Running Load and the Impact on your Joints

At SSPC we tend to see a lot of recreational runners and we are regularly asked whether running causes degeneration of joints, in particular the knee joint. I see a lot of runners with osteo arthritis (OA) of the knee, but at the same time we see equally as many non runners with OA of the knee, and some very keen older runners that don’t have OA of the knee at all. So what is the answer to the question?

Over the years health care providers have discouraged people diagnosed with OA from running, especially if they are of advancing age and overweight. One of the main reasons is we know that every extra kilogram of weight adds forces across the knee when walking and running. Conversely for every kilogram that we lose the forces across the knee are reduced dramatically. Various studies have looked at measuring peak forces across the knee joint in walking and running. The results have varied anywhere from 3 to 8 x body weight (BW) – meaning that up to 8 times BW forces may be transmitted through your knee joint, every step, when running – but it is generally accepted to be around 4 x BW. The article we have referenced for this piece (2) found peak knee force to be 4.2 x BW when running at 5 miles per hour ( that is slow) on a treadmill. The resultant thoughts have been that if the forces at the knee are high, then it must not be good to run if your joint is already showing signs of degeneration.

Both older and overweight people are in the high risk group for cardiovascular disease (CVD) and we know that vigorous physical activities, such as running, are good for prevention of all cardio vascular diseases, largely because they lead to weight loss. A reduction in weight has positive benefits for both reducing the risk of developing OA, and for helping reducing the risk of CVD. If running is largely pain free and it helps you lose weight then it is going to help both of these factors. In terms of OA risk alone, consider this:

Let’s take the above mentioned study results with the loads across the knee joint being 4.2 x BW per impact/step when running

. An 80kg person runs 5km (approximately 6500 steps, or 3250 per leg).

.The loads across the knee are 4.2 x 80kg x 3250 steps = 1,092,000kg of force across the knee during that 5km run.

.That same runner loses 2kg. The new sum becomes 4.2 x 78 x 3250 steps = 1,064,700kg of force across the knee.

.That’s 27,300kg less force across each knee in one 5km run! Imagine if this person runs 3 times a week; or runs 10km at a time!

Every kg of weight loss is significantly less force through all your lower limb joints!

Despite these loads, there is NO good evidence that running causes knee joint degeneration or even speeds up the degenerative process in those who have OA. In fact there is good evidence that running like strength and other cardiovascular exercise is good for those with knee OA (but you may have to control a few variables like speed, stride length, surface, footwear, distance, frequency – that’s what we’re here to advise on!).

I actually see many runners whose scans would indicate that they have significant knee OA but they tell me they are running without any issue. The current evidence backs up my suggestion that they keep running if they are tolerating it well. We know that there is very little correlation between radiological scans and the symptoms people have, so it is essential that your physio (or other health care provider) is treating and advising you based on your symptoms, not your scans.

The main thing is that whatever exercise you do, you are comfortable and any residual soreness from running doesn’t last longer than a few hours at most.

A recent study (2) analysing the national database in the United States compared runners to non-runners, and concluded the following:

Runners do not have more signs of structural knee OA (based on prospective x-ray results) compared to non runners. Runners do not get knee pain more than non runners. Runners with knee pain can actually improve their knee pain as a result of running.

All of this would tend to indicate that people DO NOT need to avoid running if they have knee OA. The important thing is do what you are comfortable with. Like many problems, load management is the key. Your level of fitness and severity of symptoms will influence how much load you can tolerate. Like the strengthening work that we prescribe to patients with OA, slow progressive increases in load is the key to successful management, and monitor how your body is responding to the load you are putting through it and modify as needed. The better your muscle system around your knees (quadriceps, hamstring and calf strength), the less impact you will have transferred to the joint. Thankfully though there are a few predictors that help us determine how appropriate running is for any particular person. It might be excessive body weight, lack of conditioning, poor running program etc that cause issues: whilst running gets the blame, it’s actually these other extrinsic variables that are the problem and when corrected, running isn’t an issue. One of the biggest predictors of running tolerance and OA risk is malalignment of the leg (eg bow legs) – where one compartment of the knee is loaded at the expense of the other – and this factor HAS been associated with knee pain and progression of osteoarthritis (2). If you have knee pain and bowed legs then you may be better off finding a different form of cardiovascular exercise but short of that “Happy Running”! If in doubt don’t hesitate to book in with one of our physiotherapists and have your knees assessed to see if they are suitable to run. As a general rule we would say that if you are running pain free and feeling good for it then continue.

Rob O’Donnell (SSPC Physiotherapist)

References Available on Request