Knee valgus and hip and knee muscle activations during vertical jump

Abstract

Background and aims – The muscular co‑contraction of the quadriceps, hamstrings and hip external rotators plays a crucial role in the dynamic control of joint stability, and so does specifically the frontal plane knee valgus mechanism. The purpose of this study was to describe the relationship between muscle activation and the frontal plane knee angle variation during the vertical jump stance phase. Methods – The muscular activity of rectus anterior, hamstrings and gluteus maximus muscles were recorded along 220 vertical jumps (110 jumps corresponding to each of the lower limbs) performed by 4 executors (two female and two male, mean age 28 years ± 6.4) by means of Surface Electromyography collected at 1000Hz and correlated with frontal plane knee angle variation synchronized video data collected at 25Hz. Results – It was found that there are significant correlations between activation of the rectus muscle in the descending phase of the jump at the right and the left and the tendency to a lower or higher valgus angle respectively. The gender influences the dynamics of the knee, making sure that women have different activation strategies than men. Conclusion – The decrease in hip muscle activation appears to influence the dynamic movements of the knee in the frontal plane, adjusting to the results obtained by other authors. The material used in the data collection, the synchronism between the trigger and the video, and the low number of executants that belonged to the sample, may be limitations to the study that should be taken into account in further studies.

Keywords

• estabilidade de joelho, ativação muscular, valgo, salto vertical