The Inflammatory Response to Skeletal Muscle Injury

Abstract

Injury of skeletal muscle, and especially mechanically induced damage such as contusion injury, frequently occurs in contact sports, as well as in accidental contact sports, such as hockey and squash. The large variations with regard to injury severity and affected muscle group, as well as non-specificity of reported symptoms, complicate research aimed at finding suitable treatments. Therefore, in order to increase the chances of finding a successful treatment, it is important to understand the underlying mechanisms inherent to this type of skeletal muscle injury and the cellular processes involved in muscle healing following a contusion injury. Arguably the most important of these processes is inflammation since it is a consistent and lasting response. The inflammatory response is dependent on two factors, namely the extent of actual physical damage and the degree of muscle vascularization at the time of injury. However, long-term anti-inflammatory treatment is not necessarily effective in promoting healing, as indicated by various studies on NSAID treatment. Because of the factors named earlier, human studies on the inflammatory response to contusion injury are limited, but several experimental animal models have been designed to study muscle damage and regeneration. The early recovery phase is characterized by the overlapping processes of inflammation and occurrence of secondary damage. Although neutrophil infiltration has been named as a contributor to the latter, no clear evidence exists to support this claim. Macrophages, although forming part of the inflammatory response, have been shown to have a role in recovery, rather than in exacerbating secondary damage. Several probable roles for this cell type in the second phase of recovery, involving resolution processes, have been identified and include the following: (i) phagocytosis to remove cellular debris; (ii) switching from a pro- to anti-inflammatory phenotype in regenerating muscle; (iii) preventing muscle cells from undergoing apoptosis; (iv) releasing factors to promote muscle precursor cell activation and growth; and (v) secretion of cytokines and growth factors to facilitate vascular and muscle fibre repair. These many different roles suggest that a single treatment with one specific target cell population (e.g. neutrophils, macrophages or satellite cells) may not be equally effective in all phases of the post-injury response. To find the optimal targeted, but time-course-dependent, treatments requires substantial further investigations. However, the techniques currently used to induce mechanical injury vary considerably in terms of invasiveness, tools used to induce injury, muscle group selected for injury and contractile status of the muscle, all of which have an influence on the immune and/or cytokine responses. This makes interpretation of the complex responses more difficult. After our review of the literature, we propose that a standardized non-invasive contusion injury is the ideal model for investigations into the immune responses to mechani...

The evaluation of new multi-material human soft tissue simulants for sports impact surrogates

“…Information regarding the exact mechanical loading conditions or thresholds required to illicit particular injuries is vitally important. In sports, contusion injuries are often considered as the highest risk impact injury due to their frequency of occurrence (Crisco et al, 1994;Khattak et al, 2010;Smith et al, 2008), whilst fractures and lacerations are also pertinent considerations.…”

Effects of GaAs laser and stretching on muscle contusion in rats

“…The most common skeletal muscle injury in contact sports is contusion 1 . Different physiotherapeutic intervention techniques are used to accelerate the muscle repair process and reestablish function, such as: cryotherapy 2 ; therapeutic ultrasound 3 ; laser 4 ; and early mobilization and exercises 5 .…”

The Association between Physical Exercise and Reactive Oxygen Species (ROS) Production

“…One possible explanation is that vigorous exercise triggers muscular ROS production that may activate nuclear factor redox activity and induce intracellular stimulus to protein synthesis [13][14][15][16]. Another possible explanation is that ROS can coordinate leukocyte (neutrophil and monocyte) influx to the skeletal muscle tissue, and this infiltration plays an important role in an adaptive muscle process [40][41][42][43][44][45][46][47][48][49][50][51]. Using a pharmacological antioxidant strategy (apocynin) and mutant animal model (gp91phox-/-), it is possible to block this process and possibly interrupt remodeling of tissues following exercise.…”

“…There is a large body of literature that describes how inflammation is an exercisedinduced physiological response that happens occurs after acute episodes of exercise and is capable of chronically inducing the adaptation of skeletal muscle tissue after a period of training time. It is now becoming clear that ROS play an important role in the acute inflammatory process after intense exercise [45] and that the skeletal muscle inflammatory process may play a role in the skeletal muscle adaptive response [41][42][43][44][45]. In this sense, anti-oxidant administration as a supplemental diet aid could inhibit these important adaptive responses and block the benefits of exercise from recreational levels and high levels of exercise training.…”