A Comparison of Techniques to Determine Active Motor Threshold for Quadriceps Transcranial Magnetic Stimulation Research
The determination of active motor threshold (AMT) is a critical step in transcranial magnetic stimulation (TMS) research protocols involving voluntary muscle contractions. As AMT is frequently determined using an absolute electromyographic (EMG) threshold (e.g., 200 microvolts peak-to-peak amplitude), wide variation in EMG recordings across participants has given reason to consider a relative threshold (e.g., = 2x background EMG) for AMT determination. However, these approaches have never been systemically compared. PURPOSE: We sought to compare the AMT values derived from absolute and relative criteria commonly used to determine AMT in the quadriceps muscles, and assess the test-retest reliability of each approach (absolute = 200 microvolts vs. relative = 2x background EMG). METHODS: Eighteen young adults (9 males and 9 females; mean +/- SD age = 23 +/- 2 years) visited the research laboratory on two occasions. All testing was conducted on the dominant limb. During each laboratory vis