2 MODELS OF LOADING TISSUE –
Tissue loading is one of the key variables that can be modified in rehabilitation. From more passive loading of tissues (i.e. manual therapy) to the most active approaches (i.e. max effort lifts, plyometrics), the management of load represents a critical element of what the doctor of physical therapy does with high skill to intervene.
Once the clinician establishes the need for some form of physiological adaptation, the primary clinical question is what is the dose? The clinician can determine appropriate dosage by methodically applying clinical reasoning over time to the presentation of the individual. There are a few models that assist with determining appropriate dosage. Two that are relevant to clinical practice are the TISSUE HOMEOSTASIS MODEL and that of OPTIMAL LOAD. Applied appropriately, these models give the clinician a powerful framework to guide the rehabilitation process.
TISSUE HOMEOSTASIS –
In brief, the TISSUE HOMEOSTASIS MODEL proposes that many clinical issues can be related to a disruption of the local tissue’s homeostasis due to exposure to stress beyond its adaptive ability. The local tissue is viewed as a system designed to create, accept, transfer, and dissipate biomechanical loads. The upper and lower limits of the tissue’s tolerance to load define its continuum of function. The right side of the continuum represents a dosage significant enough to stimulate adaptation but still within the tissue’s ability to recover. Loads above this threshold will cause tissue damage at a higher rate than to which it can adapt; loads below will result in a detraining effect.
Healthy individuals have a fairly wide gap between the minimal effective dose and the maximum tolerated dose. With injury, this zone narrows and it requires more precise dosage to stay within the continuum of function. The rehabilitation goal is to increase these envelope borders by driving its upper limits to the right. The image below gives a visual representation of these zones and the effects of injury and rehabilitation.
OPTIMAL LOAD –
OPTIMAL LOAD (The “O.L.” in the POLICE acronym – found on our blog at wrightpt.com) is the dosage that maximizes the tissue’s physiological adaptation. By definition, optimal load also falls within the continuum of function. Glasgow et al. aptly stated in their literature that “for loading to be optimal, it should be directed to the appropriate tissues and gradually progressed in terms of magnitude, direction and rate.”
Thus, the initial goal of the clinician is to establish the envelopes of function to ensure loading drives adaptation in the desired direction. Negative adaptations can come from either too much or too little load.
Within the envelopes of function, the clinician must determine the optimal load to expand the envelope of function so it ultimately encompasses the patient’s desired level of activity. This load reflects the individual’s current state of fitness and readiness and will therefore change based on many factors, including adaptation to previously applied loads. This is one key reason why progressive overload is so fundamental to exercise prescription and why one size does not fit all.
DYNAMIC NATURE OF ADAPTATION –
Allostasis is the process in which the body responds to stressors in order to regain homeostasis. Allostasis challenges the concept of a steady state internal environment and replaces it with the idea of multiple layers that are constantly changing to maintain an optimal level of readiness for current demands.
How does a clinician approach clinical decision making for desired outcomes with this context? The application of load must be informed by prior plausibility, modified by feedback, and updated to reflect a current best approach to loading that fits within the patient’s envelope of function. It truly is the Goldilocks principle that optimizes adaptation to stresses. It must be “just right.”
Let’s assume a female patient presents with suspected patellar tendinopathy brought on by a recent increase in loads at basketball practice.
- Current level of load is beyond her tolerance (outside of envelope of function)
- In general, tendon adaptations occur best with higher loads (>70% MVC), contraction type doesn’t matter much but time under tension does, and significant adaptations require longer durations (>12 weeks)
- Painful eccentrics to the tendon have the effect of remodeling the tendon and increasing microcirculation
- Loading with isometrics has a significant analgesic effect
- Continuing activity with tendon pain can be done with modifications
- Current tissue tolerance level
- Amount of adaptation needed to allow the local tissue to tolerate the new demands
At this point, the clinician may decide to begin loading via isometrics or painful eccentrics to initiate positive local adaptations as soon as possible. They can also take advantage of the analgesic effect. Utilizing passive loads the clinician may also initiate macrophage mediated phagocytosis through IASTM passive treatment (See our IASTM blog for more info).
To avoid driving a loss of adaptation by under dosage, the clinician may also decide to cut the weekly game time in half with self-removal during games if subjective pain reaches a mutually agreed point. This would be the estimated optimal load within the most probable envelope of function.
At the next follow-up, the clinician will assess the patient’s response and modify the load to reflect the outcome. In our example, there is a chance that the pain slightly increased. The probability that loading is necessary remains very high, but the individual’s optimal load was missed and so the dosage should be adjusted for a more favorable response. We seek to get the dosage “Just Right”. Actual therapeutic exercise prescription comes into play with the type of therex as well as dosage, but selecting the type of treatment is better saved for a different article discussion.
When implementing a systematic approach as described above, the clinician can minimize wasted time and ensure that variations in patient response are rapidly reflected in their treat ment approach. Mechanical therapeutic understanding is an important element of selecting optimal dose and restoring hysteresis to injured tissue.
SUMMARY POINTS –
- Optimal load and tissue homeostasis models are necessary tools we use to customize an individual’s return to activity.
- Healthy individuals have a wider gap between minimum effective dose and maximum tissue tolerance. Injured individuals have a more narrow gap. Rehab aims to widen that.
- The interplay between tissue response, patient feedback and clinical reasoning drive the “just right dose” decision making for patient care on a day to day basis. This is why prescribing appropriate frequency of high skilled physical therapy makes a significant difference.
- For loading to be optimal, it should be directed to the appropriate tissues and gradually progressed in terms of magnitude, direction and rate. Regression of loads can be every bit as important as progression of loads to heal.
- Call or email email@example.com for insight on this important principle that our clinicians use to guide patient outcomes.