Why does my lower back ache when I work out my abs?

Lower back soreness during abdominal exercises may be caused by incorrect exercise posture, excessive intensity, overstretching, or other reasons.

1. Incorrect Exercise Posture

If the posture is improper during abdominal training—such as relying too much on the lower back instead of engaging the abdominal muscles—it can easily lead to strain and overuse injury of the back muscles, resulting in the aforementioned discomfort. If there are no other physical symptoms, this usually isn't a cause for concern. Correcting the exercise form and properly engaging the abdominal muscles can help resolve the issue.

2. Excessive Intensity

When the amount of exercise exceeds one's physical capacity, it can lead to excessive accumulation of lactic acid in the lower back that cannot be metabolized quickly enough. This buildup may stimulate peripheral nerves and cause soreness. Applying a warm towel compress can help promote absorption of lactic acid, and professional massage techniques may also provide relief.

3. Overstretching

Inadequate warm-up before abdominal exercises or using overly large movements during training can place the back muscles in a state of excessive stretch. Continuous stimulation of the abdominal muscles under such conditions may easily result in strain of the lower back muscles, leading to back soreness during abdominal workouts. It is recommended to perform proper warm-up exercises, avoid excessively large movements during training, and reasonably schedule abdominal workout sessions.

Besides the common causes listed above, other medical conditions such as lumbar muscle strain or lumbar disc herniation may also contribute. If the soreness occurs frequently, it is advisable to seek timely medical evaluation at a hospital, including CT or ultrasound examinations if necessary.