Resistance training is accompanied by increases in hip strength and changes in lower extremity biomechanics during running. (2009)

Abstract
BACKGROUND:
Movement and muscle activity of the hip have been shown to affect movement of the lower extremity, and been related to injury. The purpose of this study was to determine if increased hip strength affects lower extremity mechanics during running.

METHODS:
Within subject, repeated measures design. Fifteen healthy women volunteered. Hip abduction and external rotation strength were measured using a hand-held dynamometer. Three-dimensional biomechanical data of the lower extremity were collected during running using a high-speed motion capture system. Measurements were made before, at the mid-point, and after a 6-week strengthening program using closed-chain hip rotation exercises. Joint range of motion (rearfoot eversion, knee abduction, hip adduction, and internal rotation), eversion velocity, eversion angle at heel strike, and peak joint moments (rearfoot inversion, knee abduction, hip abduction, and external rotation) were analyzed using repeated measures analysis of variance (P <or= 0.05). The independent variable was time (pre-, week 3, and week 6). A separate analysis of variance was conducted with the dependent variables of peak hip abduction and external rotation strength.

FINDINGS:
Hip abduction (P=0.009) and external rotation strength (P<0.0005) increased by 13% and 23%, respectively. Eversion range of motion decreased (P=0.05), hip adduction range of motion increased (P=0.05), and a trend of decreased hip internal rotation range of motion (P=0.08) were found. Rearfoot inversion moment (P=0.02) and knee abduction moment (P=0.05) decreased by 57% and 10%, respectively.

INTERPRETATION:
The hip abductors and external rotators were strengthened, leading to an alteration of lower extremity joint loading which may reduce injury risk. These exercises could be used in the rehabilitation, or prevention, of lower extremity injuries.

My comments:

I have been blogging on running related injuries and how much research is showing they are secondary to hip muscle weakness causing increased stress on the knee and ankle by allowing the thigh to adduct (bend inward), internally rotate (thigh twists to midline) causing  abduction to the knee (shin bending outward in relation to the thigh) and the shin externally rotating (twisting outwards in relation to the thigh).  This puts excess force on the knee, the tibia (primary shin bone) and drives the foot flat, stressing the posterior tibial tendon and plantar fascia among other things.  In other words it is a cornucopia of stress throughout the entire leg and foot to run, particularly for women, if their hip muscles are not strong enough to stabilize the leg in relation to the torso.

So these researchers came up with an progressive resistance exercise program (3 exercises) working on hip abduction, internal and external rotation all performed while standing with a cable machine, attaching the cable to the side of the hip with a belt. And as stated in the abstract the exercise program worked well, increased hip strength which then decreased hip internal rotation, knee abduction, and rearfoot eversion all decreasing while running.  Hip adduction for some reason increased slightly, which the researchers were unable to account for, but 3 out of 4 biomechanical measures being positive is pretty good for a 6 week intervention.