Load is Medicine: Using Training Science in Physical Therapy

In The phrase “load is medicine” reflects a growing consensus in rehabilitation and sports science: the way we apply stress to the body determines not only whether an athlete recovers from injury, but also whether they build resilience for long-term performance. Like medication, the effects of exercise depend on dosage. Too little, and the body fails to adapt. Too much, and progress gives way to breakdown.

The human body thrives on well-dosed stress. Muscles, tendons, bones, and even cartilage remodel in response to progressive loading (Kjaer, 2004; Frost, 2004). Without it, tissues lose strength and capacity, making them more vulnerable to future injury. The challenge for therapists is not whether to load, but how to calibrate it so that recovery is supported rather than disrupted. One framework used in sports science is the acute: chronic workload ratio (ACWR), which compares training over the past week with the longer-term average. Sudden spikes in load like doubling mileage or adding too many lifting sessions in a short period are closely tied to increased injury risk, while gradual progression builds resilience (Gabbett, 2016). While researchers continue to debate the predictive value of ACWR (Carey et al., 2018), the principle remains useful, and I’ve written more about how athletes can apply it practically in [Acute vs. Chronic Workload: What Every Athlete Should Know].

Strength progression brings this concept to life. Muscle fibers can adapt in weeks, but tendons and joint structures remodel more slowly, which means pushing weight too quickly often results in flare-ups. Incremental increases of 2.5–10% per week are recommended in strength programs (Haff & Triplett, 2015), and research on undulating periodization suggests that alternating heavier and lighter days not only improves long-term strength but also reduces overuse symptoms (Buford et al., 2007). When athletes understand that irritation is often the result of progress outpacing tissue tolerance, it becomes clear why patience pays off. For a more detailed breakdown of this strategy, see [How to Progress Strength Training Without Flare-Ups].

Even the best training plan cannot account for the daily variability of human physiology. Stress, sleep, nutrition, and recovery status all affect how hard the same session feels. This is where autoregulation tools like Rate of Perceived Exertion (RPE) and Heart Rate Variability (HRV) can be powerful. RPE, a subjective 1–10 scale, has been validated against objective measures like blood lactate and heart rate (Helms et al., 2016). HRV, which reflects nervous system readiness, has been shown to improve both performance and resilience when used to guide training intensity (Stanley et al., 2013; Flatt & Esco, 2016). When combined, RPE and HRV help athletes and therapists make real-time adjustments that match the body’s capacity on that day. I expand on how these tools fit into rehab and training in [Using RPE and HRV to Guide Rehab and Performance].

Recovery itself is an essential part of load management, and not just in the form of sleep or nutrition. Planned reductions in training, also known as deload weeks, allow the body to consolidate adaptations before building further. Rather than halting progress, strategic reductions in volume or intensity actually enhance it by lowering accumulated fatigue and restoring neuromuscular function (Bosquet et al., 2007). In both performance and rehab settings, this principle ensures that athletes adapt without being overextended. For examples of how to structure these recovery periods, see [The Science of Deload Weeks: When Less Training Means More Progress].

Bringing these ideas together, it becomes clear that load should be viewed as medicine. Exercise prescription is not simply about choosing movements; it is about dosing stress in the right amount, at the right time, for the right individual. By considering the relationship between short- and long-term workload, progressing strength gradually, using autoregulation tools to individualize training, and building recovery directly into the plan, therapists can help athletes return from injury stronger and more resilient. In this model, exercise is not just movement, it is the prescription and dosage that makes it therapeutic.

References

• Bosquet, L., Montpetit, J., Arvisais, D., & Mujika, I. (2007). Effects of tapering on performance: a meta-analysis. Med Sci Sports Exerc, 39(8), 1358–1365.

• Buford, T. W., et al. (2007). A comparison of periodization models during nine weeks with equated volume and intensity. J Strength Cond Res, 21(4), 1245–1250.

• Carey, D. L., et al. (2018). The acute:chronic workload ratio: A flawed metric for injury risk. Br J Sports Med, 52(3), 180–181.

• Flatt, A. A., & Esco, M. R. (2016). Evaluating individual training adaptation with smartphone-derived heart rate variability in a collegiate female soccer team. J Strength Cond Res, 30(2), 378–385.

• Frost, H. M. (2004). A 2003 update of bone physiology and Wolff's Law for clinicians. Angle Orthod, 74(1), 3–15.

• Gabbett, T. J. (2016). The training—injury prevention paradox: should athletes be training smarter and harder? Br J Sports Med, 50(5), 273–280.

• Haff, G. G., & Triplett, N. T. (2015). Essentials of Strength Training and Conditioning (4th ed.). National Strength and Conditioning Association.

• Helms, E. R., et al. (2016). RPE-based autoregulation in resistance training: current status and future directions. Sports, 4(2), 35.

• Kjaer, M. (2004). Role of extracellular matrix in adaptation of tendon and skeletal muscle to mechanical loading. Physiol Rev, 84(2), 649–698.

• Soligard, T., et al. (2016). How much is too much? (Part 1) International Olympic Committee consensus statement. Br J Sports Med, 50(16), 1030–1041.