Studies evaluating treatment effects on muscle function after an Achilles tendon rupture often use various tests for evaluating calf muscle strength. However, these tests rarely demonstrate the difference between treatment groups; therefore, new tests with a higher ability to detect possible differences in outcome are needed. The purpose of this study was to evaluate the validity and ability to detect differences in outcome of a heel-rise work test that would measure both the height of each heel-rise and the number of repetitions. Seventy-eight patients (65 men and 13 women) at a mean (standard deviation) age of 42 (9) years with Achilles tendon ruptures were included. The patients were evaluated with the new heel-rise test at 6 and 12 months after injury. The limb symmetry index (LSI = involved/uninvolved x 100) was calculated to determine the size of the difference in function between the injured and the uninjured side. The heel-rise height differed significantly between the injured and uninjured sides at the 6- and 12-month evaluations (P < 0.001). At the 6-month evaluation, the patients had achieved a mean LSI of 84% on the number of repetitions parameter but only a mean LSI of 61% on the work parameter. At the 12-month evaluation the mean, LSI of the heel-rise repetition parameter was 95%, indicating that the patients had fully recovered function, but on the work parameter the mean LSI was only 76%. The heel-rise work test in the present study has good validity and greater ability to detect differences between the injured and the uninjured sides than a test that measures only the number of heel-rise repetitions in patients with Achilles tendon rupture.