Manual Muscle Testing (MMT)
The medical term for testing muscle strength is "Manual Muscle Testing" (MMT), which uses the Medical Research Council (MRC) scale—a standardized 0-5 grading system that assesses a muscle's ability to move against gravity and resistance. 1
Core Components of MMT
The Medical Research Council (MRC) scale is the internationally recognized standard for grading muscle strength 1, 2:
- Grade 0: No visible muscle contraction
- Grade 1: Visible muscle contraction without movement
- Grade 2: Movement possible with gravity eliminated
- Grade 3: Movement against gravity but not resistance
- Grade 4: Movement against gravity with some resistance (subnormal)
- Grade 5: Normal strength against full resistance
Clinical Application
For comprehensive assessment, MMT typically evaluates 26 muscle groups bilaterally (proximal, distal, and axial muscles), though a shortened MMT8 version tests 8 key muscle groups on one side 1. Common muscle groups tested include:
- Neck flexion/extension
- Shoulder abduction
- Elbow flexion/extension
- Wrist flexion/extension
- Hip flexion/extension and abduction/adduction
- Knee flexion/extension
- Ankle dorsiflexion and plantar flexion
Alternative Terminology and Methods
Additional objective methods for measuring muscle strength include 3:
- Dynamometry: Handheld or isokinetic devices that provide quantifiable force measurements
- Grip/pinch dynamometry: Specific assessment of hand strength
- Motricity Index: Simplified strength testing at 3 key upper and 3 lower extremity segments
Critical Clinical Considerations
In ICU settings, an MRC sum score <48 for 12 muscle groups (mean <4 per group) defines ICU-acquired weakness 2. However, MMT requires patient cooperation and ability to follow commands, making it unsuitable for unconscious or severely impaired patients.
Handgrip strength dynamometry serves as a practical alternative when full MMT is not feasible, particularly for screening sarcopenia or malnutrition risk 2. Values <10 kg at discharge and <15 kg one month post-discharge correlate with mortality risk 2.
Important Caveats
The MRC scale has limited validity in grade 4 (subnormal but better than gravity), where subjective interpretation varies significantly 4. For tracking individual patients with neuromuscular disorders, objective dynamometry provides superior reliability compared to the MRC scale 4. When using MMT, ensure proper patient positioning, stabilization, and consistent technique to maximize inter-rater reliability 5, 6.