Objective: To investigate changes in nutritive blood flow as well as interstitial glucose and lactate within an active myofascial trigger point (MTrP) following massage. Design: Randomized, placebo-controlled trial. Setting: Subjects were recruited from the general population; procedures were conducted at a research center affiliated with a university hospital. Participants: Adults (N=25) (18-49y old) with episodic or chronic tension-type headache and an active MTrP in the upper trapezius muscle. Interventions: Subjects were randomized to receive a single trigger point (TrP) release massage or sham ultrasound (US) treatment at an active MTrP in the upper trapezius muscle. Microdialysis was used to continuously sample interstitial fluid from the MTrP before, during, and for 60 minutes following intervention. Main Outcome Measures: The primary outcome measure was nutritive blood flow within the MTrP as measured by microdialysis ethanol clearance; secondary measures included dialysate glucose, dialysate lactate, and subject discomfort with the procedures. Pressure-pain threshold (PPT) was determined to assess treatment effectiveness. Results: There was no treatment effect of TrP release massage on nutritive blood flow (P=.663) or dialysate glucose (P=.766). The interaction for lactate was significant indicating that dialysate lactate increased for TrP release massage vs sham US (P=.04); maximum lactate increase over baseline was observed at 60 minutes after TrP release massage (P=.007, 0.128 μM, 95% confidence interval 0.045-0.212). Pain evoked by probe placement into an active MTrP was low. An interaction effect on PPT was significant (P=.005). Conclusion: TrP release massage of an active MTrP affected anaerobic metabolism as represented by an increase in dialysate lactate without change in nutritive blood flow or dialysate glucose. The lack of a treatment effect on blood flow is discussed.