Low-back pain (LBP) in women gymnasts is relatively common. This investigation was performed to evaluate the effects of a preseason training program for the trunk extensor, lateral flexor, and flexor muscles on LBP occurrence during the subsequent competitive season. The training group consisted of 15 collegiate women gymnasts. The control group consisted of 15 nonathlete collegiate women. Pre- and posttesting for all participants consisted of static endurance tests for the trunk extensors, lateral flexors, and flexors. After pretesting, the training group completed 10 weeks of biweekly training consisting of non-foot-supported back extensions and side bridges, in addition to their usual trunk flexor exercises. The control group did not perform any specialized trunk muscle training. Mean improvements in trunk endurance, based on multivariate analysis of variance at the 5% level of significance, were significantly greater in the training group than in the control group. Mean improvements in endurance in the training group were 47 seconds for the lateral trunk flexors, 34 seconds for the trunk extensors, and 80 seconds for the trunk flexors. During the subsequent gymnastics season, none of the gymnasts reported new episodes of LBP. One gymnast with chronic LBP reported a recurrence of LBP during the season. None of the gymnasts reported that the training program adversely affected their gymnastic performance. These data suggest that training the trunk musculature twice per week during a 10-week period with a relatively simple floor exercise protocol was an effective stimulus to improve trunk endurance measures. It is encouraging that none of the gymnasts reported new episodes of LBP during the subsequent competitive gymnastics season.