Micro-expressions are fleeting facial movements lasting just 40-200 milliseconds that are believed to reveal concealed emotions. But can these subtle expressions actually be measured objectively? This study provides the first direct electromyographic (EMG) evidence that micro-expressions are real, quantifiable muscle activations—not just visual artifacts. By placing electrodes on participants' faces while they attempted to suppress genuine emotions, researchers captured the electrical activity of facial muscles during both macro-expressions and micro-expressions. The results show that micro-expressions involve significantly smaller muscle contractions than regular expressions, explaining why they're so hard to detect visually. The findings also reveal that micro-expressions are truly involuntary "leakage"—participants couldn't fully suppress their emotional responses even when trying. This research has important implications for lie detection, clinical assessment, and understanding the fundamental nature of emotional expression.

Jingting Li, Shaoyuan Lu, Yan Wang, Zizhao Dong, Su-Jing Wang, and Xiaolan Fu. 2024. Could Micro-Expressions Be Quantified? Electromyography Gives Affirmative Evidence. IEEE Transactions on Affective Computing, vol. 16, no. 4, 2024. https://doi.org/10.1109/TAFFC.2025.3575127