The primary purpose of this study was to document the influence of muscle contraction on quadriceps femoris (QF) muscle architecture [fascicle length (Lf) and pennation angle (θp)] and effective physiological cross-sectional area (effPCSA). Secondarily, we aimed to determine whether effPCSA measured during maximal voluntary contraction (MVC) had a stronger relationship to maximal strength than effPCSA at rest. Fifteen young men performed a series of voluntary knee-extension isometric ramp contractions. Isometric maximal voluntary torque (MVT) was recorded during separate MVCs. Measurements of architecture and effPCSA of each constituent muscle of the QF and, subsequently, the whole QF were made at rest, during 20% increments of maximal voluntary torque and during an MVC. The QF muscle architecture and morphology changed in a curvilinear manner with relative torque (%MVT), with significant differences being observed between incremental torque levels for Lf, θp and effPCSA. Specifically, from rest to MVC, QF Lf decreased (-23.5 ± 3.3%), whereas θp increased (+39.7 ± 6.6%). The QF effPCSA was +26.5 ± 5.7% greater during MVC than at rest. Similar moderate correlations existed for MVT and effPCSA at rest (r = 0.519, P = 0.047) and for MVT and effPCSA during MVC (r = 0.530, P = 0.042). Substantial changes in QF architecture (Lf, θp) and effPCSA occur in a curvilinear manner with relative torque production. The effPCSA during MVC was no more strongly associated with MVT than effPCSA measured at rest, which implies that resting measurements of muscle size are suitable for characterizing the muscle size-strength relationship.
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