Older adults underestimate RPE and knee extensor torque as compared with young adults

The purpose of this study was to examine knee extensor muscle recruitment, torque, and perceived exertion between healthy young and old adults.

During the first experimental session, subjects performed 6-s isometric knee extension contractions to intensities ranging from 10% to 90% (10% increments, random order) of three maximal voluntary contractions (MVC), during which RPE were obtained. During the second session, subjects performed 6-s isometric contractions to perceived exertion intensities corresponding to 1, 2, 3, 4, 5, 6, 7, 8, 9, and "maximal" on a modified Borg category-ratio scale, in a random order, to obtain the produced torque. Surface EMG were recorded from the vastus medialis (VM), vastus lateralis (VL), and rectus femoris (RF) muscles.

Perceived exertion was significantly (P < 0.05) greater for young than for old adults across 10%-90% MVC. Significantly (P < 0.05) greater VL and RF muscle EMG than the VM across 10%-90% MVC was observed for the young adults, whereas the old adults demonstrated no significant differences between the muscles. The produced torque across the perceived exertion levels was significantly (P < 0.05) greater in old than that in young adults. VL and RF muscle EMG was significantly greater than the VM muscle across the perceived exertion levels in the young adults. Recruitment of the VM, VL, and RF muscles was not significantly different across the perceived exertion levels in the old adults.

The major findings demonstrated that healthy older adults underestimate voluntary knee extensor torque as compared with young adults, which may be driven by differential patterns of muscle recruitment.