Original abstract: The aim of this thesis was (i) to investigate potential risk factors and suggested injury mechanisms involved in the development of exercise-induced rib stress fractures (RSF) in elite rowers, and (ii) to investigate biomechanical and neuromuscular differences of ergometer rowing performed in stationary vs. sliding ergometer conditions. BMD and isokinetic muscle strength were assessed along with electromyography (EMG) signals recorded in selected thoracic muscles and rowing technique during ergometer rowing in elite rowers with previous RSF (n=7) and in matched controls (n=7). The results indicated that the RSF subjects were characterized by reduced lumbar spine BMD, increased co-contraction of thoracic muscles, increased elbow-flexion strength relative to knee-extension strength and increased velocity of the ergometer seat during the initial drive phase of the rowing stroke. The retrospective nature and the small material of the studies preclude any strong conclusions and prospective investigations including larger materials are needed to further elucidate the potential risk factors and injury mechanisms Testosterone levels and BMD were measured in male lightweight rowers (n=13). Correlations between BMD and testosterone levels as well as years of training were found. Relatively high levels of BMD indicated that the mechanical stimuli from several years of rowing were more important to BMD than the relatively low levels of testosterone. Testosterone was, however, correlated to lumbar spine BMD after controlling for years of training and further studies of hormonal and nutritional factors associated with BMD in male endurance trained athletes in sports with implicit or explicit weight limits are needed. The force production during ergometer rowing with and without slides at identical power outputs was measured in 14 male and 8 female elite rowers. During slide-based ergometer rowing male rowers increased stroke rate and decreased peak force, mean force and rate of force development above 50 % of peak force. Female rowers displayed a similar but less pronounced response to ergometer rowing in slides. Slide-based ergometer rowing may be hypothesized to decrease the peak loading of the rib cage in each rowing stroke during ergometer rowing at the expense of an increased number of loading cycles. Whether slide-based ergometer rowing can decrease the risk of RSF needs to be evaluated in randomized controlled trials. The patterns of neuromuscular activity in muscles potentially involved in RSF development in addition to the force production at the handle were measured during ergometer rowing with and without slides at identical power outputs in 14 male elite rowers. Slide-based ergometer rowing did not affect the neuromuscular activation of the measured muscles significantly, except during the relatively unloaded recovery phase of the rowing stroke. The timing of peak neuromuscular activity of the scapula retractor muscles including m. latissimus dorsi coincided with the timing of peak force at the handle supporting rib cage compression as a potential injury mechanism. In conclusion this thesis has added some pieces of knowledge regarding the risk factors and injury mechanisms involved in the development of exercise-induced rib stress fractures in elite rowers. This knowledge might be useful for and give inspiration to future studies of rib stress fracture prevention in elite rowers.
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