Eccentric exercise and muscle damage : treatment, prevention and cross-education
Eccentric biased muscular contractions, when compared to concentric and isometric muscle actions have a number of benefits, which include greater hypertrophy, increased strength and a reduced metabolic cost at any given intensity. The literature has reported the benefits of eccentric contractions in a variety of populations, which include exercisers, athletes, geriatric and chronically diseased communities. However, eccentric contractions can result in temporary exercise-induced muscle damage (EIMD) that reduces function and causes soreness. Consequently, a number of interventions, such as post-exercise therapies and prior exercise have been used in an attempt to attenuate the negative effects of this muscle action. Therefore, the purpose of this thesis is to provide novel data to expand the existing body of knowledge and investigate a cryotherapeutic intervention that may attenuate the symptoms of exercise-induced muscle damage. Furthermore, this work examines the adaptation to prior exercise (the repeated bout effect) in the ipsilateral and contralateral limbs to provide additional novel data to elucidate the possible mechanisms responsible for adaptation. Study 1: The aims of the first study were to investigate the effects of repeated applications of ice massage on the markers of muscle damage using a within-subject, cross-over design and to examine the effects on muscle function during static and dynamic contractions. The results suggest that ice massage does not reduce any of the signs or symptoms of EIMD after high intensity eccentric exercise, nor does it return the function of static or dynamic muscle actions following a damaging bout of exercise. Study 2: The aims of this investigation were firstly, to determine the reliability of functional testing and the associated surface EMG signal on five consecutive days, and secondly to elucidate the reliability and precision of other dependent measures commonly used in the assessment of muscle damage following a bout of eccentric contractions. All variables displayed good reliability and therefore may be appropriate to examine longitudinal changes as a result of a damaging protocol. Study 3: The purpose of this investigation was to examine the magnitude of the repeated bout effect (RBE) from high and low volume maximal eccentric exercise followed by a high volume bout of maximal eccentric exercise after full recovery from the initial bout (two weeks later). There were no differences in dependent variables between groups in the repeated bout, indicating that the magnitude of the RBE is similar following initial low and high volume bouts of maximal eccentric exercise, which was attributable, at least in part, to changes in electromyographic frequency content. The initial high volume bout did however result in greater EIMD than the initial low volume bout; in addition, the magnitude of change from the initial bout was more profound after high volume exercise. Study 4: The aims of this investigation were to elucidate the existence of a contralateral RBE in the upper limb and to compare the magnitude of change to an ipsilateral model, which had been previously been established in Study 3. Significant differences in some variables provide evidence that a repeated bout effect is evident in the contralateral limb after a single bout of eccentric exercise. This adaptation appears to be mediated by neural mechanisms, as there is no direct stimulus for change from the initial bout to the contralateral homologous muscle group. The magnitude of change between contralateral and ipsilateral models was different for some variables suggesting that the RBE is not as profound in contralateral homologous muscle as in the ipsilateral model. These investigations provide additional novel data on interventions used to combat the negative effects of eccentric contractions and temporary EIMD. In particular, Study 4 has shown that adaptation occurs in the contralateral homologous muscle group, which has implications for a variety of populations and also for future research study design. Further investigations are warranted to elucidate the exact mechanisms responsible for the repeated bout effect.