Training Load and Adaptation in Rehabilitation

Golden State Warriors forward Jimmy Butler III suffers an apparent injury during the first quarter during game two of the first round for the 2024 NBA Playoffs against the Houston Rockets at Toyota Center. Mandatory Credit: Troy Taormina-Imagn Images

When training load is insufficient, adaptation is unlikely to occur, while an excessive training load may cause fatigue and maladaptation. A well-structured training load ensures that athletes recover effectively while making the necessary adaptations to return to competition. However, training load is a complex concept, and understanding it beyond simply increasing or decreasing workload is essential for sports injury professionals. 

One common mistake in rehabilitation settings is assuming that increasing workload over time will lead to a predictable recovery trajectory. However, as many rehabilitation professionals have witnessed, two athletes undergoing the same rehabilitation program can have vastly different outcomes. A footballer recovering from an ACL tear may return to full fitness within six months, while another player with the same injury may struggle to regain pre-injury performance. What accounts for this discrepancy? Understanding training load, stimulus, adherence, and individual variability is key to answering this question.

“…understanding training load requires more than just tracking volume and intensity.”

Exposure and Dose

A group of sports scientists from the University of Technology Sydney have completed some important work defining concepts of training load and aligning them with definitions in other medical fields such as epidemiology⁽¹⁾.  They have conceptualized the training load in terms of exposure and dose. Exposure is the overall volume and type of training an athlete undergoes, whereas dose accounts for the internal physiological impact of that training. Importantly, for a training stimulus to be effective, there must be a causal relationship between the exposure and the desired adaptation. Simply exposing an athlete to a training load does not guarantee improvement—adaptation occurs only if the dose elicits the intended physiological response.

Consider a long-distance runner recovering from a stress fracture. If their rehabilitation plan prescribes low-intensity cycling without progressive impact training, they may maintain cardiovascular fitness but fail to stimulate bone remodeling and adaptation needed to return to running. In this case, the dose required to rehabilitate the athlete involves mechanical forces applied through progressively increasing the duration and intensity of weight-bearing running activity. The cycling stimulus would create a mismatch between the intended physiological response and the stimulus required to elicit that response, and highlights why training plans must be carefully tailored to result in the required training effect.

This means that training programs that only prescribe the exercise volume are not specific enough. The choice of exercise stimulus (type of exercise prescribed) must be directly related to the physiological response required for the athlete’s recovery. This is what Impellizzeri and colleagues refer to as a causal relationship – the training plan must be linked to known and predictable physiological response⁽¹⁾. This highlights the importance of planning both external load (the type, volume, and intensity of exercise) and internal load (how an athlete physiologically and psychologically responds to the training)(see figure 1).