Both Isometric and Dynamic Testing Are Essential for a Comprehensive Assessment of the Knee Extensors

Grossio, L, Salvaggio, F, Brustio, PR, Rainoldi, A, Samozino, P, and Boccia, G. Both isometric and dynamic testing are essential for a comprehensive assessment of the knee extensors. J Strength Cond Res XX(X): 000-000, 2025 - The improvements of measurement tools and data analysis enhanced our possibilities to assess neuromuscular performance, but also created confusion regarding significance and practical applications of this available information. To simplify the strength assessment understanding, our purpose was to group force, velocity, and power metrics that could provide similar outcomes. We measured single-leg knee extensor strength under isometric and dynamic conditions on 64 young adults (33 men and 31 women). Subjects performed maximal and burst-like contractions under isometric conditions to assess maximal torque (MVT) and rate of torque development (RTD). Under dynamic conditions, a torque-velocity relationship was obtained from an incremental load test. Principal component analysis (PCA) was used to reduce the dimensionality of the data set and group variables. Principal component analysis identified 4 components: (a) "Maximal force"(composed by MVT, T0, RTD100, RTD150, Topt, Pmax), (b) "Explosiveness"(composed by RTD50, RTDpeak, RTD50N, RTD100N, RTD150N, RTDpeakN, time to peak torque, time to RTDpeak), (c) "Force at high velocity"(composed by V0 and Vopt), and (d) "Curvature"(C). When data were normalized by sex differences, "Explosiveness"resulted as the first component and Pmax was included in the "Force at high velocity"component. The present findings remark the importance of testing the explosiveness (i.e., early RTD and normalized RTD metrics) together with torque-velocity profiling, to have a more comprehensive assessment of neuromuscular qualities.