2.6. Analysis

The MRIs were analyzed using the image analysis software OsiriX (Pixmeo SARL) (Rosset, Spadola, & Ratib, ²⁰⁰⁴). All image analyses were performed by one researcher. The measurement target was GAS, SOL, and PV. The value of each item was represented by mean ± SD.

Using the rate of change, we compared the young, middle‐aged, and elderly people. The rates of change in the blood flow velocity of PV, flexor muscle area, and vein area were calculated by the following equation. The rate of change was based on 0% when ankle joint nonplantar flexion/before exercise. Rate of change in venous blood flow (%) = (blood flow velocity after ankle plantar flexion [cm/s]−blood flow velocity before ankle plantar flexion [cm/s])/ankle plantar flexion previous blood flow velocity (cm/s) × 100.

Rate of change in flexor muscle area/vein area (%) = (flexor muscle area/vein area after ankle plantar flexion [cm/s]−flexor muscle area/vein area before ankle plantar flexion [cm/s])/ankle plantar flexion from previous flexor muscle area/vein area (cm/s) × 100.

To verify the validity of the exercise in this study, we compared the venous blood flow velocity before and after the exercise. After confirming the normality of the data, we selected an appropriate method from the Wilcoxon signed‐rank sum test or the paired t test. The numerical values are shown as the mean ± SD. Then, after the normality and equal variance of the data were confirmed, the age of the subjects was compared by one‐way analysis of variance and Tukey–Kramer honestly significant difference test or Games–Howell test, or Kruskal–Wallis test. Exercise habits were compared using the χ² test. A multiple linear regression was calculated to predict the rate of change in blood flow velocity based on generations (young, middle‐aged, and elderly), posture (supine, sitting, and standing), leg muscle volume, and rate of change in the muscle cross‐sectional area (SOL and GAS). The statistical analysis was conducted using the software SPSS version 25, and the significance level was 5%.

This study was approved by the medical ethics committee of Kanazawa University (approval number 42).