Differences in Maximum Voluntary Excitation Between Isometric and Dynamic Contractions are Age-Dependent

Area of Science:

• Biomechanics and Motor Control
• Human Physiology
• Gerontology

Background:

• Accurate measurement of maximum voluntary excitation (MVE) is crucial for interpreting electromyography (EMG) data.
• Previous research suggests MVE may be harder to achieve in older adults compared to younger individuals.
• The choice of contraction type for normalization can influence EMG signal analysis.

Purpose of the Study:

• To investigate age-dependent differences in MVE obtained from maximum voluntary isometric contraction (MVIC) and (sub-)maximum voluntary dynamic contraction [(s-)MVDC].
• To examine the effect of normalizing EMG signals to MVE from different contraction types on inter-participant variance and signal overshoot (exceeding 100%).

Main Methods:

• Recorded MVIC, s-MVDC, and MVDC in 10 young women.
• Recorded MVIC and s-MVDC in 19 older women.
• Analyzed EMG amplitudes and normalized signals across different contraction modes and age groups.

Main Results:

• A significant age × contraction mode interaction was observed for the vastus lateralis muscle (P = .04).
• Young women achieved higher MVE with MVDC for vastus lateralis and rectus femoris compared to MVIC (P < .05).
• No significant differences in MVE were found across contraction modes in older women (P > .05).
• Normalization to dynamic contractions reduced EMG amplitude variance and the proportion of signals exceeding 100% in young women.

Conclusions:

• Differences in MVE across contraction modes are age-dependent, with dynamic contractions potentially yielding higher MVE in younger populations.
• Normalization strategies impact EMG data variability and signal integrity.
• Caution is advised when comparing normalized EMG signals across age groups; dynamic contractions may be preferable for normalization.