INTEGRAL monitoring of the Galactic plane has allowed the discovery of several new X-ray sources, mainly classified as new High Mass X-ray Binaries with transient X-ray emission, the so-called new class of the Supergiant Fast X-ray Transients. The actual mechanism producing their transient and bright flaring activity is still an open issue, and several models have been proposed. I will review the different explanations, and I will compare them with the results of an ongoing monitoring campaign with Swift.