Influences of hamstring stiffness and strength on anterior knee joint stability.
BACKGROUND
Excessive anterior tibial translation is a prospective risk factor for anterior cruciate ligament injury, thus factors which limit this motion may reduce injury risk. Stiffness quantifies a muscle's resistance to lengthening, and stiffer hamstrings may resist changes in length induced by anterior tibial translation more effectively.


METHODS
Anterior tibial translation, hamstring strength, and hamstring stiffness were assessed in 30 physically active volunteers. Simple correlations were used to evaluate relationships between stiffness, strength, and anterior tibial translation. Anterior tibial translation data were arranged into high and low groups based on the median value, and hamstring strength and stiffness were compared between these groups via t-tests.


RESULTS
Anterior tibial translation was correlated with hamstring stiffness (r=-0.538; P=0.002), but not with hamstring strength (r=-0.088; P=0.644). Hamstring stiffness and strength were not correlated (r=0.054; P=0.778). Hamstring stiffness was greater in the low anterior tibial translation group (t(28)=2.186; P<0.037; ES=0.36), but hamstring strength did not differ between these groups (t(28)=1.057; P<0.300; ES=0.17).


CONCLUSIONS
Greater hamstring stiffness, but not strength, results in a more stable knee joint evidenced by less anterior tibial translation. These findings suggest that the hamstrings' ability to resist lengthening rather than their overall force production capacity may be an important contributor to anterior cruciate ligament injury risk. As muscle stiffness can be modified acutely and chronically, enhancing hamstring stiffness may be an important addition to anterior cruciate ligament injury prevention programs.
Neuromuscular Research Laboratory, University of North Carolina at Chapel Hill, NC 27599-8700, USA. troyb@email.unc.edu
J Troy
JT
Blackburn
Marc F
MF
Norcross
Darin A
DA
Padua
D000328:Adult; D055119:Elastic Modulus / Q000502:physiology; D005260:Female; D006801:Humans; D007719:Knee Joint / Q000502:physiology*; D008297:Male; D009119:Muscle Contraction / Q000502:physiology*; D053580:Muscle Strength / Q000502:physiology*; D018482:Muscle, Skeletal / Q000502:physiology*; D004856:Postural Balance / Q000502:physiology*; D011187:Posture / Q000502:physiology*; D016059:Range of Motion, Articular / Q000502:physiology*