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Key takeaways:
The program improved strength in hip abductor, hamstring and quadriceps muscles in patients with knee OA.
However, it failed to impact most measures of knee joint loading during walking.
Two data sets — one published in 2021 and its recent follow-up released in February — have shed light on what can and cannot be accomplished with a strength training intervention in knee osteoarthritis.
In 2021, Stephen P. Messier, PhD, director of the J.B. Snow Biomechanics Laboratory at Wake Forest University, and colleagues published an article in JAMA that described an 18-month strength training program in patients with knee OA.
The analysis included 377 patients with knee varus alignment and medial tibiofemoral OA assigned to one of three groups: a high-intensity strength training protocol, a low-intensity strength training protocol, or a control group who received healthy lifestyle attention.
The intervention involved a warm-up, a 40-minute training session using six lower body exercises that targeted each leg, the upper body and core, and a 15-minute cool down that was supervised by study staff.
The aim was to determine whether increased leg muscle strength could reduce OA pain. According to the researchers, although strength training did improve muscle strength, no differences in pain were observed between the intervention and control groups.
This was not the expected or desired result, leading Messier’s group to dig further.
The researchers then conducted a post hoc analysis of 88 patients from the initial group who demonstrated the greatest improvements in leg muscle strength. This time, their aim was to determine whether increased strength correlated with improvements in knee abduction moment and knee compressive force. The findings were published in Arthritis Care & Researchon Feb. 16.
According to the researchers, results at 18 months showed increases in quadricep strength in the intervention group compared with controls — 45% vs. 16% (P < .05). Similarly, participants in the strength training group demonstrated greater improvements in hamstring strength — 68% vs. 11% — and hip abductor strength — 42% vs. 4% (P < .05 for both).
However, there were no significant differences between the groups in terms of mean peak internal knee abduction moment or mean peak knee compressive force, according to the findings.
Further results showed that internal knee extension moment was significantly less (27%) in the intervention group compared with controls (adjusted P = 0.03).
Healio sat down with Messier to discuss the history of strength training interventions in OA, the nuances of pain in this patient population, and how rheumatologists can talk to their patients about exercise.
Healio: What is the background of this series of studies?
Messier: For more than 3 decades, our focus for patients with knee osteoarthritis has been on reducing pain. Many of the studies have looked at the combination of diet and exercise, or diet alone or exercise alone.
Our first study, which was published in 1997, looked at walking and strength training separately compared to a control group. We showed that walking or strength training significantly reduced disability compared to controls. That helped us to move the conversation away from the idea that if you have knee pain, you should sit down, take it easy and don’t hurt yourself, to the idea that you really need to move. It does not matter if you walk, do aerobic activities or strength training. Any movement is better than no movement. That started the trend for doing exercise in knee OA.
Healio: Did you factor obesity into those trials?
Messier: Yes. In most of our work after that, we realized that many of the people in that first trial were overweight or obese. This led us to think that maybe diet plus weight loss is good. We looked at that in two separate trials and showed that the combination of weight loss and exercise is superior to weight loss alone or exercise alone.
Healio: How does strength training, vs. walking or aerobic exercise, come into play?
Messier: The trend in the field became more and more about strength training. We started to look at strength training in the hip to help with the internal knee abduction moment, which increases stress on the medial part of your knee. The thought was that increasing strength around the hips would reduce this moment, resulting in less stress on the knee. There were no data to support that either way, so we thought we would examine the data from our 2021 published study.
Healio: Results of the first study showed that strength training did not change pain levels in knee OA. The post-hoc analysis looked at knee joint loading. Why is this an important outcome?
Messier: There are two pathways to knee osteoarthritis. One is load, the other is inflammation. The one thing that really decreases both is weight loss. You lose weight, you decrease the load. When you lose weight, you lose fat and you reduce inflammatory cytokines. We thought that exercise would impact the inflammatory cytokine pathway by improving fitness and maybe have some benefit on the joint load. Our results proved that to be the case.
Healio: Your findings also address the idea of joint alignment in knee OA. What do your results show and why is this important?
Messier: One of the things that previous researchers had speculated about was that most people who have OA of the knee have it on the inside part of the knee, or the medial part. They are bow legged. Part of that is due to obesity, but part of that is due to alignment. So there has been speculation that if you strengthen the muscles around the hip, that would help to control the motion of the knee.
Healio: Could you discuss the specifics of these knee motions?
Messier: When your foot hits the ground, the force creates a moment about the knee. That is to say, an external knee adduction moment that is counterbalanced by the internal abduction moment. These moments in patients with knee OA cause the knee to go in, with pressure on the inside of the knee. If you already have an issue there, then that torque going in is going to create even more stress on the inside part of the knee.
The thought in our study was that if we strengthen the muscles around the hip, it will prevent that force from going so far on the inside part of the knee. It made sense but we never had proven or disproved it.
Healio: How did your previous work in strength training factor into this current study?
Messier: Our previous research showed that we really increased the strength in those muscles, with a 45% increase in the strength in hip abductors compared to controls, which had a less than 5% increase. Strength in the quadriceps and hamstrings also improved.
Healio: What did results of the post-hoc analysis show?
Messier: Unfortunately, strengthening those muscles did not make any difference in that moment. Although strengthening the muscles was a good thing, it did not really affect the moment that causes stress on the inside part of the knee.
Healio: Why not?
Messier: That is a great question. We figured the increase in muscle strength would help to absorb shock, but it did not. We still do not know why.
Healio: How do you find out why?
Messier: The parent trial in 2021 showed no difference in pain after strength training. The most recent study showed there was no difference in the moment after strength training. The question is: What is next for strength training?
Maybe what we need to investigate is whether it is not strength but power that impacts the knee moment. Power is essentially force divided by time, or how fast you can summon the muscle strength that you have. A recently conducted systematic review of strength training in knee OA trials suggests that fast repetitions are better than normal strength training. Currently, Paige E. Rice, PhD, MSc, and I are examining whether muscle power may actually prevent the onset of the disease.
Healio: Althoughyou did not necessarily achieve what you hoped to achieve from these trials, what is the take-home message of your results?
Messier: The most important thing for older adults with osteoarthritis, or even older adults in general, is to keep moving. Mobility is really important. When older adults lose their mobility, bad things happen. They go from independent living to being dependent on other people for activities of daily living. Let your body help you determine what days you can do more and what days you can do a little bit less, but keep moving and after a while that pain is going to subside. It doesn’t really matter what exercise you do. Just do one that you enjoy and can do for the rest of your life.
