Combining isometric knee extension exercises with hip adduction or abduction does not increase quadriceps EMG activity.

OBJECTIVE: To determine if the combined isometric contractions of knee extension/hip adduction and knee extension/hip abduction will elicit a different quadriceps and gluteus medius electromyographic (EMG) pattern as compared to isometric contraction of a uniplanar knee extension exercise. METHODS: Eight healthy young adult volunteers without history of knee or quadriceps injury participated. Surface EMG data were collected from the vastus medialis oblique (VMO), vastus lateralis (VL), and gluteus medius (Gmed) muscles of the dominant leg of each subject during three single leg, weight bearing, isometric exercises (uniplanar knee extension, knee extension/hip adduction, knee extension/hip abduction). All exercises were performed at a position of 60 degrees knee flexion. Three trials lasting 5 s each were performed for each of the three exercises. EMG data from each muscle were integrated and the maximum root mean square activity over a 0.5 s window for each trial was averaged. Analyses of variance were performed with exercise (straight extension, extension/adduction, extension/abduction) as the independent variable and VMO, VL, and Gmed activity and VMO:VL ratio as dependent variables. RESULTS: A significant main effect for exercise was found for the VMO (p = 0.006) and VL (p = 0.02), but not the Gmed (p = 0.25) or the VMO:VL ratio (p = 0.13). For the VMO and VL, the uniplanar knee extension task produced significantly more EMG activity than the extension/adduction or extension/abduction tasks. CONCLUSIONS: Uniplanar knee extension exercises may be more appropriate than combining isometric knee extension exercises with hip adduction or abduction when eliciting maximal VMO and VL contractions.

Activation of the VMO and VL during dynamic mini-squat exercises with and without isometric hip adduction.

OBJECTIVE: the purpose of this study was to compare vastus medialis obliquus (VMO) and vastus lateralis (VL) activity while performing a mini-squat with and without isometric hip adduction. DESIGN AND SETTING: a repeated measures within subjects design was used. Subjects performed two sets of three repetitions of a traditional mini-squat and a mini-squat with concurrent hip adduction (squeeze). SUBJECTS: 20 recreationally active subjects (10 men, 10 women age=28.10+/-5.91 years, height=170.94+/-11.03 cm, mass=72.32+/-16.66 kg) with no history of patellofemoral pain (PFP), quadriceps injury, or other knee injury participated in the study. MEASUREMENTS: the EMG signal of the VMO and VL was recorded bilaterally during both exercises. EMG data were normalized to the maximal voluntary isometric contraction (MVIC) of the quadriceps produced during seated, isometric knee extension. RESULTS: results of repeated measures ANOVA's revealed that the squeeze squat produced significantly greater VMO and VL activity than the traditional squat (p=0.02). For both the traditional and squeeze squats, intrasession reliability from the first to the second set was calculated using intraclass correlation coefficient (ICC) formula (3:1) bilaterally for both the VMO and the VL. All ICC values were greater than 0.9. CONCLUSION: combining isometric hip adduction with a mini-squat exercise significantly increases the activity of the quadriceps. Performing mini-squats with isometric hip adduction will be beneficial to patellofemoral patients as they increase quadriceps activity, however, based on our data we cannot conclude that this exercise preferentially recruits the VMO. Further research is needed to determine the exact mechanism by which quadriceps function is altered.