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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.

Background. The alpha-actinin-3 (ACTN3) R577X polymorphism has been associated with muscle power performance in cross-sectional studies. Methods. We examined baseline knee extensor concentric peak power (PP) and PP change with ~10 weeks of unilateral knee extensor strength training (ST) using air-powered resistance machines in 71 older men (65 [standard deviation = 8] years) and 86 older women (64 [standard deviation = 9] years). Results. At baseline in women, the XX genotype group had an absolute (same resistance) PP that was higher than the RR (p = .005) and RX genotype groups (p = .02). The women XX group also had a relative (70% of one-repetition maximum [1-RM]) PP that was higher than that in the RR (p = .002) and RX groups (p = .008). No differences in baseline absolute or relative PP were observed between ACTN3 genotype groups in men. In men, absolute PP change with ST in the RR (n = 16) group approached a significantly higher value than in the XX group (n = 9; p = .07). In women, relative PP change with ST in the RR group (n = 16) was higher than in the XX group (n = 17; p = .02). Conclusions. The results indicate that the ACTN3 R577X polymorphism influences the response of quadriceps muscle power to ST in older adults.

To determine sex and race differences in muscle power per unit of muscle contraction, knee-extensor muscle power normalized for knee-extensor muscle volume was measured in 79 middle-aged and older adults (30 men and 49 women, age range 50–85 years). Results revealed that women displayed a 38% faster peak movement velocity than men and African Americans had a 14% lower peak movement velocity than Whites of a similar age when expressed per unit of involved muscle (p < .001). As expected, men exhibited greater knee-extensor strength and peak power per unit of muscle than women, but women had a faster knee-extension movement velocity per unit of muscle than men at the same relative strength level. Moreover, African Americans had greater knee-extensor muscle volume than Whites but exhibited lower knee-extensor strength and lower movement velocity per unit of muscle when tested at the same relative strength levels. [ABSTRACT FROM AUTHOR]

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) β2Glu27 polymorphism versus noncarriers and between carriers of ADRα2b Glu9 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 ADRβ2 Glu27 (-2. 3 ± 1.0 cm². p = .028), but no significant change was observed with ADRβ2 Glu27 noncarriers. The decrease in IMF in ADRα2b Glu9 carriers (-1.9 ± 1.0 cm², p = .066) was significantly different (2.9 ± 1.5 cm², p = .043) from a nonsignificant increase in ADRα2b Glu9 noncarriers. ADRβ2 Glu27 carriers who also carried ADRα2b Glu9 significantly lost IMF with strength training (-3.8 ± 1.5 cm², p = .018). Conclusion. ADR genotype influences IMF response to strength training. [ABSTRACT FROM AUTHOR]