Hypothesized mechanism yielding active and latent trigger points. At the site of the myofascial trigger point, there is restriction of blood flow increasing the proton concentration ([H+]) locally. There is also an increase of local [ROS]. The plot shows the normalized concentrations of these substances as a function of the distance from the trigger point center. As the distance from the trigger point center increases, the levels of [ROS] (blue) decrease more gradually than the levels of [H+] (red). If the nociceptors are located close to the center of the trigger point, they are active as the levels of [ROS] and [H+] protons are high enough to activate the ASIC and TRPV1 channels. If these neurons/receptors are farther away the, trigger point would be latent. Upon palpation the [ROS] increases due to mechanical deformation of the microtubule network and activation of NADPH oxidase and the [ROS] increases (green) so that the nociceptors see sufficient ROS to be activated.
