recommend the ZS as a monitoring tool for softball acceleration-time bat swing variables. ... Use of performance testing form monitoring overtraining in elite.
Associations Between Performance Measures of Vertical Jumping and Bat Swing Mechanics Batcher, J.J., Raszeja, N. J. Embry, T. C. and Bailey, C.A. Sport Performance Enhancement Education and Development (SPEED) Center, Department of Exercise Science, LaGrange College, LaGrange, GA
INTRODUCTION
DISCUSSION
The ability to hit the ball comes from the dynamics of the bat swing which can be most thoroughly understood when measurement utilizes three-dimensional motion capture. However, A study by King et al. (2012) provides an inexpensive and portable measurement method for on the field of play to support player training, coaching, rehabilitation, and player-bat fitting. This method employs a small, wireless microelectromechanical systems (MEMS) inertial measurement unit (IMU) used at the knob of the bat. The IMU uses a tri-axial accelerometer with a low-power radio frequency transmitter to transmit bat swing data to a host computer. Analysis of data shows an instant summary of three-dimensional bat dynamics. While the King et al. study presents a novel device with practical applicability, continuation of this research seems to be lacking. Athletic performance monitoring is a frequent trend in sports science and strength and conditioning (Hoffman and Kaminsky, 2000, Sands, 1991). Specifically concerning jump performance monitoring, force plate analysis is commonly used and vertical jumping evaluations have been indicated as a good measure for monitoring athletes (Nimphius, 2011). To the current author’s knowledge, the relationship between athlete monitoring variables derived from jumps and swing analysis has not been evaluated. Therefore, the purpose of this study was to evaluate the relationship between bat swing analysis variables as measured by a new IMU unit (Zepp sensor) and jump performance characteristics in softball players.
The purpose of this investigation was to evaluate the relationship between bat swing mechanics (as measured by the ZS) and jump performance variables. The ZS appears to be a reliable tool for monitoring the acceleration-time related variables, but Vert θ and CMJ PV was not reliable. From the athlete monitoring perspective, reliability is critically important. As a result, the investigators recommend the ZS as a monitoring tool for softball acceleration-time bat swing variables. Concerning association between bat swing mechanics and jumping performance, if there were strong associations between the two assessments, only one would need to be evaluated. However, this was not the case. The only statistical correlations were between PV@Con, Vert θ, and jump performance variables that were only moderate. Without strong associations between the two tests, it may be important to monitor both bat swing mechanics and jumping performance.
SJ JH SJ PV SJ PP` CMJ JH CMJ PV CMJ PP SJ PP/kg CMJ PP/kg
PV @Con 0.42* 0.27 0.56* 0.39 0.05 0.50* 0.33 0.20
PV 0.37 -0.01 -0.13 0.34 0.18 0.00 0.02 0.24
TtoCon (s) -0.06 0.16 0.17 -0.10 -0.20 -0.05 0.13 -0.13
Vert θ 0.07 0.27 0.68* 0.06 -0.09 0.46* 0.25 -0.15
Attack θ 0.15 0.08 0.18 0.12 0.07 0.08 0.04 -0.06
In this study two outliers were found that skewed the data distribution in SJ PP and CMJ PP, which influenced the trend of the relationship. There was a large difference between the average body mass of the sample and two of the subjects, leading to a large difference in power. When these two variables were normalized for body mass (PP/kg), the relationship strength between PV @Con and SJ PP/CMJ PP decreases. SJ PP & PV@Con
SJ PP & PV@Con (adjusted for body mass)
5500 5000 4500 4000 3500 3000 2500 2000 1500 1000
6000 5000
SJ PP (W)
20 collegiate softball players (19.1±1.2 yrs, 76.2±19.2 kg) completed jump testing and bat swing analysis on the same day. Jump testing consisted of squat (SJ) and countermovement jumps (CMJ) and was performed on a force plate collecting data at 1000 Hz (Bertec 6090D). All jumps were performed without the contribution of an arm swing, as athletes held a PVC pipe of negligible weight behind the neck. SJ knee angles were standardized to 90°, but countermovement depth was not controlled for to ensure ecological validity. Jump performance variables included jump height (JH), Peak Velocity (PV), peak power (PP), and PP scaled by body mass (PP/kg). Following jump testing, bat swing analysis was completed with the ZS and all athletes swung 3 times. The ZS was affixed to the knob of the athlete selected bat and all athletes hit 3 balls off a tee. Bat swing variables consisted of peak velocity (PV), PV at contact (PV@Con), time to contact (TtoCon), vertical angle (Vert θ) and attack angle (Attack θ). Within session reliability was evaluated with intraclass correlation coefficients (ICC) and relationships with jumping performance were evaluated with Pearson’s bivariate correlations with statistical significance set at p0.9 is nearly perfect (Hopkins, 2013).
All variables had acceptable reliability measures, ranging from 0.790 to 0.932, with the exception of Vert θ (ICC=0.634) and CMJ PV (ICC=0.481. Moderate statistically significant relationships were observed between SJ JH and PV @C (r = 0.42), CMJ PP and Vert θ (r = .46), SJ PP and PV @C (r = 0.56), SJ PP and Vert θ (r = 0.68), CMJ PP and PV @C (r = 0.50). No other statistically significant relationships were observed.
SJ PP (W)
METHODS
RESULTS
4000 3000 2000 1000 0
47
52
57 62 PV@CON
67
-5 -1000 0
5
10 PV@CON
15
20
25
An interesting finding of this study was that athletes did not perform better in the CMJ than the SJ, which is not consistent with previous research. Bobbert et al. (1996) showed that subjects are able to jump higher 3.4 cm greater in a CMJ than in a SJ.
CONCLUSION The ZS appears to be a reliable tool for evaluating bat swing mechanics variables such as swing velocities and time to contact. Bat swing PV@Con is moderately related to jumping performance, but the other swing variables seem to vary independently from jumping performance. As a result, the authors recommend monitoring bat swing mechanics along with jump performance. Future researchers should consider to evaluating the association between subjects swing analysis variables measured on a force plate and swing analysis variables measured by an IMU. This would provide a further knowledge of the process of how force developed through the ground translates into rotational movement and potentially provide implications for performance enhancement.
ACKNOWLEDGEMENTS This research was not funded or supported by any outside source.
REFERENCES Bobbert, M., Gerritsen, K., Litjens, M., & Van Soest, A. (1996). Why is countermovement jump height greater than squat jump height?. Medicine & Science in Sports & Exercise, 28(11), 14021412 11p. Hoffman, J., Kaminsky, M. (2000). Use of performance testing form monitoring overtraining in elite youth basketball players. Strength and Conditioning Journal, 22(6):54-62. Hopkins, W.G. (2013). A new view of statistics. Retrieved 11/9, 2015, from http://www.sportsci.org/resource/stats/effectmag.html King, K, Hough, J., McGinnis, R., & Perkins, N. (2012). A New Technology for resolving the dynamics of a swinging bat. Sports engineering (Springer Science & Business Media B.V.), 15(1), 41-52. Milanovich, M., & Nesbit, S. M. (2014). A Three-Dimensional Kinematic and Kinetic study of College-Level Female Softball Swing. Journal Of Sports Scicence & Medicine. 13(1), 180-191. Nimphius, S. (2011). Monitoring neuromuscular fatigue in amateur baseball players during a national tournament. Journal of Australian Strength and Conditioning, 19:110-114. Sands, WA. 2005. Monitoring the elite athlete. USOC Olympic Coach E-Mag,17(3):4-12. Sawchik, T. (2014). MLB Pitchers setting velocity records, altering balance of power TRIB Total Media:Sports. Suchomel, TJ and Bailey, CA. 2014. Monitoring and managing fatigue in baseball players. Strength and Conditioning Journal, 36(3):39-45. Taylor, KL, Chapman, DW, Cronin, JB., Newton, MJ, & Gill, ND. 2012. Fatigue monitoring in high performance sport: A survey of current trends. Journal of Australian Strength and Conditioning, 20(1), 12-23.
www.lagrange.edu/strength www.facebook.com/LCSPEEDCenter
