Effects Of Rate Of Force Production On Vastus Lateralis Pennation Angle During Isometric Squats And Knee Extensions

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Previous literature has shown that force exerted by muscle is closely related to its size, length (i.e. joint angle) and pennation angle (PA). For a mono-articular muscle such as the vastus lateralis (VL), its ability to produce maximal force is dependent on the joint angle of the knee. However, since the VL shares a joint action with a bi-articular muscle, the rectus femoris (RF), it’s possible that its performance may also be affected by the angle of the hip (i.e. the RF contribution to knee extension is hip angle dependent, which may influence VL performance as well). It is unknown how the pennation angle of the VL during contraction differs between maximal multi- and single-joint exercises, such as the isometric squat (SQ) and knee extension (KE), and whether those changes are dependent on the rate of the force production. PURPOSE: To examine the pennation angle of the VL during slow and rapid maximal force production of the isometric SQ and KE exercises. METHODS: Fifteen lower-body resistance trained males (mean ± SD age = 24 ± 3 yrs) performed two separate maximal voluntary contractions (MVC) for both SQ and KE exercises. The first MVC (MVC1) cue was used to elicit peak force, with no instructions on the rate,while the 2nd (MVCR) was used to elicit rapid force production. Knee joint angles were set at 110° during both exercises, while hip angle was ~110° and ~105° during the SQ and KE, respectively. During all MVCs, ultrasonography was used to measure pennation angle of the VL muscle at peak force production. RESULTS: A two-way [MVC speed (slow vs. rapid) × exercise (SQ vs. KE)] repeated measures ANOVA indicated no significant differences in pennation angle of the VL between slow vs. rapid MVCs of the squat (mean MVC1 = 16.19 ± 3.18°, MVCR = 16.13 ± 3.26) and knee extension exercises (mean MVC1 = 16.21 ± 2.23, MVCR = 16.08 ± 2.34), nor were there any differences between the exercises (p > 0.05 for all analyses). CONCLUSION: When knee angle is controlled for, the pennation angle of the VL during isometric squats and knee extensions do not differ. Furthermore, neither the rate of force, nor the slightly different hip angles had an effect.