For years, a persistent myth has haunted gyms and rehab clinics: deep squats are bad for your knees. This belief has led countless individuals—from athletes to everyday fitness enthusiasts—to intentionally limit their range of motion, fearing damage to their joints. As a physiotherapist, I've spent years challenging this notion, guided by the principle that a deep squat is not an extreme movement but a natural expression of full, healthy joint mobility.
Now, a comprehensive scientific review published in Frontiers in Sports and Active Living provides robust evidence to settle the debate. After analysing over 2,000 studies, the researchers reached a clear conclusion that aligns perfectly with clinical experience.
The Core Finding: The review, which synthesised 15 high-quality studies, found that 14 out of 15 studies showed no negative impact of deep squats on knee joint health. The single study that suggested risk was a lone case report, heavily outweighed by the body of evidence from randomised trials and cohort studies.
This article will break down the science, explain why the old fears are unfounded, and give you practical, evidence-based guidance on how to squat safely and effectively for stronger, more resilient knees.
What the Scoping Review Actually Found
This was a scoping review, a type of study designed to systematically map the existing research on a topic. The authors followed rigorous PRISMA-ScR guidelines and sifted through 2,274 records from major databases like PubMed and Scopus. Their goal was to answer one central question: What does the current literature say about the impact of deep squats on the knee joints of resistance-trained people?
The Evidence Breakdown
The final analysis included 15 studies of various designs, providing a multi-faceted look at the problem:
| Study Type | Number of Studies | Key Purpose |
|---|---|---|
| Randomised Controlled Trials (RCTs) | 3 | Compare training effects & safety of different squat depths |
| Cohort Studies | 5 | Observe long-term outcomes in groups performing deep squats |
| Systematic Reviews / Meta-Analysis | 2 | Synthesise findings from multiple previous studies |
| Narrative Reviews | 4 | Provide expert commentary and biomechanical analysis |
| Case Study | 1 | Report on a single instance (the one suggesting risk) |
The overwhelming consensus from this body of work was that deep squats do not increase the risk of knee injury in individuals without pre-existing pathology. Furthermore, several studies pointed to potential benefits, including greater strength gains and performance improvements compared to partial squats.
Why the "Dangerous" Myth Persists (And Why It's Wrong)
The fear of deep squats isn't new; it has deep roots. The review traces much of the concern back to research from the 1960s by Dr. Karl Klein, who used unvalidated measurement tools and concluded deep squats caused ligament laxity. Later arguments often focus on two biomechanical concepts:
- Increased Shear Forces: It's true that shear forces on the knee change with depth. However, the review notes that in a healthy knee with intact ligaments, these forces are managed effectively by the joint's structures and do not lead to injury.
- Higher Compressive Forces: Compression does increase with depth. But the body's tissues—especially cartilage—are adaptive and respond positively to appropriate loading. One interesting point from the review is that in the deepest position, contact between the calf and hamstrings can actually reduce compressive force by about 30%.
The critical clinical perspective that's often missing is this: The problem is almost never the range of motion itself. It's the load (using too much weight) and the technique (moving poorly under load) that create risk. This is true for any exercise, not just the squat.
Practical Takeaways: How to Squat for Healthier Knees
Based on this evidence and my clinical experience, here is your actionable guide. The goal is not just to squat deep, but to squat well.
1. Technique is Non-Negotiable
Proper form distributes load safely and effectively. The review emphasises that the "innocuousness" of the exercise depends on correct execution. Key checkpoints include:
- Maintain a Neutral Spine: Avoid excessive rounding or overarching of the lower back. Think of keeping your chest proud.
- Control Knee Alignment: Knees should track in line with your toes, not collapsing inward (valgus).
- Manage Your Centre of Mass: Keep weight distributed evenly across your entire foot, not just the toes or heels.
- Ankle Mobility Matters: Limited ankle dorsiflexion is a common technical limiter. If you struggle, consider targeted mobility work or a temporary heel lift.
A 2024 biomechanical review supports this, noting that factors like trunk and tibia (shin) inclination dramatically influence where the load is felt, highlighting why technical coaching is so valuable.
2. Prioritise Load Management Over Fear of Depth
This is the most important shift in thinking. Do not sacrifice depth to lift more weight. The research is clear: strength and performance gains are superior with full range-of-motion training. Start with a load that allows you to achieve full depth with impeccable technique for all your reps. Progressive overload should be gradual and technique-led.
3. Who Might Need Modifications?
While the review focused on resistance-trained individuals without pathology, clinical judgment is always key. In my practice:
- Post-Surgical Patients (e.g., ACL reconstruction): Depth is progressed carefully within a rehabilitation timeline, but the end goal is often to restore full, strong range of motion.
- Those with Acute Pain: Pain during the movement is a signal. We reduce load, modify range, or change the exercise variation (e.g., box squat, goblet squat) to find a pain-free entry point before rebuilding.
- Individuals with Specific Structural Diagnoses: Conditions like advanced bone-on-bone osteoarthritis require individualised programming, which may involve limiting depth based on symptom response.
Understanding the Study's Scope and Limits
To apply science well, we must understand its boundaries. The review authors openly discussed the limitations of their work and the underlying studies, which is a hallmark of good science.
- Short- to Medium-Term Focus: Most included training studies lasted 6-12 weeks. While reassuring, we have less data on the effects of deep squatting over decades of training.
- Healthy, Trained Populations: The findings most directly apply to individuals without known knee issues who are already doing resistance training. More research is always needed on broader populations.
- Technique-Dependent Conclusion: The safety verdict is explicitly tied to maintaining proper technique. This isn't a license to perform maximally loaded, poorly executed deep squats.
These limitations don't invalidate the findings; they simply define the context. For the general active population seeking to get stronger and stay healthy, the evidence is compelling and practical.
