Muscles transmit forces to bones via tendons. The moment created by a muscle about a joint on which it acts depends on the moment arm, and that is determined by the geometry of insertion of its tendon to the bone. Unlike the muscle, the tendon has more or less a constant cross-sectional area. In vitro, tendons have been stretched under the application of tensile loads. The stress-strain relationship is highly nonlinear. The tendon is more compliant at low loads than at high loads. Tendons typically have linear properties to a strain of about 9%. Physiologically, they appear to operate at a stress of 5 to 10 N/mm2.
Ligament properties are similar to those of tendons. Ligaments like tendons carry tension and again like tendons can store elastic energy. They will stretch small amounts under the application of tensile force, and under normal circumstances, they return to their resting length upon the lifting of load. Their ultimate tensile strength is comparable to that of tendons.
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The use of dumbbells gives you a much more comprehensive strengthening effect because the workout engages your stabilizer muscles, in addition to the muscle you may be pin-pointing. Without all of the belts and artificial stabilizers of a machine, you also engage your core muscles, which are your body's natural stabilizers.