Effects of Age, Joint Angle, and Test Modality on Strength Production and Functional Outcomes.

This study investigated the impact of age, knee joint angle, and strength testing modality on lower body maximal and rapid strength production and assessed the transferability of these characteristics to mobility-related function. Twenty young (age=21.9 yrs) and eighteen elderly (71.1 yrs) adults performed single-joint and multiple-joint isometric maximal voluntary contractions at three knee angles. Outcome measures included peak torque (PT), rate of torque development (RTD), jump height, power, 10 and 400 m walk, and timed chair stand. Older adults exhibited greater reductions in RTD for the multiple-joint (45%) than for the single-joint mode (18%). The 10 m walk was best predicted by multiple-joint RTD at 90°, the 400 m walk by jump height, and the chair stand by single-joint PT at 20°. Single-joint strength tests may underestimate age-related rapid strength impairments, likely due to requirements to exert muscular force in excess of one's body mass in an upright position.

The Influence of Age, Joint Angle, and Muscle Group on Strength Production Characteristics at the Knee Joint.

The current understanding of age-related declines in muscle strength capacities is largely based upon strength testing at joint angles of optimal performance, but many activities of daily living involve force generation at muscle lengths/angles outside of optimal force. This study investigated the influence of age, joint angle, and muscle group (knee extensors and flexors) on maximal and rapid strength characteristics. Young (n = 21; age = 22.1 years) and older (23; 72.6 years) adults performed maximal voluntary contractions for the knee extensors and flexors at 20°, 60°, and 90° joint angles. Peak torque (PT) and rate of torque development (RTD) were calculated. An age, angle, and muscle interaction was found for PT, revealing differences for the knee flexors at all three joint angles for the older adults, whereas the young adults were similar between the 20° and 60° angles. The later RTD variable showed an age and muscle group interaction, whereas no interactions were found for early RTD. The angle of strength testing for maximal strength (PT) of the knee flexors showed dissimilar changes in strength characteristics for young versus older adults across joint angles. For later RTD variables, the testing angle was a more prominent factor for the knee extensors, but less so for the flexors.

Echo Intensity Versus Muscle Function Correlations in Older Adults are Influenced by Subcutaneous Fat Thickness.

Recently, an equation that allows investigators to correct echo intensity for subcutaneous fat was developed. We evaluated correlations between uncorrected and corrected echo intensity versus measures of lower-extremity function. Twenty-three older adults (11 men, 12 women; mean age = 72 y) participated. B-Mode ultrasonography was used to quantify rectus femoris echo intensity and subcutaneous fat thickness. Knee extensor isometric peak torque and rate of torque development at 200 ms (RTD200) were determined (joint angle = 90°). Fast gait speed was evaluated at 10- and 400-m distances. Partial correlations between normalized peak torque, RTD200 and 10- and 400-m gait speed versus uncorrected echo intensity were weak and insignificant. Correction for subcutaneous fat strengthened the correlations (peak torque r = -0.500, RTD200 r= -0.425, 10-m r = -0.409, 400-m r = -0.410). Correcting echo intensity values for subcutaneous fat strengthened the associations with lower-extremity muscle function in older adults.