What is the best strength exercise for knee pain?

There are a multitude of strengthening exercises that you can do for knee pain, but the leg press machine is by far my favourite exercise to make your knees stronger. Now, you may very well have tried it in the past and found that it didn't work for you, but please let me explain where you may have gone wrong before you stop reading!

Why I like it? No other exercise allows you to control every single variable e.g. foot position, knee angle and force to the same level as the leg press and this is crucial during the early stages of treating knee pain. It also exercises the glutes, hamstrings and quadriceps muscles which are all important to prevent as well as help treat knee pain.

In this article:

• Knee pain: Why you have to strengthen your muscles

• Why the leg press may have hurt you in the past

• Step 1 – Establish a baseline

• The importance of getting your foot placement right

• The importance of getting the depth of the movement right

• The importance of getting the load right

• What to do if your knee hurts afterwards

Knee pain: Why you have to strengthen your muscles

Your main knee joint is formed by your femur at the top and your tibia at the bottom. The two bones are covered by cartilage and there are also 2 soft cartilage cushions (the menisci) inside the joint to help with shock absorption. The muscles around your knee and hip joints have 2 very important roles:

1. To control the joint as you move – uncontrolled movements can cause strains to the ligaments and cartilage.

2. To absorb a significant amount of the force when you walk, run and jump. So if the muscles are weak, your knee joint, cartilage and ligaments will have to carry more weight than intended which can lead to injury and pain.

Why the leg press may have hurt you in the past

Yes, of course the leg press does not work for every single person, but in practice I find that it is often due to how people use it.

Some of the common things that you may have done include:

1. Our knees are dynamic joints and different parts of the joint will take strain depending on how far you bend it or where you place your feet. It may be that you did not pay enough attention to this or that you followed advice that wasn’t right for your specific injury. Each person will/should have a slightly different technique on the machine as we all have differently shaped bodies. Check the relevant sections below for a detailed description of how to cater for this.

2. You upped the weight too quickly. I find that people often underestimate how long the adaptation period can be that the body needs before it is happy for you to move on to heavier weights.

3. You trained too often. You need to give your body enough time to recover between strength training sessions. If you’re not a trained athlete, it is good to leave at least 48 hours between sessions.

4. You actually did another exercise on that day that flared your knee up and is wrongly blaming the leg press machine. This can easily happen because knees often only start to hurt a few hours after a gym session or even the next day.

Step 1 – Establish a baseline

The first step for any exercise programme aimed at improving knee pain should be to establish what activities you can do without causing your pain to increase. We call this the baseline.

Once you’ve established your baseline, you should train at that level for at least 2 weeks, before you try and change anything. This can sometimes be quite challenging as it may feel that you’re not doing enough, but it is really important that you give your knee and body time to fully get used to the baseline level of exercise.

When using the leg press machine, part of establishing your baseline should include exactly where on the plate your feet should be positioned, how far you bend your knees when going down and also how much weight you use. I will explain each of these in more detail below.

It doesn’t matter if you can’t bend the knee fully. If you train it for long enough at the pain free level, it usually allows you to bend your knee further over time.

The importance of getting your foot placement right

Test this with only the weight of the plate and no extra weight on the machine.

As mentioned before, different parts of the knee joint carries the weight or takes strain depending on the angle you bend your knee at. So play with your foot position by moving your feet up and down on the plate (see A in picture above) until you find a position or angle that works for you.

If for instance you place your feet on the plate so that you knees are bent more than 90 degrees, you will carry the weight more in the front of the knee. This position is often painful if you suffer with patello-femoral pain e.g. runner’s knee.

It is good to keep your feet hip distance apart, but your feet does not have to point straight up if it feels uncomfortable to do so. Our hips and bones are all different shapes and it is OK if your toes are slightly turned out to the sides (see B in picture above). BUT you have to make sure that your knees move in line with the middle of your feet when you use the machine.

Still cannot do the full movement? That's OK. Just pick the position that allows you to go down the furthest without pain and use that as your baseline. You will be able to go down lower as your knee gets stronger in that range.

The importance of getting the depth of the movement right

Test this with only the weight of the plate and no extra weight on the machine.

For the same reason explained above, you may find that you can, for example, only bend your knee to 60 degrees when using the leg press before you feel pain (see C in picture above). That is OK. This will be your baseline from where you start and you will initially only do the exercise to this level until it allows you to go down further. Just remember to check – can you maybe go down further if you move your feet to a different position on the plate?

Some of my patients find that they can never go below 90 degrees (right angle) knee flexion. Again, that's OK. You will still get very good strength gains if you strengthen it in that range. We only use about 45 degrees knee flexion when we run or climb stairs.

The importance of getting the load right

So you know where to place your feet and you know how far you can bend your knees. All that is left is to decide how much you should load your knee. The total load on your knee during this exercise is made up of:

1. The weight you use

2. How many repetitions your do

3. How many sets you do

4. How long you rest between sets

I usually ask my patients to start with a weight that allows them to do 3 sets of 15 repetitions without pain. You have to rest about 2 minutes between the sets.

BUT you may not be able to do that, even on the lightest weight, and that's OK. If, for example, you get to rep number 8 and you feel that that's enough (because your knee just doesn’t feel right, or it's starting to hurt or it's hard work) STOP there. You can then either do 3 sets of 8 or, if your knee does not feel up to it, 1 or 2 sets of 8.

The most important thing is to find the baseline weight, sets and reps your knee will tolerate without flaring up and being painful afterwards.

Remember, your knee may only flare up after your gym session or the next day so err on the side of caution. Also, make sure that you don’t do any other exercises or activities on the day that you do the leg press for the first time. Otherwise you won’t be able to tell if it was the leg press or something else that made it feel sore.

What to do if your knee hurts afterwards

Don’t just give up. First make sure that you didn’t do anything else on the same day that may have contributed to your pain.

If you followed the guidelines above and were very gentle with your attempt, your knee should calm down within a few days. Think about the reasons why the exercise may have flared it up. Did you maybe do too many sets or have it slightly too heavy? Could you place your feet in a different position. Should you maybe not go down quite so low?

Adapt what you did the first time and try it again. It may be that you need some assistance to get it right and we're always happy to help. You’re welcome to consult one of the team at SIP online via video call for an assessment of your injury and a tailored treatment plan.

About the Author

Maryke Louw is a chartered physiotherapist with more than 15 years' experience and a Masters Degree in Sports Injury Management. Follow her on LinkedIn or ReasearchGate.