Expanding the Affordance Landscape
Integrating Newell’s Model of Constraints for Return to Play
A Special Guest Edition by Jarred Boyd
In sport, a successful rehabilitation is often deemed as one that has either met a pre-ordained timeline or demonstrated more latent and emergent task completion, while perhaps failing to discern if the requisite adaptations have been acquired to augment performance or afford protection. Unfortunately, this can lead to immature capacities and capabilities that can result in a shrunken affordance landscape and lowered safety margin.
The affordance landscape is denoted as the spectrum of opportunities for action available to an athlete, shaped by the environment and internal resources owned by the athlete. Return to play testing attempts to measure related constructs, ranging from hop symmetry to CMJ force time signatures to kinematic analysis of deceleration, to infer whether an athlete can manipulate space and maintain pace once back on the field. Starting with the goal of the game, rather than a sequential checklist, is what makes Newell's model of constraints useful for discerning the requisite constituents that can shift the probability to a more favorable return to performance.
Every game, or at least team sport, has a goal: expand the possibilities to prevent goals and expand the possibilities to attempt them. This is essentially predicated on invasion, reducing an opponent's space (defense) and evasion, avoiding defenders, to open more solution space.
Meeting that goal requires distinct tasks: organizing solutions to the spatial and temporal constraints the game imposes, another way of saying an athlete must manipulate space(s) and maintain pace. Those tasks, however, mandate actions where athletes generate and regulate time-constrained movements to enable effective solutions. These movement solutions are accomplished by manipulating mass in motion, which warrants sufficient impulse.
The game's actions, in turn, demand internal capacity predicated on biology, the structural hardware, and neurology, the functional software that recruits and coordinates it. Whether an athlete can meet those demands depends on two further constructs: capacity and tolerance. Capacity is the ceiling of what that hardware can produce; tolerance is what the biology can currently withstand repeatedly under the game's demands. During the return to performance transition, it is recognizable that the athlete who presents with seemingly restored tolerance simply because they were neither exposed to force time signatures that the game engenders nor resolved the antecedent physical capacities, thereby giving the illusion of preparedness, that is, until competition supplies the exposure the rehabilitation continuum did not.
Finally, repeated action(s) can carry a consequence: the mechanical and energetic costs that accumulate over time, resulting in mechanical fatigue. At the most proximate causal level, injuries arise from insufficient resources to contend with the stress, resulting in internal strain exceeding exposure.
Take reduced quadriceps capacity, where a single constraint can moderate two consequences at once: (1) it moderates deceleration and effective defense, since it diminishes the internal knee extensor moment available to counter the external knee flexion moment during braking, and (2) it moderates deceleration and patellar tendinopathy, since less force generating capacity means less ability to sustain the high tension, quasi isometric action that may more effectively distribute joint load, pushing that demand onto the tendon instead. Thus, deliberately constraining the knee extensor mechanism to hedge the bet on adapting the quadriceps-specific bottleneck may rectify the unfavorable outcomes.
Knowing which constraint to target requires understanding what drives the loading in the first place. Newell's model frames task constraints as emerging from the organism-environment relationship, part of a feedback loop rather than a straight line (Balagué et al., 2019). A given biological state shapes which movement strategy emerges to meet a task, contingent on that context and those constraints. That strategy's kinetics, the forces produced, determine its kinematics, the resulting motion. Together, they set the mechanical loading, a ground reaction force with both magnitude and direction, applied to a given joint and its corresponding tissue. That loading then reshapes the biological state carried into the next demand, which reshapes what emerges next.
Within any action capability- sprinting, accelerating, decelerating, jumping- the nervous system has variable solutions available, a property called degeneracy: structurally different elements of a system yielding the same output (Whitacre et al., 2010; Seifert et al., 2016). It's a real evolutionary benefit, the variable movement solutions (i.e., adaptability), but also a liability, since an athlete can exploit a solution that isn't consistently viable, and the cost often surfaces as a performance inhibitor, the affordance landscape quietly shrinking, well before it ever shows up as an injury.
The clinical evidence on ACL reconstruction shows exactly how that shrinkage can hide behind a passing score. Post ACL reconstruction patients who'd cleared an 85 percent hop symmetry threshold were still carrying a 40 percent knee extension moment deficit, offset by higher hip and ankle output (Orishimo et al., 2010), and conventional strength and hop symmetry criteria carried almost no ability to predict a second injury at all (King et al., 2021).
Thus, degeneracy is what makes constraining a movement purposeful, particularly when the adaptive intent is directionally correct. Left alone, however, degeneracy can displace loading elsewhere while preserving the task; reducing the knee extensor mechanism's degrees of freedom closes off the alternative routes and shifts probability toward the intended tissue receiving the stimulus.
Restoring capacity, however, only addresses half of what determines whether an athlete can truly act on it. What an athlete perceives as achievable in each moment is scaled to, though not limited to, their internal constraints. Restoring local capacity, biological and neurological, lets action-scaled perception catch up to what the tissue can deliver; restitution is necessary but not sufficient. Owning the requisite determinants for higher-order force-generating capacities: maximal, explosive, reactive, and for tissue-specific mechanical properties such as stiffness doesn't guarantee an athlete will perceive an affordance or act to exploit it; it only increases the potential, and potential isn't the same as realization. Instead, it reduces the probability that an internal constraint is the bottleneck between the athlete and a task goal. Representative tasks must be embedded alongside that restitution to calibrate perception and action together; otherwise, when the two decouple, perception can end up living outside the bandwidth of action, in either direction.
One direction is an athlete perceiving an affordance their capacity can't support: perception running on pre-injury references, a gap that looks exploitable, while the substrate, altered mechanoreception, or a depressed rate of force development, remains unsatisfactory. The athlete attempts to exploit an affordance they don't own, and by Newton's third law, the tissue receives a reaction force and a potential demand it was never conditioned to buffer. That's the protection failure: perception overestimating what capacity can afford. The other direction is the reverse: capacity restored but perception never recalibrated to it. The athlete looks prepared in the gym and hesitant on the field, still moving as though the deficit is present, unable to imbue restored capacity into a live environment. That's the performance failure: perception underestimating what capacity can now afford.
A linear rehab model- heal the tissue, strengthen the muscle, return to the field- addresses half the equation, restoring capacity without re-coupling perception to it, especially when rehab often exists in a sterile and partitioned environment with none of the informational constraints sport provides. If we return athletes to chaos, then the perceptual system must recalibrate in real time, under competitive pressure, to information it was never exposed to; thus we may inadvertently invite subpar performance or capacity-exceeding mechanical stress. The two halves should develop together instead: restitution rebuilding the biophysiological substrates while calibration comes from embedding representative tasks, progressively in that same loading phase, well before the isolated work is finished, so perception keeps re-learning what current capacity can achieve against real-time information.
Perception and action are moderated by constraints, and clinicians have the most direct influence over organism, or internal, constraints: the biology and neurology determining whether a substrate is sufficient to realize a capability. Constraints are often treated as boundaries; in practice they function more like biological moderators. But task and environment are constraints in that same sense, not lesser ones, and every representative element described above is an intentional manipulation of the task and environment (Woods et al., 2020). Expanding what an athlete can demonstrate, while possessing the requisite adaptations, means not overinvesting in the organism side alone; it comes from treating all three domains as levers, since action capabilities only get realized through the interaction of what the athlete can produce, what the task demands, and what the environment offers.
Each of these variables determines how effectively an athlete can exploit the affordances in front of them. Capacity and neurology demonstrate true preparedness, augmenting performance; biology and tolerance demonstrate true readiness, affording protection. The job, especially in the middle to late stages of reconditioning, is developing capacities that exploit affordances while ensuring an athlete can tolerate what that exploiting demands: scaling the task to the athlete's physical apparatus where it currently is, while layering the sensorimotor and neurocognitive constituents of perception back in, so the trained substrate funnels toward emergence rather than being asked to produce it before the capacity exists.
About the Author:
Jarred Boyd is a seasoned NBA performance and rehabilitation professional with extensive experience leading reconditioning and return-to-play in professional sport. His approach integrates biomechanics, tissue-specific adaptation, and performance readiness within a systems-based framework that considers objective data, athlete context, and the demands of competition. Jarred emphasizes risk-aware decision-making, transdisciplinary collaboration, and servant leadership to align medical, performance, and coaching teams around the athlete’s return to performance.
Connect with Jarred at @dr.fjitboyd and check out his many educational offerings!
References:
Balagué, N., Pol, R., Torrents, C., Ric, Á., & Hristovski, R. (2019). On the relatedness and nestedness of constraints. Sports Medicine - Open, 5, Article 6.
King, E., Richter, C., Daniels, K. A. J., Franklyn-Miller, A., Falvey, E., Myer, G. D., Jackson, M., Moran, R., & Strike, S. (2021). Biomechanical but not strength or performance measures differentiate male athletes who experience ACL reinjury on return to level 1 sports. The American Journal of Sports Medicine, 49(4), 918-927.
Orishimo, K. F., Kremenic, I. J., Mullaney, M. J., McHugh, M. P., & Nicholas, S. J. (2010). Adaptations in single-leg hop biomechanics following anterior cruciate ligament reconstruction. Knee Surgery, Sports Traumatology, Arthroscopy, 18(11), 1587-1593.
Seifert, L., Komar, J., Araújo, D., & Davids, K. (2016). Neurobiological degeneracy: A key property for functional adaptations of perception and action to constraints. Neuroscience & Biobehavioral Reviews, 69, 159-165.
Whitacre, J. M. (2010). Degeneracy: A link between evolvability, robustness and complexity in biological systems. Theoretical Biology and Medical Modelling, 7(1), 6.
Woods, C. T., McKeown, I., Rothwell, M., Araújo, D., Robertson, S., & Davids, K. (2020). Sport practitioners as sport ecology designers: How ecological dynamics has progressively changed perceptions of skill "acquisition" in the sporting habitat. Frontiers in Psychology, 11, Article 654.
Guest Author: Jarred BoydPT, DPT, MSAT, SCS, CSCS
Physical Therapist - Orlando Magic
READ MORE
As sport science becomes increasingly data-driven, every measurement, model, and prediction comes with assumptions. This edition of The Film Room explores the assumptions hidden within data collection, processing, injury epidemiology, and prediction—while arguing that the goal isn’t to eliminate assumptions, but to understand them and let their limitations shape our confidence in the decisions we make.