Biomechanical and Nonfunctional Assessment of Physical Capacity in Male ICU Survivors*

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Abstract

Objectives:

ICU admission is associated with decreased physical function for years after discharge. The underlying mechanisms responsible for this muscle function impairment are undescribed. The aim of this study was to describe the biomechanical properties of the quadriceps muscle in ICU survivors 12 months after ICU discharge.

Design:

Case-control study with consecutive inclusion of ICU survivors and age- and sex-matched controls.

Setting:

Patients were treated at a mixed 18-bed ICU at a tertiary care university hospital and tested at a biomechanical university laboratory.

Patients:

We included 16 male ICU patients (Acute Physiology and Chronic Health Evaluation II score 20 ± 7, mean ± SD), who had stayed in the ICU >72 hrs and survived to 12 months and 15 age- and sex-matched controls.

Interventions:

None.

Measurements and Main Results:

An extensive battery of biomechanical tests, including maximum, fast, and endurance contractions, was administered during isometric knee extensions while simultaneously recording surface electromyography (quadriceps and hamstrings). Compared to controls, ICU survivors had reduced maximal voluntary torque (22%, 179 ± 64 Nm vs. 230 ± 57 Nm, p = 0.03), absolute rate of force development (50%, 868 ± 372 Nm/sec vs. 1739 ± 470 Nm/sec, p < 0.001) and relative rate of force development (32%, 512 ± 260% maximum voluntary contraction/sec vs. 754 ± 189% maximum voluntary contraction/sec, p < 0.01), and endurance time (40%, 136 ± 84 sec vs. 226 ± 111 sec, p < 0.02). Rate of force development, but not maximal voluntary torque, was significantly reduced after adjusting for muscle mass. Electromyography data indicated no impairment of motor activation strategy or central motor drive. Also, no difference in reaction time was found between patients and controls.

Conclusions:

ICU survivors had reduced rate of force development and muscular endurance 1 yr after ICU discharge. Our data indicate that the functional deficits experienced by ICU survivors originate in muscle tissue rather than the nervous system. Also, increased attention to velocity-orientated exercise during rehabilitation of ICU patients may have the potential to better physical outcome after critical illness.

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