Understanding how healthy and tendinopathic human Achilles tendon (AT) deforms at the regional level in three-dimensional (3D) space under load could provide better insight into in vivo AT mechanobiology, physiology, recovery, pathophysiology, injury, and function This thesis investigated the 3D morphology of the healthy and tendinopathic human AT at the level of whole AT (e.g., gastrocnemius muscle-tendon junction (MTJ) to calcaneus), free AT (e.g., soleus MTJ to calcaneus), and proximal AT (e.g., gastrocnemius MTJ to soleus MTJ) under load using freehand 3D ultrasound. In studies 1 and 2, the regional 3D deformation of healthy AT was investigated during and immediately following 10 successive 25-second (s) plantarflexion contractions at 50% maximal voluntary isometric contraction (MVIC), and at 5 further time points [15, 30, 60, 90, and 120 minutes (min)] during recovery. The longitudinal creep response of whole AT during repeated loading was found to be primarily driven from free AT and was accompanied by a corresponding transverse creep response of free AT that was most pronounced within the mid-portion. Further, the longitudinal and transverse creep of AT reached steady state simultaneously following three contractions.