1. ABSTRACT The purpose of the present study was to investigate the test-retest reliability of force-time derived parameters of an explosive push up. Seven highly strength trained males participated in two independent trials, separated by 48 hours, and completed six maximal effort explosive push up trials on dual mounted Kistler force platforms. Subsequently, various performance parameters were calculated. Systematic and random error was assessed to evaluate intersession reliability, together with coefficient of variation (CV) and typical error (TE). No systematic bias was detected between trials for any parameter. Moderate to high reliability was observed for the majority of variables (CV= 0.7-8.7%), with the exception of peak displacement and contact time (CV= 13.8-15.8%). Average and peak force and power measures exhibited the highest reliability (CV= 0.1-8.7%). Findings establish that selected force platform derived kinetic and kinematic parameters of an explosive push up are reliable in highly strength-trained individuals. TEST-RETEST RELIABILITY OF AN EXPLOSIVE PUSH-UP AS A MEASURE OF UPPER BODY POWER Rob Miller 1, Dr. Rodney Kennedy 2 1 British Athletics / English Institute of Sport, Loughborough, 2 University of Ulster, Jordanstown, N. Ireland Figure 2. Typical Vertical Ground Reaction Force (vGRF) traces derived from dual mounted integrated force platforms during a maximal effort explosive push-up. Figure 1. Starting position of an explosive push up trial with self selected hand-width, elbows straight and feet together. CONCLUSION The present study indicates that no systematic bias is present when examining explosive push up performance variables in strength-trained men. While comparison to previous literature is limited, moderate to high reliability is noted for the majority of performance measures. Therefore, it may be reasonable to suggest that upper body power output can be reliably assessed using force platforms in well trained populations. REFERENCES 1)Atkinson, G., Nevill, A. (1998). Statistical Methods For Assessing Measurement Error (Reliability) in Variables Relevant to Sports Medicine. Sports Medicine. 26(4). 217-238. 2)Cormie, P., McBride, J. M., McCaulley, G. O. (2007). Validation of Power Measurement Techniques in Dynamic Lower Body Resistance Exercises. Journal of Applied Biomechanics. 23. 103-118. 3)Hogarth, L. W., Deakin, G., Sinclair, W. (2013). Are Plyometric Push-Ups a Reliable Power Assessment Tool? Journal of Australian Strength and Conditioning. 21(1). 67-69. 4)Hopkins, W. G. (2000). Measure of Reliability in Sports Medicine and Science. Sports Medicine. 30(1). 1-15. ACKNOWLEDGMENTS This study was supported by the University of Ulster Sports Academy, it’s academic staff, the Sports Institute Northern Ireland Strength and Conditioning Department, and the participants who volunteered for the investigation. A special note of thanks is made to Dr. Rodney Kennedy for overseeing the investigation. Statistical Analysis: The presence of systematic bias was examined using a paired t-Test. Subsequent intersession variation was determined by calculating the coefficient of variation (CV), and typical error (TE) (4). INTRODUCTION Upper body muscular power output is a key aspect of athletic ability, and a major determinant for the outcome of many explosive, short duration sporting performances such as throwing, wrestling and swimming. Consequently, assessment of an individual’s power output capability could be imperative in the understanding of the performance potential of that individual, evaluating training programs and for talent I.D. purposes. Currently, no commonly accepted and standardised isoinertial test exists for assessing upper body power output. Recently, force platforms have been used to assess upper body power output with an explosive push up (3), but the reliability of this testing procedure and derived variables are unclear. The purpose of the present study is to investigate the test-retest reliability of force platform derived parameters of an explosive push up in a trained population. METHODS Experimental Approach to the Problem and Participants: Seven highly strength-trained males participated in a single group repeated measures study design. Testing sessions were separated by a week, and took place at the same time of day. All participants were required to have a minimum of 18 months high intensity strength training history that incorporated explosive upper body exercises, and were free of any upper or lower body injuries. RESULTS Descriptive and reliability statistics for each explosive push up performance variable are presented in Table 1. Paired t-Tests revealed no significant difference for any derived parameter between each testing session. Within subject CV indicates that the majority of derived performance parameters have moderate to very high test-retest reliability (CV= 0.1-8.7%), with the exception of peak displacement and contact time (CV= 13.8-15.8%). DISCUSSION Corresponding to previous research (3), moderate to high reliability (CV= 0.1 – 8.7%) was exhibited for most derived parameters, with the exception of peak displacement and contact time (CV= 15.8% and 13.8% respectively). This may be attributed to variation in push-up technique. No systematic bias, and therefore no learning effect, appeared to be present in the current study. This can be attributed to the highly strength-trained status of the participants, who may have possessed the necessary motor skills required for this test. A limitation of the present study is due to a small sample size, with recommendations for reliability studies suggesting a sample size of at least 20 participants (1). Furthermore, additional testing days would have increased the precision of estimated reliability (4). Data Processing: Vertical force-time data collected from each trial (Figure 2) was used to calculate peak velocity, peak displacement, average eccentric force, average concentric force, peak force, average eccentric power, average concentric power, peak power, contact time and stiffness (2). Results were obtained by an average of six trials for each participant. Testing Procedures: Participants undertook a standardised warm up, and 5 explosive push-ups at increasing perceived intensities (50%, 70%, 80%, 90%, 95% respectively). Participants then undertook six individual maximal effort explosive push- up trials, separated by a 2-minute rest interval. All trials were performed on adjacent dual mounted integrated Kistler force plates, sampling at 1000Hz.