Perfil funcional y estructural del músculo esquelético en adultos mayores con sarcopenia: comparación con adultos jóvenes mediante fuerza de prensión, isocinesia y ultrasonido

Abstract

Introduction:

Sarcopenia is a geriatric syndrome characterized by the progressive loss of skeletal muscle mass, strength, and function, leading to increased risk of falls, disability, hospitalization, and mortality. According to the revised European Working Group on Sarcopenia in Older People (EWGSOP2), diagnosis prioritizes reduced muscle strength, supported by low muscle mass and poor physical performance. Although handgrip strength is widely used in clinical settings, it may not fully capture impairments in lower-limb function or early muscle deterioration. Complementary tools such as isokinetic dynamometry and ultrasound imaging offer valuable insights into muscular performance and quality.

Objective:

To describe differences in isokinetic strength and power, structural and morphological muscle parameters (texture and echogenicity via ultrasound), lean mass, and handgrip strength between older adults diagnosed with sarcopenia and healthy young adults.

Methods:

A cross-sectional, analytical-comparative study was conducted including two groups: Group 1 (healthy young adults aged 18–35) and Group 2 (older adults aged ≥65). Exclusion criteria included contraindications for testing or incomplete evaluations. Assessments included handgrip strength (Jamar® dynamometer), body composition via dual-energy X-ray absorptiometry (DXA), and isokinetic strength testing of knee extensors at 60°/s and 180°/s in concentric and eccentric modes (Contrex MJ®). Ultrasound imaging (Hitachi Arieta S60®) was performed at the rectus femoris to measure anatomical cross-sectional area (ACSA), thickness, volume, echogenicity, and texture (ImageJ software). Sarcopenia diagnosis followed EWGSOP2 criteria, using two pathways: (A) low handgrip strength + low appendicular lean mass (ALM), and (B) poor performance in the sit-to-stand test (STS ≥12 s) + low ALM. Statistical analysis included parametric/non-parametric tests, effect size (Cohen’s d), and chi-square tests.

Results:

A total of 62 participants were included (Group 1: n=30, 25 women; Group 2: n=32, 17 women). Older adults had significantly lower handgrip strength (35% lower on average) and ALM (p<0.01). Isokinetic analysis revealed significantly reduced peak torque and power in older adults at both testing speeds (p<0.01), with more pronounced differences at 60°/s. Power at 180°/s was markedly reduced, highlighting deficits in rapid force production. The eccentric/concentric (E:C) ratio was higher in older adults, especially at 60°/s, suggesting relative preservation of eccentric strength. Ultrasound analysis showed greater echogenicity and lower homogeneity in older adults, particularly in those with sarcopenia defined by low handgrip strength. The STS-based sarcopenia criterion identified more cases than the grip strength-based criterion, with low diagnostic overlap.

Conclusions:

Aging is associated not only with quantitative muscle loss but also with qualitative and functional deterioration. Power deficits at high contraction speeds may appear earlier than maximal strength loss, indicating the importance of assessing and training rapid and eccentric muscle function in rehabilitation. The relative preservation of eccentric strength suggests therapeutic opportunities for targeted, safe, and effective exercise programs in frail older populations. Integrating isokinetic and ultrasound assessments enhances diagnostic precision and supports individualized rehabilitation strategies addressing both muscle quantity and quality.