Final answer:
Endorphins are the opioid neuromodulators released with skin stimulation that contribute to the decreased lower back pain.
Step-by-step explanation:
The opioid neuromodulator that is released with skin stimulation and is more than likely responsible for the decreased lower back pain is endorphins. Endorphins play a major role in the body's inhibitory response to pain and can be triggered by vigorous aerobic exercise. They contribute to the positive effect of exercise on anxiety and depression and are known to provide a sense of comfort and relief.