Parkinson’s disease (PD) is a chronic progressive neurodegenerative disorder characterized by both motor and non-motor symptoms (Bloem et al., 2021). The prevalence of PD is increasing among elderly patients in China (Qi et al., 2021). The main motor features are resting tremor, bradykinesia, rigidity, shuffling gait, and postural instability, which have negative impacts on health-related quality of life (HrQOL) of PwP (Beitz, 2014). Early in the course of the disease, symptoms are usually mild, the drug response is usually reliable and the patient functions well. As the disease progresses, there is an increasing impact on and dependence on activities of daily living (Sveinbjornsdottir, 2016).

There is an increasing clinical focus on HrQOL which provides a multi-dimensional view of the patient’s well-being, and a guiding principle for researchers and clinicians (Bock et al., 2022). Strong evidence indicates that motor and non-motor symptoms in PwP limit their independence, essential activities of daily living and social participation. Impairment in these domains can alter social roles by affecting employment status, home management, friendships, and other relationships. Conversely, a decline in HrQOL can have a negative impact on motor and non-motor symptoms (Galeoto et al., 2022).

Previous studies (Gomez-Esteban et al., 2007; Kurihara et al., 2020; Bock et al., 2022) have demonstrated a significant negative correlation between motor symptoms and HrQOL. However, their assessments were self-reported and did not specifically explore which aspect of motor symptoms had the determinant impact on HrQOL at different disease stages. Scalzo et al. (2012) recruited thirty-six patients and found that the impairment in balance while performing functional activities and the reduction in walking capacity negatively affect the perception of HrQOL. But the study had some limitation such as small sample size and incomplete assessment of motor function. There are numerous studies (San Martín Valenzuela et al., 2020; Szefler-Derela et al., 2020; Li et al., 2021) showing improvements in motor function and quality of life through rehabilitation. However, there is still a lack of consensus on how to implement more effective rehabilitation training programs. Therefore, this observational cross-sectional study aims to investigate the relationship between motor function and HrQOL across different disease severity and hypothesizes that balance function and risk of falling would have the greatest impact on HrQOL.

PD is a progressive multi-system neurodegenerative disease affecting people mainly in later years of life. Treatment should focus on functional capacity and quality of life throughout the entire course of disease (Barbosa et al., 2022). However, rehabilitation training is likely to have a more obvious impact in the early to mid-stage of the disease and may prevent or slow down further functional decline (Kluger et al., 2014). This study aims to identify the most impaired motor function caused by the disease and the most relevant HrQOL factors, and then provide a target for rehabilitation training to improve HrQOL in early to mid-stage PD.

FOG is a unique and disabling clinical phenomenon characterized by brief episodes of inability to step or by extremely short steps that typically occur on initiating gait or on turning while walking. Physiological, functional imaging, and clinical pathological studies point to disturbances in frontal cortical regions, the basal ganglia, and the midbrain locomotor region as the probable origins of FOG (Gao et al., 2020). FOG is very common in PD and one of the most relevant features of PD closely related to falls (Bloem et al., 2004; Bekkers et al., 2018; Zhang et al., 2021). Frequent falls lead to injury, fear of falling, reduced mobility and social isolation (Thanvi and Treadwell, 2010). Mehdizadeh et al. (2016) showed that regardless of balance impairments, fear of fall has a negative association with HRQOL in PwP. This study showed that FOG was correlated with HrQOL at H&Y stages I ~ III,which accord with the finding of Ellis et al. (2011) and Nakano et al. (2021). Further analysis showed FOG was correlated with mobility, ADL, and communication. Previous study (Cosentino et al., 2020) proved that physical therapy may improve FOG, for instance, action observation, treadmill combined with cueing, and prolonged home-based exercise trainings. In this study, step length and speed of gait have moderate correlation and toe-off angle had weak correlation with PDQ-39 SI at H&Y stages III, which mainly affected mobility domain. In rehabilitation practice, targeted training, e.g., LSVT BIG (Flood et al., 2020) can be made to address these gait problems of patients.

This study found the moderate association between balance function and HrQOL at H&Y stages II& III, but with no significant association at H&Y stages I. This study shows that patients at H&Y stage I have the highest BBS score and little or mild balance impairment, which is not significantly associated with their HrQOL. Poor balance will lead to poor HrQOL (Nakano et al., 2021), which was found in patients at H&Y stages II& III in this study. Meanwhile, Scalzo et al. (2012) found that patients with severe balance dysfunctions assessed by the BBS and who scored lower distances in the 6 min walking test had worse HrQOL. Furthermore, longer time of TUG and FTSST led to poor HrQOL, which means that high risk of fall negatively affected HrQOL. According to the further analysis, BBS, TUG and FTSST mainly affected mobility and ADL domains. Bailey et al. (2022) also found that PwP who performed better on the 4 m walk speed test, the standing balance test, had higher scores on the total PDQ-39, mobility, ADL, cognition and bodily discomfort domains. Conventional understanding suggests that patients at H&Y stage II do not experience balance symptoms, but this study showed that their balance function had deteriorated and negatively affected their HrQOL. Therefore, balance training should be considered earlier in clinical practice.

Muscle strength in PwP is impaired compared with healthy controls (Skinner et al., 2019; Renee et al., 2021), with the largest deficits observed in the lower extremity in the “OFF” medication state and of concentric contractions (Gamborg et al., 2023). Yokote et al. (2022) found that lower muscle strength correlates with gait performance in advanced Parkinson Disease. As a meta-analysis (Hart et al., 2023) reported that the prevalence of probable sarcopenia, a condition associated with the loss of skeletal muscle strength and mass, ranged from 23.9–66.7% in the PwP population. This study showed moderately correlation between knee strength and HrQOL in patients at H&Y stages III. Therefore, muscle strength training, especially in patients at H&Y stages III may improve in gait performance and HrQOL and prevent the presence of sarcopenia.

This study found that motor function correlated with HrQOL especially in mobility and activities of life. The most interesting finding of the current study showed that motor function has strong correlation with communication at H&Y stages III. Communication impairment is common in PD and may be due to motor language control and cognitive-linguistic disorder (Smith and Caplan, 2018). PDQ-39 has one question on speech and two question on communication with other people. Motor function assessments represent disease severity and the relationship with motor language control or cognitive-linguistic disorder should be further explored.

Strengths of the study include the identification of FOG as the most important factor affecting HRQOL, and the differential association between motor function and HRQOL in patients at different H&Y stages, supported by a robust sample size. Additionally, the potential correlation between motor function and communication function warrants further investigation. However, this study has some limitations. This analysis was cross-sectional and therefore conclusions were restricted to one point in time. Therefore, further studies should be done to investigate whether increasing or decreasing motion function results in HrQOL changes in PwP. In the future, there will be a need for a larger and longer cohort.

In conclusion, motor function correlated with HrQOL in early to mid-stages PwP, and FOG was the main factor, especially in mobility, activities of daily life and communication. In addition, HrQOL was correlated with gait and risk of fall at H&Y stage I, and gait, balance, and risk of fall at H&Y stages II. All motor function were associated with HrQOL and multiple dimensions in patients at H&Y stage III. Therefore, Physical therapy should be targeted according to disease stages to obtain the most improvement of HrQOL.

The raw data supporting the conclusions of this article will be made available by the authors, without undue reservation.

The studies involving humans were approved by the Ethics Committee and Institutional Review Board of the Peking Union Medical College Hospital. The studies were conducted in accordance with the local legislation and institutional requirements. The participants provided their written informed consent to participate in this study.

YG: Formal analysis, Writing – original draft. WZ: Investigation, Writing – review & editing. LZ: Project administration, Methodology, Writing – review & editing. XZ: Supervision, Writing – review & editing. XS: Writing – review & editing. JL: Writing – review & editing. YL: Conceptualization, Funding acquisition, Writing – review & editing.