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Single-leg squat

Also called single-legged squat, single-leg squat test, skater squat

A squat on one leg. What studies measured it loading, from the buttock muscles to the kneecap joint and the ACL, and what it showed when used as a test of how the knee moves.

Region
Knee
Muscles
gluteus maximus, gluteus medius, gluteus minimus, quadriceps, hamstrings, adductor magnus
Updated
October 23, 2026
Reviewed
October 23, 2026 · how entries are checked

Movement

What the movement is

The single-leg squat is a squat done standing on one leg, with the other leg held free6. A systematic review of body-weight exercises that extend the hip found it was the most studied upright one1.

The versions studies have used

Studies have held the free leg straight, or bent at the hip and knee1,6. The skater squat bends the free knee behind the body1. Other versions include a rotational single-leg squat and a loaded version called the modified single-leg squat7,8.

How trunk lean changes the work

One modelling study, which estimates forces with a model rather than measuring them, compared moderate and minimal forward trunk lean in 12 recreationally active people3. With the forward lean, modelled forces in the hamstrings, the muscles at the back of the thigh, were 35% higher through most of the squat3. Forces in the quadriceps, the muscles on the front of the thigh, were lower with the lean only beyond 65 degrees of knee flexion (bending)3.

What it loads

The buttock muscles

Across 9 studies, one review found high average gluteus maximus activity in the single-leg squat1. Activity is given as a share of a maximal voluntary isometric contraction, a muscle’s hardest effort while the joint stays still. The average was 47.8%, but the range between studies was wide, from 18.9% to 81.2%1.

The same review suggested that the spread may relate to depth, experience and where the free leg was held1. It reported figures for two versions1:

VersionGluteus maximus activity, share of a maximal contraction
Free leg straight86%1
Skater squat, free knee bent behind66.2%1

The gluteus medius, a buttock muscle beneath the gluteus maximus, is one of the hip abductors9. These are the muscles that move the thigh out to the side. Pooling 13 studies, a meta-analysis, which pools the results of earlier studies, found moderate activity in its middle part, about 39% of a maximal contraction10. The studies differed widely in depth, technique and repetitions10. One study in the same review found very high activity in all three parts of the muscle, 87% to 92%10.

The gluteus minimus is a buttock muscle beneath the gluteus medius. In one study in a systematic review, the squat gave moderate activity in its front part (25%) and high activity in its back part (46%)10.

The thigh muscles

Two studies compared a loaded single-leg version with other lifts8,11:

  • 11 Division I female athletes at 85% of their three-repetition maximum, the heaviest load they could lift three times. The modified single-leg squat gave more gluteus medius and hamstring activity than the two-leg squat, and less quadriceps activity8.
  • 18 young women with training experience, at an 8-repetition maximum. The modified single-leg squat gave more gluteus maximus activity than a two-leg squat or stiff-leg deadlift, and more hamstring activity than the deadlift11.

Where the free leg sat also mattered, in a study of 10 people6. The biceps femoris is a hamstring on the outer back of the thigh. With the free hip and knee at 90 degrees, biceps femoris activity was 40% higher than with the free hip at 0 degrees6. The rectus femoris is the front thigh muscle that also bends the hip. Its activity was 29% higher with the free hip at 0 degrees than at 90 degrees6.

A systematic review of eight studies in healthy females looked at co-contraction, opposing muscles working at the same time12. It concluded that two-leg squats gave poor ratios of hamstring to quadriceps activity12. Single-leg exercises with the knee bent from 30 to 90 degrees gave adequate ratios12.

The kneecap joint and patellar tendon

The patellofemoral joint is the joint between the kneecap and the thigh bone. One study measured load on this joint in 20 healthy people2. The full single-leg squat had a loading index, the study’s score for load on the joint, of 0.6692.

The study grouped it in one tier with two other challenging squat variations2. These were the 3-second Spanish squat, held with a strap behind the knees, at 0.774, and the single-leg decline squat at 0.8752. The decline squat is done on a board sloped so the heels sit higher than the toes. In the same 20 people, modelled peak patellofemoral force in the single-leg squat was 6.9 times body weight2.

The patellar tendon continues from the kneecap to the front of the tibia (shinbone), just below the knee13. Two studies estimated its load:

  • Depth and slope, in 20 healthy adults. The one-leg decline squat scored a higher tendon loading index than a flat full single-leg squat, 0.747 against 0.58014. A single-leg squat to 60 degrees scored 0.41114.
  • Board and weight, in 12 healthy people. In heavy single-leg back squats, modelled peak tendon force was significantly higher on a decline board than on level ground15. Raising the weight from 70% to 90% of the one-repetition maximum did not significantly raise it15.

The knee ligaments

The anterior cruciate ligament is the front one of two ligaments that cross inside the knee. In the trunk lean study, moderate forward lean lowered its modelled peak force by 24% and peak strain by 16%, compared with minimal lean3.

The medial collateral ligament (MCL) mainly steadies the knee side to side, resisting valgus, or knee-inward, stress16. One study filmed 16 patients with ACL deficiency, a knee without a working ACL, on a two-angle X-ray system during a single-leg squat17. As the knee bent from 0 to 30 degrees, the MCL was longer before ACL reconstruction than 18 months or more after it17. The same study found no differences for the lateral collateral or posterior cruciate ligament17.

The single-leg squat as a test

How the squat is rated

In 34 people without symptoms, three clinicians rated how well each person did the squat18. Their ratings agreed with an expert panel 73% to 87% of the time18.

In 378 young players of four team sports, a physiotherapist rated knee control in the squat as good, reduced or poor19. Those ratings matched differences in measured knee angles19. In 20 of them, agreement between that rater and an inexperienced tester was fair to poor19.

What it showed about later injury

Several prospective studies, which follow people forward in time, rated the squat and then recorded injuries4,5,20. Their findings differed:

  • 306 young basketball and floorball players, over 12 months. Those with a large frontal plane knee projection angle, a video measure of the knee angling inward, had more injuries4. They were 2.7 times more likely to have an acute lower limb injury4. The angle was not significantly linked to knee injury4. The authors judged it not accurate enough to screen for future injury risk4.
  • 558 youth football players, under-11 to under-14. The knee angle was not a risk factor for lower limb injury5.
  • 111 incoming NCAA Division I athletes. After adjusting for sex and injury history, those rated poor had a lower limb injury rate 1.62 times that of the others21. The confidence interval, a range showing how precise a result is, ran from 0.98 to 2.66, a range that includes no difference21.
  • 880 elite female handball and football players, 65 of whom later had a non-contact ACL injury. Visual ratings of the squat did not tell the injured apart from the uninjured20.
  • 135 male military recruits, over six weeks. The 14 who developed patellofemoral pain had shown a larger knee angle at the start, by about 5.6 degrees22.

How people with knee and ankle problems squatted

Patellofemoral pain is pain around or behind the kneecap. In 20 females with it and 20 healthy females, the pain group moved the knee further inward during single-leg squats23. A meta-analysis found more trunk lean toward the standing leg in people with this pain24.

A second meta-analysis pooled four studies of 130 people during single-leg and overhead squats25. People with dynamic knee valgus, the knee moving inward, had higher activity than healthy people in five muscles, including the adductor magnus25. The adductor magnus is the largest of the inner thigh muscles, part of the hip adductors26.

Two studies of chronic ankle instability, an ankle that stays loose or keeps giving way after one or more sprains, disagreed about the gluteus maximus27,28:

  • 48 people. Those with chronic ankle instability used more gluteus maximus activation in the single-leg squat test than healthy controls27.
  • 9 people with the condition and 9 without. In a rotational single-leg squat, the ankle instability group had lower gluteus maximus activity, 51.1% against 78.6%28. Gluteus medius activity did not differ28.

How the body adapts

The studies below did not test the single-leg squat. They show how two muscles it works respond to training in general29,30:

  • Gluteus maximus. A meta-analysis of resistance training lasting at least 5 weeks, in healthy adults aged 18 to 45, found a moderate effect on its growth29.
  • Quadriceps. Ten untrained young men did resistance training30. The vastus lateralis is the quadriceps muscle on the outer side of the thigh. Its cross-sectional area, the size of a slice across it, was about 2.7% larger by week three30. It was about 10.4% larger at 10 weeks30.

Progressive overload

A 2026 position stand describes progressive overload as the need to raise the stimulus on the muscle through a training programme31.

Changing the free leg

In one 6-week study, 8 recreationally active adults did 3 sets of 12 single-legged squats in front of a mirror, 3 times a week32. For 3 weeks the other foot touched the floor, and in weeks 3 to 6 the other leg was bent behind them at 90 degrees32.

This skill group and a hip-strengthening group, 17 adults together, both improved the squat32. Their frontal plane projection angle, hip adduction angle and a quality score got better, and stayed better at a 12-week retest32. Hip adduction is moving the thigh toward the body’s midline. The skill group’s two hip strength tests did not change, and the authors put its gains down to the nervous system32.

Later in a programme

In a 4-week movement training programme for 20 females, a single-leg squat came only in weeks 2 to 433. It was done with an elastic band around both knees, as 3 sets of 10 to a 60-degree knee bend33. The first week used wall or form squats, forward lunges and step-downs from a 4-inch step33.

Adding weight

In a randomised study of young adult females with athletic experience, an 8-week free-weight programme raised the load for the unilateral (one-leg) squat34. Along with the lunge, step-up and Romanian deadlift, it went from a 15-repetition maximum to a 6-repetition maximum34. A repetition maximum is the heaviest load a person can lift a set number of times. In the 29 women, the whole programme did not change knee valgus in drop jumps compared with controls34. A drop jump is a jump straight up done right after landing from a box.

Stability, depth and speed

In 12 strength-trained men lifting about a 4-repetition maximum, unilateral squats in a Smith machine produced higher peak force than with free weights35. A Smith machine is a barbell that slides on fixed vertical rails. The authors put the higher force down to greater stability35. They concluded that the less stable free-weight version caused more gluteus and vastus medialis activation35. The vastus medialis is the quadriceps muscle on the inner side of the thigh.

In 30 healthy college students, each extra centimetre of squat depth went with a larger range and area of body sway36. Faster single-leg squats went with a smaller range and area of sway, but a higher sway speed36.

Connections

The muscles it works

The knee structures it loads

The one-leg decline squat scored a higher patellar tendon loading index than flat single-leg squats in one study14.

Single-leg squat loads

Single-leg squat is progressed by

Sources

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  2. Song K, Scattone Silva R, Hullfish TJ, Silbernagel KG, Baxter JR (2023). Patellofemoral Joint Loading Progression Across 35 Weightbearing Rehabilitation Exercises and Activities of Daily Living.. The American journal of sports medicine. doi:10.1177/03635465231175160 PMID 37272685
  3. Kulas AS, Hortobágyi T, DeVita P (2012). Trunk position modulates anterior cruciate ligament forces and strains during a single-leg squat.. Clinical Biomechanics. doi:10.1016/j.clinbiomech.2011.07.009 PMID 21839557
  4. Räisänen AM, Pasanen K, Krosshaug T, Vasankari T, Kannus P, Heinonen A, Kujala UM, Avela J, Perttunen J, Parkkari J (2018). Association between frontal plane knee control and lower extremity injuries: a prospective study on young team sport athletes.. BMJ Open Sport & Exercise Medicine. doi:10.1136/bmjsem-2017-000311 PMID 29387448
  5. Räisänen AM, Arkkila H, Vasankari T, Steffen K, Parkkari J, Kannus P, Forsman H, Pasanen K (2018). Investigation of knee control as a lower extremity injury risk factor: A prospective study in youth football.. Scandinavian Journal of Medicine & Science in Sports. doi:10.1111/sms.13197 PMID 29672932
  6. Olivier B, Quinn SL, Benjamin N, Green AC, Chiu J, Wang W (2019). Single-Leg Squat Delicacies-The Position of the Nonstance Limb is an Important Consideration.. Journal of Sport Rehabilitation. doi:10.1123/jsr.2018-0181 PMID 30426818
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  12. Dedinsky R, Baker L, Imbus S, Bowman M, Murray L (2017). EXERCISES THAT FACILITATE OPTIMAL HAMSTRING AND QUADRICEPS CO-ACTIVATION TO HELP DECREASE ACL INJURY RISK IN HEALTHY FEMALES: A SYSTEMATIC REVIEW OF THE LITERATURE.. International Journal of Sports Physical Therapy. PMID 28217412
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  15. Hagen M, Chebly J, Dhaen B, Fassian N, Salvalaggio M, Catelli DS, Verschueren S, Vanrenterghem J (2024). Peak patellar tendon force progressions during heavy load single-leg squats on level ground and decline board.. Clinical Biomechanics. doi:10.1016/j.clinbiomech.2024.106179 PMID 38219457
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  17. Agostinone P, Di Paolo S, Lucidi GA, Marchiori G, Bontempi M, Bragonzoni L, Davidoni V, Grassi A, Zaffagnini S (2024). Changes in the Elongation Pattern of the Medial Collateral Ligament During a Single-Leg Squat After Anterior Cruciate Ligament Reconstruction.. Orthopaedic Journal of Sports Medicine. doi:10.1177/23259671241283795 PMID 39507327
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  33. Wouters I, Almonroeder T, Dejarlais B, Laack A, Willson JD, Kernozek TW (2012). Effects of a movement training program on hip and knee joint frontal plane running mechanics.. International Journal of Sports Physical Therapy. PMID 23316427
  34. McCurdy K, Walker J, Saxe J, Woods J (2012). The effect of short-term resistance training on hip and knee kinematics during vertical drop jumps.. Journal of Strength and Conditioning Research. doi:10.1519/JSC.0b013e31824f2386 PMID 22344064
  35. van den Tillaar R, Larsen S (2020). Kinematic and EMG Comparison Between Variations of Unilateral Squats Under Different Stabilities.. Sports Medicine International Open. doi:10.1055/a-1195-1039 PMID 32685673
  36. Talarico MK, Lynall RC, Mauntel TC, Wasserman EB, Padua DA, Mihalik JP (2019). Effect of Single-Leg Squat Speed and Depth on Dynamic Postural Control Under Single-Task and Dual-Task Paradigms.. Journal of Applied Biomechanics. doi:10.1123/jab.2018-0327 PMID 31034324

Every source the library cites

Changes

  • Added a Progressive overload section.
  • A supporting claim was narrowed to match its source; the page text is unchanged.