Currently there is little research that has quantified the countermovement push-up (CMPU) power indices or investigated the validity and reliability of the CMPU as a practical upper-body muscular performance test. The current study investigated the force-time characteristics of the CMPU, the reliability and validity of the Just Jump ® mat (JJ) to assess CMPU height as an index of upper-body extensor muscular performance. Fifteen trained participants (13 = males and 2 = females); (mean ± SD) age = 26.87 ± 2.72 yrs, height = 178.83 ± 7.92 cm, body mass = 84.85 ± 15.53 kg, and bodyfat percent = 17.31± 6.20 % were recruited from the University of Utah and the Department of Exercise and Sport Science. The CMPU vertical displacement (CMPU-Ht), measured with 3-D motion analysis (MA) was 24.64 ± 7.01cm. A force platform was used to measure peak rate of force development (PRFD) = 6,254.93 ± 4409.89 N˙s^-1, peak power (PP) = 329.15 ± 178.06 W, impulse (IMP) = 198.40 ± 77.99 N˙s, and peak force (PF) = 477.74 ± 179.73 N. A significant correlation (r > 0.70) was observed between motion analysis CMPU-Ht and PF and PP. Given the high relationship between CMPU-Ht and PP and PF, potential use of the use of JJ-derived Ht as a measure of upper body extensor performance was examined. While there was some support for the reliability of the JJ measures of CMPU-Ht, large coefficient of variation % (> 10%), standard error of measurement, random error, and statistical differences (p < 0.05) between the motion analysis and Just Jump mat® derived CMPU-Hts suggest that the JJ should not be used to assess CMPU power. Furthermore, through analyses of JJ CMPU-Ht for construct, convergent, and divergent validity demonstrated that the CMPU-Hts derived with the Just Jump mat® had low validity. Further research is needed to determine if another contact mat or CMPU protocol may improve the reliability and validity of the CMPU as an upper-body extensor muscle performance test.