Understanding the S.A.I.D. Principle in Rehab
An important concept I apply to my rehab, borrowed from the strength and conditioning world, is the SAID principle, which stands for Specific Adaptations to Imposed Demands. What this means is that how and what we train determines how our body adapts. Or even simpler, we get better at what we do.
For example, if a runner mainly trains with short sprints and drills to build maximum speed, they’ll become a better sprinter, but that won’t prepare them to complete a marathon. On the flip side, a runner focused on long distance endurance will do well in a marathon but won’t be the fastest sprinter. Both may include some elements of each other’s training, but their bodies adapt specifically to the type of work they do. That is the SAID principle in action- our body adapts to the demands we place on it.
In rehab, applying the SAID principle helps the body prepare for the stresses and demands of sport or activity. This becomes especially important in the later stages of recovery as we bridge the gap between rehab and competition.
Using our runner example again, after a hamstring strain, we want to load the hamstring early, but appropriately. This might start with a simple exercise like digging the heel into the floor and sliding it toward the hips at a tolerable intensity. From there, we’d progress to a weighted hamstring curl and gradually increase load. Because they’re a runner, we’d also include other lower-body exercises like leg extensions, hip abductions, and calf raises.
As their strength improves, we can progress to multi-joint exercises like squats, deadlifts, or RDLs. Squats are great because they don’t heavily load the hamstrings but still strengthen the quads and glutes. Deadlifts and RDLs may also be well tolerated since they involve multiple muscles and place more emphasis at the hip — depending on the location of the strain.
Next, we’d add single-leg work, followed by plyometric or power exercises like hopping, skipping, and bounding. These more closely resemble the single-leg loading and push-off nature of running.
We’d also begin to reintroduce running itself — starting with slower speeds and shorter durations, then building from there. Returning to running is a graded exposure to the specific demands of running. It’s not about sport mimicry; it’s about directly applying the SAID principle by progressively exposing the hamstring to the real forces it will face.
Sometimes, though, the SAID principle is taken too far. We start believing every exercise must match or mimic the sport exactly — using single-limb movements, unstable surfaces, or weighted sport-specific motions. These have their place, but it’s important to recognize the different roles of strength training and sport practice.
The goal of strength and conditioning is to build muscular strength and power — to help your body generate more force.
The goal of sport and skills training is to improve coordination, timing, and technique within the sport itself.
Working out in the gym won’t automatically make you a better soccer player, just like playing soccer won’t make you jacked. Both are vital — but they need to be trained separately. If the goal is to build strength that transfers into sport, we need to maximize load on the muscles. Single-leg squats and lunges are useful, but they can’t be loaded as heavily as a barbell squat. Both can be included in a training week or within a periodized plan — but our gym sessions don’t need to look like our practice sessions.
Of course, the SAID principle can also be underused. Sometimes rehab consists only of a resistance band and a few easy exercises, with minimal load or challenge. In these cases, there’s not enough demand on the muscle to drive adaptation.
There’s always nuance and context to every rehab plan. But overall, we want to apply the SAID principle by ensuring our exercises appropriately load and challenge the injured area, progress in complexity and demand, and build capacity for return to sport. What we don’t need to do is make every exercise look like the sport itself — because we’ll reintroduce those sport movements separately, starting at low intensity and building from there.
In summary, the SAID principle reminds us that our body adapts to exactly what we demand of it. In rehab, that means loading the injured area appropriately and progressing toward the real demand of your sport, without trying to turn every exercise into a copy of the sport itself.
