--- title: "Why Muscle Strengthening Helps Some Knees and Hurts Others" entity: "blog" canonical_url: "https://www.betterknees.com/blog/why-muscle-strengthening-helps-some-knees-and-hurts-others" markdown_url: "https://www.betterknees.com/llms/blog/why-muscle-strengthening-helps-some-knees-and-hurts-others" lastmod: "2026-10-04T22:32:54.000Z" --- You do your squats on Monday. You feel fine. Maybe even good. Wednesday, your knee aches on the stairs. Thursday, it is stiff when you stand up from your desk chair. Meanwhile, a friend does nearly the same routine and says her knees feel better than they have in years. So what is going on? Most people assume the difference is effort, form, or "just bad knees." In my experience, it is usually something else. It is whether your knees can tolerate the force that muscle strengthening puts on them. That measure is [Load Tolerance](https://www.betterknees.com/blog/load-tolerance-knee-pain). It decides who improves with muscle strengthening and who needs to start somewhere else. ## How to Decide Whether Strengthening Helps or Hurts Your leg muscles determine whether you can perform a movement. If they are too weak to squat, climb stairs, or walk a hill with good form, you feel it in your thighs and hips. But there is a second kind of strength that often sets the limit when knee pain is present. It is the strength inside the knee. I call it Knee Joint Strength, and it comes from your cartilage and the fluid in the joint (synovial fluid), not your quadriceps or glutes. Here is why it matters: When your leg muscles contract, they pull your thigh bone and shin bone together. That squeezes the cartilage and synovial fluid between them, as I explain in [How to Make Painful, Sensitive Knees Stronger.](https://www.betterknees.com/blog/how-to-make-painful-sensitive-knees-stronger) Strong cartilage and thick, egg-white-like fluid absorb that squeeze without complaint. Weaker cartilage and watery fluid cannot. Knee Joint Strength is also less obvious than muscle strength. You cannot see it, and you cannot feel it in the moment. That is because cartilage has no nerve supply. [A review of osteoarthritis pain mechanisms](https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5675866/) notes that every structure in the joint except cartilage has pain-sensing nerves. Meanwhile, [large observational imaging studies](https://pmc.ncbi.nlm.nih.gov/articles/PMC6153568) link osteoarthritis pain with inflammation of the joint lining (synovitis), though observational data cannot prove cause and effect. So when an exercise overloads the cartilage, the joint lining reports the problem later, once it becomes irritated. That is why the pain often arrives a day or two afterward. I explain this pattern in more detail in [Why Knee Pain Shows Up After Exercise.](https://www.betterknees.com/blog/why-knee-pain-shows-up-after-exercise-even-when-it-feels-fine-at-the-time) ## When Muscle Strengthening Works Strengthening is not a bad idea. Far from it. The authors of a [2016 study](https://link.springer.com/article/10.1186/s40064-016-2048-1) describe strengthening exercise as the cornerstone of conservative treatment for knee osteoarthritis. And it makes sense. To get stronger, muscles need forces high enough to fatigue them. But here is the condition that matters: If your Load Tolerance is above to the amount of load the exercise requires, you can strengthen your leg muscles without knee joint pain, swelling, or stiffness. In that case, muscle strengthening can take you all the way back to the activities you want. So how much load does a strengthening exercise require? Sitting down on a chair and standing up without your hands places about half of your bodyweight through each leg. A standard squat does the same. Add weight or change the position, and the demand climbs. In my breakdown of the [New York Times knee workout](https://www.betterknees.com/blog/the-truth-about-the-nytimes-knee-workout-everyone-s-talking-about), a goblet squat with a moderate kettlebell put roughly 60 percent of my bodyweight through each leg, and a Bulgarian split squat measured close to 80 percent. If your knees tolerate that much force with no pain during the exercise and no residual pain, swelling, or stiffness over the next day or two, muscle strengthening is likely a good fit. ## When Muscle Strengthening Hurts Now consider the other group. Their Load Tolerance is below what muscle strengthening exercises require. The same routine sends more force into the joint than the cartilage and fluid can absorb. The tissues become irritated instead of stronger. This is the Goldilocks idea in research language: A [2024 review of mechanical loading in knee osteoarthritis](https://www.ncbi.nlm.nih.gov/pmc/articles/PMC10886318/) describes the need for adequate but not excessive loading. And a [short commentary in the Journal of the American Academy of Orthopaedic Surgeons](https://pmc.ncbi.nlm.nih.gov/articles/PMC5007862) notes that both underuse and overuse are risk factors for cartilage degradation, while moderate dynamic loading is a potential preventive and therapeutic strategy. Too little load, and tissues weaken. Too much load, and tissues become irritated. Just enough, and tissues adapt. There is a second cost, too. When strengthening hurts, people stop, and their muscles stay weak. The authors of that [2016 study](https://link.springer.com/article/10.1186/s40064-016-2048-1) note that strengthening programs often produce small strength gains in knee osteoarthritis and raise the possibility that pain limits what strengthening can achieve. Their own cross-sectional data on muscle activation did not settle the question, so this remains a hypothesis rather than a proven mechanism. Either way, the practical point holds. If an exercise leaves your knee sore, swollen, or stiff, you cannot keep repeating it and expect a different result. I wrote about a client whose trainer had him squatting with a barbell for a long stretch. The squats were manageable, but his knees did not improve, and eventually the pain began waking him at night. The muscles were not the limiting factor. His knees were. You can read his story in [When Stronger Muscles Don't Help Knee Pain](https://www.betterknees.com/blog/when-stronger-muscles-don-t-help-knee-pain-here-s-what-does). ## What About Strengthening Your Hips, Glutes, and Core? A lot of knee advice skips the thigh muscles and points to the hips instead. The idea is that weak hips and glutes leave your knee absorbing force it should not have to carry. That idea is not baseless. But it is incomplete. In a [randomized controlled trial by Bennell and colleagues](https://pubmed.ncbi.nlm.nih.gov/20175973/), 89 people with medial knee osteoarthritis and varus (bowlegged) alignment did either a 12-week hip strengthening program or no exercise. Their symptoms improved. But the program did not reduce knee load, which the researchers measured with three-dimensional gait analysis. And a [2022 systematic review and meta-analysis of hip abductor strengthening](https://www.ncbi.nlm.nih.gov/pmc/articles/PMC9241212/) found that pain and function scores favored strengthening, though the pooled analysis included only three trials of good methodological quality. Both findings come from specific groups of people with knee osteoarthritis, so they do not settle the question for every knee. But together they point in the same direction. Hip work tends to help people feel better. However, it does not reliably change how much force reaches the knee joint itself. That is the difference between strength around the knee and Knee Joint Strength. I explain it further in [Strong Glutes Won't Fix Your Knee Arthritis (What to Do Instead)](https://www.betterknees.com/blog/strong-glutes-wont-fix-your-knee-arthritis-what-to-do-instead). Hip and glute work belong primarily in phase three of [Inside Out Knee Health](https://www.betterknees.com/blog/the-inside-out-knee-health-approach-a-smarter-way-to-build-stronger-knees). And it does not replace phase one and phase two. I go deeper on hip and core work in [The Muscle-Strength Trap: What Hip and Core Work Really Does for Your Knee](https://www.betterknees.com/blog/the-muscle-strength-trap-what-hip-and-core-work-really-does-for-your-knee). ## Why Taking Steps Back Is Not Going Backward Picture a long jumper at the Olympics. She does not start at the line in the sand. She walks back several steps and takes a running start. Nobody would call that a retreat. The run-up is what makes the jump possible. Knees work the same way. Muscle strengthening is the jump. If your knees cannot yet tolerate the force of that jump, you need the run-up first. Consider the foundation for your dream home. You would not want builders to construct the second floor before the foundation has cured. Skipping the foundation does not save time. It just makes for a more expensive problem. ## The Inside Out Knee Health Sequence The Inside Out Knee Health approach builds the run-up in three phases. Phase 1 : Improve the quality of your synovial fluid and reduce irritation inside the joint. Phase 2 : Improve your cartilage and Squat Load Tolerance so your knees can handle more force. Phase 3 : Strengthen the muscles and structures outside your knee and return to your functional activities. This is a sequencing correction, not a rejection of physical therapy or strength training. Many conventional programs begin at phase three, as I describe in [What Is Load Tolerance? The Missing Link in Solving Knee Pain.](https://www.betterknees.com/blog/load-tolerance-knee-pain) That works well for knees that are ready. It stalls, or backfires, for knees that are not. ## How to Tell Which Group You Are In You do not have to guess. Start with the activity you care about most: walking, hiking, stairs, weightlifting, etc. Load Tolerance is specific to each activity, as I explain in [Is Your Knee Pain a Sign of Low Load Tolerance?](https://www.betterknees.com/blog/is-your-knee-pain-a-sign-of-low-load-tolerance) Walking asks your knees to absorb moderate force with every step. Stairs ask for more, and going down puts more stress on the joint than going up. Squatting depends on how deep you go and how much weight you hold. Hiking adds steep climbs, downhill distances and uneven ground. (I cover this in [Why Your Knee Hurts the Day After Hiking](https://www.betterknees.com/blog/why-your-knee-hurts-the-day-after-hiking-and-what-it-actually-means).) You may have strong Load Tolerance for one activity and low Load Tolerance for another. That is normal. For squatting, you can estimate your Squat Load Tolerance at home with a standard chair: - Sit down on the chair and stand up five times in a row without using your hands. - Notice your knees during the movement. - Notice them again over the next 36 hours. - If you have no pain, swelling, or stiffness, your Squat Load Tolerance for each knee is at least 50 percent of your bodyweight. - If you feel even mild pain in either knee, that knee tolerates less than 50 percent. I walk through this estimate in [How to Make Painful, Sensitive Knees Stronger.](https://www.betterknees.com/blog/how-to-make-painful-sensitive-knees-stronger) This is an estimate, not an exact measurement. Now compare your result to the exercise you want to do. If the exercise asks for more than your knees can currently tolerate, you have found the gap. To measure Squat Load Tolerance precisely, I use a [Variable Incline Plane (VIP)](https://youtu.be/e3ejkSK-c4c). It lets you bend and straighten your knee using only a fraction of your bodyweight. You increase the level until the knee first becomes painful, and the last pain-free level is your [Squat Load Tolerance](https://youtu.be/ukhPCzFbLmk). Measurement matters for another reason. Knees often improve before you feel any different in daily life. A measurement closes that gap, so you keep going instead of quitting too early. If your result is below what your exercises require, it's usually necessary to start with [phase one](https://insideoutkneehealth.com/). And in the meantime, keep your activities at a level that leave your knees neutral, with no pain during and no added symptoms, stiffness or swelling afterward. (I use the same idea, and a 36-hour rule for progressing, in [Is Biking Good for Knee Pain?](https://www.betterknees.com/blog/why-the-bike-should-help-your-knees-but-doesn-t)) ## Common Mistakes When Strengthening With Knee Pain ### Mistake 1: Choosing the exercise your muscles can do instead of the load your knees can tolerate Your muscles may be strong enough for a goblet squat. Your knees may not be. Strong muscles tell you that you can complete the movement. They do not tell you whether the cartilage and fluid inside the joint can absorb the force. I show the math behind this in [The Truth about the NYTimes "Knee Workout" Everyone's Talking About](https://www.betterknees.com/blog/the-truth-about-the-nytimes-knee-workout-everyone-s-talking-about). If your knees hurt when you sit down on the couch, a weighted squat asks for well over what they can tolerate. ### Mistake 2: Judging the exercise by how it feels that day Because cartilage has no nerve supply, the joint cannot warn you in real time. As [a review of osteoarthritis pain mechanisms](https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5675866/) notes, the other joint structures are the ones that carry pain-sensing nerves. So an exercise can feel great on Monday and cost you on Tuesday or Wednesday. Watch your knees for the next day or two, not just during the workout. I cover this in [Why Knee Pain Shows Up After Exercise.](https://www.betterknees.com/blog/why-knee-pain-shows-up-after-exercise-even-when-it-feels-fine-at-the-time) ### Mistake 3: Treating rest as the plan Rest lowers the load, so it can calm symptoms. But rest does not raise your Load Tolerance. When you return to the same activity at the same intensity, the same symptoms return. I explain this cycle in [Why Rest Isn't Fixing Your Knees](https://www.betterknees.com/blog/why-rest-isn-t-fixing-your-knees-and-what-actually-helps) and in [Why 'Good' Exercises Still Cause Knee Pain Later.](https://www.betterknees.com/blog/why-good-exercises-still-cause-knee-pain-later) The alternative to rest is not more of the same exercise. It is the right type and dose of load, in the right order. ## The Real Question Is Not Whether to Strengthen If you were told to strengthen your legs and it hurt, you were not weak-willed. You may have been handed phase three on day one. The common advice to strengthen the muscles around your knee is not always wrong. It is incomplete. It works for a knee that can tolerate the load, and it backfires for a knee that cannot. This is the part rarely explained: Muscle strength does not predict Load Tolerance. Some knees can start at the line in the sand. Some need the run-up. And for the second group, the sequence is the whole point. Phase one and phase two are what make phase three possible. If your knees have felt stuck in a cycle of exercise, flare-up, rest, you may not need more effort. You may need a better starting line. I created a free guide to help you begin. You can get it here: [enjoystrongerknees.com](http://enjoystrongerknees.com). For Inside Out Knee Health, here's a [guide](https://enjoystrongerknees.com/) to get started: You can access it [here](https://enjoystrongerknees.com/) . ## Frequently Asked Questions ### Why does my knee hurt after strengthening exercises even when my form is good? Good form means your muscles can complete the movement. It does not tell you whether the cartilage and fluid inside your knee can tolerate the force. Because cartilage has no nerve supply, [the joint lining and other structures report the problem later](https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5675866/), often a day or two after the exercise. I describe this pattern in [Why Knee Pain Shows Up After Exercise](https://www.betterknees.com/blog/why-knee-pain-shows-up-after-exercise-even-when-it-feels-fine-at-the-time). ### Is muscle strengthening good for knee pain? Often, yes, when your knees can tolerate the load. The authors of a [2016 scientific study](https://link.springer.com/article/10.1186/s40064-016-2048-1) describe strengthening exercise as the cornerstone of conservative treatment for knee osteoarthritis. But when your Load Tolerance is below what the exercise requires, the same exercise can irritate the joint instead. In that case, phase one and phase two of [Inside Out Knee Health](https://www.betterknees.com/blog/the-inside-out-knee-health-approach-a-smarter-way-to-build-stronger-knees) come first. ### How do I know if my knees can handle strengthening exercises? Start with the chair test. Sit down and stand up from a standard chair five times without using your hands. If you have no pain, swelling, or stiffness during the movement or over the next 36 hours, your Squat Load Tolerance for each knee is at least 50 percent of your bodyweight, as I describe in [How to Make Painful, Sensitive Knees Stronger](https://www.betterknees.com/blog/how-to-make-painful-sensitive-knees-stronger). That figure matters because each leg carries about half of your bodyweight during the movement. To measure it precisely, I use a [Variable Incline Plane (VIP)](https://www.betterknees.com/blog/the-best-investment-for-knee-or-hip-pain). ### How long after exercise can knee pain show up? Sometimes hours, sometimes a day or two. In [What Is Load Tolerance? The Missing Link in Solving Knee Pain](https://www.betterknees.com/blog/load-tolerance-knee-pain), I explain that stress builds inside the joint, the synovial tissue becomes irritated, and inflammation develops over time. For that reason, I ask clients to watch their knees for 36 hours after a new activity, a rule I describe in [Is Biking Good for Knee Pain?](https://www.betterknees.com/blog/why-the-bike-should-help-your-knees-but-doesn-t) ### Should I stop strengthening my legs if my knees hurt afterward? Not forever, but it is worth stepping back. Rest can calm symptoms, but it lowers load without raising Load Tolerance, as I explain in [Why Rest Isn't Fixing Your Knees](https://www.betterknees.com/blog/why-rest-isn-t-fixing-your-knees-and-what-actually-helps). A [2024 review of mechanical loading](https://www.ncbi.nlm.nih.gov/pmc/articles/PMC10886318/) describes the goal as adequate but not excessive loading. Building Load Tolerance through phase one and phase two lets you return to strengthening without the flare-ups or set backs. ### What is Squat Load Tolerance? [Squat Load Tolerance](https://youtu.be/ukhPCzFbLmk) is the percentage of your bodyweight that you can squat without knee pain. I measure it with a [Variable Incline Plane (VIP)](https://www.betterknees.com/blog/the-best-investment-for-knee-or-hip-pain). Daily activities such as sitting on a couch, standing from a desk chair, and getting out of a car require at least 50 percent, because each leg carries about half of your body weight as you bend and straighten your knees. You can read how I measure it in [How to Make Painful, Sensitive Knees Stronger](https://www.betterknees.com/blog/how-to-make-painful-sensitive-knees-stronger). ### Will strengthening my glutes or hips fix my knee pain? It can help how your knee feels, but it usually does not change the limit inside the joint. In a [randomized controlled trial of people with medial knee osteoarthritis](https://pubmed.ncbi.nlm.nih.gov/20175973/), 12 weeks of hip strengthening improved symptoms without reducing knee load. The limit is often the capacity of the cartilage and fluid inside the knee, which I measure as Squat Load Tolerance. I cover this in [Strong Glutes Won't Fix Your Knee Arthritis (What to Do Instead)](https://www.betterknees.com/blog/strong-glutes-wont-fix-your-knee-arthritis-what-to-do-instead). ## Related Articles - [Strong Glutes Won't Fix Your Knee Arthritis (What to Do Instead)](/blog/strong-glutes-wont-fix-your-knee-arthritis-what-to-do-instead) - [The Muscle-Strength Trap: What Hip and Core Work Really Does for Your Knee](https://www.betterknees…