Amyotrophic lateral sclerosis (ALS) is a neurodegenerative disease characterized by the loss of upper and lower motor neurons.1–3 Symptoms include motor aspects, such as muscle weakness and atrophy, general fatigue, dysphagia, speaking difficulties and respiratory dysfunction.1–3 and non-motor aspects, such as cognitive, psychiatric and autonomic disorders.1,2 The most common cause of death for people with ALS is respiratory failure.1–3

ALS is considered one of the most disabling chronic neurodegenerative diseases, as progressive generalized muscle weakness leads to activity limitations and participation restrictions. Falls are often reported in this population3,4 and can result in serious problems, such as pain, injury, the loss of confidence, dependence, a reduction in quality of life, an increase in healthcare costs and even death.3,5 The consequences of falls in individuals with degenerative diseases can exert strong impacts, leading to a cycle of disuse/dysfunction that accelerates the decline in muscle function and the loss of the ability to perform activities of daily living in an independent manner, such as standing and walking.6,7

Falls are considered multifactorial events, as the predictors of such events involve biological, behavioral, environmental and socioeconomic aspects.8 Some of the factors described as contributing to falls in ALS are muscle weakness, postural instability, mobility decline and changes in muscle tone.3,6 However, no studies have performed a broad investigation of the factors actually associated with the occurrence of falls in ALS. In a retrospective study on the occurrence of falls, a low correlation was found between falls and lower limb weakness.3 However, studies that prospectively investigate this outcome and potential predictors are needed for a better understanding of falls in ALS.

Falls can occur in individuals with different degrees of dysfunction from those with the capacity for independent walking in the community to those who rely on wheelchairs for mobility.7 However, the few studies that have investigated falls in ALS only analyzed individuals with the capacity for functional ambulation,3,6 leaving an important portion of people with ALS who have lost their functional ability to walk out of their analyses.

Investigating falls and associated factors, both in people with ALS with a functional gait and in people who only locomote in a wheelchair, is important to expand knowledge about the occurrence of falls in individuals with ALS. Such information can assist health professionals in the implementation of care and more effective fall prevention programs to improve wellbeing in this population. Therefore, the aim of this study was to investigate the frequency of falls in individuals with ALS with and without functional ambulation, and to identify predictors of falls at three and six months in the group with functional ambulation.

Among the 66 participants in the study at baseline, nine died before the six-month follow-up and 86.4% completed the two follow-up stages. The participants who died between follow-ups were not included in the statistical analysis. At baseline, 63.6% of the participants had functional ambulation and 36.4% had non-functional ambulation. None of the participants with functional ambulation at baseline lost their ability to ambulate functionally at the three- and six-month follow-up (Fig. 1).

Fig. 1.

Flowchart of study.

To the best of our knowledge, this study is among the first to investigate the frequency of falls in individuals with ALS, both with and without functional ambulation, and to identify predictors of falls specifically among those capable of functional ambulation. Falls have been observed in both walkers and wheelchair users. The predictors of falls between baseline and the three-month follow-up among those with functional ambulation were lower limb strength and general fatigue, whereas only lower limb strength was a predictor of falls at the six-month follow-up. It was not possible to identify predictors of falls among those without functional ambulation due to the small sample size. Further research on falls in ALS patients should include those without functional ambulation to identify predictors. The rate of falls among the participants with functional ambulation was greater than that among the non-ambulators at both the three-month (47.4%vs 18.2%) and six-month (59.5%vs 10.0%) follow-up, as expected. Individuals with ALS capable of functional ambulation are more exposed to situations that increase the odds of falling, as they are still capable of performing activities that involve walking, transfers and the maintenance of the standing position.4,19 Studies comparing falls among ambulators and non-ambulators with other neurological conditions, such as multiple sclerosis and spinal cord injury, also report a greater frequency of falls among those with the capacity to walk.8,19,20

Falls are frequently reported during clinical appointments and are considered an adverse outcome in ALS clinical trials. However, the actual occurrence of falls in this population is still not well characterized. The mean number of falls observed in the present study (2.39±2.64) was lower than that reported in a previous study (5.46±8.56 falls).3 This difference may reflect variations in participants’ functional profiles, as that study included only individuals capable of walking independently for at least 20 feet (6.1 m).3 A notable finding of the present study was that the number of falls increased over the follow-up period in both groups, indicating recurrent falls over time. These findings highlight the importance of implementing prevention strategies tailored to individual needs7 to reduce the risk of new fall episodes, morbidity, and mortality in this population.21 Further studies are needed to investigate the frequency and recurrence of falls in individuals with different functional conditions and populations to better understand this outcome in ALS.

Among participants who fell, limitations in daily activities were commonly reported in both ambulatory and non-ambulatory individuals. This outcome may be related to reduced confidence and an increased fear of falling, which may lead to a further mobility restrictions and greater dependence in daily activities.20,22 In individuals with ALS, reduced activity can be particularly debilitating, as the weakness from inactivity adds to the progressive loss of strength caused by the disease.23 Prolonged inactivity may result in muscle atrophy, shortening, joint stiffness, and osteoporosis, increasing the risk of contractures, pain, and fractures.23 Therefore, research into strategies to prevent falls and minimize their functional impact is essential.

Despite the frequency of falls, none of the ambulatory participants required medical care due to a fall, whereas a fracture requiring medical attention occurred in the non-ambulatory group. Similar findings have been reported in other neurological populations, such as spinal cord injury and multiple sclerosis, where ambulators sustained milder injuries and required less medical care despite more frequent falls.8,19,20 The significant dysfunction and limitations of ALS among individuals who have lost the ability to walk make them more vulnerable, as they are likely to be less able to react to protect themselves in a fall (i.e., reduce control of the fall by activating muscles or using the upper limbs), resulting in more severe injuries.19,20 Minor injuries not requiring medical attention (e.g., bruises or scratches) were not systematically collected in this study, which could be considered in future investigations.

Among individuals with functional ambulation, the predictors of falls were lower limb muscle strength and the presence of fatigue at three months, whereas only lower limb muscle strength remained a predictor at six months. These results confirm the previously identified association between lower limb strength and falls in individuals with ALS.3 This association is well established and has also been reported in other populations and diagnostic groups.22,24 Muscle activation is required to move, stabilize, and balance the body; insufficient strength increases fall risk. Therefore, an inability to produce enough strength increases susceptibility to falling. In the present study, each unit reduction in the lower limb muscle strength score increased the odds of falling by 16% in three months and by 14% in six months. The progressive decline in muscle strength is unavoidable in individuals with ALS, as the disease is characterized by the continuous degeneration of motor neurons throughout the nervous system.1,2 ALS begins as a focal process and gradually spreads to different body regions.1,2 Beyond disease-related weakness, ALS patients lose strength due to disuse, especially in unaffected muscles, and often adopt a sedentary lifestyle.10,23,25 Even those who remain ambulatory tend to adopt a more sedentary lifestyle as an adaptation to the challenges imposed by the disease. Barriers to activity include walking risks, fear, deconditioning, weakness, and fatigue.11

Although the course of ALS cannot be modified, several studies have reported beneficial effects of physical training on maintaining or improving muscle strength, especially during the early stages of the disease.10,23,25,26 Strength maintenance and even gains may occur in affected muscles through compensatory mechanisms such as collateral sprouting of surviving motor neurons. However, as motor units are progressively lost, the adaptive capacity to training declines, and positive effects are limited to the initial disease stages.10,23,25,26 Therefore, considering the finding of a reduction in lower limb strength as a predictor of falls, future studies should investigate whether interventions for improving strength can reduce the occurrence of falls in this population.

In the present study, general fatigue increased the odds of falling 7.8 times among individuals with functional ambulation in the three months following the initial assessment. Fatigue is a disabling symptom that has also been considered a predictor of falls in other populations, such as patients with multiple sclerosis27 and Parkinson’s disease.28 Although fatigue is a frequent symptom in ALS, it remains poorly understood, investigated and treated clinically.23,29 Recent evidence from a Brazilian cohort supports the multidimensional nature of fatigue in ALS.30 reinforcing its multifactorial etiology.29,30 Fatigue in ALS manifests as general fatigue, experienced as generalized tiredness or lethargy, and physical fatigue, characterized by an objective decline in muscle force capacity.29 The perception of fatigue in ALS tends to worsen throughout the day and exerts an impact on the motivation to perform simple tasks due to the considerable need of effort and low performance.29 Fatigue in ALS reduces strength and functioning, affecting daily activities, quality of life, 29 and participation, highlighting the importance of addressing fatigue in rehabilitation. In this study, fatigue predicted falls only between baseline and the three-month follow-up (shorter follow-up period). The wide variation in the perception and intensity of fatigue over time, influenced by factors such as respiratory function, medication use, nutrition, activity level, and psychological aspects, may have contributed to this finding. 29 This highlights the complexity of fatigue in ALS and reinforces the need for further research on this symptom.

The present study contributes to the longitudinal investigation of falls in ALS by including individuals both with and without functional ambulation and evaluating potential predictors specifically in the functional ambulation group. However, this study has limitations. A convenience sample of ALS patients from a single neuromuscular diseases reference clinic limited the overall sample size. The small number of participants in the non-functional ambulation group made it impossible to perform predictive analyses. In the functional ambulation group, the relatively small number of fall events may have limited statistical power and restricted the number of predictors that could be included in the multivariate regression model. Although larger studies are needed to confirm these findings, longitudinal research in ALS remains challenging due to the disease’s rarity, short survival, and heterogeneity. Nevertheless, this study is the first to investigate falls longitudinally in individuals with ALS, providing valuable insights into potential predictors of this outcome. Other variables, such as age, which is frequently reported as a determinant of fall risk in other populations, were not included, as the age distribution was similar between fallers and non-fallers. However, future studies should investigate whether age contributes to fall risk in ALS or whether disease-related weakness predominates. The fall monitoring method used during follow-up also represents a limitation, and future studies may benefit from more frequent monitoring, such as fall diaries. Another limitation is that cognitive status was evaluated through routine clinical judgment by the neurology team, rather than through a standardized cognitive screening instrument. This approach reflects common clinical practice in ALS care, particularly in motor-focused studies. However, incorporating validated ALS-specific cognitive screening tools in future research could improve diagnostic precision and enhance comparability across cohorts. Future research should further investigate factors related to falls in ALS, including recurrent and injurious falls, as well as the potential influence of non-motor symptoms such as cognitive dysfunctions.

Falls can occur across different functional profiles in ALS but are most frequent among ambulatory individuals. These findings highlight the importance of assessing fall risk and implementing preventive strategies. In ambulatory individuals, interventions should target fatigue and lower limb strength early in rehabilitation to help prevent falls. Future studies should also consider individuals with ALS without functional ambulation.

This research did not receive any specific grant from funding agencies in the public, commercial, or not-for-profit sectors.