Hack Squats: Going Past 90 Degrees, Benefits, Risks, and Safe Practice

Should I go past 90 degrees on a hack squat?

Going past 90 degrees on a hack squat can be highly beneficial for muscle development and joint mobility, provided it is executed with proper form, adequate mobility, and without pain. The decision to go deeper should always be individualized, prioritizing safety and controlled movement over arbitrary depth.

Understanding the Hack Squat

The hack squat is a compound lower body exercise primarily targeting the quadriceps, but also engaging the glutes, hamstrings, and calves. Performed on a specialized machine, it stabilizes the torso and often allows for a more upright posture compared to a barbell back squat, which can make it feel more accessible for some individuals to achieve greater depth and isolate the quads.

The 90-Degree Debate: A Biomechanical Perspective

The "90-degree rule" – the idea that squatting deeper than parallel (where the hip crease is below the top of the knee, typically past a 90-degree knee angle) is inherently dangerous for the knees – is a persistent myth in fitness. Modern exercise science and biomechanical research largely refute this blanket statement.

• Knee Joint Mechanics: The knee joint, specifically the patellofemoral joint (where the kneecap meets the thigh bone), experiences varying stress levels throughout the squat. While stress on the patellofemoral joint does increase as the knee flexes past 90 degrees, the stress on the tibiofemoral joint (between the shin and thigh bones) actually decreases in deeper ranges due to increased hamstring and gastrocnemius activation providing a protective "pull" on the tibia.
• Tissue Adaptation: Human joints, ligaments, and tendons are designed to withstand load and adapt over time. Training through a full, pain-free range of motion can actually strengthen these tissues and improve joint resilience, not degrade them.

Advantages of Deep Hack Squats (Past 90 Degrees)

When performed correctly, squatting past 90 degrees on a hack squat offers several significant benefits:

• Enhanced Quadriceps Development: A greater range of motion places the quadriceps under tension for a longer duration and through a more complete contractile range, leading to superior hypertrophy (muscle growth).
• Increased Glute and Hamstring Activation: As you descend deeper into a squat, the gluteal muscles and hamstrings become increasingly engaged to control the movement and initiate the ascent. This contributes to more balanced lower body development and improved posterior chain strength.
• Improved Joint Mobility and Flexibility: Consistently training through a full, deep range of motion can improve ankle dorsiflexion, hip flexion, and knee flexion, contributing to overall better functional mobility and joint health. This is a form of active flexibility training under load.
• Greater Functional Strength Transfer: Deep squats mimic many real-world movements (e.g., sitting down, picking something off the floor) more closely than partial squats. Training this full range enhances functional strength and reduces the risk of injury in daily activities.
• Reduced Shear Forces at the Knee: As mentioned, deeper squats engage the hamstrings more, which helps to stabilize the knee joint by counteracting the forward shear forces on the tibia.

Potential Risks and Considerations

While beneficial, deep hack squats are not without potential risks, especially if performed improperly or by individuals with specific limitations:

• Pre-existing Conditions or Injuries: Individuals with a history of knee injuries (e.g., meniscal tears, ACL/PCL issues), hip impingement, or severe osteoarthritis should consult a medical professional or physical therapist before attempting deep squats.
• Mobility Limitations: Inadequate ankle dorsiflexion, hip flexion, or thoracic spine mobility can compromise form during a deep squat, leading to compensatory movements that place undue stress on other joints (e.g., lumbar spine rounding, knees caving in).
• Improper Form:
  • Spinal Rounding (Butt Wink): If the lower back rounds excessively at the bottom of the squat, it places compressive and shear forces on the lumbar spine, increasing injury risk.
  • Knees Caving In (Valgus Collapse): This indicates weakness in the hip abductors/external rotators and can place significant stress on the medial knee ligaments.
  • Lack of Control: Dropping quickly into the bottom of the squat rather than controlling the eccentric (lowering) phase can reduce muscle activation and increase impact forces on the joints.
• Ego Lifting: Attempting to lift too much weight with poor form to achieve depth is a primary cause of injury. Prioritize form and control over load.

How to Safely Go Deeper

If you aim to incorporate deeper hack squats into your routine, follow these guidelines:

• Assess Your Mobility: Before adding load, perform bodyweight deep squats to identify any limitations in ankle, hip, or thoracic mobility. Incorporate mobility drills (e.g., ankle dorsiflexion stretches, hip internal/external rotation drills) to improve your range of motion.
• Start Light and Master Form: Begin with a light weight, or even just the machine's carriage, focusing entirely on maintaining a neutral spine, keeping your chest up, and driving your knees in line with your toes.
• Control the Eccentric Phase: Slowly lower yourself into the squat, taking 2-3 seconds to reach the bottom. This increases time under tension and allows for better control.
• Listen to Your Body: Never push into pain. A mild stretch or muscle fatigue is acceptable, but sharp, pinching, or persistent pain indicates a problem. Reduce depth or discontinue the exercise if pain occurs.
• Progress Gradually: Once you can comfortably and safely achieve depth with a light weight, incrementally increase the load. Avoid large jumps in weight.
• Consider Foot Position: On a hack squat, a slightly higher foot placement can emphasize the glutes and hamstrings more, while a lower placement can target the quads. Adjusting stance width can also affect comfort and depth. Some individuals benefit from placing a small plate under their heels to improve ankle dorsiflexion and allow for a more upright torso.
• Incorporate Core Bracing: Engage your core muscles by taking a deep breath into your belly and bracing your abdominal wall before descending. This stabilizes the spine.

Conclusion: Individualization is Key

Ultimately, whether you should go past 90 degrees on a hack squat depends on your individual anatomy, mobility, strength, training goals, and injury history. For most healthy individuals with good mobility and proper form, training through a full, deep range of motion is not only safe but highly beneficial for comprehensive lower body development and joint health.

Prioritize:

• Pain-free movement.
• Controlled execution.
• Maintaining proper spinal alignment.
• Gradual progression.

If you have concerns or pre-existing conditions, consult with a qualified fitness professional or healthcare provider to ensure deep squatting is appropriate for you.