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.