Effects of cold and hot water immersion on the mechanical properties of human muscle and tendon in vivo

Background Cooling and heating have been shown to affect the contractile properties of muscles. However, the reasons for these changes remain unclear. The present study aimed to quantify the mechanical properties of muscle and tendon during passive stretch and active contraction, and to investigate the effects of cooling and heating on the mechanical properties of muscle and tendon. Methods Before and after these conditions, the elongation of the muscle fascicle, tendon and aponeurosis of the medial gastrocnemius muscle was directly measured by ultrasonography, while the ankle joint was passively moved within the joint range of +15 to −30 deg (0 deg = neutral anatomic position; positive values for plantar flexion) and subjects performed ramp isometric plantar flexion up to the voluntary maximum. Findings While the muscle fascicle, tendon and aponeurosis stretched during passive dorsi-flexion, the elongation of the tendon was significantly greater than that of the aponeurosis. During isometric contraction, the maximal elongation of the tendon was significantly greater than that of the aponeurosis. After cooling and heating, no significant changes in the elongation of muscle fascicle, tendon and aponeurosis were found during passive stretch. Similarly, after both the immersions there were no changes in the relationship between the estimated muscle force and elongation of each structure (tendon–aponeurosis complex, tendon) during isometric contraction. Interpretation These results implied that the general application of icing and hot pack did not change the mechanical properties of muscle and tendon.