Hamstrings act in hip extension, knee flexion, hip and knee rotation, as well as in simple stabilization of the pelvis and lumbar spine during movement. In older adults, these functions may be compromised due to age-related changes in both muscle structure and function. Thus, the biomechanical and viscoelastic properties could be altered due to the decrease in muscle fiber size, decrease in collagen content and increase in fibrosis. Associated with these aging-related changes, postural demands such as standing for prolonged periods or maintaining an upright posture, could further exacerbate these changes, leading to increased muscle stiffness and reduced elasticity. Therefore, it is possible that the biomechanical and viscoelastic properties of hamstrings are affected by postural demands, particularly in community-dwelling older adults.

To evaluate and compare changes in the biomechanical and viscoelastic properties of hamstrings at rest and during the orthostatic position.

Descriptive analytical cross-sectional study. Individuals aged 60 years or older, without muscle tone alterations and without conditions affecting functional mobility, were evaluated. Individuals with cardiorespiratory, metabolic, or neurological health conditions without medical follow-up were also excluded. Initially, the individuals answered an evaluation form developed by the researchers. Next, the MyotonPro (Myoton AS, Estonia) was used to assess the passive stiffness, elasticity, relaxation, and creep of the biceps femoris (BF) and semitendinosus (SMT) muscles in prone position (PP) and in the orthostatic posture (OP). Mean values for the left lower limb (LLL) and right lower limb (RLL) were calculated from the values obtained in BF and SMT. Means and standard deviations were used to describe the data and, to compare the different situations between MIE and LID, the Wilcoxon test was used with a significance level of p<0.05.

Seven female participants were evaluated, with a mean age of 65.57(±4.68) years and a mean body mass index of 29.61kg/m²(±5.81). In RLL, the passive stiffness (PP=262.31N/m±38.71; OP=286.71N/m±71.58), elasticity (PP=1.85±0.16; OP=1.63± 0.27), relaxation (PP=23.35ms±4.38; OP=20.71ms±4.95), and creep (PP=1.45±0.26; OP=1.29±0.30) showed a significant difference between groups. In the LLL, only the elasticity (PP=1.85±0.14; OP=1.59±0.29) showed a significant difference.

The findings of this study indicate that maintaining the orthostatic posture would imply an increase in stiffness and a reduction in elasticity, relaxation and creep of the hamstrings, in at least one of the lower limbs.

Understanding the biomechanical and viscoelastic properties of tissues in different postures can help design and optimize training and rehabilitation programs.