Precise limb-speed afference reveals rhythmogenic drive modality and declines with age

Area of Science:

• Neuroscience
• Biomechanics
• Human Motor Control

Background:

• Human locomotion relies on coordinated limb movements, which deteriorate with age, leading to frailty.
• Age-related decline in motor control affects independence and increases fall risk.

Purpose of the Study:

• To investigate the nervous system's ability to detect subtle inter-limb speed variations.
• To determine if limb speed sensing is load-independent and how it changes across the human lifespan.

Main Methods:

• A two-alternative forced-choice task was employed on a split-belt treadmill.
• Participants detected minute differences in treadmill belt speeds.
• Whole-body load was manipulated to assess its effect on speed discrimination.

Main Results:

• Healthy young adults detected speed differences as low as 1.3%.
• Varying body load did not affect the detection thresholds, suggesting speed computation.
• Limb speed discrimination followed a U-shaped curve across ages 6-80, with lowest thresholds in young adults and increased thresholds in children and older adults.

Conclusions:

• The human nervous system possesses high acuity in sensing limb speed.
• Age-related decline in limb speed discrimination impacts motor control and mobility.
• Limb speed sensing is a potential biomarker for age-related mobility decline and a target for rehabilitation.