SUMMARY BACKGROUND DATA: Tennis players asymmetrically load the trunk while playing. Neuromuscular imbalances are risk factors for low back injuries. The association between neuromuscular activity patterns of the lower back and back exercise has not been researched yet. METHODS: Simultaneous maximum isometric trunk extension test and surface-electromyographic recordings from lumbar erector spinae in 82 amateur tennis players in a specially built apparatus before and after a seven-week back exercise home program. RESULTS: Left-right neuromuscular imbalances of lumbar erector spinae were present amongst 48 (58.5 %) out of 82 tennis athletes, statistically closely related to handedness. Within the training group (n = 70), neuromuscular imbalances of erector spinae were significantly evened out without a significant increase of maximum trunk extension strength. No such effects were detected within the control group (n = 12). CONCLUSION: Tennis specific biomechanics seems to predispose to lumbar neuromuscular imbalances. A back exercise program for tennis player can significantly even out those imbalances.