The study, led by Nestor-Julian Zarate-Herran and colleagues at the Universidad de Caldas and the Hospital Departamental Santa Sofía in Manizales, is significant because muscle wasting in older ICU patients has long been recognized as a driver of poor outcomes, yet it has remained frustratingly difficult to measure. The gold standard techniques for quantifying muscle mass, including magnetic resonance imaging, computed tomography, and dual-energy X-ray absorptiometry, are impractical in intensive care settings. They are expensive, often require transporting unstable patients, and in some cases expose them to radiation. Ultrasound, by contrast, is portable, safe, inexpensive, and can be performed at the bedside by a trained operator in minutes, making it an ideal candidate for routine monitoring of a problem that has historically gone unquantified until patients leave the unit weakened and disabled.

Between December 2024 and May 2025, the team enrolled fifty patients admitted to the ICU of a tertiary hospital in the Colombian Andes, all aged sixty or older. The median age was 72.5 years, sixty percent were male, and the cohort carried a heavy burden of chronic disease: seventy-four percent had systemic arterial hypertension, thirty-eight percent had dyslipidemia, and nearly a quarter had diabetes mellitus or hypothyroidism. The median APACHE II score at admission was 19, indicating severe critical illness, and the median SOFA score was 6. Most patients had been functionally independent before admission, with a median Barthel index of 100, meaning the muscle loss observed was occurring in people who had been walking and caring for themselves just days earlier.

The ultrasonographic protocol was meticulous. Using a high-frequency linear transducer in musculoskeletal mode, a critical care specialist with more than five years of ultrasound experience measured three distinct parameters in each patient within forty-eight hours of admission and again on day seven. The first was the cross-sectional area of the rectus femoris, the large superficial muscle at the front of the thigh, measured at the distal third of the right lower limb using the ultrasound software’s planimetry function. The second was quadriceps muscle layer thickness, measured at two standardized points on both legs, defined as the distance between the femoral cortex and the inferior border of the rectus femoris fascia. The third was the pennation angle, the angle between muscle fascicles and the deep aponeurosis, captured by tilting the transducer fifteen to thirty degrees laterally. To exclude patients whose subcutaneous fluid accumulation might distort the images, the team applied a FLUID Protocol score and excluded anyone scoring two or higher at either time point.

The results were stark. The rectus femoris cross-sectional area fell from a median of 2.525 square centimeters at admission to 2.115 square centimeters on day seven, a reduction of 16.2 percent. Right quadriceps thickness decreased by 14.6 percent, from 2.012 to 1.719 centimeters, while left quadriceps thickness fell even further, by 20.2 percent, from 2.049 to 1.635 centimeters. The pennation angle dropped by 18.2 percent, from 7.664 to 6.270 degrees. All changes were statistically significant at p less than 0.001, and robust statistical methods, including Yuen’s t-test with Algina-Keselman-Penfield effect size estimators, confirmed large effect sizes ranging from 0.77 to 0.93. These reductions exceed accepted thresholds of measurement variability, meaning the team was observing genuine biological loss rather than statistical noise or operator error.

The pennation angle finding deserves particular attention because it captures something beyond simple shrinkage. Pennation angle reflects the orientation of muscle fibers within the muscle architecture, and its reduction suggests qualitative remodeling, potentially impairing the muscle’s capacity to generate force. Prior research has documented that greater reductions in pennation angle are associated with accelerated thickness loss and the development of intensive care unit-acquired weakness, a debilitating condition that prolongs ventilation and delays recovery. The Colombian team’s data now add a darker dimension: in their multivariate models, ICU mortality was strongly associated with reduced pennation angle, with deceased patients showing significantly lower values. The authors suggest that frailty may be the pathophysiological link, though they did not formally assess frailty in this cohort, leaving that hypothesis for future confirmation.

Who lost muscle fastest? The multivariate analysis, performed using median quantile regression selected for its robustness to outliers and heteroscedasticity, identified a constellation of risk factors. Advanced age was independently associated with greater loss in both cross-sectional area and distal thickness. Female sex emerged as a particularly noteworthy predictor: women lost more muscle than men, with a median rectus femoris cross-sectional area reduction of 18.5 percent compared with 14.1 percent in men, a difference the authors attribute to lower baseline muscle mass, hormonal influences, or differential metabolic responses to critical illness stress. Higher SOFA scores, reflecting greater acute physiological derangement, correlated with greater thickness loss, while a lower premorbid Barthel index, indicating worse functional status before admission, was independently associated with accelerated wasting. Intriguingly, the use of hypoglycemic agents, including insulin, was consistently linked to greater muscle loss across multiple parameters, and statin therapy was associated with reduced distal thickness, raising questions about pharmacological exposures that clinicians rarely consider in this context.

The mortality figures underscore the stakes. Thirty percent of the fifty patients died in the ICU, and the muscle loss itself was entwined with survival. The authors emphasize that the association between ultrasonographic muscle parameters and mortality suggests bedside muscle assessment could serve as a prognostic biomarker, informing decisions about intensity of care, rehabilitation planning, and communication with families. This is a population in which low skeletal muscle mass reaches a prevalence of fifty-one percent in prior meta-analyses, and in which low muscle mass increases mortality risk with a combined odds ratio of 2.35. The pathophysiology is well understood in principle: critical illness triggers systemic inflammation, insulin resistance, immobilization, cytokine action, and impaired nutritional support, all of which promote protein catabolism. During the first two weeks of ICU stay, patients can lose ten to twenty percent of total body protein, with daily reductions of up to three percent, and the muscle catabolism serves the acute demands of coagulation factor synthesis, immune cell energy supply, and gluconeogenesis, essentially cannibalizing the body’s largest protein reservoir to fuel survival.

The study has limitations the authors acknowledge candidly. It was conducted at a single center with a modest sample size, which may restrict generalizability and statistical power. Muscle function was not assessed, so the functional significance of the morphological changes remains inferential. Nutritional intake and physical therapy interventions were not systematically quantified, and no validated frailty instrument was administered, a gap the authors attribute to limited familiarity with frailty tools among critical care specialists and the practical constraints of administering them in the ICU. They argue this underscores the need for interdisciplinary approaches that bring geriatric expertise into the intensive care evaluation of older adults. The seven-day follow-up, while well suited to capturing early changes, cannot characterize the full trajectory of recovery or longer-term outcomes.

Nevertheless, the clinical implications are immediate and actionable. The early onset and substantial magnitude of muscle loss support prompt identification and intervention within the first days of ICU admission, when the catabolic storm is at its peak. Bedside ultrasonography offers a practical, reproducible method for real-time monitoring, and the identification of high-risk patients, including the very old, women, those with severe illness, those with reduced baseline function, and those receiving hypoglycemic agents, enables targeted preventive strategies such as optimized nutrition, early mobilization, and individualized rehabilitation. The authors call for larger multicenter studies to validate these findings and to determine whether interventions aimed at attenuating muscle loss translate into meaningful improvements in survival and functional recovery. For now, the message for intensivists is clear: the muscle that older patients lose in their first week in the ICU is measurable, rapid, and tied to whether they leave the unit alive, and the tool needed to see it is already sitting on the ward cart.

Subject of Research: Ultrasonographic evaluation of quadriceps femoris muscle mass in critically ill patients aged 60 years and older: a prospective observational study

Article Title: Ultrasonographic evaluation of quadriceps femoris muscle mass in critically ill patients aged 60 years and older: a prospective observational study

Article References: Ultrasonographic evaluation of quadriceps femoris muscle mass in critically ill patients aged 60 years and older: a prospective observational study. (n.d.). https://doi.org/10.3389/fragi.2026.1792585

Image Credits: AI Generated

DOI: 10.3389/fragi.2026.1792585

Keywords: Ultrasonographic, evaluation, quadriceps, femoris, muscle, mass, critically, patients, aged, years, older, prospective