Changes in knee joint angle affect torque steadiness differently in young and older individuals

Area of Science:

• Biomechanics
• Human Physiology
• Gerontology

Background:

• Torque steadiness is crucial for motor control and declines with age.
• Knee joint angle influences muscle activation and performance.
• Understanding age-related changes in torque steadiness is vital for rehabilitation and performance enhancement.

Purpose of the Study:

• To investigate the impact of knee joint angle and age on knee extensor (KE) torque steadiness.
• To examine torque steadiness across different submaximal isometric contraction intensities (20%, 50%, 80% MVIC).
• To explore the relationship between muscle activation (EMG) and torque steadiness in young and older adults.

Main Methods:

• 22 young (24.0 ± 2.6 years) and 22 older (69.4 ± 2.4 years) healthy adults participated.
• Maximal voluntary isometric contractions (MVIC) of KE were measured at 90° and 60° knee flexion.
• Isometric contractions at 20%, 50%, and 80% MVIC were performed to assess torque steadiness, with concurrent surface EMG of vastus lateralis and biceps femoris.

Main Results:

• Age-related impairment in torque steadiness was evident only at 20% MVIC (p < 0.01).
• Knee flexion at 90° resulted in lower steadiness and higher agonist/antagonist activation compared to 60° (p < 0.001).
• Young adults showed reduced steadiness at 90° vs. 60° (p < 0.001), while older adults did not. Muscle activation influenced steadiness only in young participants.

Conclusions:

• Knee joint angle differentially affects torque steadiness in young and older individuals.
• Age-related steadiness impairment is intensity-dependent, appearing only at low contraction forces.
• Muscle activation patterns did not correlate with torque steadiness in older adults, suggesting different control mechanisms.