## 3 Results
### Characteristics of the Study Group
The mean rSO\({}_{2}\) value from the tibialis anterior was 69.94 \(\pm\) 7.96, being significantly higher compared to all other ROIs determined in the lower limb (ankle joint, biceps femoris, popliteal fossa, gastrocnemius, Achilles tendon, plantar fascia), both in the entire study group and after dividing into the younger and older groups. The mean rSO\({}_{2}\) value from the ankle joint was low, averaging 50 \(\pm\) 13.38, being significantly lower than the rSO\({}_{2}\) value from the biceps femoris, popliteal fossa, gastrocnemius and plantar fascia, and higher only than that of the Achilles tendon. The mean rSO\({}_{2}\) value from the biceps femoris was 63.98 \(\pm\) 8.18 and was significantly higher than the values from the popliteal fossa, Achilles tendon and plantar fascia in the entire study group. For the separately analyzed younger group, the average rSO\({}_{2}\) value from the biceps femoris was significantly higher than the rSO\({}_{2}\) value from the Achilles tendon and plantar fascia. In the older group, rSO\({}_{2}\) from the biceps femoris was significantly higher than the rSO\({}_{2}\) value from the popliteal fossa and Achilles tendon. The mean rSO\({}_{2}\) value from the popliteal fossa was 61.09 \(\pm\) 9.56 and was significantly lower than the rSO\({}_{2}\) value from the gastrocnemius in the entire study group and in the older group and significantly higher compared to the rSO\({}_{2}\) value from the Achilles tendon for the entire study group and after division into the younger and older groups. Additionally, the rSO\({}_{2}\) value from the popliteal fossa was significantly higher than the rSO\({}_{2}\) value from the plantar fascia in the younger group. The mean rSO\({}_{2}\) value from gastrocnemius was 64.8 \(\pm\) 9.79, from plantar fascia 59.56 \(\pm\) 11.73 and Achilles tendon only 40.34 \(\pm\) 18.74. The mean value of rSO\({}_{2}\) from the gastrocnemius was higher than rSO\({}_{2}\) from the Achilles tendon for all groups (younger and older groups) and higher than rSO\({}_{2}\) from the plantar fascia in the entire tested group and the younger group. The rSO\({}_{2}\) value from the Achilles tendon was significantly lower than the rSO\({}_{2}\) from the plantar fascia in all analyzed groups. A detailed analysis of the Gini index values revealed that the average rSO\({}_{2}\) values from individual regions, assessed in the entire study group as well as separately for the younger and older groups, exhibited a fairly even distribution/concentration of data (Gini index \(<\) 0.3). Only the mean rSO\({}_{2}\) values recorded from the Achilles tendon in the younger group had a higher Gini coefficient value (0.338), indicating a moderate distribution/concentration of the data collected in this area (Table 3). The results of the correlation analysis of rSO\({}_{2}\) values from the analyzed ROIs with selected anthropometric characteristics and age are shown in Table 6. There was a significant relationship between the decrease in rSO\({}_{2}\) value with the age of the subjects in the following ROIs: forehead, middle neck, trapezius, C-Th, Th-L and femoral triangle, and between an increase in the rSO\({}_{2}\) value from the ankle joint and Achilles tendon and the age of the subjects (\(p<0.01\); \(p<0.001\)). The study showed a significant negative correlation between the values of adiposity indices (BMI, %PBF) and fat mass content (WBSAT, FM) and rSO\({}_{2}\) values for most of the analyzed ROIs (\(p<0.05\), \(p<0.01\), \(p<0.001\)). Except for the negative correlation of the rSO\({}_{2}\) value with the Achilles tendon, no relationship was found between the rSO\({}_{2}\) value and the LBM content in the analyzed ROIs (\(p<0.01\)).