The secondary outcome measures include psychological, psychosocial, muscle strength, functional balance, and neuromuscular variables as well as the healthcare utilization of the treatment for knee OA. They are described in the following sections.
Psychological and psychosocial functioning measures
The Patient’s Global Assessment is a visual analogue scale that measures the level of Knee OA severity on a 10 point scale with 10 reflecting the most extreme severity and 0 reflecting no severity.
Health Related Quality of Life (HRQL) assessments are made using the Medical Outcome Study Short Form 36 Short-Form Health Survey (SF-36)[
39]. The SF-36 is a self-administered, 36-item questionnaire that assesses the concepts of physical functioning, role limitations due to physical problems, social function, bodily pain, general mental health, role limitations due to emotional problems, vitality, and general health perceptions. Note that both the physical and mental component summaries can be combined. Scores range from 0 to 100, with higher scores indicating better health status[
40].
The
Beck II Depression Inventory is a 21-question, validated, self-report instrument that measures the severity of depressive symptoms. Higher scores reflect a greater degree of symptom severity[
41].
The
Perceived Stress Scale (PSS) is the most widely used psychological instrument for measuring the perception of stress. The scale also includes a number of direct queries about current levels of experienced stress. For this instrument, higher scores reflect a greater degree of symptom severity. The PSS shows high levels of internal consistency (alpha = 0.92)[
42].
The
Chronic Pain Self-Efficacy Scale (CPSS) is a modified version of The Arthritis Self-Efficacy Scale that has been validated for patients with chronic pain[
43]. It contains 8 questions divided into 3 subscales (pain coping, physical functioning, and coping with symptoms). The score is obtained by means of a Likert scale with a range of 0–10, where higher scores indicate better self-efficacy.
The Medical Outcome Study Social Support Survey assesses social support by using the Social Support for Physical Activity Scale adapted from Sherbourne and colleagues[
44]. It comprises 19 questions rated from 0 to 5 to assess the influences of family and friends have on patients as they performed regular physical activity. Higher scores reflect more perceived social support from these individuals.
Outcome expectations are beliefs that carrying out a specific behavior such as physical activity will lead to a desired outcome. The brief, validated, outcome expectations scale[
45] contains 9 questions that ask about physical and mental benefits and are used to assess outcome expectations. Scores can range from 1 to 5, with 1 indicating low outcome expectations for the exercise and 5 suggesting high outcome expectations. This questionnaire is used prior to randomization to assess the outcome expectation for any exercise intervention. It is also assessed after randomization prior to the first session to assess the outcome expectation for the assigned intervention.
Participants enrolled in the trial also complete six Participant-Reported Outcomes Measurement Information System (PROMIS) static short-forms, version 1.0 instruments including PROMIS Pain Impact, Physical Functioning, Emotional Distress-Anxiety, Emotional Distress-Depression, Sleep Disturbance, Satisfaction with Participation in Social Roles, and. All of the included PROMIS instruments contain 5-point Likert-based items capturing intensity, frequency, or duration. The instruments use a seven-day recall period, with the exception of PROMIS Physical Function, which does not reference any timeframe. Higher scores reflect greater symptom severity across the pain, anxiety, depression and sleep disturbance scales. Higher scores reflect better outcomes for the satisfaction and physical function scales.
The
Health Assessment Questionnaire (HAQ), developed originally at Stanford in the late 1970’s to assess patients with rheumatoid arthritis, has been validated in a broad range of rheumatic and non-rheumatic disease populations[
46,
47]. In particular, the HAQ Disability Index (HAQ-DI) assesses disability and the full HAQ collects data on disability, pain, medication effects, mortality, and healthcare resource use (care costs),[
46] including both direct (e.g. physician visits, medication use, arthroplasty) and indirect costs (e.g. loss of productivity) and mortality. We substitute the Improved HAQ for the original HAQ-DI to assess disability because of its improved responsiveness and precision[
48‐
50]. The
NEO Five-Factor Inventory is a validated 60-item questionnaire that measures the five domains of personality including Neuroticism, Agreeableness, Conscientiousness, Extraversion, and Openness[
51]. It consists of five 12-item, 5-point Likert scales that measure each of the domains.
The
Five Facet Mindfulness Questionnaire (FFMQ) is a validated, 39-item questionnaire that measures five facets of mindfulness: observe, describe, act aware, nonjudge, and nonreact[
52]. Participants answer each of the questions on a five-point Likert scale with higher scores reflecting higher mindfulness.
The
Credibility/Expectancy Questionnaire (CEQ) is a validated, 6-item instrument that assesses how believable, convincing, and logical the treatment seems to the participant as well as what improvements the participant thinks will be achieved. This questionnaire has been adapted to reflect the participant population of this study. Higher scores reflect greater credibility and expectancy by the participant[
53].
The
Pre-Clinical Disability (PCD) Questionnaire is an adapted 12-item, yes/no questionnaire that assesses whether participants have changed the way or how often they do a series of daily activities such as climb a flight of stairs or carry groceries[
54]. More positive answers reflect greater preclinical disability.
The
Self-Reported Alignment Questionnaire is an 8-item questionnaire in which participants identify the angle of their knees and feet with those shown in the pictures for their current adult life as well as their early adult life[
55].
The
CHAMPS Physical Activity Questionnaire for Older Adults (CHAMPS) is a validated, 40-item questionnaire that measures weekly physical activity levels for older adults by calculating caloric expenditure[
56] and frequency of various common exercises completed by older adults such as swimming or walking. Higher scores reflect greater physical activity levels.
Physical performance assessments include the timed chair stand, the six-minute walk test, 20-meter walk test, functional balance, and lower extremity strength and power.
The
timed chair stand tests measures time taken to complete ten full stands from a sitting position and is a reliable measure of lower body strength and dynamic balance[
57,
58]. The recorded time is the average on two tries.
The six-minute walk test is a reliable measure of functional exercise capacity[
59,
60]. Participants are asked to walk as fast and as far as possible within the six-minute period. Participants are given verbal encouragement every minute throughout the 6 minutes and are informed of the remaining time every minute. The distance covered at the end is noted and recorded.
The 20-meter walk test is a reliable measure of gait speed. Prior to the assessment, the assessor demonstrates the walk at a comfortable walking pace. The outcome is the total time it takes to walk 20 meters. The assessor asks participants to complete two trials and computes the average time to complete the trials[
61].
Two functional balance tests have been used: Berg Balance Scale and Postural Sway as measured by a Force Plate.
The Berg Balance Scale measures balance among older adults with balance impairment by assessing a participant’s performance during 14 functional tasks. The tasks include standing from a seated position, standing unsupported for 2 minutes, turning 360 degrees, and standing on one foot. The Berg Balance Scale has been evaluated in several reliability studies. Berg scores range from 0 to 56 and higher is better[
62].
Postural sway is also used to determine balance by measuring the distance from center of pressure (CoP) defined as the vertical forces exerted by both feet on a force plate (Model BP5050, Bertec Corporation, Columbus, OH, USA). Similar to previous research[
63], participants are asked to stand barefoot on the force plate with feet approximately at hip width and arms by their side. Participants are instructed to stand as stationary as possible for 30 seconds, repeated for 8 trials, alternating eyes open and eyes closed. The data are collected in both the anterior-posterior (CoPx) and medio-lateral (CoPy) axes at a sampling rate of 1000 Hz. Subjects’ postural stability is quantified as the mean standard deviation of CoPx and CoPy for eyes open and eyes closed trials.
Measures of muscle strength/power
Participants’
Muscle Strength and Power is measured using a leg press. Participants are seated on the bilateral leg press apparatus with knees flexed to 90 degrees and hips flexed to approximately 110 degrees (Leg Press A420, Keiser Corporation, Fresno, CA). Knee angle is measured using an electrogoniometer (ADInstruments, Colorado Springs, CO). Each participant is given the opportunity to familiarize themselves with the testing equipment through the use of a visual demonstration and practice at low resistances. Force, position, and velocity of each repetition are sampled at 400 Hz and saved to disk for offline analysis. Using software provided by the manufacturer, these data are then converted to force, position and velocity at the footplate (Software Release 7.8, Keiser Corporation, Fresno, CA). Leg extensor muscle strength are quantitatively assessed using the one-repetition maximum (1RM) technique and are defined as the maximum load that could be moved only once throughout the full range of motion (ROM) while maintaining proper form[
64]. Subjects perform the concentric phase, maintain full extension, and perform the eccentric phase of each repetition over 2, 1, and 2 seconds, respectively. After measurement of the 1RM, assessment of leg press peak muscle power is made after a 5 minute rest period. Performance of this multiple attempt peak power test has been previously described and validated[
64]. Briefly, each participant is instructed to complete a total of five repetitions each separated by 30 seconds as quickly as possible through their full ROM at both 70% and 40% of the 1RM. The highest measured power output is recorded as the leg press peak power.