Isometric strength refers to the ability of our muscles to hold a position or stay still without moving or bending. It involves exerting force against an immovable object or resisting force without any joint movement. Full definition
An influential 21 - week study by Ahtiainen J.P. et al. showed a correlation between T levels and the changes in isometric strength and muscle size, which means that both serum basal testosterone concentrations and training - induced acute testosterone responses are strongly associated with muscle and strength gains. (fitnessandpower.com)
Interestingly, there was very clear evidence of velocity - specific transfer to the trained speed, and this transfer tapered away to either side of the trained speed, even though that zone included isometric strength at 0 degrees / s. (strengthandconditioningresearch.com)