. The x-factor has been shown to be a contributor to athletic performance in rotational sports and athletes would benefit from feedback about their ability to use the body’s core musculature to execute axial rotations. Aguinaldo speculated that by optimally rotating the trunk, baseball pitchers could better transfer energy from the core to the throwing arm 7. The inability to maximise separation between the upper torso and pelvis may cause pitchers to rely more on the shoulder during pitching. Improper pitching mechanics have been shown to increase shoulder and elbow forces which have been suggested as risk factors for injury 10. Vad et al. (2004) examined asymmetries between the lead and non-lead hip during the golf swing and found asymmetries existed in golfers with low back pain. Tsai et al. (2010) examined torso rotation in amateur golfers and found golfers with a history of low back pain had less trunk rotation than those without a history of low back pain. They speculated that history of back injury could result in biomechanical changes affecting the ability to maximise the x-factor during the golf swing. Any negative change in rotation of the torso or pelvis could alter the x-factor and reduce ball velocity as well as decreased sports performance. The ability to measure and interpret the x-factor allows coaches to provide feedback in order to maximise performance. To date the x-factor and angular velocities have been measured using cinematography or three-dimensional motion capture analyses which are considered accurate and reliable for analysing human movement 12, 13. Although it provides such feedback, it is too expensive for use in most coaching situations and a more practical tool to assess axial rotation is needed. Recently, a device called the Turning Point–Core Trainer 4.0 (TP) was developed (Figure 2) as a training tool for developing strength and range of motion for both athletic and rehabilitative populations. The TP provides information regarding rotational angles and velocities that was previously only available using motion capture analysis. Furthermore, results are available in real
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the definition provided by the American College of Sports Medicine Position Stand 17. Participants were excluded if they had an injury that interferes with their ability to perform rotational movements. Participants were also excluded if they had a history of back injury including bulging, herniated, or ruptured disc. Participants were also excluded if they had osteopenia, osteoporosis, or a neurological condition. This study was approved by the Institutional Review Board (IRB) at the University of Utah.
Figure 2. Turning Point–Core Trainer 4.0.
time and do not require lengthy time periods for cinematographic analysis. Using electromyogram analysis Pincivero et al. (2009) determined the TP is an effective tool for engaging the core musculature; however, little is known regarding the reliability of the TP. Reliability refers to the consistency of scores for a given measurement 15 and is an important prerequisite for measurement validity 16. The purpose of this study was to evaluate the test-retest reliability of the measurement scores obtained from the TP for the x-factor, and angular velocities of the upper torso and hips. We hypothesised there would be strong test-retest reliability for all variables using the TP. Furthermore, we hypothesised no significant differences for the x-factor, or angular velocities between the two testing sessions.
METHODS Participants Sixty two healthy and physically active adults were recruited from the Department of Exercise and Sport Science at the University of Utah (Table 1). ‘Physically active’ was determined according to
Protocol: Participants were asked to arrive at the testing laboratory in a rested and well hydrated state and wearing comfortable exercise clothing. Upon arrival participants provided written consent and completed a health history questionnaire. Participants were then measured for height using a wall mounted stadiometer (KWS Medical Supplies, LLC, North Bend, WA) and weighed using an electronic scale (Omron Healthcare Inc., IL). Upon completion, participants were given verbal instructions on the testing process. Participants were given 5 minutes to perform a self-selected warm up prior to using the TP. The TP (The Turning Point, LLC, Toledo, OH) is a device designed to assess and exercise the core muscles while in an upright position. The device has a padded structure for the hips and a horizontal movement arm for the shoulders, which allow independent movements for the hips and upper torso in the transverse plane (Figure 2). Resistance is provided by computer controlled hydraulic linear actuators operating with a rack-and-pinion mechanism allowing 1 point increments in resistance up to level 20. The resistance for each level was not quantified by the manufacturer. The base of each attachment contains rotational potentiometers which allow for 140 degrees of rotation 14. Finally, the device allows for a forward lean between 0 and 40 degrees 14. Software built into the TP records torque and range of motion for the upper torso and hips. Investigators adjusted the height of the TP movement arm to the position where it is above the
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shoulder near level of C-7 spine. Forward trunk inclination was set to 0° of trunk flexion. Hip pads were adjusted in height and secured firmly at the anterior superior iliac spine. The participant placed their back against the shoulder and hip pads and placed forearms and hands on the horizontal arms of the TP. Participants placed their feet hip width apart with a slight bend in the knees as described by Pincervero et al. 2009. This position was considered the neutral position (Figure 3a). From the neutral position, participants rotated the shoulders and hips (like a backswing) either direction (Figure 3b), returned to the neutral position, and rotated to the opposite direction (Figure 3c). Participants performed these movements following the cadence of a metronome (30 bpm) to control for the number of repetitions. Three sets of 10 repetitions, 5 per side, were performed for each testing day. Participants were given 1 minute of rest between trials. Participants performed all bouts with maximal speed and force and the greatest value for shoulder and hip angles for each test was retained for analysis. The peak x-factor and angular velocity from each set was used to calculate the mean for each testing session. No sooner than 3 days and no later than 14 days, participants returned to the laboratory and repeated
A
the tests to examine the stability reliability 18, 19 or test-retest reliability of the TP. Statistical Analysis Descriptive data was reported as mean and standard deviation. Intraclass correlation coefficient (ICC) tested the stability and consistency of the scores 18. The ICC was interpreted as follows: 0-0.2 indicates poor agreement; 0.3-0.4 indicates fair agreement; 0.5-0.6 indicates moderate agreement; 0.7-0.8 indicates strong agreement; and >0.8 indicates very strong agreement. Standard error of measurement (SEM) was calculated as SD*√1-ICC 18. Paired t-tests were used to examine differences in the x-factor and angular velocities between testing days. Data was sorted and t-tests were run to examine differences for each variable between males and females. Data was exported from the TP and entered into an Excel spreadsheet in order to calculate the x-factor which was calculated as peak hip angle subtracted from peak shoulder angle. Statistical analysis was performed using SPSS ver. 19. Level of significance was set at p
