Adrenergic receptor genotype influence on midthigh intermuscular fat response to strength training in middle-aged and older adults

Background. There is little information regarding the effects of strength training on intermuscular fat (IMF). This study examines changes in IMF in response to strength training in carriers of the adrenergic receptor (ADR) [Beta]2Glu27 polymorphism versus noncarriers and between carriers of ADR[Alpha]2b [Glu.sup.9] polymorphism versus noncarriers. Methods. Midthigh IMF and muscle area were measured by computed tomography (CT) before and after 10 weeks of single-leg strength training in healthy, sedentary middle-aged and older (50-83 years) men ([Eta] = 46) and women ([Eta] = 52) in both their trained and untrained (control) legs. Results. The strength training program resulted in a substantial increase in one-repetition maximum strength (p < .001) and muscle area (p < .001), but no significant changes in IMF in the whole group. However, IMF was significantly reduced with strength training in participants carrying ADR[Beta]2 Glu27 (-2. 3 [+ or -] 1.0 [cm.sup.2], p = .028), but no significant change was observed with ADR[Beta]2 Glu27 noncarriers. The decrease in IMF in ADR[Alpha]2b [Glu.sup.9] carriers (-1.9 [+ or -] 1.0 [cm.sup.2], p = .066) was significantly different (-2.9 [+ or -] 1.5 [cm.sup.2], p - .043) from a nonsignificant increase in ADR[Alpha]2b [Glu.sup.9] noncarriers. ADR[Beta] Glu27 carriers who also carried ADR[Alpha]2b [Glu.sup.9] significantly lost IMF with strength training (-3.8 [+ or -] 1.5 [cm.sup.2], p = .018). Conclusion. ADR genotype influences IMF response to strength training.