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High-Intensity Interval Training for Knee Osteoarthritis: A Narrative Review

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Submitted:

23 March 2023

Posted:

30 March 2023

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Abstract
Knee osteoarthritis (OA) is the most common joint disease worldwide. Exercise therapy has been identified as a first-line treatment option in patients suffering from knee OA. High-intensity interval training (HIIT) is an innovative exercise modality with potential in improving various disease-related outcomes. The purpose of this review is to explore the impact of HIIT on knee OA symptoms and physical functioning. A comprehensive search of scientific electronic databases was conducted to identify the articles on the effects of HIIT on knee OA. Thirteen studies were included in this review. Nine compared the effects of HIIT with those of low-intensity training, moderate-intensity continuous training, or a control group. Three evaluated the effects of HIIT alone. Eight reported a decrease in knee OA symptoms, and eight reported an increase in physical functioning. HIIT was shown to improve knee OA symptoms and physical functioning, but also aerobic capacity, muscle strength, and quality of life with minimal or no adverse events. However, compared to other exercise modalities, no clear superiority of HIIT was found. HIIT is a promising exercise strategy in patients with knee OA: anyway, the actual quality of evidence remains very low, and more high-quality studies are needed to confirm these promising outcomes.
Keywords: 
high intensity interval training
;  
knee osteoarthritis
;  
exercise therapy
;  
rehabilitation
;  
exercise rehabilitation
Subject: 
Medicine and Pharmacology  -   Orthopedics and Sports Medicine

Introduction

Osteoarthritis (OA) is the most common joint disease worldwide, affecting approximately -15% of the worldwide population [1]. Moreover, the incidence of symptomatic OA is on the rise due to the aging of the population and the global obesity epidemic [2]. OA is a leading cause of disability and can affect people’s physical and mental well-being. Symptoms are joint pain and stiffness with relevant consequences on functional status, significantly restricting daily activities, and often resulting in a reduction of quality of life (QoL) [3,4]. Knee OA is the most prevalent form of OA [5], and it is a leading cause of disability among older people, with recent data affirming that over 560 million people living with knee OA worldwide [6].
Physical activity is a safe, cost-effective, and recommended first-line knee OA treatment option for the management of pain and mobility for affected patients [7,8,9,10,11,12,13,14]. Exercise showed effect sizes comparable to those for simple analgesics and nonsteroidal anti-inflammatory drugs [15]. Unfortunately, few people with knee OA achieve recommended physical activity levels (i.e., 150 min/week of moderate intensity) [16,17,18,19], mainly demonstrating sedentary or inadequate physical activity behaviours [16,17]. Furthermore, people with knee OA have the added barriers of pain and functional limitations that make the recommended quantity of exercise intolerable [18,19].
Clinical guidelines recommend strength and aerobic training for patients with knee OA based on clinical trial evidence of effectiveness [9,15,20,21,22]. Aerobic training can promote the metabolism of adipose tissue, prevent muscle atrophy, accelerate the recovery of damaged cartilage, enhance the body’s immunity, and reduce pain [23]. Strength training mediates pain relief [24], enhances psychological well-being [25], maintains cartilage integrity in animal models [26,27], and may increase the shock absorbing capability of lower extremity muscles during walking [28]. Even if exercise has been recognized as a core treatment for knee OA [29], it is still unclear which program is more effective [30]. One promising modality of therapeutic exercise in those with knee OA could be represented by high-intensity interval training (HIIT) [31].
HIIT involves short bursts of very intense activity alternated with short periods of rest or low-intensity exercises [32]. HIIT has been proposed as a time-efficient form of exercise that may overcome motivational barriers associated with traditional moderate intensity training [33]. Several studies have demonstrated the effectiveness of HIIT on both healthy and pathological subjects [34,35,36]. Prior research shows that performing HIIT two to three times per week is sufficient to promote adherence and important physiological changes, such as improvements in cardiorespiratory health, body composition, and insulin sensitivity [37,38]. HIIT has promising long-term adherence rates and offers similar physiological benefits as less intense long-duration exercise in a shorter period and with more pronounced effects on cardiorespiratory fitness [39,40]. Time efficiency and flexibility of exercise mode have supported the successful implementation of HIIT among individuals with obesity and older adults [41,42].
Previous studies have provided conflicting evidence regarding the impact of HIIT on knee OA symptoms. Some suggested that HIIT may be detrimental for knee OA symptoms due to the greater contact forces exerted on the joint [43], and that it might aggravate symptoms such as pain and swelling [44], although others did not support these findings [45,46]. In contrast, one study even suggested that short-term, high-intensity strength training is in fact safe and well tolerated by older adults with knee OA [47]. Additionally, preliminary evidence from a small-sample study has suggested that high-intensity resistance training may have beneficial effects on muscle strength compared to low-intensity resistance training in patients with knee OA [44].
Given these premises, the aim of this review was to understand what the benefits of HIIT in patients with knee OA are compared to other exercise modalities or no physical therapy regarding knee OA symptoms and physical functioning, and to what extent are these benefits superior to other exercise modalities.

Materials and Methods

To address the lack of available literature on the effects of HIIT on knee OA, the authors conducted a narrative review using a systematic approach. A comprehensive search of scientific databases, including PubMed, Scopus, and Web of Science, was performed by two independent authors (D.T. and J.V.) to collect relevant articles on the topic.
The included articles reported on the benefits of HIIT without a comparator group, or HIIT compared to other forms of training (such as low-intensity or moderate-continuous), or HIIT compared to control, on knee OA, and reported primary or secondary outcomes related to knee OA symptoms, muscle strength and physical or functional status. Reported improvements were defined as statistically significant for p-values <0.05.
Furthermore, to ensure the training protocols were considered as HIIT by the authors of the present review, only articles explicitly labelling their interventions as HIIT were included, and specific keywords “high-intensity interval training”, “high-intensity interval training AND osteoarthritis”, “high-intensity interval training AND osteoarthritis AND knee” were used during the search. Finally, the selected studies were evaluated using the CERT tool (Table 1), that is designed specifically for the reporting of exercise programs across all evaluative study designs for exercise research [48].

Results

The results of the research lead to the selection of 13 articles. A summary of the characteristics of the included studies is provided in Table 2. To facilitate understanding of the results, we categorized the studies into the following sections: HIIT (alone), HIIT vs low-intensity training (LIT), HIIT vs moderate-intensity continuous training (MICT), HIIT vs control (CT), and HIIT vs LIT vs CT. We recommend that readers refer to the individual articles for additional details regarding the training protocols.
  • HIIT (without a comparator group)
Three studies reported the outcomes of HIIT alone for knee OA.
A pilot study by Golightly et al. [49] assessed the feasibility and changes in outcomes of a HIIT program in patients with symptomatic knee OA. Twenty-nine participants were enrolled to a 12-week (2x/week) supervised HIIT program. The authors stated that their HIIT program improved the Western Ontario and McMaster Universities Osteoarthritis Index (WOMAC) scores (32.4 ± 14.0, 28.8 ± 19.2, and 20.0 ± 13.7 at baseline, six and 12 weeks, respectively), 20-meters fast-paced walk test measured in seconds (12.5 ± 5.4, 11.5 ± 5.0, 10.0 ± 2.8 at baseline, six and 12 weeks, respectively), 30-second chair-stand test measured in repetitions (12.6 ± 5.4, 14.5 ± 6.1,16.4 ± 6.4 at baseline, six and 12 weeks, respectively), stair-climb test measured in seconds (13.8 ± 7.3, 11.5 ± 6.4, 10.6 ± 6.2 at baseline, six and 12 weeks, respectively), timed up and go test measured in seconds (7.9 ± 4.8, 7.3 ± 4.4, 6.0 ± 1.4 at baseline, six and 12 weeks, respectively), balance measured as single leg stance in seconds (15.1 ± 11.0, 19.2 ± 11.6, 21.0 ± 11.9 at baseline, six and 12 weeks, respectively), isometric knee extensor strength measured in Newton meter (Nm) (average right knee 71.1 ± 33.4, 72.5 ± 36.5, 77.8 ± 37.9 at baseline, six and 12 weeks, respectively, average left knee 68.3 ± 35.0, 72.2 ± 37.3, 72.1 ± 33.5 at baseline, six and 12 weeks, respectively), and cardiorespiratory fitness, with most changes occurring as early as six weeks.
Another pilot and feasibility study by Smith-Ryan et al. [31] examined the feasibility of a 6-week HIIT program in patients with symptomatic OA. Sixteen participants were enrolled to a 6-week (12 exercise sessions + two testing sessions at baseline + two post-test sessions) HIIT program (2x/week). The authors stated that their HIIT program improved cardiorespiratory fitness and OA symptoms measured with WOMAC (pre-testing total score 36.15 ± 8.60, post-testing at six weeks 25.46 ± 16.09) in concert with metabolic alterations indicative of improved skeletal muscle energetics.
The last study on HIIT alone for knee OA was performed by King et al. [45] to evaluate the effects of a HIIT knee extensor and flexor resistance training program on strength, pain, and adherence in patients with advanced knee OA and varus malalignment. Fourteen patients with medial compartment knee OA and malalignment were enrolled to a 12-week (3x/week) HIIT program. The authors concluded that their supervised HIIT training can produce substantial increases in knee extensor and flexor strength (strength increased from 28% to 46%, relative to baseline values) in middle-aged patients with advanced knee OA and varus malalignment, without concomitant increases in pain, adverse events, or decreases in adherence. Adherence was generally good throughout the studies (the drop-out rate was 27.59%, 18.75% and not defined in the last article, respectively), and no adverse events related to the training programs were reported.
Table 2. Characteristics of included studies.
Table 2. Characteristics of included studies.
Study and year Exercise modality NOS; Age (mean, years); Sex (female, n) Groups Exercise duration & sessions Outcomes Results Drop-out rate
Golightly,
2021		 CIT: cycling or walking 29; 63 ± 7; 19 I: High-intensity (n = 29) 12 weeks; 24 sessions; 2x/week Adverse events; feasibility; physical function; knee OA symptoms; balance; muscle strength; cardiorespiratory fitness; body composition 70% adherence
No adverse events related to the program
↑ Physical function*
↓ Knee OA symptoms*
↑ Balance*
↑ Muscle strength*
↑ Cardiorespiratory fitness*
Body composition: no significant changes		 27.59%
Smith-Ryan,
2020		 CIT: cycling 16; 59.9 ± 8.3; 12 I: High-intensity (n = 16) 6 weeks; 12 exercise sessions + 2 testing sessions at baseline + 2 post-test sessions; 2x/week exercise sessions Primary: feasibility
Secondary: cardiorespiratory fitness (i.e., VO2peak); knee OA symptoms; circulating biomarkers of metabolism		 Moderate feasibility: no adverse events related to the program, >96% adherence
↑ Cardiorespiratory fitness*
↓ Knee OA symptoms*
↓ Amino acids (i.e., methionine*, phenylalanine*, tyrosine*, serine)
↑ Aspartate/ asparagine
↓ Acylcarnitine		 18.75%
King,
2008		 RT: lower extremity 14; 48.35 ± 6.51; 2 I: High-intensity (n = 14) 12 weeks; 36 sessions; 3x/week Primary: knee extensor and flexor strength; pain; adherence
Secondary: dynamic knee joint loading; patient-reported outcomes; self-efficacy after training		 No adverse events
↑ Knee extensor and flexor strength*
No increases in pain during or after training
High adherence
Dynamic knee joint loading & patient-reported outcomes: no significant changes
↑ Self-efficacy after training (i.e., function subscale)*		 N.A.
Keogh,
2018		 CIT: cycling 27; 62.4 ± 8.3; 13 I1: High-intensity interval training (n = 9)
I2: Moderate-intensity continuous training (n = 8)		 8 weeks; 32 sessions; 4x/week Primary: feasibility (i.e., enrolment rate, withdrawal rate, exercise adherence, number of adverse events)
Secondary: efficacy (i.e., health-related quality of life, physical function, body composition)		 54% enrolment rate
37% rate of withdrawal
Very high exercise adherence
28 adverse events (24 related to one HIIT participant)
↑ Health-related quality of life*
↑ Physical function*
Body composition: no significant changes 		37%
De Zwart,
2002		 RT: lowerextremity 177; 67.7 ± 5.8; 107 I1: High-intensity (n = 89)
I2: Low-intensity (n = 88)		 12 weeks; 36 sessions; 3x/week Primary: isokinetic muscle strength; estimated 1-RM
Secondary: knee pain; physical functioning; knee OA symptoms		 No adverse events related to the program
↑ Isokinetric muscle strength
↑ estimated 1-RM**
↓ Knee pain
↑ Physical functioning
↓ Knee OA symptoms		 6%
Foroughi,
2011		 RT: lower extremity 54; 64 ± 7; 54 I1: High-intensity (n = 26)
I2: Low-intensity (n = 28)		 6 months; 78 sessions; 3x/week Primary: dynamic shank angles; knee adduction angles; knee adduction moment of the most symptomatic knee
Secondary: muscle strength; gait speed; osteoarthritis symptoms		 Two minor adverse events in the control group
Dynamic shank angles: knee adduction angles, knee adduction moment: no change over time
↑ Muscle strength**
↑ Gait speed*
↓Osteoarthritis symptoms*		 9%
Mangione,
1999		 Cardio-respiratory continuous training: cycling 39; 71 ± 6.9; 26 I1: High-intensity (n = 19)
I2: Low-intensity (n = 20)		 10 weeks; 30 sessions; 3x/week Functional status; gait; overall and acute pain; aerobic capacity ↑ Functional status*
↑ Gait*
↓ Overall pain*
No increase in acute pain
↑ Aerobic capacity* 		7.8%
Bressel,
2014		 CIT + balance training: aquatic treadmill 18; 64.5 ± 10.2; 16 I: High-intensity (n = 18)
C: Control group (n = 18)		 High-intensity: 6 weeks; 2-3x/week
Control: 4 weeks		 Pain; balance; physical function; mobility No adverse events related to the program
↓ Pain**
↑ Balance**
↑ Physical function**
↑ Mobility** 		0%
Thorstensson,
2005		 RT: lower extremity 61; 56 ± 6; 31 I: High-intensity (n = 30)
C: Control (n = 31)		 6 weeks; 12 sessions; 2x/week Primary: self-reported pain; function; knee-related quality of life
Secondary: health status; functional performance		 Self-reported pain & function: no significant differences between groups
↑ Quality of life** (at 6 weeks & 6 months)
↑ Health status** (at 6 weeks)
↑ Functional performance*		 8%
Waller,
2017		 RT: aquatic 87; 63.8 ± 2.4; 87 I: High-intensity (n = 43)
C: Control (n = 44)		 16 weeks; 48 sessions; 3x/week Primary: body composition; walking speed
Secondary: leisure time physical activity		 High adherence
↓ Fat mass** (after 4 months intervention)
Lean mass: no significant changes
↑ Walking speed** (after 4 months intervention and 12 months follow-up)
Leisure time physical activity: significant effect on fat mass loss 		2% (after 16 weeks)
13% (after 12-months follow-up)
Calatayud,
2017		 RT: lower extremity 50; I: 66.8 ± 4.8, C: 66.7 ± 3.1; 37 I: High-intensity (n = 25)
C: Control (n = 25)		 8 weeks; 24 sessions; 3x/week WOMAC; SF-36; VAS; isometric knee flexion; isometric knee extension; isometric hip abduction; active knee range of motion; functional tasks ↓WOMAC**
↑ SF-36**
↓VAS**
↑ Isometric knee flexion**
↑ Isometric knee extension**
↑ Isometric hip abduction**
↑ Active knee range of motion (i.e., flexion and extension)**
↑ Functional tasks**		 12%
Messier,
2021		 RT: lower & upper extremity, core 377; 65; 151 I1: High-intensity (n = 127)
I2: Low-intensity (n = 126)
C: Control (n = 124)		 18 months; 3x/week Primary: knee pain; knee joint compressive force
Secondary: physical function; mobility; disease progression; thigh skeletal muscle volume; thigh fat volume; IL-6 serum levels; knee extensor strength; hip abductor strength		 29 nonserious adverse events related to the program
No statistically significant difference between high-intensity and control group or high-intensity and low-intensity group		 25%
Jan,
2008		 RT 102; 63.3 ± 6.6 (high-intensity), 61.8 ± 7.1 (low-intensity), 62.8 ± 7.1 (control); 79 I1: High-intensity (n = 34)
I2: Low-intensity (n = 34)
C: Control (n = 34)		 8 weeks; 24 sessions; 3x/week Pain; function; walking time; muscle torque ↓ Pain*
↑Function*
↓Walking time*
↑Muscle torque*
No statistically significant differences between the high-intensity and low-intensity groups		 4%
Note. NOS: Number of subjects; RT: Resistance Training; CIT: Cardiorespiratory Interval Training; 1-RM: One Repetition Maximum; OA: osteoartritis; IL-6: interleukin 6; VO2peak: peak oxygen consumption; N.A.: Not Available; WOMAC: Western Ontario and McMaster Universities Osteoarthritis Index; SF-36: Physical Functioning Scale of the Short Form-36; VAS: Visual Analogue Scale. *p < 0.05. **significant difference between groups.
  • HIIT vs MICT
Only one study by Keogh et al. [50] evaluated the feasibility and potential benefits of HIIT cycling as an alternative exercise option to MICT cycling for patients with knee OA. Twenty-seven participants were enrolled to an 8-week (4x/week) HIIT or MICT program. Significant benefits in health-related QoL measured with WOMAC (pre- and post-test scores for the HIIT group 36.1 ± 15.0 and 34.8 ± 15.5, respectively, pre- and post-test scores for the MICT group 21.2 ± 14.6 and 22.9 ± 14.4, respectively) were found for both groups, with the HIIT group also reporting significant increases in functional performance as assessed using the Timed Up and Go measured in seconds (pre- and post-test 8.9 ± 2.0 and 7.8 ± 1.1, respectively) and Sit to Stand measured in seconds (pre- and post-test 11.1 ± 2.2 and 13.1 ± 2.7, respectively) functional tests. The enrolment rate and adherence rate for both the HIIT and MICT groups was comparable to other cycling studies involving similar populations [51,52,53] with a withdrawal rate of 37%. Nonetheless, the number of adverse events (HIIT: two of nine participants, 26 adverse events; MICT: one of eight participants, two adverse events) appeared very high, although 24 of these adverse events were reported by one HIIT patient with a Bakers cyst on their knee, who still completed 25 of the requested 32 exercise sessions.
  • HIIT vs LIT
Three studies evaluated the outcomes of HIIT vs LIT for knee OA.
One recent study by de Zwart et al. [54] assessed whether resistance HIIT led to increased muscle strength compared to resistance LIT in patients with knee OA. One-hundred and seventy-seven participants were enrolled to a 12-week (3x/week) HIIT or LIT program. In both HIIT and LIT groups, muscle strength measured in Nm per kilogram (Nm/kg) (0.98 ± 0.40 and 1.11 ± 0.40 at baseline and 12 weeks, respectively, for the HIIT group, 1.02 ± 0.41 and 1.15 ± 0.42 at baseline and 12 weeks, respectively, for the LIT group), knee pain measured with the Numeric Rating Scale (4.8 ± 2.3 and 2.9 ± 2.0 at baseline and 12 weeks , respectively, for the HIIT group, 5.1 ± 2.4 and 2.7 ± 2.4 at baseline and 12 weeks, respectively, for the LIT group) and WOMAC-Physical Functioning (21.3 ± 13.0 and 16.8 ± 12.2 at baseline and 12 weeks, respectively, for the HIIT group, 20.4 ± 13.3 and 16.4 ± 12.6 at baseline and 12 weeks, respectively, for the LIT group) were significantly increased after 12 weeks of training and at follow-up compared to the start of the training. Interestingly, it was found a higher estimated 1 RM strength values favouring HIIT. Interestingly, significant differences were found in the Hospital Anxiety and Depression scale between the HIIT and LIT groups in favour of the HIIT group. The authors concluded that HIIT did not result in greater improvements in isokinetic muscle strength, pain and physical functioning compared to LIT in patients with knee OA but was well-tolerated so they suggested that either intensity of resistance training could be utilised in exercise programs for patients with knee OA.
In a study by Foroughi et al. [55], the authors hypothesized that HIIT progressive resistance training would improve lower limb dynamic alignment and function (lower knee adduction moment, increased muscle strength, and fewer knee OA symptoms). Fifty-four women with knee OA were enrolled in into a 6-month (3x/week) HIIT or LIT exercise program. Dynamic alignment and knee adduction moment did not change over time or between groups. Muscle strength improved in both groups over time, but significantly more in the HIIT group (overall relative change in strength was 52.5% in the HIIT and 33.0% in the LIT group). By contrast, gait speed measured in meters per second (m/s) (1.1 ± 0.17 and 1.2 ± 0.17 at baseline and six months, respectively, for the HIIT group, 1.1 ± 0.19 and 1.2 ± 0.17 at baseline and six months, respectively, for the LIT group) and pain measured with WOMAC (5.7 ± 3.3 and 3.83 ± 2.7 at baseline and six months, respectively, for the HIIT group, 6.7 ± 3.5 and 5.5 ± 3.6 at baseline and six months, respectively, for the LIT group) improved over time in both groups. Improvements in shank adduction angle were related to improvements in self-reported disability, but not to changes in muscle strength, gait velocity, or pain. Although muscle strength improved significantly more in the HIIT group, the hypothesized reduction in knee adduction moment, shank and knee adduction angles were not evident after either exercise modality.
Mangione et al. [56] evaluated the effects of HIIT and LIT stationary cycling on functional status, gait, overall and acute pain, and aerobic capacity were examined. Thirty-nine adults with knee OA were randomized to either HIIT or LIT exercise group for 10 weeks (3x/week) of stationary cycling. The authors concluded that participants with knee OA in both groups improved in timed chair rise measured in seconds (23.31 ± 9.10 and 19.11 ± 6.62 at baseline and after 10 weeks, respectively), in the distance walked in six minutes measured in meters (489.59 ± 109.16 and 533.78 ±104.99 at baseline and after 10 weeks, respectively), in the range of walking speeds measured in m/s (1.04 ± 21 and 1.05 ± 20 at baseline and after 10 weeks, respectively, for slow walking, 1.59 ± 33 and 1.67 ± 33 at baseline and after 10 weeks, respectively, for fast walking), in the amount of overall pain relief (in the 70% of training sessions subjects reported that pain decreased immediately after cycling), and in aerobic capacity measured at the treadmill GXT test in minutes (10.98 ± 3.95 and 13.17 ± 4.21 at baseline and after 10 weeks, respectively) with no differences between HIIT and LIT groups. Anyway, the authors stated that the intensity of exercise did not have a differential effect on these outcomes. The authors finally highlighted that the improvements in function and aerobic capacity demonstrated in their study suggested that training was more than a “practice effect,” because testing was carried out using a variety of walking-based measures, and training was performed by stationary cycling. Adherence was generally very good throughout the studies (the drop-out rate was of 6%, 9%, and 7.8%, respectively). Interestingly, two minor adverse events during testing occurred in the LIT group in the study by Foroughi et al. [55], and two minor adverse events occurred during the testing and training in the study by Mangione et al. [56], but it was not specified in which group.
  • HIIT vs CT
Four studies evaluated the effects of HIIT vs CT for knee OA.
Bressel et al. [14] quantified the efficacy of a HIIT aquatic treadmill exercise program on measures of pain, balance, function, and mobility in patients with knee OA. Eighteen participants were enrolled into a 6-week HIIT protocol (2-3x/week). The participants involved in the study first completed a 4-week non-exercise control period followed by a 6-week aquatic treadmill exercise program that incorporated a balance and HIIT training component. The authors observed that patients with OA display reduced joint pain measured with the Knee Injury and Osteoarthritis Outcome Score’ (KOOS) subscale, with scores being 30–49% greater at six weeks than at pre-test evaluation, reduced usual pain values (at six weeks being 213% lower than the pre-test), improved balance measured with the sensory organization test equilibrium and strategy scores (values after the 6-week intervention being 10 and 2.5% greater than baseline, respectively), improved also function measured with the sit-to-stand test (rising index scores improved from 0.49 ± 0.19% at baseline to 0.33 ± 0.11% after six weeks), and mobility measured with walking speeds in seconds (8.6±1.4 at baseline to 7.8 ± 1.1 after six weeks, 10% lower). The same benefits were not observed after a non-exercise control period. The authors suggested that aquatic treadmill exercise that incorporates high-intensity intervals is well tolerated by patients with OA and seems to be effective at managing symptoms of OA.
Thorstensson et al. [57] tested the effects of a short-term, HIIT on self-reported pain, function, and QoL. Sixty-one middle-aged participants were randomly randomized to HIIT or CT groups. Thirty participants were enrolled to a 6-week (2x/week) HIIT program. The authors stated that a 6-week high-intensive exercise program had no effect on pain or function in middle-aged patients with moderate to severe radiographic knee OA. Anyway, in the HIIT group, an improvement was seen at six weeks in KOOS subscale QoL after six weeks compared to the CT group (40 ± 15 and 46 ± 21, respectively), and the difference between groups was still persistent at six months.
A RCT study by Waller et al. [58] investigated the effects of a 4-month (3x/week) HIIT aquatic resistance training on body composition and walking speed in post-menopausal women with mild knee OA, immediately after intervention and after 12-months follow-up. Additionally, influence of leisure time physical activity was also investigated. Patients were randomly allocated into one of the two arms of the study (HIIT or CT). The authors found that HIIT aquatic resistance training program is effective at decreasing fat mass four months after intervention, as well as improving walking speed calculated as m/s (1.74 ± 0.15, 1.83 ± 0.16 and 1.82 ± 0.14 for HIIT at baseline, four and 12 months, respectively, 1.73 ± 0.17, 1.76 ± 0.17 and 1.77 ± 0.13 for CT, at baseline, four and 12 months, respectively) in post-menopausal women with mild knee OA. Furthermore, daily leisure time physical activity (recorded as any type of activity and self-perceived intensity of each activity, i.e., low, moderate or high) over the 16-month period had a significant effect on fat mass loss but no effect on walking speed.
Calatayud et al. [59] evaluated the effectiveness of a 8-week (3/week) HIIT preoperative resistance training program in patients waiting for total knee arthroplasty (TKA). Fifty patients were randomly allocated to the HIIT group or CT. The main finding of this study was that high-intensity pre-operative training improved strength: isometric knee flexion measured in kg (9.2 and 9.1 at baseline, 9.4 and 4.4 three months after surgery for HIIT and CT, respectively), isometric knee extension measured in kg (23.5 and 23.5 at baseline, 22.8 and 14.3 three months after surgery for HIIT and CT, respectively) and hip abduction measured in kg (7.3 and 7.2 at baseline, 7.8 and 5.0 three months after surgery for HIIT and CT, respectively), active knee range of motion (knee flexion was 104.0° and 104.2° at baseline, 101.2° and 96.4° at three months after surgery for HIIT and CT, respectively, while knee extension was 14.4° and 14.0° at baseline, 8.2° and 13.9° at three months after surgery for HIIT and CT, respectively) and functional measures such as the timed up and go test measured in seconds (8.6 and 8.5 at baseline, 7.0 and 8.7 at three months after surgery for HIIT and CT, respectively), as well as reduced pain measured with WOMAC (54.0 and 53.2 at baseline, 25.0 and 30.7 at three months after surgery for HIIT and CT, respectively) and length of hospitalization in the early post-operative periods compared with CT. Adherence was generally very good throughout the studies (the drop-out rate was of 0%, 8%, 2% after 16 weeks and 13% after 12-months, and 12%, respectively). No adverse events were reported throughout the studies.
  • HIIT vs LIT vs CT
Two studies evaluated the effects of HIIT vs LIT vs CT for knee OA.
A recent study by Messier et al. [60] was performed to determine whether strength HIIT reduces knee pain and knee joint compressive forces more than strength LIT and more than CT in patients with knee OA. A total of 377 participants were randomized into strength HIIT or LIT or CT. The exercise protocols for both HIIT and LIT were performed for 18 months (3x/week). Among participants with knee OA, strength HIIT did not significantly reduce WOMAC knee pain or knee joint compressive forces at 18 months compared with strength LIT or with an attention CT group. Some improvements were reported in the mean knee flexor strength that was statistically significantly greater in both exercise groups than in the CT group at 18 months measured in Nm (35.0 ± 20.1, 38.2 ± 20.3, and 38.1 ± 22.5 at baseline, 51.5, 52.6 and 43.8 at 18-month follow-up for HIIT, LIT and CT, respectively), and in the proportion of participants using pain medication that declined across the 18-month intervention period (45%, 34% and 55% for HIIT, LIT and CT, respectively), with no statistical difference among the groups at the 18-month follow-up.
Another study by Jan et al. [44] compare the effects of resistance strength HIIT and strength LIT in elderly subjects with knee OA. One-hundred and two participants were randomized into HIIT, LIT, and CT groups, and trained for eight weeks (3/week). The authors reported that both HIIT and low-intensity resistance strength trainings reduced pain measured with WOMAC pain subscale (8.5 ± 3.8 and 4.8 ± 3.5 in the HIIT group at baseline and after eight weeks, 7.8 ± 3.3 and 4.8 ± 2.7 in the LIT group at baseline and after eight weeks, 8.3 ± 4.6 and 7.1 ± 3.4 in the CT group at baseline and after eight weeks) and improved function measured with WOMAC physical function subscale (26.4 ± 9.0 and 14.7 ± 8.5 in the HIIT group at baseline and after eight weeks, 26.1 ± 8.1 and 14.8 ± 9.2, in the LIT group at baseline and after eight weeks, 25.4 ± 11.3 and 22.5 ± 10.9 in the CT group at baseline and after eight weeks) in patients with knee OA. Although HIIT strength training demonstrated effect sizes that consistently were slightly greater than those achieved with low-intensity resistance strength training, the differences in improvement between the HIIT and low-intensity groups were not significant.
Adherence was generally good throughout the studies (the drop-out rate was 25% and 4%, respectively). There were 87 non-serious adverse events in the study by Messier et al. [60]: 53 in the HIIT, 30 in the LIT, and 4 in the CT groups. Of those, 29 were related to the program: 20 in the HIIT, 9 in the LIT, none in the CT groups. No adverse effects related to the program were reported in the study by Jan et al. [44].

Discussion

HIIT gained significant popularity worldwide as a fitness trend, and recent research has demonstrated its potential in reducing disability in people with different chronic musculoskeletal disorders such as fibromyalgia [36], axial spondylarthritis [61] and chronic non-specific low back pain [62,63,64,65]. In our review, we examined the effects of HIIT on knee OA as a standalone exercise modality or in comparison to training modalities with other exercise intensities such as MICT and LIT, or to CT. To the best of our knowledge, this is the first review that assessed the potential role of HIIT in mitigating symptoms associated with knee OA.
HIIT showed good outcomes in improving pain, physical functioning, muscle strength, cardiorespiratory fitness and QoL, when evaluated alone or compared with CT [14,31,45,49,57,58,59]. However, HIIT was shown to have similar effects in improving pain, function and strength when compared with other exercise intensity, especially LIT. The included studies utilized various exercise modalities ranging from resistance training to aquatic treadmill training, with all exercise intensities showing superiority over no exercise.
Exercise therapy is known to provide significant improvements to patients suffering from chronic musculoskeletal pain conditions (including OA). This improvement is thought to occur through different possible underlying mechanisms, including the reconceptualization of pain-related fears, a hypo-analgesic effect, and changes in the immune system, ultimately leading to better pain control, functional ability, and overall well-being [23,66,67].
According to Beckwée et al. [68], several explanatory models can be described for exercise-induced improvement of knee OA related symptoms, which can be categorized in five main components: neuromuscular, peri-articular, intra-articular, psychosocial components, and general fitness and health. The authors suggest that the clinical benefits of exercise therapy observed in patients with knee OA are likely due to a combination of these underlying mechanisms, and that future exercise studies taking all possible pathways into consideration should help in providing more targeted exercise recommendations for patients suffering by knee OA.
Furthermore, Runhaar et al. [69] stated that an increase of upper leg strength, a decrease of extension impairments and improvement in proprioception were identified as possible mediators in the positive association between physical exercise and OA symptoms.
Although several studies investigated optimal training parameters for resistance training in patients with knee OA, no uniform training dose can be proposed due to the great heterogeneity in training protocols limiting a direct comparison. In the included studies, resistance training treatment duration ranged from six weeks to 18 months and was performed using different kinds of equipment. For instance, de Zwart et al. [54], Thorstensson et al. [57], Waller et al. [58], and Messier et al. [60] used resistance bands in their protocols, resulting in improvements in knee OA symptoms, muscle strength and physical functioning. Foroughi et al. [55] and Jan et al. [44] used machines such as leg press and leg extension/flexion, finding improvements in knee OA symptoms and muscle strength.
Regarding cardiorespiratory exercise training, the included studies mainly used cycling as a modality, and treatment duration ranged from six to 12 weeks. Golightly et al. [49] and Smith-Ryan et al. [31] found benefits in knee symptoms and cardiorespiratory fitness with cycling, as well as Keogh et al. [50], who found improvements in health-related QoL and physical function, and Mangione et al. [56] who found benefits in physical function, overall pain and aerobic capacity. In a recent review, Zeng et al. [23] stated that low-intensity aerobic exercise is better for patients with severe knee OA, while high-intensity aerobic exercise is more suitable for patients with mild knee OA. In contrast, for mild knee OA patients with chronic diseases, HIIT was found to be better, so it might be advocated that physicians should choose the most appropriate treatment basing on each single patient’s health status.

Strengths and limitations

A strength of this narrative review is the use of the CERT tool [48], which provides a systematic and clear display of all relevant exercise components, which supports the reproducibility of exercise modalities, and thus patient outcomes. CERT can be used in all types of exercise interventions, and has a good inter-rater agreement in musculoskeletal exercise interventions [70]. The main limitation of this review is the small number of relevant studies found in the scientific literature about the effects of HIIT for knee OA. Furthermore, in the included studies there was a great heterogeneity of exercise programs in terms of modality and duration, making it difficult to compare the effects of the exercise programs. However, both short-term and long-term programs showed that HIIT is a feasible and effective strategy for lowering pain and improving function, with minimal to no adverse events.

Clinical implications

Given the great variety in applicability of the HIIT protocol, the authors recommend adapting the exercise modality to the patient’s preferences and available equipment of the physical therapist to maximize patient’s motivation and exercise adherence. Moreover, physical therapists should choose together with the patient between cardiorespiratory or resistance training, given the evidence that the application of one of the exercise modalities is superior to a mixed program in patients suffering from knee OA [71].

Future recommendations

Given the promising results of the articles included in this review, more high-quality research should be performed for a further understanding of the beneficial effects of HIIT in patients with knee OA., since there is still too little knowledge about its effectiveness. The evaluation of the effects of a multimodal HIIT program (i.e., resistance training in combination with cardiorespiratory training) [72], patient profiling in order to prescribe a tailored HIIT program [73], and the evaluation of the effects of HIIT on other important outcome measures in knee OA such as depression, inflammation, sleep quality, etc [74], should be considered as topics of interest for future research.

Conclusions

In conclusion, it is possible to state that HIIT showed promising results as a therapeutic exercise for patients with knee OA. However, the actual quality of evidence remains very low, and further high evidence studies (such as RCTs) are needed to confirm the promising outcomes reported in this review.

Author Contributions

Conceptualization, D.T. and J.V.; writing—original draft preparation, D.T., T.T., R.M., J.V.; writing—review and editing, D.T., T.T., R.M., J.V.; supervision, D.T., J.V. All authors have read and agreed to the published version of the manuscript.

Funding

This research received no external funding.

Institutional Review Board Statement

Not applicable.

Informed Consent Statement

Not applicable.

Data Availability Statement

Not applicable.

Conflicts of Interest

The authors declare no conflict of interest.

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Table 1. Consensus on Exercise Reporting Template (CERT).
Table 1. Consensus on Exercise Reporting Template (CERT).
Study and year WHAT (equipment) WHO (experienced therapist?) HOW WHERE WHEN, HOW MUCH TAILORING (of exercise intensity, based on…) HOW WELL (Delivered and performed as expected?)
Individual/ group (S/US) Adherence/ adverse events (reported by...) Motivation strategies Progression Exercise program replicable/ home program available? Nonexercise components
Golightly,
2021		 Cycle ergometer or treadmill ; chest strap heart rate monitor Yes Individual (S) Physiotherapist : number of sessions attented or completed/ participant + investigator N.A. N.A. Yes, except exercise progression/ N.A. In-centre 20 min (without warm-up/ cooling-down); 10 reps of 1-min high-intensity bouts
HI: 90% VO2peak
Rest: 1 min complete rest between reps; 24 h between training sessions		 Exercise modality; exercise intensity Yes
Smith-Ryan, 2020 Electronically braked cycle ergometer Yes Individual (S)
 Physiotherapist : number of sessions completed or total available/ participant + investigator N.A. N.A. Yes, except exercise progression/ N.A. In-centre 20 min (without warm-up/ cooling-down); 10 reps of 1-min high-intensity bouts
HI: 90% peak power output
Rest: 1 min between reps; 24 h between training sessions		 Peak power output Yes
King, 2008 Cycle ergometer; dynamometer (and accompanying software) Yes N.A. (S) Researcher/ participant N.A. New targets of 60% peak torques based on test protocols every 3 weeks Yes/ N.A. In-centre 45 min (including warm-up)
Part 1 -> 3 sets; 10 reps; concentric isokinetic knee extension and flexion at 60, 90 and 120°/sec angular velocity; 60% of baseline strength
Part 2 -> 3 sets; 15 reps; concentric isokinetic knee extension and flexion at 180°/sec angular velocity; maximum effort
Rest: minimal 24 h between sessions		 Peak torques Minimal modification (due to increases in pain)
Keogh, 2018 Stationary bicycle N.A. Individual (US) Participant (training diary)/ participant N.A. N.A. Yes/ yes Home-based 25 min
HI: 7 min warm-up (progressively increasing intensity); 5 sets of high-intensity intervals at 110 rpm for 45 sec with 90 sec relative rest between sets at 70 rpm (low-intensity); 6-7 min cool-down (light-moderate intensity)
Moderate-intensity: 3 min warm-up (light intensity); 20 min at 60-80rpm (moderate intensity); 2 min cooldown (light intensity)		 Personal experience Yes
De Zwart, 2022 Fitness devices; weighted vests; ankle weights; resistance band Yes 2x/week in group (S) Physiotherapist/ participant + investigator N.A. ↑ 5% 1-RM/ week, based on 1-RM measurement from week 0, week 6 & week 10 Yes/ yes (paper hand-out) 2x/week in-centre 60 min; 3 sets; 10 reps

HI: 70-80% 1-RM, weighted vests during weight-bearing exercises

LI: 40-50% 1-RM, no additional weighted vests

Rest: 90 sec between sets; 48h between training sessions		 % 1-RM Yes
1x/week individual (US) Log book/ participant + investigator 1x/week home-based
Foroughi, 2011 Fitness devices Yes N.A. (S)
 Researcher/ participant N.A. ↑3% 1-RM Yes/ N.A. In-centre 3 sets; 8 reps (6-9 sec/rep); 80% 1RM (equal to 15-18 on the Borg Rating of Perceived Exertion)
Rest: 10-15 sec between reps; 1-2 min between sets
C: minimal resistance; no progression		 % 1-RM Main protocol deviation: changing to an isometric form of training if the dynamic mode was causing pain, reducing the intensity of the intervention group and/ or limiting the range of motion
Mangione, 1999 Cycle ergometer; heart rate monitor N.A. N.A. (S) Researcher/ N.A. N.A. N.A. Yes, except exercise progression/ N.A. In-centre HI: 60min (including warm-up and cool-down); 70% HR reserve
LI: 60min (including warm-up and cool-down); 40% HR reserve
Target HR zone is reached by an increase in speed of pedaling instead of an increase in resistance		 Maximum heart rate Yes
Bressel, 2014 Pool; water jet; aquatic treadmill N.A. N.A. (S) Researcher/ participant + investigator Verbal motivation Progression visualized in table in study article Yes/ N.A. In-centre 18-30 min; 3-6 reps
HI: 14-19 RPE; 30 sec – 2 min 30 sec
Rest: 10 RPE; 1 min – 1 min 30 sec
C: maintenance of typical activities of daily living; no new treatment		 RPE Yes
Thorstensson, 2005 Heart rate monitor (not obligatory); thera band Yes Group (S)
 Researcher/ N.A. N.A. Gradually increase in intensity by increased lever arm or range of motion Yes/ yes In-centre + home-based Weight-bearing exercises; 1 h; minimal 60% maximum HR Maximum heart rate Yes
Waller, 2017 Pool; heart rate monitors; therabands; Hydro-boots Yes Group (S)
 Researcher/ investigator N.A. Progression from barefoot to small resistance fins and large resistance boots Yes/ N.A. In-centre 1 h (i.e., 15 min warm-up, 30 min intensive aquatic resistance training program, 10-15 min cool-down); as hard and fast as possible
C: maintenance of usual leisure time activities with the possibility to participate in 2 sessions of 1 hour, including light stretching, relaxation, social interaction		 RPE, heart rate, blood lactates Yes
Catalayud, 2017 Fitness devices; Bosu® Balance Trainer Yes N.A. (S) N.A./ N.A. N.A. Adding a maximum of 2 or 3 kg Yes/ N.A. In-centre 1 h (i.e., 15 min warm-up, 5 sets of 10 reps of each exercise, 5 min cool-down); 10-RM
C: treatment including exercise which may explain the absence of between-group difference
Rest: at least 48 h between sessions; 1 min between sets		 1-RM Yes
Messier,
2021		 Nautilus resistance training machine; Thera-Bands Yes Group (S) Participant/ participant Frequent contact; positive feedback; incentives; establishing personal commitment; promoting a sense of community ↑ 5% 1-RM/ 2 weeks, based on 1-RM measurement (measured each 9 weeks) Yes/Yes In-centre 60 min; 3 sets

HI: 4-8 reps; 75-90% 1-RM

LI: 15 reps; 30-40% 1-RM

C: 60 min educational workshops and seated stretching 2x/month for the first 6 months and the other months 1x/month

Rest: 60-90 sec between sets		 % 1-RM Yes
Jan, 2008 Leg press machine; bicycle (warm-up); cold pack (after exercise) Yes Individual (S)
 Researcher/ N.A. N.A. ↑5% 1-RM/ 2 weeks Yes/N.A. In-centre HI: 30 min; 60% 1-RM; 3 sets; 8 reps
LI: 50 min; 10% 1-RM; 10 sets; 15 reps
C: no intervention
Rest: 1 min between sets; 5 min between left and right knee sessions		 %1-RM Yes
Abbreviations. S: supervised; US: unsupervised; HI: High-Intensity; LI: Low-Intensity; reps: repetitions; 1-RM: One Repetition Maximum; HR: heart rate; rpm: revolutions per minute; I: intervention group; C: control group; 1-RM: One Repetition Maximum; N.A.: Not Available; RPE: Rate of Perceived Exertion.
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