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Context: Achilles tendinopathies are common injuries during sport participation, although men are more prone to Achilles tendon injuries than women. Heel-raising and -lowering exercises are typically suggested for Achilles tendon rehabilitation.Objective: To compare the estimated Achilles tendon loading variables and the ankle range of motion (ROM) using a musculoskeletal model during commonly performed heelraising and -lowering exercises.Design: Controlled laboratory study. Setting: University biomechanics laboratory.Patients or Other Participants: Twenty-one healthy men (age ¼ 21.59 6 1.92 years, height ¼ 178.22 6 8.02 cm, mass ¼ 75.81 6 11.24 kg).Intervention(s): Each participant completed 4 exercises: seated heel raising and lowering, bilateral standing heel raising and lowering, bilateral heel raising and unilateral lowering, and unilateral heel raising and lowering.Main Outcome Measure(s): A repeated-measures multivariate analysis of variance (a ¼ .05) was used to compare Achilles tendon stress, force, and strain and ankle ROM for each exercise. Kinematic data were recorded at 180 Hz with 15 motion-analysis cameras synchronized with kinetic data collected from a force platform sampled at 1800 Hz. These data were then entered in a musculoskeletal model to estimate force in the triceps surae. For each participant, we determined Achilles tendon stress by measuring cross-sectional images using ultrasound.Results: Peak Achilles tendon loading was lowest when performing the seated heel-raising and -lowering exercise and highest when performing the unilateral heel-raising and -lowering exercise. Loading was greater for the unilateral exercise or portions of the exercise that were performed unilaterally.Conclusions: Bilateral and seated exercises with less weight-bearing force resulted in less Achilles tendon loading. These exercises may serve as progressions during the rehabilitation process before full-body weight-bearing, unilateral exercises are allowed. Ankle ROM did not follow the same order as loading and may need additional monitoring or instruction during rehabilitation.Key Words: kinematics, kinetics, strain, therapeutic exercise, rehabilitation Key PointsBilateral and seated heel-raising and -lowering exercises resulted in less Achilles tendon loading. Unilateral exercises and the unilateral phase of the bilateral heel-raising and unilateral heel-lowering exercise resulted in more Achilles tendon loading.