Normalized Torque of the Quadriceps Femoris is Similar Between Active Old and Young Adults

Abstract

2435 Age related losses in maximum force production are well documented. The loss in strength could be attributed to a loss in skeletal muscle mass or a reduced ability to centrally activate available muscle. Previous research has reported mixed results as to whether the force per unit area of skeletal muscle is different between old and young subjects. PURPOSE: To determine if normalized torque (torque per unit area of skeletal muscle) is different between active older and younger adults. METHODS: Skeletal muscle cross sectional area (CSA) and torque from maximum voluntary contraction (MVC) of the m. quadriceps femoris (QF) was determined in 18 individuals. Nine active older subjects (67 ± 7 yrs, 175 ± 10 cm, 81 ± 9 kg, 2 females) were matched with nine young subjects (27 ± 3 yrs, 175 ± 7 cm, 75 ± 15 kg, 2 females) for height, weight, and gender. QF skeletal muscle CSA was measured with magnetic resonance imaging (MRI) and MVC of the knee extensors was measured using the burst superimposition technique. RESULTS: Subjects' height and weight were not different (p > 0.05). Young subjects had higher MVC (248 ± 52 vs. 195 ± 52 Nm, p < 0.05) and larger QF CSA (78 ± 14 vs. 63 ± 12 cm2, p < 0.05). Central activation (%) as determined by the burst superimposition technique was not different in young vs. old subjects (96 ± 2 vs. 97 ± 3 %, respectively, p > 0.05). Normalized torque was not different between groups (3.2 ± 0.4 vs. 3.0 ± 0.6 Nm/cm2, p > 0.05). CONCLUSIONS: These results suggest that the primary reason for reduced force output with aging is skeletal muscle atrophy. Available muscle that can be voluntarily activated by this sample of older subjects has the same force generating capacity as young muscle. Interventions to increase strength in older adults should focus on increasing muscle size. Supported, in part, by NIH grants HD 39676 and 39479 (GAD)