Impact of the deep squat on articular knee joint structures, friend or enemy? A scoping review

Key points

1. 0187% of included studies (13 of 15) affirmed that deep squats do not increase the risk of knee joint injury
2. 02Only one case study and one narrative review suggested a plausible adverse link between deep squats and knee injury risk
3. 03Deep squats produce greater strength, muscle hypertrophy, and athletic performance gains than partial-range squats
4. 04Early concerns about deep squat safety (from Dr. Karl Klein's 1960s studies) were based on an unvalidated instrument and unsubstantiated conclusions
5. 05Injury risk appears linked more to incorrect technique and excessive load than to squat depth itself

How it was conducted

Design

Scoping review following PRISMA-ScR guidelines

Databases searched

PubMed, Scopus, Web of Science, SPORTDiscus, Google Scholar, PEDro

Search period

Publications from 2000 to 2024; search conducted October 2023 and updated September 2024

Studies included

15 studies comprising cohort studies, randomized controlled trials, narrative and systematic reviews (one with meta-analysis), and a case study

Population

Resistance-trained individuals without pre-existing knee pathology

Primary focus

Effect of deep squats (knee flexion 40-45 degrees) on knee osteoarticular health and injury risk

What they found

• 87% of included studies (13 studies) affirmed the safety of deep squatting and found no increased risk of knee injury
• Only 2 studies suggested a plausible adverse correlation between deep squat practice and elevated injury risk: one case study and one narrative review
• The full squat produced significantly greater improvements in cross-sectional area (CSA), lean body mass, maximum isometric strength, and squat jump (SJ) performance compared to the half squat in an RCT (Bloomquist et al.)
• In a systematic review with meta-analysis (Wolf et al.), the primary model across all outcomes showed a trivial standardized mean difference (0.12; 95% CI 0.26) favoring full over partial range of motion
• Male Division I athletes with a relative squat strength below 2.2 times body weight and female athletes below 1.6 times body weight had elevated risk of lower limb injuries (Case et al.)
• FMS screening showed low sensitivity (2%-24%), 74% PPV, and 50%-58% AUC across all seven tests for injury prediction in soldiers (Bushman et al.)
• Deep squat contact between the back of the thigh and calf reduces knee compressive forces by approximately 30% (Zelle et al., as cited in the review)
• Pallarés et al. RCT reported greater knee discomfort in the partial range of motion group compared to the full squat group

Limitations

• Most included intervention studies used relatively short durations, typically ranging from several weeks to a few months; long-term data spanning years are lacking
• Many studies relied on questionnaires to assess knee pain and injury risk rather than validated objective measures
• Although some studies report increased compressive forces in deep squats as a potential risk factor, no direct cause-effect relationship between compressive forces and injury has been established
• Heterogeneity across included studies, with several exhibiting moderate to high risk of bias, limits the strength of conclusions

Why it matters

For patients

Healthy individuals performing resistance training can include deep squats without fear of knee damage, as long as they use proper technique and do not use excessively heavy loads.

For clinicians

Clinicians and strength coaches should not routinely restrict squat depth in healthy individuals; the evidence base for this common caution is weak, and deeper squats may offer superior performance and possibly protective benefits.

For readers

This review challenges a long-standing misconception rooted in methodologically flawed 1960s research, consolidating current evidence that squat depth is not the primary driver of knee injury risk.