Impacts and Mechanisms of Age and Muscle Fatigue on Postural Control and Force Control

This study aims to investigate the effects of muscle fatigue on postural control and gait performance in healthy older adults (≥65 years) and young adults (20-40 years). Neuromuscular fatigue has been associated with postural instability, but its influence on gait and potential age-related differences remain unclear. Therefore, this study will compare fatigue-induced changes in motor performance between age groups and examine whether fatigue of the upper and lower extremities produces similar functional effects.

Healthy older adults and young adults will be recruited from the community. Eligible participants must be in good health, able to walk independently, demonstrate normal cognitive function, and provide informed consent. Individuals with neurological, cardiovascular, musculoskeletal, or other conditions that may affect motor performance will be excluded.

A repeated-measures design will be used. The study will involve two laboratory sessions separated by at least one week. Participants will undergo pre-test assessments, a fatiguing exercise protocol, and post-test assessments. Motor outcomes-including maximal voluntary isometric contraction, postural control, and gait performance-will be measured before and after the fatiguing exercises. Fatiguing exercises will consist of repeated cycles of maximal contractions with rest periods, while heart rate and perceived exertion are monitored to ensure safety. The protocol will terminate if exertion reaches a predefined threshold or heart rate exceeds the age-predicted maximum.

Surface electromyography and electrical stimulation will be used to assess neuromuscular function. Postural control will be evaluated using a force plate under multiple standing conditions, and gait parameters will be measured while participants walk at comfortable and fast speeds. Statistical analyses will use repeated-measures mixed-model ANOVAs to examine the effects of age group and fatigue on motor outcomes.

Inclusion criteria

• 20 to 40 years (young), and 60-85 years (old)
• walk independently
• able to follow commands (Mini Mental Status Exam (MMSE) scores greater than 21
• able and willing to provide informed consent.

Exclusion criteria

• pregnancy
• neurologic, psychiatric, cardiac, vascular, pulmonary, musculoskeletal, immune, integumentary disease or disorder which might influence this study
• any current loss of sensation in the arms, wrists, hands, fingers, hips, knees, ankles or toes
• any pain at the time of testing
• any restriction in range of motion of lower extremity.