Healthy peripheral nerves have the ability to adapt to increased neurodynamic tension generated by body movements. However, this adaptive capacity is reduced in pathological conditions. Although peripheral neuropathies are common in older adults, there is an absence of knowledge about the behavior of peripheral nerves in asymptomatic older adults.

To compare the behavior of the sciatic and median nerves to neurodynamic tension in older adults and asymptomatic adults.

Sixty-eight asymptomatic participants (34 older adults and 34 sex-matched adults) were evaluated by ultrasound imaging of the sciatic and median nerves, in two positions with different degrees of neurodynamic tension for each nerve. For the median nerve, the first position kept the participant's right upper limb at 90 degrees of shoulder abduction and external rotation, elbow flexion at 90 degrees, forearm supination with the palm facing the participant, and the wrist and metacarpophalangeal joint in a neutral position. In position 2, the second examiner passively extended the elbow, wrist, and metacarpophalangeal joint until the perception of resistance limits the range of motion. For the sciatic nerve, the hip flexion was maintained at 60° in both positions. In Position 1, the knee was flexed at 90 degrees, and the tibiofibular joint remained neutral. In position 2, the knee was passively extended, and the tibiofibular joint dorsiflexed. The cross-sectional area and the nerve-skin distance of each nerve were measured in each position in both groups. The measurements were compared by analysis of variance for repeated measures.

The sample was predominantly composed of females [n = 25, (73.52%)], with a mean age of 30.47 years (6.84) for adults and 70.47 years (5.22) for older adults. The nerve-to-skin distance increased significantly between positions 1 and 2 for the median nerve (F = 54.04; p < 0.001) and between positions 1 and 2 for the sciatic nerve (F = 107.54; p < 0.001), regardless of age group. Similarly, the cross-sectional area of the sciatic nerve was greater in position 1 compared to position 2 for the sciatic nerve (F = 17.27; p < 0.001). No significant interactions were observed between age group and position for any of the variables, indicating that both adults and older adults responded similarly to the increase in neural tension. Moreover, the sciatic nerve was significantly more superficial in older adults than younger adults (t = -3.09; p = 0.018) in position 2.

The sciatic and median nerves responded similarly to increased tension in older adults and adults for the variables: cross-sectional area of the sciatic and median nerves and the nerve-skin distance of the median nerve. However, for the nerve-to-skin distance of the sciatic nerve, it was observed that the nerve was more superficial in older adults.

The neurodynamic response to tension was similar between asymptomatic older and younger adults. Although the sciatic nerve was more superficial in older adults, it is reasonably explained by the body mass index difference and the age-related trend of muscle mass decline.