Muscle injury and pain : Effects of eccentric exercise, sprint running, forward lunge and sports massage

Abstract: Muscle injuries are the most common injury in sports and both athletes and non-athletes are commonly seen in general practice and in the emergency department. Muscle pain is a common cause for absence from work and the cost to society is high. The present thesis was aimed to study biomechanical and biological causes of muscle injury and pain in order to better design prevention programs and treatment of muscle injury. Hamstring injuries in sprinters are common, and not caused by external trauma, thus making them a good model for the study of general causes of muscle injury. In study 1 we compared sprinters with a history of hamstring strain with uninjured runners. Sprinters with a previous hamstring injury were weaker in eccentric contractions, especially at high velocities, compared to uninjured runners. They also showed less flexibility of their hamstrings. One reason for the high recurrence rate of this injury might be that the athletes are not fully rehabilitated after their injury. In order to make biomechanical studies of fast movements and to compare different muscles we developed the technique of measuring EMG of lower limb muscles during maximal sprint running in study II. The EMG was expressed as percentage of EMG at maximal isometric contraction. This study resulted in normalized EMG graphs for each muscle during sprint running, representing the degree of activity of each muscle. We used this EMG normalization method in study III when performing descriptive biomechanical evaluation of two types of forward lunge (walking forward lunge and jumping forward lunge). Forward lunges are often used by athletes and are thought to be complex eccentric exercises. We managed to simultaneously record the EMG activity with the calculation of muscle length changes by an optic motion analysis system of the hamstrings, rectos femoris and gastrocnemius. Eccentric contractions were found of both rectos femoris and the hamstrings during the first part of the stance phase. In order to further evaluate these exercises we also performed a study of the acute impact of the exercises on pain and muscle function, as well as after six weeks of training in study IV. Thirty-two football players from one team were included. The forward lunge training was done as an addition to ordinary football training. Whereas walking lunge improved concentric hamstring torque compared to baseline, jumping lunge improved sprint running. Algometer testing showed an increase in pain detection threshold with time in all subjects, including the controls. This is important to consider when using algometers in clinical trials. Muscle pain often occurs after eccentric exercise, the so called delayed onset muscle soreness (DOMS). Eccentric exercise does not only cause DOMS, it has also been found effective in treating chronic injuries of tendons, and have been suggested as treatment of muscle injury. The pathophysiology behind DOMS is, however, not fully clear. Sensory and autonomic neuropeptides, such as Calcitonin Gene Related Peptide (CGRP) and Neuropeptide Y (NPY) play an important role in pain modulation within the central nervous system. In study V we thus attempted to detect CGRP and NPY in vivo in human skeletal muscle at rest and after eccentric exercise. Eight healthy subjects performed strenuous eccentric exercises. Microdialysis of the quadriceps was performed immediately post exercise, after two days and at rest. We were able to detect CGRP but not NPY in vivo in human muscle by this technique even though the measured concentrations were low. The detectability of CGRP was significantly increased after exercise, indicating that CGRP after exercise may be involved in the regulation of DOMS, Moreover, CGRP may possibly also be involved in regulating tissue regeneration. Sports massage has become popular among athletes when treating muscle pain. In study VI we therefore evaluated whether sports massage could prevent DOMS and impaired muscular function following eccentric exercise. Sixteen subjects performed maximal eccentric contractions of the quadriceps in both legs. Massage was given to one leg once daily for three days, whereas the other leg served as a control. The exercise induced soreness and caused reduced strength and function. However, using our evaluation methods we could not verify that sports massage treatment could reduce DOMS or impaired muscle function. In conclusion, muscle injuries are common among athletes, in particular sprinters, and have a high recurrence rate. The athletes are not always fully rehabilitated before returning to sport. One important factor is decreased eccentric strength. Forward lunge is a complex eccentric exercise that is easy to perform and does not require any equipment. It could be used by athletes, not only to increase strength and speed performance, but it may also be beneficial in the prevention and treatment of thigh muscle injury. Certain neuropeptides such as CGRP can be involved in muscle pain after eccentric exercise. Sports massage is appreciated by athletes but we could not in this study show any benefits regarding pain or recovery.