Abstract
BACKGROUND:
Squat exercise, in which eccentric and concentric contractions are present simultaneously in different muscle groups, is one of the closed kinetic chain exercises commonly used in knee rehabilitation.
OBJECTIVE:
In the scope of the study, our objective is to determine the effectiveness of a structured squat-based exercise approach in patients with knee osteoarthritis.
METHODS:
In this study, 75 patients diagnosed with knee osteoarthritis were randomly assigned to three distinct groups: isoinertial exercise, a combination of home exercise and electrotherapy, and exercise solely. The assessment encompassed the application of the Western Ontario and McMaster Universities Osteoarthritis Index (WOMAC), the Time Up and Go test, evaluation of quadriceps and hamstring muscle strength and activation levels, along with pain threshold assessment. The treatment program was administered three days a week over a span of eight weeks and was assessed both prior to and following the intervention.
RESULTS:
Across all groups, considerable enhancements were noted in the majority of parameters. Particularly noteworthy were the substantial improvements observed in the first group, specifically concerning WOMAC total score (p = 0.001), muscle strength, activation levels (p = 0.001), and pain tolerance (p = 0.05).
CONCLUSIONS:
In the group in which we applied isoinertial exercise, a positive increase was observed in most of the parameters.We suggest that isoinertial exercise applications, which are generally encountered in sports fields, should be used in different fields in future studies.
Introduction
Knee osteoarthritis is a degenerative joint condition characterized by the breakdown of cartilage in the knee joint, leading to pain, stiffness, and reduced mobility. The muscles around the knee joint losing strength often as a result of knee OA, and the quadriceps muscle in particular atrophy. Walking and stair climbing are two key movements that stabilize the knee and are controlled by the quadriceps muscle [1]. Fast fatigue and poor muscle control are observed due to muscle weakness in the quadriceps muscle. It was found that this causes cartilage damage by bringing about alignment problems and increases the symptoms [2].
The exercise practices recommended with a high level of evidence in the recently published international guidelines are of great significance in OA rehabilitation [3]. Being at the forefront of exercise practices, strengthening exercises increase strength and endurance as well as increase resistance in individuals diagnosed with knee OA. Skeletal muscles contract eccentrically to support the body’s weight against gravity and absorb shock. Eccentric strength is an integral part of daily living activities specific to lower extremity [4]. However, concentric, and isometric exercises are generally used in strengthening exercises. In a study in which healthy adults with knee OA that were at similar ages were examined, no significant difference was found between the two groups in concentric and isometric muscle strength [2]. On the other hand, a decrease was observed in eccentric muscle strength, especially in Type 2b fibers, in patients with knee OA [5].
Squat exercise provides increase in strength in the knee extensor muscle group, which takes up a significant place in the rehabilitation of knee OA patients [6]. While squat exercises could be performed with body weight using no equipment, it is also possible to perform device-assisted exercises [7].
Isoinertial training is one of the methods employed, which facilitates the development of a secure exercise regimen utilizing light weights. Isoinertial exercise is based on eccentric force, which provides constant resistance and maximum muscle strength at every angle. Compared to traditional gravity-based exercise, it offers greater eccentric overload and variable resistance [8]. It was stated that squat exercises applied in the isoinertial system increase the excitability and strength development of Type 2 fiber of the knee extensor muscles more than traditional squat exercise [9]. Hence, our objective is to assess the efficacy of squat-based exercises, implemented through various methods, on functional outcomes, muscle strength, muscle activation, and pain levels in individuals diagnosed with knee OA.
Materials and methods
Design
Patients who met the inclusion criteria were randomly divided into three groups via https://www.random.org using a single-blind randomization method. The single-blind assessment was structured based on the principle of having different evaluators and physiotherapists administering the exercises.
Participants
The participants for the study were selected from patients who applied to the Physical Therapy Department of Sefaköy Medipol Health Application and Research Center. The sample size was determined using the G-Power program based on the minimal clinically important difference on the WOMAC scale. In the studies conducted by Kaya Mutlu and colleagues, the smallest clinically significant difference in WOMAC score ranged between 0.51 to 1.33 points. We also conducted a power analysis based on these values, resulting in a two-sided alpha value of 0.05, a power of 0.90, and a sample size of 21 per group. The sample size was set at 25 per group [10]. This trial was approved by the ethics committee of our Medipol of Hospital under the number10840098-604.01.01-E.19406. Clinical trials registration number: NCT04588558. The study was conducted in accordance with the principles of the Declaration of Helsinki.
Group 1 was given isoinertial exercise and home exercise, Group 2 was given home exercise and received electrotherapy, and Group 3 was given only home exercise. The patients were included in the treatment program three times a week throughout eight weeks, 24 times in total.
The inclusion criteria for this study specified that participants had to be between the ages of 40–65 and have a clinical and radiographic diagnosis of knee osteoarthritis. They were required to meet the criteria set by the American College of Rheumatology for knee OA in at least one knee, and radiographic findings consistent with Kellgren-Lawrence grade II-III OA in the knee joint. In addition, the patient had to be able to do one of the traditional squat exercises.
If a patient had acute knee OA, had used NSAIDs and similar drugs within the last month, had exercised regularly and/or undergone intra-articular injection and arthroplasty surgery within the last 6 months, and an exercise was contraindicated, he/she was excluded from the trial.
The participants personal information, age, weight, height, body mass index and Kellgren Lawrence classification were recorded.
Outcome measures
Before and after therapy, patients’ physical function, pain threshold, muscle strength, and muscle activation were assessed. Assessments were conducted before the first intervention session and again at the conclusion of the eighth week.
Western Ontario and McMaster Universities Osteoarthritis Index (WOMAC) which consists of a total of 24 questions used in the evaluation of lower extremity OA, carries out evaluations in three dimensions, namely pain, stiffness and physical function. The maximum score in is 20 points for pain, 8 points for stiffness, and 68 points for physical function. Higher scores indicate worse symptoms and maximal limitations [11].
Pressure pain threshold was measured using the Wagner Force (Ten FDX 50 Wagner Instruments, Greenwich, CT) on the medial side of the patient’s knee.
Vastus medialis and biceps femoris muscle activation was assessed by means of a superficial EMG device following the protocol defined by the European Project SENIAM (Chattanooga, Intelect Neo TN, US) [12].
The strength of the quadriceps and hamstring muscles of both sides were measured with a hand-held dynamometer (kg/Newton), the Commander Muscle Tester, (JTech, USA) [13].
Timed Up and Go Test (TUG), how long it takes for the patient to stand up from the chair and walk to for three meters and to return and sit back in the chair was calculated [14].
Pressure pain threshold, muscle activation and strength, as well as the Time Up and Go Test, were assessed on three separate occasions, and the arithmetic average of these measurements was calculated.
Treatment program
Group 1: Isoinertial exercises, which are strengthening exercises, were applied with the flywheel device (AOSm Box, Trainer System). During the eccentric phase, resistance was achieved through rotating flywheels.
In the first two weeks of the isoinertial exercise program, mini squats and terminal knee extension. In the second week, full squat and four-way strengthening exercises were added. Heel raise squat was performed in the fourth week and split squat exercise in the sixth week, then the program was completed. The exercise program was structured as four sets of eight repetitions as in similar studies [8]. In addition to isoinertial exercise, a squat-based home exercise program was given.
Group 2: Each patient was treated with TENS (Chattanooga Intelect Hixson, TN) for 20 minutes and with continuous mode therapeutic ultrasound (Intellect 340 Combo, Chattanooga Group) at 3mHz and 1 W/cm2 for 8 minutes. In addition, a squat-based home exercise program was recommended.
Group 3: This group only performed squat-based home exercises. Exercise charts were provided to the patients, which included detailed information regarding the prescribed exercises. The number of repetitions and the specific content of the exercises were updated on a weekly basis to ensure progressive and tailored training for everyone.
The first two weeks of the exercise program include ankle pump exercise, isometric and concentric hip and knee exercise in supine position, and mini squat. In the second week, full squat and four-way strengthening exercise performed with an exercise band and in the standing position were added to these exercises. The exercise program was finalized by adding heel raise squat exercise in the fourth week and split squat exercise in the sixth week.
Statistical analyses
Statistical analyses were conducted via the Statistical Package for the Social Sciences (SPSS) 20.00. A p-value of 0.05 was set for statistical significance. The scores obtained from the questionnaires and functional tests and the pre- and post-treatment values were compared via a paired sample test (parametric test), and the between-group evaluation via an ANOVA test (parametric test). All analyses were considered significant when the p-value was less than 0.05, with an alpha level of 0.05 and Bonferroni equality.
Results
A total of 120 individuals were initially evaluated for the study. Three participants were excluded from the trial due to their inability to perform the traditional squat exercise, as required by the inclusion criteria. Additionally, two participants were excluded due to recent intra-articular injections, two due to contraindications to exercise, two due to age range limitations, and six due to the severity of knee osteoarthritis indicated by their Kellgren-Lawrence grade. Consequently, a total of 15 individuals were excluded from the trial for not meeting the inclusion criteria. Subsequently, a total of 25 patients dropped out of the study, with six attributing their departure to the impact of the COVID-19 pandemic, nine citing various health-related problems, and five stating difficulties in taking time off work. Ultimately, the evaluation of 75 individuals in total was completed.
Demographic information of the participants in our study is given in Table 1. Groups were similar at inclusion for age, body mass index and Kellgren Lawrence score.
Baseline descriptive variables according to groups
Baseline descriptive variables according to groups
BMI: Body Mass Index; K/L: Kellgren Lawrence.
A significant improvement was observed in the WOMAC scores of all groups across all dimensions. The treatment yielded a significant increase in the TUG test scores for both the first and third groups. However, the second group did not exhibit a statistically significant increase in TUG test scores following the treatment (Table 2).
WOMAC, TUG, muscle strength, muscle activation scores and algometer results of groups
WOMAC: Western Ontario and McMaster Universities Osteoarthritis Index TUG: Timed Up and Go Test, BT: Before Treatment, AT: After treatment.
In the muscle strength evaluation, both the quadriceps and hamstring muscle groups in both legs were assessed, and a significant increase in strength was observed across all groups.
The evaluation of muscle activation in the vastus medialis, a component of the quadriceps muscle group, and the biceps femoris, a part of the hamstring muscle group, consistently demonstrated an increase in muscle activation across all measured results. Algometer results demonstrated an increase in pain tolerance, except for the third group (Table 2).
In the study, which investigated the effectiveness of squat exercise with and without a device in knee OA patients, it was found that the isoinertial group had positive impacts on functionality, muscle strength, muscle activation and reduced pain compared to other groups.
In a comprehensive study, the favorable effects of strengthening exercises for people with osteoarthritis (OA) were noted, including symptom relief and improved physical function. Additionally, they revealed that compared to low-intensity resistance exercises, high-intensity ones had a greater effect on pain and functioning of the body [15].
Isoinertial exercises, one of the high-intensity resistance exercises, result in continuous resistance and eccentric overload due to its gravity-independent character. It increases gains by providing both concentric and eccentric loading while exercising [16]. It is usually used in professional athletes and healthy young adults [8]. It is thought that the elderly or individuals with chronic diseases cannot tolerate isoinertial exercise, but, contrary to popular belief, this is not correct [17]. As a result of the study by Floreani et al. in which they applied isoinertial exercise with elderly individuals, it was observed that the muscle strength and TUG score increased [18]. In the review examining the effects of isoinertial training on elderly individuals, it was observed that squat exercises positively affected daily functional activities by increasing balance, postural stability and walking activity as well as muscle strength gain [19].
To our knowledge, there is no study in the literature in which isoinertial exercises are applied in orthopedic or rheumatic patients. To the best of our knowledge, this is the first study to practice isoinertial exercises with in knee osteoarthritis. However, there are studies examining eccentric exercise in individuals diagnosed with knee OA. It is thought that patients may experience an increase in pain during eccentric exercise or that the intensity of exercise cannot be endured. In the study Gür et al. conducted, patients with knee OA patients were examined and the effectiveness of concentric exercise and that of eccentric exercise added to concentric exercise were compared [20]. The group performing both concentric and eccentric exercises improved more in the parameters in which functional capacity was evaluated and in pain. In our study, in the isoinertial exercises that we assigned to the first group, eccentric and concentric contractions are obtained simultaneously. It was found that the isoinertial exercise group improved more in muscle strength, functional ability and pain compared to the other groups. We believe these results from the fact that the muscles work in a controlled manner and provide muscle strength balance.
It was observed that TENS and ultrasound application reduce pain-related discomfort in individuals with knee OA, but the level of evidence is insufficient in increasing functional capacity [10]. It was found that home exercise program which is used in support of electrotherapy applications is more effective [21]. In accordance with the literature, electrotherapy applications and squat-based home exercise were recommended to the second group in our study. Although a decrease in pain and an increase in functional ability were observed in the second group, more significant results were found in the first group. We believe that electrotherapy applications should be used in painful cases as they provide support in the treatment. However, it has been revealed that it is necessary to include exercises that provide muscle strength balance as well as pain control in the treatment.
According to Suzuki et al., home exercise improved the physical function and strength of the knee extensor muscles while reducing discomfort in patients with osteoarthritis [22]. Planning an exercise program is a very difficult process requiring experience [23]. In our study, home exercise was assigned to all three groups. All three groups reported a decrease in discomfort, an improvement in physical function, and an increase in muscle strength. Treatment for knee OA shows to benefit from regular exercise done under a physiotherapist’s supervision.
It was observed that squat exercise leads to improvement in whole body vibration, muscle strength and TUG results in knee OA patients [6]. In our study, we achieved more effective results in muscle strength and functional status by assigning squat exercise both in home exercise program and isoinertial program. We think the squat exercise that was performed functionally with the device in different positions provided muscle balance and increased awareness, which we believe enabled us to obtain positive results.
It is still not clear which muscle works more in different squat exercises [8]. In addition to a decrease in muscle mass, reduced voluntary muscle activation and altered coactivation of the knee joint’s antagonist and synergist muscles also contribute to muscle strength inadequacies in knee OA [24]. For this reason, in our study, the vastus medialis part of the quadriceps muscle group, the biceps femoris part of the hamstring muscle and gastrocnemius muscle group were evaluated by EMG in addition to the muscle strength evaluation of the muscles with dynamometer. In both muscle groups, there was an increase in the level of muscle activation in all groups. As a result of the two assessments, a statistically higher increase was observed in the quadriceps muscle in the group in which we assigned squat exercises in the isoinertial system. The balance between the muscles was achieved after motor control was achieved thanks to isoinertial exercise.
The effectiveness of different physiotherapy approaches in individuals with knee OA was evaluated through WOMAC and algometry. As a result of the study, both pain tolerance and WOMAC score increased [10]. Physical function using WOMAC, pain sensitivity was examined using an algometer in our study. According to the results, there was significant improvement in pain tolerance in all groups except for the home exercise group. We are of the opinion that the application of an additional treatment such as electrotherapy or isoinertial exercise in addition to home exercise is effective for pain tolerance and physical performance.
Limitation
The primary limitation is the relatively short follow-up period of eight weeks, which restricted conduct long-term assessments or subsequent follow-ups. In future research endeavors, we intend to address these limitations by extending the duration of the study and incorporating follow-up evaluations to gain a more comprehensive understanding of the effects over time. Additionally, we recommend conducting studies that integrate both electrotherapy and isoinertial exercise interventions simultaneously, as this may provide valuable insights into their combined effects and potential synergies in the treatment of knee osteoarthritis.
Conclusions
The findings of the study indicated that both the squat-based home exercise program and the electrotherapy program, when combined with isoinertial exercises, demonstrated favorable outcomes in patients with knee OA. In the group that received isoinertial exercise, notable improvements were observed in quadriceps and hamstring muscle strength, as well as increased muscle activation in the vastus medialis and biceps femoris muscles. Additionally, enhancements in physical function and walking activity, along with a reduction in pain sensitivity, were observed in this group compared to the other intervention groups. Based on these results, it is recommended to implement squat training incorporating the isoinertial exercise system for individuals with knee OA.
Conflict of interest
None.
Funding
The work outlined in this article has no funding, according to the author(s).