Association between Physical Activity and Sarcopenia among Individuals with Knee Osteoarthritis: An Observational Study

INTRODUCTION

Aging beyond 30 leads to declining muscle mass and strength with increased fat. These changes impact health, with adiposity linked to knee osteoarthritis (KOA), diabetes, heart disease, and reduced life quality. Muscle loss due to sarcopenia combined with KOA, causes physical inactivity and joint instability, worsening disability.^[1] Physical activity (PA) helps maintain muscle mass and mobility, while KOA patients often reduce activity, risking sarcopenia.^[2] A common musculoskeletal condition, particularly in older persons, KOA is characterized by stiffness, joint pain, increasing cartilage degradation, and decreased functional mobility.^[3]

Osteoarthritis (OA) involves the progressive breakdown of the cartilage in joints. Among older adults, KOA is one of the most prevalent degenerative conditions. Along with the mechanical deterioration of articular cartilage, this inflammatory disease also affects the synovium, meniscus (in the knee), periarticular ligament, and subchondral bone, causing structural and functional alterations throughout the joint. Management of KOA is classified into non-surgical and surgical techniques. Both pharmacological and nonpharmacological treatments are part of non-surgical care; for OA patients, non-pharmacological approaches are the first line of treatment. These strategies include weight loss, exercise, self-management, and education. Pharmacological interventions can involve intra-articular corticosteroids, topical or oral non-steroidal anti-inflammatory drugs, or paracetamol. The most effective treatment for severe KOA is complete knee arthroplasty and rehabilitation; surgery is only used as a last option.^[4] Scientific evidence indicates that aerobic, strength, and endurance programs combined with land-based and aquatic exercises are safe and effective for individuals who have already been diagnosed with knee OA. In addition, patient-specific physical therapy may shorten the recovery period following a knee replacement.^[5]

Sarcopenia is the gradual decrease of skeletal muscle mass (SMM) and function. Low muscle mass with decreased strength or physical performance indicates sarcopenia. As people age, their SMM and strength decline, which are hallmarks of sarcopenia. SMM declines by 6% every 10 years after middle age. Age, sedentary lifestyle, inflammation, and metabolic dysfunction are risk factors that overlap between KOA and sarcopenia.^[6] Research shows patients with knee OA can safely benefit from aerobic, strength, and aquatic workouts.

Physical therapy may speed recovery after knee replacement. Sarcopenia management includes non-medication and medication approaches. Resistance exercise is the primary non-medication treatment. Proper nutrition, protein, Vitamin D, and healthy fats play a key role in improving sarcopenia.^[7] OA frequently impacts the knee, leading to chronic pain, reduced quality of life, restricted physical abilities, mental well-being decline, and considerable economic strain. There is no cure for KOA, and knee replacement surgery is advised for the end stages of the condition. Due to the absence of a cure, research has concentrated on methods to decelerate or halt the progression of the disease.^[8] Given that OA and sarcopenia are common conditions, they frequently occur together. Reduced levels of PA in non-surgically treated OA patients are linked to the higher severity of the disease and are known to aggravate pain and functional mobility in OA patients.^[9] Although there is an absence of information in many developing nations, physical inactivity is a significant risk factor for chronic diseases. Guthold et al., used the International PA Questionnaire (IPAQ) to analyze World Health Survey data (2002–2003) from more than 212,000 adults in 51 countries. The prevalence of physical inactivity varied greatly, ranging from 1.6% in Comoros to over 50% in Mauritania, with higher rates among urban populations, women, and older adults. Overall, 20% of women and 15% of men were physically inactive, indicating significant cross-national disparities and the need for focused public health initiatives.^[10] As of 2022, one-third of the global adult population do not engage in the recommended PA, with the highest levels of inactivity observed among older adults and women. With over half of the countries showing worsening trends of knee osteoarthritis, the 2030 reduction target remains unattainable. Urgent multi-sectoral strategies are needed to encourage PA without worsening disparities.^[11]

The coexistence of excess adiposity and low SMM/function, which is known as sarcopenic obesity (SO), is linked to poor clinical and functional outcomes. Because there were no uniform standards, ESPEN and EASO proposed a consensus definition and diagnostic framework. Assessing muscle function and body composition, screening at-risk individuals, and staging SO according to the existence of complications are all part of the diagnosis process.^[12]

MATERIAL AND METHODS

After receiving approval from Sri Ramachandra Institute of Ethical Education’s Institutional Ethical Committee, the observational study was conducted. (CSP-III/24/ MAY/05/168). This study has been registered in Clinical Trials Registry - India (ICMR-NIMS) with CTRI Reg. No - CTRI/2025/01/079621 CTRI Reg. Date - December 28, 2024, Reference No- REF/2024/12/096927. The recruitment of the participants for the study began after approval was received. Patients who were referred to the Outpatient Department of Physiotherapy, Sri Ramachandra Hospital, Chennai, from the orthopedic unit of Sri Ramachandra Hospital were recruited for the study.

The recruitment process was started in December 2024 and completed in February 2025. When the patient arrived at the outpatient department of physiotherapy, we explained the aim and objective of the study and its process and asked for their informed consent. After getting, we took the patient to the body composition analyzer and got data about their muscle mass, fat mass, and body mass index (BMI). We filled the study proforma, which has the following information: biographical data, medical history, and IPAQ.

The study involved 86 participants. The study’s inclusion criteria were individuals over 30 years of age, both male and female, with KOA. Individuals were excluded from the study if they had chronic or acute heart and lung conditions, systemic diseases, recent musculoskeletal injuries in lower limbs, a history of orthopedic surgery, neurological disorders affecting mobility, systemic illnesses besides OA, insulin-dependent diabetes, or medication-induced fatigue and drowsiness [Table 1].^[13]

RESULTS

Statistical Package for the Social Sciences version 23 was used to analyse the data. The association between PA level, sarcopenia, and KOA was analysed using analysis of variance (ANOVA) or repeated measures ANOVA based on the normality test findings. After controlling for potential confounding factors like age, gender, and comorbidities, generalized linear models were used to assess the relationship between sarcopenia status and physical activity levels among people with knee osteoarthritis (KOA). Physical activity levels were divided into ordered groups using ordinal logistic regression analysis.

The Chi-square test was used to assess the association between sarcopenia and physical activity levels among individuals with knee osteoarthritis. A p-value of <0.05 was considered statistically significant. Table 2 Shows the participants’ average age was 55.2 ± 10.5 years, and 68% of them were female and remaining 32% were male. The mean BMI was 26.5 ± 4.2 kg/ m². A mean of 21.5 ± 12.0 hours and 4.5 ± 2.0 days per week of physical activity were reported by the participants. With a mean muscle mass of 38.0 ± 8.0 kg and a fat mass of 24.0 ± 7.0 kg, the sarcopenia score was 6.8 ± 1.8. Among the 86 participants, 37 had sarcopenia, and 49 did not. PA levels were higher in those without sarcopenia (about 4.5 days/week) compared to those with sarcopenia (about 3.8 days/week). Nonsarcopenic individuals also engaged in more vigorous, moderate, and walking activities and spent less time sitting. Table 3 distinguishes between people with and without sarcopenia. The frequency of physical activity was higher in participants without sarcopenia (4.52 ± 1.74 days/week) than in those with sarcopenia (3.80 ± 1.76 days/week). Sarcopenia scores were also higher in the non-sarcopenic group (7.82 ± 0.91) than in the sarcopenic group (5.69 ± 0.62), suggesting a strong association between sarcopenia and lower levels of physical activity. The frequency of physical activity was higher in participants without sarcopenia (4.52 ± 1.74 days/week) than in those with sarcopenia (3.80 ± 1.76 days/week). Sarcopenia scores were also higher in the non-sarcopenic group (7.82 ± 0.91) than in the sarcopenic group (5.69 ± 0.62), suggesting a strong association between sarcopenia and lower levels of physical activity.

Interpretation: Higher PA duration and frequency are significantly associated with a lower sarcopenia score (less severe sarcopenia), greater muscle mass, and lower fat mass, which implies that increased PA may serve as a protective factor in KOA patients.

Interpretation

The Table 4 odds ratio of 3.50 indicates that individuals with KOA who report low PA levels have a 3.5-fold higher odds of being sarcopenic compared to those with high PA. The 95% confidence interval (1.85–6.62) does not include 1, and the result is statistically significant (p < 0.001) as supported by Table 5. This strongly supports the notion that reduced PA is independently associated with an increased risk of sarcopenia as supported by Table 5.

Table 4: Multivariate logistic regression analysis of factors associated with sarcopenia among individuals with knee osteoarthritis.

Variable	Adjusted OR (95% CI)	pvalue
Physical activity	3.50 (1.85–6.62)	<0.001

OR: Odds ratio, CI: Confidence interval

Table 5: Association between physical activity and sarcopenia metrics.

PA metric	Sarcopenia score	Muscle mass	Fat mass
PA duration (hours/week)	r=−0.45, p<0.01	r=+0.40, p<0.01	r=−0.30, p=0.02
PA frequency (days/week)	r=−0.42, p<0.01	r=+0.35, p=0.02	r=−0.28, p=0.03

PA: Physical activity

In this study, out of the 86 subjects, 37 individuals were sarcopenic, and 49 were non- sarcopenic. (based on the values for males <−7.0, females <−5.4). The mean age of the group was around 60 years, and females were higher and more prone to sarcopenia than males [Figure 1]. Table 3 shows that individuals without sarcopenia have higher PA levels than those who have sarcopenia. The mean value of PA frequency was around 4 days/week and 3 days/week for those who do not have sarcopenia and those who have sarcopenia, respectively as shown in Figure 2. Individuals without sarcopenia tended to have good vigorous, moderate, walking, and sitting physical activities, whereas individuals with sarcopenia were less likely to be physically active as shown in Figures 3-5 respectively. Individuals who were non-sarcopenic spend more than a day and a half of vigorous activities, whereas sarcopenic individuals could not even do so for a day [Figure 4]. Individuals with sarcopenia spend 2 days of moderate activities, whereas non-sarcopenic individuals spend more than 3 days [Figure 3]. Figure 4 Illustrates that Individuals who were sarcopenic walk less, which is about <3 days/week, whereas non-sarcopenic people walk about 5 days a week. However, whereas in sitting, people who were sarcopenic tend to spend more than 6 h in a day as shown in Figure 6. These results illustrates that PA levels tend to be lower in individuals with sarcopenia, and physically active people reduce the risk of sarcopenia.

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Figure 1:

Strobe flow diagram of participant recruitment, enrollment, analysis and results.

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Figure 2:

Sarcopenia prevalence by gender.

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Figure 3:

Comparison of physical activity levels.

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Figure 4:

Comparison of Moderate Physical activity levels with People with and without Sarcopenia.

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Figure 5:

Comparison of vigorous activity and walking activity levels with people with and without sarcopenia.

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Figure 6:

Sitting activities during last 7 days, how much time did you spend siting on a week day?

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DISCUSSION

This study highlights the connection between sarcopenia and reduced PA in individuals who have KOA. The findings indicate that those with sarcopenia participate in less PA and show increased sedentary behavior, which is consistent with previous research linking muscle loss to mobility difficulties.^[3] The IPAQ results demonstrate significantly lower PA levels in participants with sarcopenia, which brings out the impact of muscle atrophy on mobility limitations.^[16] The combination of sarcopenia and knee OA will lead to more functional decline, as joint pain and stiffness further limit movement.^[17] In this population, reducing sedentary behavior and encouraging physical exercise can enhance quality of life and functional outcome. The study highlights how sarcopenia and a reduction in PA are related in ndividuals with KOA. The results show that individuals with sarcopenia engage in significantly less PA and exhibit higher sedentary behavior, supporting earlier studies linking muscle loss to mobility challenges.^[3] The findings of the study highlight the need and importance of interventions to address and overcome physical inactivity associated with sarcopenia in individuals with KOA. Resistance training and movement-based therapies emerge as promising strategies to improve the negative effects of muscle loss and joint pain on PA levels.^[18] By focusing on reducing sedentary behavior and encouraging PA, healthcare professionals can improve functional outcomes in these individuals. These interventions may enhance joint and muscular function, enhance general quality of life, and promote independence in day-to-day activities. Future studies should look into the long-term consequences of such interventions and their potential to slow or reverse the progression of both sarcopenia and KOA.

Weight loss improves many associated metabolic risk factors, and obesity is associated with cardiometabolic diseases and some types of cancer. However, diet-induced weight loss frequently results in a loss of lean muscle mass, which raises the risk of sarcopenia, particularly in postmenopausal women and older adults. Because muscle quality varies, muscle mass alone cannot accurately predict strength or function. Therefore, rather than just reducing body fat, weight-loss interventions should focus on maintaining or improving muscle mass and function.^[19]

Using the CHARLS 2015 data, this cross-sectional study looked at the relationship between SO and dementia risk in 5,320 Chinese adults over 60 who lived in the community. Abdominal obesity by itself did not significantly increase the likelihood of probable dementia, but SO and possible sarcopenia did. SO demonstrated the highest risk, and the association held true across age and gender strata. Compared to BMI alone, waist circumference plus sarcopenia measurements may be a more accurate indicator of dementia risk^[20] Using data from the study by Wu et al., this study investigated the role of sarcopenia in the progression of KOA and the risk of knee replacement. Over a 24–48 month period, radiographic and symptomatic KOA progression were significantly correlated with screened and probable sarcopenia. The risk of a subsequent knee replacement was significantly higher in both types of sarcopenia. These results imply that sarcopenia could be a therapeutic target and contribute to the progression of KOA.^[21]

CONCLUSION

This observational study clearly shows that among people with KOA, sarcopenia is associated with lower levels of PA. Among the 86 individuals evaluated, those with sarcopenia had elevated sedentary behavior and considerably lower participation in vigorous, moderate, and walking activities in comparison to those without the condition. Higher sarcopenia severity scores, increased fat mass, and decreased muscle mass were all significantly correlated with less PA, according to statistical analysis. In addition, logistic regression showed that the risk of developing sarcopenia was 3.5 times higher for those with low levels of PA. This emphasizes how maintaining appropriate levels of PAis a crucial therapeutic and preventative measure. Frequent exercise can help maintain muscle mass, improve joint function, lower inflammation, and improve overall quality of life. This is especially true for resistance training, aerobic activity, and functional mobility exercises.

From a clinical perspective, early detection of sarcopenia risk factors and focused PA therapies may reduce functional decline and enhance independence. The cycle of inactivity and muscle loss may be broken by incorporating regular PA programs into KOA care plans. This would improve patient outcomes and minimize disability.