Choosing the right load in rehabilitation: locating the “sweet spot.”

When an external force exceeds the muscle’s ability to generate an equal or greater force, skeletal muscle injuries occur. For whatever reason, the muscle did not develop the necessary internal force to manage the external load. Injury causes impaired muscle activation due to pain inhibition, as well as decreased muscle activity due to immobilization. 

Exercise rehabilitation involves regaining anatomical form and physiological function after an injury . The load applied to structures that amplify physiological adaptation is known as optimal loading . The application of varying loads by varying loading variables such as magnitude, intensity, duration, and direction would maximize neural and cellular adaptation via metabolic, mechanical, and functional mechanisms. Because of the presence of pain, practitioners may postpone rehabilitation; however, exercise is hypoalgesic, though the optimal dosage has yet to be determined . 

Loading sets off a chain reaction of beneficial biochemical processes . The process by which the body converts physiological-mechanical loading into cellular responses is known as mechanotransduction. Mechanotherapy is broken down into three steps: mechanocoupling, which is the mechanical trigger, cell-to-cell communication, which is how the tissues distribute the loading message, and the effector response, which is the cellular level response. In the absence of load, mechanotransduction is impaired, and connective tissue is lost. When a load exceeds the tissue’s set point, mechanotransduction occurs, and the body adapts to improve tissue density. Following injury, tissue loading via skeletal muscle contractions promotes angiogenesis and increased stem cell activity . Early graded rehabilitation after an acute hamstring strain, for example, can shorten recovery time by three weeks .

Fig. 1

The body as a whole makes an effort to maintain homeostasis. Skeletal muscle is no different from a subsystem. Athletes in this situation must accept, refocus, and dissipate external stimuli to avoid injury . Athletes operate at a load that exceeds their structural capacity when this fails, and failure is likely to be harmful. The muscle’s capacity to contract is not completely lost, though. For instance, a sportsperson who suffers a grade one hamstring strain can still run, albeit more slowly than before. 

The pathophysiology of patellofemoral pain can be conceptualised using a theoretical tissue homeostasis model. The envelope of function, which is the amount of load that a system can safely withstand and transmit without suffering damage, is the core of this model (see figure 1). When the load or frequency is greater than the tissue can handle, the risk of injury increases. Either a load that leads to structural failure or a load that gradually causes supra-physiological overload can achieve this. Despite the fact that this model mainly explains patellofemoral pain, applying it to acute soft tissue injuries gives clinicians the chance to develop and advance rehabilitation programs. Practitioners can determine the athlete’s post-injury envelope of function through a thorough subjective and objective assessment, which enables them to create an individual objective outcome measure and useful starting point (see figure 2). 

Exercise-induced cellular and neural responses are

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