These investigations support previous inference that active MTPs in sub-occipital muscles might contribute to headache. It was hypothesized that muscle atrophy of the RCP minor was associated with active MTPs and CTTH. The cross-sectional area of RCP minor was significantly smaller in those with active MTPs compared to those with latent MTPs. Active MTPs were found in 55% of patients and the rest had latent MTPs. A subsequent study was conducted in 11 subjects to evaluate the cross-sectional area of the RCP major and minor with MRI and its relationship with active MTPs in chronic tension-type headache (CTTH) patients ( Fernandez de las Penas et al 2008). Of the ETTH patients, 60% had active MTPs which reproduced their symptoms while the rest had latent MTPs. In one study, 10 patients with ETTH were compared with 10 asymptomatic controls for the presence of sub-occipital MTPs. Clinical investigations demonstrate that MTPs in the sub-occipital muscles may be associated with episodic tension-type headache (ETTH) ( Fernandez de las Penas et al 2006c). The MTPs in the sub-occipital muscles may refer pain to the occiput and temporal region and cause bilateral headache ( Simons et al 1999). Myofascial trigger points may occur in the mid belly of both RCP major and minor and inferior oblique. Kerrie Bolton, Peter Selvaratnam, in Headache, Orofacial Pain and Bruxism, 2009 Trigger point location