The purpose of this study was to evaluate the effectiveness of short-term stability ball (SB) training on males and females by comparing the strength changes produced in the core muscles. Forty-two previously untrained subjects, mean age = 23.62 ± 2.89 years were matched by their maximum strength (back strength: male = 190-200 kg, female = 45-50 kg and abdominal strength: male = 110-120 kg, female = 35-40 kg 1RM) and randomly placed in either one of these 3 groups; unstable SB group (n = 14), stable floor group (n = 14) and control group (n = 14) who did no exercise. SB training showed greatest improvement (p < 0.001) in back and abdominal strength (25.79 % and 29.51 % respectively), compared with the gain in floor training (FT) back and abdominal strength (10.28 % and 8.47 % respectively). Untrained female subjects achieved a higher percentage of improvement in strength compared to males in both back and abdominal muscles, and this is most evident in the SB training group. It is apparent that performing core training exercises on unstable surfaces stressed the musculature, possibly activating the neuro-adaptive mechanisms that led to the early phase gains in strength.