Andrea Biscarini, Rita Borio, Francesco Coscia, Giovanni Mazzolai, Simonetta Simonetti, Gabriella Rosi
A two-dimensional model was developed for dumbbell/barbell and cable biceps curl exercises, in quasi-static and isokinetic regimes. Analytical expressions for the ratios of the biceps force (F) and the tangent (ft) and normal (fn) components of the joint reaction to the dumbbell (Mg) and cable (c) external load were deduced as a function of the joint angle q and the other relevant parameters. For standing/ preacher dumbbell curl, F and fn take their maximum values at the critical wrapping angle q*=27.4°, for any value of the preacher bench inclination a within the range 0²a²90°-q*. An increase of a yields: a) an increase in the initial value of F, and in the peak values of F and |fn| (up to 15Mg and 14Mg, respectively); b) a steeper decrease of F between q* and 180°-a where F=0; c) a shift of the ft(q) curve towards lower joint angles. For a³38°, the joint load becomes of compressive type (fn<0) within the whole range [0,180°-a] of the joint motion. In cable curl, high values of the distance dP of the elbow joint from the pulley center give the same results as the standing dumbbell curl (a=0). When dP approaches the smallest allowed values, the model predicts: a) a steep increase of F and a steep decrease of fn and ft, just above q=0; b) high peak values of F and |fn| at q=q* (up to 15c and 13c, respectively); c) tractional values of fn smaller than 2c and nearly constant values (~3c) of F, above q=100°.