Horses with tendon problems distinguish from others by a long period of convalescence. Especially the transition from box rest to movement is usually accompanied by overstrain on the tendons. The question is if support boots possess a supporting function and if using them during this period makes sense. In this study the difference of the fetlock angle with or without boots was determined by measuring both fore limbs of 26 horses. Therefore the horses were filmed with six high-speed-videocameras in walk and trot after a period in which the horses had been accustomed to the treadmill (MUSTANG 2200, Kagra AG, Switzerland). The received raw data were processed with the computer system ExpertVision of the Motion Analyses Corporation (USA). For the measurement four types of support boots were used, which were fastened with equal strength using a spring balance which had been constructed especially for this study. After the video recordings had been divided into separate movement cycles, the smallest dorsal fetlock angles (which correspond to the deepest hyperextension) were determined and the results of each boot were compared with those of the measurement without support boots. After that the boot-results were tested for normal distribution and statistically proved with the Dependent two sample t-test (paired t-tesf). The differences of the angles resulting from the measurements with and without support boots are in the range of 0,9 degree in walk and in the range of 1,5 degree in trot. With a formula, which was developed by Meershoek et al. (2001b), a force reduction on the M. interosseus medius of up to 3,6% in walk and up to 2,5% in trot can be calculated. The evaluation of the data corpus shows a supporting function of all boots, whereby differences probably result from the material properties and winding methods. The Musculus Interosseus medius, a structure which purely consists of tendons, shows a strength-reduction. Due to assumable effects on the superficial digital flexor tendon, support boots seem useful in the treatment of tendon problems.