Vertical stiffness and lower limb inter-joint coordination in older versus younger runners.

Older runners (OR) are increasing their participation in races. Aging may impact the adopted running pattern. Hence, the analysis of stiffness and the inter-joint lower limb coordination in the sagittal plane could contribute to investigating this impact. This study aimed to compare the vertical stiffness (Kvert) and the inter-joint lower limb coordination in the sagittal plane between younger runners (YR) and OR. This cross-sectional study recruited 15 YR males and 15 OR males. The pelvis and lower limb motions were assessed while running on a treadmill at self-selected (range OR: 1.94-3.75 m.s-1, YR: 2.08-4.17 m.s-1) and fixed speeds (3.33 m.s-1). Hip-ankle, knee-ankle, and hip-knee coupling angle (CA) and its variability (CAV) were extracted using the vector coding method. Mann-Whitney U tests compared Kvert between groups at each running speed. Watson's U2 tests compared the mean CA between groups in three intervals of the contact phase at each running speed. Statistical Parametric Mapping independent t-test compared the CAV curve between groups at each running speed. OR showed greater Kvert than YR at both speeds. Hip-ankle CA pattern differed between groups during the early stance at both speed conditions. OR showed in-phase, distal dominancy in hip-ankle CA, whereas YR showed anti-phase, proximal dominancy. Knee-ankle CA was distinct only at self-selected speed, in which OR showed in-phase, proximal dominancy, while YR exhibited anti-phase, proximal dominancy. CAV did not differ between groups. The findings showed that OR adopted a stiffer pattern characterized by distinct inter-joint lower limb CA, at early stance, during self-selected and fixed speeds.

Lower limb inter-joint coordination patterns are associated with walking experience in toddlers according to limb and stance periods.

Walking experience is crucial for inter-joint coordination during gait acquisition. Toddlers show asymmetrical lower limb function during early locomotion for transferring body weight (regulatory limb) and steering the direction of walking (impulse limb). This study aimed to investigate the association between coordination patterns and walking experience, and between coordination variability and walking experience according to healthy toddlers' lower limb function and stance periods. Typically developing toddlers (n = 22; 17.27 ± 3.13 months) were distributed into two groups: up to (LWE) and greater than (GWE) three months of walking experience. The lower limbs were classified as regulatory or impulse limb and analyzed during the onset (SO), mid (MS), and late (LS) stance intervals. Hip-ankle, knee-ankle, and hip-knee coupling angle (CA) and its variability (CAV) were assessed. A relationship was found between inter-joint coordination pattern and groups, which was distinct according to stance period and lower limb function: (a) hip-ankle CA: at SO for both limbs, MS for the regulatory limb, and LS for the impulse limb; (b) knee-ankle CA: at SO for both limbs and MS for the regulatory limb; (c) hip-knee CA: at SO for both limbs, at MS for the regulatory limb, and LS for the impulse limb. These findings were linked to differences observed in distal joints between groups, mainly at the ankle during stance onset. The CAV was negatively associated with walking experience only in the regulatory limb in the following variables: hip-ankle at MS, knee-ankle at SO, and hip-knee at LS. Findings showed different functional roles of the lower limbs in dealing with the demands of balance and propulsion during early walking.