# Respiratory and limb muscles’ ability to repeatedly generate maximal isometric strength in patients with intensive care unit-acquired weakness: an observational study

## TL;DR

This study found that ICU patients with muscle weakness show different strength recovery patterns in leg and breathing muscles during repeated efforts.

## Contribution

The study reveals distinct time course evolutions of maximal strength in respiratory and limb muscles in ICU-acquired weakness patients.

## Key findings

- Quadriceps muscle force decreased significantly during repeated maximal isometric contractions.
- Inspiratory muscles showed stable strength during repeated efforts.
- Quadriceps strength improved after one-minute recovery, while inspiratory muscle strength did not.

## Abstract

Intensive care unit-acquired weakness (ICU-Aw) is a prevalent complication in critically ill patients, affecting both limb and respiratory muscles, individually or concurrently. The precise mechanisms by which muscle weakness influences the distinct functional roles of each muscle group remain to be fully elucidated. The objective of this study was to compare the time course evolution of inspiratory and quadriceps muscles strength during repeated maximal isometric contractions in patients with limb muscles and inspiratory muscles weakness.

A single-center, observational study was conducted in critically ill patients after extubation, presenting with both inspiratory and limb muscle weakness (defined as maximal inspiratory pressure (Pimax) < 30 cmH2O and an MRC score < 48). The patients’ ability to sustain maximal voluntary effort was measured using electronic manometers and dynamometers, with repeated efforts performed 10 times. Following each measurement, a 10-second rest period was observed, and strength measurements were repeated to evaluate recovery.

A total of 20 patients (90% male, mean age 61 ± 10 years, SAPS II score 28 ± 17) were included. The mean first maximal inspiratory pressure was 32.6 ± 17 cmH2O, and the mean first quadriceps maximal force was 135 ± 90 Newtons (N). Investigation revealed a decline in quadriceps muscle force of -15.45 ± 28.61 N (95% CI: -28.84 to -2.05) while inspiratory muscles demonstrated stability (mean difference: 1.75 ± 7.57 cmH2O (95% CI: -1.80 to 5.30)). A statistically significant interaction between time and muscle group was identified (p = 0.0017), suggesting a different time course evolution of maximal voluntary strength between muscle groups. After a one-minute recovery, significant improvement in quadriceps strength was observed (p = 0.009), while no statistically significant change was detected in inspiratory muscle strength (p = 0.16).

The results of this study indicate potential disparities in the maximum force maintenance capacity between the quadriceps muscles and inspiratory muscles in patients with ICU-acquired weakness.

Registered on ClinicalTrials.gov Identifier NCT05396066.

The online version contains supplementary material available at 10.1186/s12871-025-03008-y.