Muscle matters: Transforming the care of intensive care unit acquired sarcopenia and myosteatosis

Table 3 Functional tests and neuromuscular assessments in the intensive care unit

Assessment method	Description and parameters	Advantages	Limitations	Clinical utility
MRC sum score (manual muscle testing)	Clinician-performed manual strength exam of 6 muscle groups bilaterally (scored 0–5 each; max score 60). ICU-AW defined by MRC < 48	No equipment needed; bedside clinical exam. Standardized scoring system with prognostic significance. Validated for diagnosing ICU-AW when patient is awake	Feasible only in conscious, cooperative patients (often < 50% of ICU patients early on). Subjective effort can vary; inter-rater variability in scoring. Cannot detect subclinical weakness in sedated patients	Primary diagnostic tool for ICU-AW once patient can participate. Identifies patients requiring rehab interventions; a score < 48 correlates with difficulty in weaning and prolonged ICU stay
Handgrip dynamometry	Patient squeezes a handheld dynamometer to measure grip strength (kg force). Typically, the best of 2-3 attempts is recorded for each hand	Objective, numeric measure of strength. Quick (< 1 minute) and reproducible. Can be done in bed; minimal patient movement required (just hand squeeze)	Requires patient arousal and minimal cognitive function. Assesses primarily forearm/hand strength (may not reflect leg weakness). Grip may be impaired by local hand issues (arthritis, injury)	Useful surrogate for global strength; prognostic indicator (low grip strength on ICU admission associated with higher mortality). Can track strength improvements over ICU stay and guide nutrition/physio needs
Electrophysiological studies (nerve conduction studies and EMG)	Nerve conduction studies: Stimulate motor nerves and record muscle action potentials; EMG: Needle electrodes measure muscle electrical activity at rest and contraction. Detects CIP or CIM	Does not require patient cooperation or movement. Can diagnose the presence of neuropathy vs myopathy, aiding etiologic understanding. Highly sensitive to electrical changes in muscle/nerve function	Specialized personnel and equipment needed (not available in all ICUs). Time-consuming and somewhat uncomfortable (needle EMG). Edema and electrical noise in ICU can interfere with signals. Primarily diagnostic, not for routine monitoring of recovery	Confirms ICU-AW and differentiates CIP vs CIM in patients with unexplained or severe weakness. Often employed if weakness is profound or prolonged and other causes need exclusion. Helps prognostication (e.g., pure CIP has different recovery profile than CIM)
Functional mobility tests (e.g., sit-to-stand, 6-minute walk, etc.)	Performance-based tests of muscle function and endurance administered when patient is ambulatory. 5 × sit-to-stand: Time to rise from chair 5 times; 6-minute walk test: Distance walked in 6 minutes, etc.	Directly assesses integrated muscle function, balance, and endurance. Relates to real-world functional outcomes and independence. Useful for discharge planning and rehab goals	Not applicable during acute ICU phase (requires patient to be awake, off most support, and able to stand/walk). Influenced by cardiopulmonary fitness and motivation in addition to muscle strength. Safety concerns if patient is frail (risk of falls)	Employed at ICU discharge or step-down to evaluate recovery. For example, a very low 5 × sit-to-stand performance at ICU discharge indicates ongoing weakness and high rehab needs. These tests connect ICU-acquired muscle deficits to patient-centered outcomes like mobility and quality of life after critical illness

CIM: Critical illness myopathy; CIP: Critical illness polyneuropathy; EMG: Electromyography; ICU: Intensive care unit; ICU-AW: Intensive care unit acquired weakness; MRC: Medical research council.