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Leg muscle strength and neuromuscular control and valgus loading of the knee
Author(s):
Ryman Augustsson Sofia (Sweden)
,
Ryman Augustsson Sofia (Sweden)
Affiliations:
Tranberg R.
,
Tranberg R.
Affiliations:
Zügner R.
,
Zügner R.
Affiliations:
Augustsson J.
Augustsson J.
Affiliations:
ESSKA Academy. Ryman Augustsson S. May 9, 2018; 209301; P02-765
Dr. Sofia Ryman Augustsson
Dr. Sofia Ryman Augustsson
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Abstract
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Objectives: The aim of this study was to 1) investigate which drop jump technique, "countermovement" or "bounce" drop jump, result in the highest knee valgus angles and 2) to identify whether leg muscle strength is a predictive factor for neuromuscular control and valgus loading of the knee during vertical drop jump performance in women.

Methods: Eighteen young female subjects (age 23 ± 3 years, weight 63 ± 7 kg; height 169 ± 7 cm, knee extensor muscle strength 510 ±137 Nm) performed an isometric knee-extension test for leg muscle strength determination and different hop tests for biomechanical analysis of neuromuscular control of the knee: a 1) "bounce jump" with a wide foot stance (BJ), and as a deep "countermovement jump", with 2) wide (CMJW) and 3) narrow foot position (CMJN). In addition, 4) a single-leg drop jump was also performed as a bounce jump (SLBJ). The strength test was dichotomized to analyze 'weak' versus 'strong' subjects according to the median (weak vs strong group). In addition, to identify subjects with poor knee control, "poor" was identified as having a knee valgus angle larger than -10° (according to previous normative data). The X2 test was used to assess the association between muscle strength (weak vs strong) and the outcome of poor knee control (yes/no). The independent sample t-test was used to compare means, in absolute knee valgus angles, hip internal rotation and knee abduction moment, between weak and strong subjects.

Results: From the biomechanical analysis, it could be noted that there was a significant difference (p< 0.001) in knee valgus angle between the CMJN (-12.35°) and the BJ (-4.5°) (n=18). Differences in knee valgus between weak and strong subjects appear to be trending toward significance in BJ (p=0.059), CJN (p=0.083) and SLBJ (p=0.085) with greater valgus angle for the weak group. No significant differences were found between the strength groups (weak vs strong) in hip internal rotation or knee abduction moment for any of the jump protocols (p >0.05). There were more subjects with poor knee control in the weak group, compared to the strong group at the BJ test (weak (5/9), strong 1/9, p=0.046) and at the SLB (weak (4/9), strong 0/9, p=0.023).

Conclusions: The findings from the present study indicates that the BJ technique do not seem to be sufficiently challenging when it comes to evaluating valgus loading of the knee and suggests that the deep countermovement, narrow stance drop jump test has better ability to discriminate between subjects concerning knee valgus. In addition, leg muscle strength seems to influence the neuromuscular control of the knee, but more studies are warranted to confirm this.

Keywords:
Drop jump, knee valgus, muscle strength, lower extremity
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