repeated measure design cross over design (source: http://www.sbu.se/Filer/Content0/publikationer/1/literaturesearching_1993/glossary.html) a repeated measure design which ensures that experimental units receive, in sequence, the treatment (or the control), and then, after a specified time interval (aka *wash-out periods*), switch to the control (or treatment). In this design, subjects (patients in human context) serve as their own controls, and randomization may be used to determine the ordering which a subject receives the treatment and control Philippe Rocca-Serra cross over design Participants receive one of two (or more) alternative interventions during the initial phase of the study and receive the other intervention during the second phase of the study PMID: 17601993-Objective: HIV-infected patients with lipodystrophy (HIV-lipodystrophy) are insulin resistant and have elevated plasma free fatty acid (FFA) concentrations. We aimed to explore the mechanisms underlying FFA-induced insulin resistance in patients with HIV-lipodystrophy. Research Design and Methods: Using a randomized placebo-controlled cross-over design, we studied the effects of an overnight acipimox-induced suppression of FFA on glucose and FFA metabolism by using stable isotope labelled tracer techniques during basal conditions and a two-stage euglycemic, hyperinsulinemic clamp (20 mU insulin/m(2)/min; 50 mU insulin/m(2)/min) in nine patients with nondiabetic HIV-lipodystrophy. All patients received antiretroviral therapy. Biopsies from the vastus lateralis muscle were obtained during each stage of the clamp. Results: Acipimox treatment reduced basal FFA rate of appearance by 68.9% (52.6%-79.5%) and decreased plasma FFA concentration by 51.6 % (42.0%-58.9%), (both, P < 0.0001). Endogenous glucose production was not influenced by acipimox. During the clamp the increase in glucose-uptake was significantly greater after acipimox treatment compared to placebo (acipimox: 26.85 (18.09-39.86) vs placebo: 20.30 (13.67-30.13) mumol/kg/min; P < 0.01). Insulin increased phosphorylation of Akt (Thr(308)) and GSK-3beta (Ser(9)), decreased phosphorylation of glycogen synthase (GS) site 3a+b and increased GS-activity (I-form) in skeletal muscle (P < 0.01). Acipimox decreased phosphorylation of GS (site 3a+b) (P < 0.02) and increased GS-activity (P < 0.01) in muscle. Conclusion: The present study provides direct evidence that suppression of lipolysis in patients with HIV-lipodystrophy improves insulin-stimulated peripheral glucose-uptake. The increased glucose-uptake may in part be explained by increased dephosphorylation of GS (site 3a+b) resulting in increased GS activity.