Optimal Loading in Rehabilitation: Finding the “Sweet Spot”
There is an undisputed role for exercise in the early rehabilitative phase. However, exercise prescription remains a challenge. There is a growing interest in the use of loading in early rehabilitation. Physiotherapists and Strength and Conditioning (S&C) coaches play a central role in this process. In this series of articles, we will expand on the principles of optimal loading, the physiotherapist-S&C relationship and clinical implications for practice.
Skeletal muscle injuries occur when an external force overwhelms the muscle’s ability to generate an equal or greater force. For whatever reason the muscle did not generate the appropriate internal force required to manage the external force. Once an injury has occurred there is impaired muscle activation which can be due to pain inhibition and/or reduced muscle activity caused by immobilization.
Rehabilitation through exercise i.e. loading, is the restoration of anatomical form and physiological function following an injury. Optimal loading is defined as” the load applied to structures that maximises physiological adaptation”. The introduction of varied loads through the manipulation of different loading variables such as magnitude, intensity, duration and direction would maximise the neural and cellular adaptation through metabolic, mechanical and functional mechanisms. Rehabilitation is often delayed due to presence of pain; however, exercise has been shown to relieve pain (i.e. hypoalgesic) although optimal dosage is yet to be established.
At a cellular level, loading initiates a cascade of positive biochemical processes. Mechanotransduction refers to the process by which the body converts physiological-mechanical loading into cellular responses. Mechanotherapy is generally simplified into three steps: 1) mechanocoupling – the mechanical trigger, 2) cell-to-cell communication – communication through which the tissues distribute the loading message and 3) effector response – cellular level response. The mechanotransduction is weak in the absence of load and connective tissue is lost . When there is a load above the tissues set point, there is a stimulus through mechanotransduction so that the body adapts to improve tissue density. It has been shown in the literature that loading through skeletal muscle contractions promotes angiogenesis and increased stem cell activity following injury. A recent paper showed that early graded rehabilitation following acute hamstring strain can improve recovery time by up to 3 weeks.
Developing and progressing rehabilitation is based on the principle that the post-injury tissue capacity has been thoroughly evaluated. A comprehensive assessment is thus vital. Working closely with the S&C coach, physiotherapists can apply their assessments skills with the exercise knowledge of S&C coaches to determine the tissues set point and then apply an appropriate mechanical trigger to facilitate mechanotransduction.
As a system, our bodies endeavour to remain in a state of homeostasis. As a subsystem, skeletal muscle is no different. In this context, we need to be able to accept, redirect and dissipate external stimuli to prevent injury. When this is not successfully achieved, we are operating at a load that is beyond our structural capabilities and failure is likely to cause injury - homeostasis is temporarily lost. However, the ability of the muscle to complete the functions above is not lost entirely but rather altered to a new level. An example of this is seen when an athlete sustains a grade 1 type 1 hamstring strain. They are still able to run, albeit at 25% of their previous maximum effort. The level of homeostasis has been re-established.
Dye (2005) proposed a theoretical model of a tissue homeostasis perspective to understanding the pathophysiology of patellofemoral pain. At the heart of this model is the envelope of function, this is the amount of load that a system can safely withstand and transmit without sustaining injury. When either the load or frequency are increased beyond the tissues capacity the risk of injury is increased. This can either be through a gradual supra-physiological overload or a load that causes structural failure. Although this model was primarily developed to explain patellofemoral pain, adapting it to acute soft tissue injuries provides an opportunity to clinically develop and progress rehabilitation programs. Through a thorough subjective and objective assessment we can establish where the athletes’ post-injury envelope of function is and thus develop an individualised objective outcome measure and practical starting point.
The cellular and neural responses to exercises are important in the promotion of healing. This natural, non-pharmalogical approach is a positive intervention in rehabilitation. However, optimal exercise dosage has currently not been established. This is most likely due to the multifactorial nature of injuries and there is a need for individualised management strategies. The envelope of function provides clinicians with the ability to create individualised rehabilitation programs that expose the athlete to variable loads and facilitate the healing response whilst still meeting the specific needs of the athlete. I hope you have enjoyed this article and I look forward to sharing part 2, in which we will apply this model clinically and provide guidelines for clinicians when determining optimal load. In the famous words of Tim Gabbet, “Train hard, Train Smart.”
Frontera, W., 2003. Rehabilitation of Sports Injuries: Scientific Basis. 1st ed. Cornwall: Black Science Ltd
Glasgow, P., Phillips, N., Bleakley, C., 2015, “Optimal loading: key variables and mechanisms”, British Journal of Sports Medicine 49; 278-279
Naugle, K.M., Fillingim, R.B., Riley III, J.L., 2012, “A meta-analytic review of the hypoalgesic effects of exercise”, Journal of Pain 13(12); 1139–1150.
Kahn, K.M., Scott, A., 2009, "Mechanotherapy: how physical therapists prescription of exercise promotes tissue repair", British Journal of Sports Medicine 43(4);247-251, viewed on 8 March 2018, from http://bjsm.bmj.com
Asgari, A., Bazgir, B., Fathi, R., Mozdzika, P., Valojerdi, M.R. 2017, "Satellite Cells Contribution to Exercise Mediated Muscle Hypertrophy and Repair", Cell Journal 18(4); 473-484
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Dye, S.F. 2005, “The pathophysiology of patellofemoral pain, A Tissue Homeostasis Perspective”, Clinical Orthopaedics and Related Research 436; 100-110