The data consist of morpholgy measures for selected foot muscles and plantar fascia derived from ultrasound images repeatedly collected at two occasions, 1-8 days apart, in older and younger adults using two different ultrasound machines. The package also contains the measurement properties (i.e., ICC and standard error of measurement) and the scripts used to obtain these. The main goal of this study was to investigate the intra-assessor reliability and measurement error of ultrasound measures for the morphology of selected foot muscles and the plantar fascia in older adults using a tablet-based ultrasound machine. The secondary aim was to compare the measurement error between older and younger adults and between two different ultrasound machines.

Additional documentation and metadata can be found in the file "STIFF_I_Data Report.pdf". Method: Ultrasound images of selected foot muscles and the plantar fascia were collected by a single trained novice operator in younger and older adults on two separate occasions, 1-8 days apart, using a tablet-based device and a mainframe system. Cross-sectional area and/or thickness for 10 tissues were defined afterwards. The intra-assessor reliability and standard error of measurement for these morphology measures were assessed by analysis of variance. The error variance was statistically compared across age groups and machines. Universe: The sample consisted of mobile older adults (≥65 years) and younger adults (18-45 years) recruited in the region of Eindhoven, The Netherlands. Volunteers had to be free of any known condition or disease affecting foot muscles and had to be able to ambulate ten meter without using a walking aid in order to represent a mobile population. Volunteers were excluded from study participation if they reported bilateral musculoskeletal injuries or bilateral symptoms distal to the knee (i.e., current musculoskeletal pain or overuse symptoms, orthopedic surgery or acute injury within the past 5 years, amputation) or if mobility or lower extremity motor function was likely to be affected by medical conditions (i.e., neurological condition, systemic disease, cardiovascular or pulmonary disease).