A person can experience back pain during a whole host of activities for a number of reasons, like aging, weight gain, stress, poor sleep, or being in poor physical condition. Any factor at play can also make an individual’s body more vulnerable to bodily trauma. For as pleasurable as fisting can be for some people, this sexual act is considered risky and even traumatic for the body to endure because it can cause severe tissue damage and pain.
In getting to the bottom of what’s causing the back pain, it would be best to have your partner get checked out by a doctor, since the pain may be the sign of a condition like bulging disc. It may, however, simply be the effects of aging, with her body’s tolerance for fisting perhaps further compromised by a sexual position that can cause the spine to be overly strained or compressed. Finally, your partner should consider if she has been doing anything lately, like carrying small children or a heavy backpack, which could be making her back more sensitive during other activities. Regardless, make sure that you’re taking it easy on her during fisting until what’s causing her back discomfort is resolved.
All the best,