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) beta2Glu27 polymorphism versus noncarriers and between carriers of ADRalpha2b Glu(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 (n = 46) and women (n = 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 ADRbeta2 Glu27 (-2. 3 +/- 1.0 cm(2), p =.028), but no significant change was observed with ADRbeta2 Glu27 noncarriers. The decrease in IMF in ADRalpha2b Glu(9) carriers (-1.9 +/- 1.0 cm(2), p =.066) was significantly different (-2.9 +/- 1.5 cm(2), p =.043) from a nonsignificant increase in ADRalpha2b Glu(9) noncarriers. ADRbeta2 Glu27 carriers who also carried ADRalpha2b Glu(9) significantly lost IMF with strength training (-3.8 +/- 1.5 cm(2), p =.018). CONCLUSION ADR genotype influences IMF response to strength training.