Age-related differences of inter-joint coordination in elderly during squat jumping

Background
Explosive movement requires that the individual exerts force and power with appropriate magnitude and timing. These coordination aspects have received less attention despite being a basic prerequisite for daily mobility and physical autonomy, especially in older people. Therefore, the purpose of this study is to characterize the effect of age on inter-joint coordination during explosive movement.
Methods
Twenty-one elderly and twenty young participants performed three maximal vertical jumps, while kinematics were recorded throughout each squat jump. Inter-joint coordination and coordination variability were calculated for selected sagittal hip-knee, knee-ankle, and hip-ankle joint couplings using the continuous relative phase method.
Results
The young participants produced significantly greater jump height performance (0.36 ± 0.07 m vs. 0.12 ± 0.04 m, p < 0.001). The mean absolute continuous relative phase for ankle-knee and knee-hip joint couplings were significantly greater for the elderly in comparison to the young group (p < 0.01 for the both). No significant differences between senior and young participants in the mean absolute continuous relative phase for ankle-hip joint couplings (p = 0.25) was observed. However, there was significantly more variability in inter-joint coordination in the elderly marked by greater continuous relative phase variabilities in ankle-knee, ankle-hip and knee-hip joint couplings (p < 0.001) than those observed in young adults.
Conclusion
In this study, seniors demonstrated proximodistal inter-joint coordination but with different delays in the pattern of inter-joint coordination during squat jumps compared to young adults. In addition, a higher continuous relative phase variability in the elderly may be needed to improve stability or compensate for strength deficits in jump achievement.