In persons with SCI, the loss of voluntary muscle contraction and weight-bearing activity below the level of the lesion can lead to bone loss. The 2019 International Society for Clinical Densitometry (ISCD) Official Positions highlight the significant impact of bone loss in individuals with SCI. Significant and rapid declines in areal bone density occur very early following SCI, with losses reported at the hip, proximal tibia, and distal femur. BMD of the lower limbs decreased up to 28% to 50% below that of age-matched peers at 12 to 18 months postinjury. Most studies that examined BMD and level of injury compared with individuals with paraplegia versus tetraplegia did not find a relation between level of injury and bone loss. No significant changes in BMD after SCI were found in the proximal and distal forearm (radius and ulna). However, upper extremity activities (eg, wheelchair basketball) may result in higher-than-normal upper extremity bone density. ^, Bone loss is greater around the knee than in the hip region after SCI, and the loss is greater in individuals with motor-complete lesions. Studies comparing the BMD loss in the distal femur and the proximal tibia after SCI show a greater loss at the distal femur as well as in the proximal tibia, often without major differences between the sites.

There is agreement in the literature that lower extremity bone density is reduced in individuals with SCI who have a prevalent fragility fracture. Dual-energy X-ray absorptiometry (DXA) scans of the lumbar spine in the same patient population may appear normal despite severe demineralization in the lower limbs. This discrepancy may be due to overestimation of spine bone density due to osteophyte formation or because weight-bearing and functional demands on the lumbar spine are maintained, while the lower limbs lose bone mass due to immobilization and lack of weight-bearing. Individuals with complete SCI are more likely to have osteoporosis than those with incomplete injuries. Over half of those with motor-complete SCI experience osteoporotic fractures, commonly at the distal femur and proximal tibia. Fractures may be associated with serious complications such as delayed healing, infections, skin breakdown, amputations, and increased mortality. The ISCD emphasizes the importance of early and targeted bone density assessments using DXA at the total hip, distal femur, and proximal tibia to diagnose osteoporosis and assess fracture risk in this population.

Bone demineralization in athletes with unilateral lower limb amputation is found at the impaired hip but not at the lumbar spine and may therefore be site-specific. The extent of hip demineralization was influenced by the level of amputation, with about 80% of individuals with above the knee amputation and 10% of individuals with below the knee amputation showing areal BMD below the expected range for age. Athletes with lower-limb amputations may have asymmetric loading that leads to decreased BMD in the residual limb and compensatory bone stress in the intact limb. ^,, In children with congenital limb deficiencies, bone geometry and density may be affected from early development, further increasing fracture risk during sports participation. This group may be at risk for decreased bone density, due to factors such as reduced mechanical loading, nutritional challenges, and limited mobility, although direct studies on bone density in children with congenital limb deficiency are scarce.

Individuals with CP have elevated risk for low bone density due to a combination of factors including decreased mobility, anticonvulsant medication use, nutritional deficiencies, and hormonal alterations. Adults with CP have lower bone density at the lumbar spine, femoral neck and whole femur compared to age-matched and sex-matched adults. Sixty-four percent of adults with CP over the age of 50 have osteoporosis based on bone density by DXA. Male sex, nonambulatory status, and bilateral CP may be risk factors for more severe bone loss.

Assessing bone health in adaptive athletes can be clinically challenging. DXA, the standard method for measuring bone density, may be inaccurate for a variety of reasons. A 2024 study by Ponmzano and colleagues highlighted factors such as facet sclerosis, lumbar instrumentation, osteophyte formation, difficulty identifying bone edges, and outlier BMD values that frequently hinder the analysis of 3 contiguous vertebrae in patients with SCI. These challenges contribute to unreliable bone density measurements in the lumbar spine. As a result, Ponmzano and colleagues recommended that lumbar spine BMD not be used for fracture risk assessment or clinical decision-making in this population. Bone loss may also be evaluated by peripheral quantitative computed tomography (pQCT) or calcaneus quantitative ultrasound (US), but these methods also have limitations. pQCT is a high-cost method and is not available everywhere. US shows promise as a sensitive tool for detecting early bone loss in individuals with acute SCI. However, the current body of peer-reviewed literature is limited, and further research is necessary to establish standardized protocols, validate its diagnostic accuracy, and compare its effectiveness with gold-standard methods like DXA.

Fractures in adaptive athletes are not only more likely to occur but may also result in greater loss of function, independence, or sports participation. In the general population, low-trauma fractures, such as those occurring during transfers, wheelchair propulsion, or falls, are relatively common, particularly in the lower extremities. Inadequate bone strength can also interfere with rehabilitation efforts, prosthetic fitting, and performance goals, making early identification and prevention strategies critical. In the adaptive athlete population, this increased fracture risk must be considered and monitored closely, particularly for athletes participating in high-speed sports such as para-alpine skiing and para cycling.

LEA interferes with hormonal pathways essential for proper bone remodeling, notably affecting the hypothalamic-pituitary-gonadal axis, summarized in Fig. 1 . In females, this disruption often results in menstrual irregularities, while in males it leads to lower testosterone levels, and both outcomes impair osteoblast function and elevate bone resorption. LEA is also linked to decreased levels of insulin-like growth factor-1, leptin, and triiodothyronine (T3), hormones that are vital for bone growth and maintenance. ^, This hormonal suppression creates an imbalance between bone formation and breakdown, ultimately lowering BMD, increasing the risk of fractures, and hindering skeletal development, particularly in adolescent athletes.

Mechanism of RED-S: Hormonal pathways linking LEA to bone health impairments.

Data on the prevalence of RED-S in adaptive athletes is limited, but recent studies have begun to highlight trends. A survey of elite para-athletes, regardless of sex or sport type, found that a significant proportion exhibited symptoms consistent with LEA, including persistent fatigue, frequent illness, menstrual irregularities, and stress fractures. Risk factors in this population are multifaceted and include reduced muscle mass, chronic inflammation, comorbid conditions, and barriers to adequate nutrition such as dysphagia, gastrointestinal issues, or limited food access during travel.

Moreover, adaptive athletes often engage in intense training with high energy demands and may misjudge their energy requirements due to differences in body composition or mobility status. Individuals with SCI, for example, may have lower resting metabolic rates but higher caloric demands during upper-body propulsion or wheelchair sports. These mismatches between energy intake and expenditure may contribute to unintentional LEA, particularly in the absence of tailored nutritional guidance.

Conventional tools used to assess LEA and RED-S, such as the Low Energy Availability in Females Questionnaire (LEAF-Q), while validated for female endurance athletes and dancers, have not been validated for use in adaptive athletes and may yield inaccurate results due to the population’s distinct characteristics. Hormonal markers, body composition analysis, and dietary logs must be interpreted in the context of disability, training modality, and medical history. Given these challenges, there is a clear need for the development of assessment tools that are specifically validated for adaptive athletes. Such tools should consider hormonal markers, body composition analysis, medical, and nutritional factors affecting this population to ensure accurate identification and management of LEA and RED-S.

Many adaptive athletes have coexisting conditions that independently affect bone health and exacerbate disuse osteoporosis (discussed earlier). For example, individuals with CP or traumatic brain injury may require anticonvulsant medications, which can interfere with vitamin D metabolism and calcium absorption. Glucocorticoid use (common in autoimmune or inflammatory conditions) further increases bone resorption and reduces bone formation. Athletes with gastrointestinal dysfunction, common in SCI, may also have compromised nutrient absorption affecting calcium, vitamin D, and protein reserves, which are critical for bone maintenance.

The endocrine consequences of LEA are magnified in adaptive athletes, especially among females. Menstrual dysfunction, amenorrhea, and oligomenorrhea are hallmarks of LEA and are prevalent among elite female athletes with disabilities. ^, A 2019 study by Brook and colleagues surveyed 260 elite US para-athletes and found that 44% of premenopausal females reported menstrual dysfunction, and 9% of all athletes reported bone stress injuries. For women with SCI or CP, these irregularities may be further exacerbated by physiologic stress, insufficient energy intake, or the use of certain medications. These disruptions contribute to reduced estrogen levels, a hormone critical for maintaining bone mass. Consequently, impaired estrogen production leads to compromised bone health and increased long-term fracture risk. ^,

Adaptive athletes may face additional challenges in meeting their nutritional needs. Figel and colleagues (2018) reviewed energy and nutrient issues in athletes with SCI, noting that this group may be at increased risk for LEA due to unique physiologic and nutritional challenges. Dysphagia, altered appetite, and gastroparesis can further limit energy and nutrient consumption, heightening the risk of LEA even in athletes who are not purposefully restricting intake. Para-athletes reported that approximately 40% required assistance with meal procurement and preparation, particularly during travel, due to reduced independence and manual dexterity. Furthermore, dependency on caregivers is a barrier to consistent nutritional intake in a subset of the adaptive athlete population, especially those with upper-limb impairments or power wheelchair users.