Electromyogram and force patterns in variably timed manual muscle testing of the middle deltoid muscle

The objective of the study was to compare force curves and surface electromyogram from examiners and subjects during manual muscle testing with 3 examiner-identified variants of manual muscle testing (MMT)-examiner-started (ESMMT), patient-started (PSMMT), and undifferentiated/near-simultaneous (NSMMT).

Forty-two volunteer applied kinesiologist doctors tested 36 volunteer students, doctors, and spouses at a professional conference. Start-time difference between examiner and subject muscle contraction, peak force, time of peak force and duration of force was measured. Force and surface electromyogram from examiner and subject were recorded simultaneously during MMT of the middle deltoid muscle for each style of testing used in practice.

The congruence between examiner label and timing was as follows: ESMMT, 39%; PSMMT 61%; and NSMMT 28% within 50 milliseconds of simultaneous. Mean subject/examiner start-time difference differed significantly between PSMMT (-0.116 seconds) and both ESMMT (-0.018 seconds) and NSMMT (-0.0053 seconds). No clear cutoff between styles was evident. Peak force ranged from 0.548 to 23.615 lb (mean, 8.806 lb; SD, 4.543 lb), and all styles were significantly different. Duration of force ranged from 0.325 to 3.490 seconds (mean, 1.338 seconds; SD, 0.576 seconds), with NSMMT significantly shorter than ESMMT or PSMMT. The shape of force curves did not differ between styles of muscle testing, but differed between facilitated vs inhibited tests.

In this group of doctors, neither start-time difference nor the shape of force curves distinguished styles of MMT. Differences in peak force and test duration may account for differences in outcomes when examiners purposely vary their muscle testing style.