'Strong' is PIE *strenk- (tight) — strength was conceived as tautness, not size. A coiled muscle.
Having the power to move heavy weights or perform physically demanding tasks; able to withstand force, pressure, or wear; powerful in effect or influence.
From Old English 'strang' or 'strong' (physically powerful, vigorous, robust, firm), from Proto-Germanic *strangaz (tight, taut, rigid, drawn tense), from PIE *strenk- (tight, narrow, constrained, drawn together). The original Germanic sense was not force but tension: a strong rope is one pulled taut; a strong bowstring is one drawn tight for maximum release. Physical power was understood as a property of tautness and resistance to deformation. The same PIE root *strenk- generated
'Strong,' 'string,' 'strangle,' and 'stringent' all come from the same PIE root *strenk- meaning 'tight, drawn together.' Strength was originally conceived not as bulk or mass but as tautness — the power of a drawn bowstring. Interestingly, the Germanic cognates in German and Dutch ('streng') now mean 'strict' rather than 'strong,' preserving the older sense of tightness and severity.