Effects of muscle composition and architecture on specific strength in obese older women

Muscle impairment and body mass excess are very common among older people. Since the effect of obesity on strength production has been scarcely studied in older individuals, we analysed functional and structural characteristics of Quadriceps Femoris (QF) in obese (OB) and normal weight (NW) older women, with comparable habitual physical activity. In 5 OB (BMI = 36.8 ± 1.9 kg m2 , age = 72.4 ± 2.3 yr.) and 6 NW (BMI = 24.3 ± 1.8 kg m2 , age = 72.7 ± 1.9 yr.) well functioning older women, peak knee extension torque (KET) was measured in isometric (90° knee flexion) and isokinetic conditions (240, 180, 120, 60°/sec). Mid-thigh QF cross sectional area (CSA) and muscle tissue fat content (MF%) were determined with MRI (Dixon sequence). Muscle fascicle length (FL) and pennation angle (PA) were assessed with ultrasonography for each muscle belly of the QF (vastus lateralis, vastus intermedius, rectus femoris, vastus intermedius). Despite similar values in KET, CSA was 17.0% larger in OB than in NW (P < 0.05), so that KET/CSA, was significantly lower (P < 0.05) in OB. Compared to NW, OB had 28.7% higher MF% (P < 0.05) and 24.9% higher average PA (P < 0.05), while FL was similar. Overall, isometric KET/CSA was negatively affected by both MF% (P < 0.05) and PA (P < 0.05), while isokinetic KET/CSA only by MF% (P < 0.01). Muscle composition and architecture seem to be important determinants of KET/CSA in elderly. In fact, due to the effect of obesity overload, OB have larger QF size than NW, but unfavourable muscle composition and architecture. The higher MF% and steeper PA observed in OB are associated with reduced levels of muscle specific strength. This article is protected by copyright. All rights reserved.