Low-Frequency Oscillations and Force Control Capabilities as a Function of Force Level in Older Women

Abstract

Force variability is potentially related to altered low-frequency oscillations in motor outputs. This study examines the contributions of low-frequency oscillations in force to altered force control performances from lower to higher targeted force levels in older women. Fourteen older women executed unilateral hand-grip force control tasks at 10% and 40% of maximum voluntary contraction (MVC). Force control performances were estimated by calculating force accuracy (root-mean-square-error), force variability (standard deviation), and force regularity (approximate entropy). We additionally quantified low-frequency oscillations in force using absolute powers across four different frequency bands: (a) 0–0.5 Hz, (b) 0.5–1.0 Hz, (c) 1.0–1.5 Hz, and (d) 1.5–2.0 Hz. The findings reveal that from lower to higher targeted force level older women show greater force error, force variability, and force regularity with increased values of absolute power in force across the four frequency bands. The multiple regression models identified a significant relationship between greater force frequency power below 0.5 Hz and more impairments in force control performances. These findings suggest that force frequency oscillation below 0.5 Hz is a key predictor indicating altered stability of task performances across different targeted force levels in older women.

Aging Impairs Unimanual and Bimanual Hand-Grip Force Control Capabilities

“…For the isometric hand-grip force tasks, a customized isometric force control device (SEED TECH Co., Ltd., Bucheon, Republic of Korea; Figure 1a) was used. Based on previous studies [24,37,38], participants sat 80 cm away from a 54.6 cm LCD monitor and grabbed handles embedded with a force transducer (Micro Load Cell-CZL635-3135, range = 220 lbs., Phidgets Inc., Calgary, AB, Canada) in a comfortable position (i.e., 15 • -20 • of shoulder flexion and 20 • -45 • of elbow flexion; Figure 1b). While performing force control tasks, all force signals were collected at a 200 Hz sampling rate using a 16-bit analog-to-digital converter (A/D; ADS1148 16-bit 2kSPS and a minimum detectable force = 0.0192 N) and amplified using an INA122 with a 5 V excitation voltage (Texas Instruments Inc., Dallas, TX, USA).…”