Muscle strength, activity limitations, and proprioception in hEDS
Hypermobile EDS produces weakness that is not primarily a muscle problem. It produces autonomic instability that is not primarily an autonomic nerve problem. Both — the weakness and the autonomic dysregulation — share a common upstream factor: degraded proprioceptive signaling from connective tissue that is too lax to provide reliable sensory information about the body's position and movement. A 2016 study by Scheper and colleagues published in Disability and Rehabilitation established the proprioceptive impairment in hEDS with direct measurement, and in doing so provided a mechanistic bridge between the connective tissue problem and the neuromuscular and autonomic consequences that follow from it.
The Study: Measuring Proprioception Directly
Scheper and colleagues recruited women with hypermobile Ehlers-Danlos syndrome and age-matched healthy controls and assessed three domains: maximal muscle strength using isokinetic dynamometry, activity limitations using standardized functional performance tests, and proprioceptive acuity using joint position sense testing at multiple joint sites.
Joint position sense is a direct measure of proprioceptive function. In a standard joint position sense test, the patient is blindfolded and the assessor moves the joint to a specific angle, holds it briefly, returns it to neutral, and asks the patient to reproduce the target angle without visual feedback. The accuracy of reproduction — how close the patient can get to the target angle using only proprioceptive information — quantifies the precision of the mechanoreceptor signals being received from that joint and the accuracy with which the nervous system interprets them.
The results confirmed significant deficits across all three domains in hEDS patients. Muscle strength was reduced, consistent with the Rombaut findings. Activity limitations were greater than in controls. And proprioceptive acuity was measurably worse across multiple joint sites — the hEDS patients could not accurately reproduce joint positions without visual feedback as well as healthy controls could. The proprioceptive deficit was not subtle and was not limited to one joint. It was systemic, reflecting the systemic nature of the connective tissue compromise.
Why Ligaments Are Sensory Organs, Not Just Structural Elements
The mechanistic significance of this finding requires understanding what ligaments actually do beyond their structural role. Ligaments are not passive cables that hold joints together. They contain mechanoreceptors — specialized sensory nerve endings that detect deformation, rate of change of deformation, and tension — and continuously transmit this information to the spinal cord and brain. These signals are a primary input for proprioception: the moment-to-moment sense of where each body part is, how fast it is moving, and how much load it is bearing.
When ligaments are lax — as they are in hypermobility — several things happen to proprioceptive signaling. The mechanoreceptors fire at different thresholds than they do in appropriately taut ligaments: they may not be activated until the joint has moved further from neutral than in a taut ligament, producing delayed and less precise positional information. The signal is noisier relative to the actual joint position, because the relationship between ligament deformation and joint angle is less linear when the ligament has excess slack. The brain receives degraded positional information: late, imprecise, and potentially inconsistent across different positions in the joint's range of motion.
This is not a theoretical concern. The Scheper joint position sense data are the direct measurement of what degraded mechanoreceptor signaling from lax ligaments produces: objectively impaired ability to perceive joint position without visual confirmation. The proprioceptive system is receiving unreliable input and producing unreliable output.
The Connection Between Proprioception and Motor Control
Degraded proprioceptive input has direct consequences for motor control. The nervous system generates motor commands based on a continuously updated model of where the body is and where it needs to go. This model is built from proprioceptive signals — from joints, tendons, muscles, and the vestibular system — integrated in real time. When proprioceptive signals are less precise, the motor model is less precise, and the motor commands it generates are calibrated to a body-state estimate that may not match actual body state.
The result is that hEDS patients cannot produce coordinated, powerful muscle contractions with the same reliability as people with normal proprioceptive feedback. The nervous system holds back from maximal activation because it cannot confidently monitor what is happening in the joint during high-force contraction. The Rombaut finding that EDS-HT patients show reduced strength with near-normal muscle mass is the functional output of this impaired motor control: adequate contractile tissue, impaired nervous system command and coordination of that tissue. The Scheper proprioception data provide the mechanistic explanation for why impaired motor command occurs in hEDS.
The Proprioception-Interoception-Autonomic Connection
The link between proprioceptive impairment and autonomic dysfunction is the interoceptive pathway. Interoception — the brain's monitoring of internal body state — relies on sensory signals from multiple sources, including the viscera, the cardiovascular system, and the musculoskeletal system through proprioceptive afferents. The brain uses these signals to continuously update its model of the body's current physiological state and generate regulatory responses accordingly.
The autonomic nervous system's regulatory output — heart rate, vascular tone, respiratory rate, digestive motility — is calibrated based on this continuously updated interoceptive model. The brain modulates autonomic output based on what it perceives about the body's current demands and resources. When the sensory inputs informing that model are noisy and imprecise — as they are when proprioceptive signals from lax ligaments and tendons are systematically degraded — the model is less accurate, and the autonomic regulatory outputs based on it are less precisely calibrated.
This provides a physiological mechanism for the high rate of autonomic dysfunction observed in hEDS patients. The Eccles research on hypermobility, neurodivergence, and autonomic symptoms documented that hypermobile individuals show significantly higher rates of orthostatic intolerance symptoms and autonomic symptom burden. The Scheper data establish the sensory-degradation mechanism through which hypermobility produces that result: lax connective tissue degrades the proprioceptive input quality that the autonomic system depends on for accurate regulatory calibration.
What This Means for Rehabilitation
If proprioceptive impairment is a primary driver of both motor control deficits and autonomic instability in hEDS, then proprioceptive retraining is not a peripheral rehabilitation component — it is a mechanistic target. The GoodHope GEAR program includes proprioceptive training as a core component precisely because the research supports it as addressing the relevant mechanism, not just as a general rehabilitation practice.
Proprioceptive training in EDS involves deliberate, repeated practice of joint position sense — balance tasks that challenge postural stability without visual feedback, joint repositioning exercises that force reliance on mechanoreceptor signals, and movement patterns that require precise positional awareness. Through repeated practice, the nervous system becomes more accurate at interpreting and using the imprecise mechanoreceptor signals that lax connective tissue provides. The ligaments are not changed. The brain's capacity to extract accurate positional information from the signals those ligaments generate is improved — a neuroplastic adaptation that improves function within the physical constraints of the condition.
For patients who have been told their weakness is unexplained or that their autonomic symptoms are unrelated to their connective tissue, the Scheper data provide a specific mechanistic counter: proprioceptive degradation from hypermobile connective tissue produces measurable impairment in joint position sense, which degrades motor control, which limits functional strength, and which — through the interoceptive pathway — contributes to imprecise autonomic regulation. These are not three separate problems. They are three consequences of one underlying sensory impairment.