Muscle architecture and morphology as determinants of explosive strength

Neural drive and contractile properties are well-defined physiological determinants of explosive strength, the influence of muscle architecture and related morphology on explosive strength is poorly understood. The aim of this study was to examine the relationships between Quadriceps muscle architecture (pennation angle [Θ_P] and fascicle length [F_L]) and size (e.g., volume; Q_VOL), as well as patellar tendon moment arm (PT_MA) with voluntary and evoked explosive knee extension torque in 53 recreationally active young men.

Following familiarisation, explosive voluntary torque at 50 ms intervals from torque onset (T₅₀, T₁₀₀, T₁₅₀), evoked octet at 50 ms (8 pulses at 300-Hz; evoked T₅₀), as well as maximum voluntary torque, were assessed on two occasions with isometric dynamometry. B-mode ultrasound was used to assess Θ_P and F_L at ten sites throughout the quadriceps (2-3 sites) per constituent muscle. Muscle size (Q_VOL) and PT_MA were quantified using 1.5 T MRI.

There were no relationships with absolute early phase explosive voluntary torque (≤ 50 ms), but θ_P (weak), Q_VOL (moderate to strong) and PT_MA (weak) were related to late phase explosive voluntary torque (≥ 100 ms). Regression analysis revealed only Q_VOL was an independent variable contributing to the variance in T₁₀₀ (34%) and T₁₅₀ (54%). Evoked T₅₀ was also related to Q_VOL and θ_P. When explosive strength was expressed relative to MVT there were no relationships observed.

It is likely that the weak associations of θ_P and PT_MA with late phase explosive voluntary torque was via their association with MVT/Q_VOL rather than as a direct determinant.