Managing or preventing knee pain can very confusing because advice is often contradictory.  Exercise approaches promoting functional movements are a favourite amongst fitness and health professionals, yet many people gravitate to exercise machines that are specialized for targeting problem areas.  In this article, I hope to provide some clarity to help you make the best decision for your individual needs and goals.

Functional training has become the most popular method rehabilitation and fitness professionals use to return clients to sports, as well as improve performance and reduce injury risk.  This is because performing exercises that look like sports movements is believed to be significantly better than strengthening using machines that focus only on a single muscle or muscle group.

But that’s not all.  Some research studies caution that the use of exercise machines may cause potentially-damaging forces in both ligaments and cartilage that could lead to osteoarthritis of the knees.  Of these, the seated knee extension is recognized to be the most dangerous.  The most important arguments against exercise machines for the knees are:

  • Research has shown that knee strain when using machines can be much higher for the same muscular effort than during functional exercises like squats or lunges with even very heavy weights.
  • Exposing your knees to high forces may lead to progressive problems including arthritis and surgery to reduce pain.  This can have a significant impact on activity level in the long term, especially for anyone who has had a knee injury in the past.
  • Exercise machines often focus on a single muscle, or localized area of the body.  However, the opinion of many experts is that lower body strengthening should condition more muscles than just the quads, such as the muscles of the hips, which are used in many sports movements. 

Low pad position on knee extension machine. Raise on shin to help decrease strain on knee ligamentsSeated Knee Extension Machine

Despite such clear warnings that people may be training their thighs at the expense of their knees, gyms continue to fill their spaces with these machines because of their popularity with members.  They have not only been touted by famous bodybuilders for building a muscular physique, but they are also easy to perform without detailed instruction.  Additionally, there are several relevant points that suggests that research may not have all the answers.  These include:

  • Biomechanical analysis that estimates forces and injury risk does not agree with the clinical research studies. In other words, the laboratory and the clinic don’t seem to agree.  For example, injuries almost always happen during functional movements such as lunging or landing on one’s feet, and there are no medical reports of this injury happening when performing a knee extension exercise.
  • Medical research also shows that quadriceps strength is the most important factor in avoiding future injury.  However, additional research has also shown that functional exercises, such as squats and lunges, alone may not sufficiently strengthen the quads.  This unfortunately places the person in a difficult position, because expert advice may not be best for their long-term recovery.

Given the strong points on both sides of this discussion, can we actually say that it is possible to safely use exercise machines for strengthening that will also not increase the risk of future injuries to the knees?  Yes of course!  But only as part of your whole program, because you have to consider your individual needs.  Here are some guidelines to help you do it safely and effectively:

  • Make sure the equipment is set up properly (Here is a great video with tips on how to perform this exercise correctly.) And always do the following:
    • Make sure your knee lines up with the point of rotation of the machine.
    • Instead of placing the pad just above the ankle joint (as seen in the picture), adjust it to about mid-shin level as this has been shown to help decrease stresses on the knee ligaments (Escamilla et al, 2012).
    • If you have knee pain or a previous injury, make sure you use an exercise machine that allows you to adjust the starting angle and range to a safe amount, or at bare minimum, stay within your pain-free range of motion.
  • Don’t use heavy weights! Even if it’s possible to select hundreds of pounds on the machine, there is a clear trend for increased knee ligament strain with increased knee extension force.  And by itself, the seated position used on this exercise means you won’t improve your athletic ability, either.  Keep these stresses and strains in check by aiming for moderate resistance that lets you perform around 10-15 repetitions with *perfect technique*. 
  • Another strategy to increasing resistance in an exercise is to try going very slowly up and down (counting to between 5 and 10 in each direction), experiment with static holds at full extension, or reduce your rest period between sets to between 30 and 60 seconds. This increases both muscle activity and limits additional stresses in the knee joint structures, and lastly:
  • Pay close attention to how your knees feel during and after your workout, and never let your knee pain increase during a set of exercise. Signs of swelling, redness, heat may indicate an irritation to the joint that could turn into bigger problems in the future.  If pain or swelling does not return to normal after one-to-two days, consider seeing a musculoskeletal health professional for help.

In general, people who are trying to prevent knee pain, or who are back playing sports pain-free, will likely benefit from including exercise machines for the legs because the forces are not likely to be greater than when doing squatting or lunging movements.  This also includes people with mild knee osteoarthritis.  However, those following a knee rehab program should focus on body weight exercises that restore normal movement in the knees, hips and ankles.  Knowing how much of each type of exercise to use not only depends on your stage of recovery, but also your particular medical and activity history, individual physical characteristics, and goals.  So it pays in the long term to have a specialist see where you need the most attention first, and work with you to plan a return to the activities you love the most.

The advice in this article is not meant to replace professional advice from a therapist or trainer.  If you would like to find out how you can safely prevent or manage knee pain, or to schedule an appointment, please feel free to contact John Gray at jgray@orthophysio.com, or call us at The Orthopaedic Therapy Clinic at 416-925-4687.