Research papers on the dangers of using the Smith machine for squats
Pro Research Analysisby 
Searched over 200M research papers
Consensus Meter
Dangers of Using the Smith Machine for Squats
Flexion-Distraction Injuries in the Thoracolumbar Spine
One of the significant dangers associated with using the Smith machine for squats is the risk of flexion-distraction injuries to the thoracolumbar spine. This type of injury is typically seen in motor vehicle collisions but has been reported in weight lifters using the Smith machine with improper technique. The rigid vertical path of the Smith machine can lead to improper spinal alignment and increased risk of injury, especially for novices who may not engage the locking mechanism correctly or lack proper spotter support.
Biomechanical Stress and Joint Torques
The Smith machine's design, which allows only vertical displacement of the barbell, can lead to increased biomechanical stress on certain joints. Research indicates that using a backward-inclined Smith machine can decrease knee torque but increase hip and lumbosacral torques. Conversely, a forward-inclined machine increases knee torque and compressive forces on the tibiofemoral and patellofemoral joints. This variability in joint loading can lead to strain on the posterior cruciate ligament at different knee flexion angles, potentially causing injury.
Muscle Activation and Force Production
Studies comparing muscle activation between free weight squats and Smith machine squats show that free weight squats result in significantly higher electromyographic (EMG) activity in key muscles such as the gastrocnemius, biceps femoris, and vastus medialis. This suggests that free weight squats may be more effective for overall muscle activation and strength development. The constrained movement path of the Smith machine may limit the engagement of stabilizing muscles, potentially leading to imbalances and increased injury risk.
Poor Biomechanical Regions and Sticking Points
The Smith machine squat has been shown to have a "sticking region," a point during the lift where force output is significantly reduced. This region is considered a poor biomechanical area, making it difficult for lifters to maintain proper form and increasing the risk of injury. The co-contraction of hip and knee extensors, along with the potentiation of the vastus muscles, contributes to this sticking region, particularly during one-repetition maximum (1-RM) attempts.
Conclusion
While the Smith machine offers a controlled environment for squatting, it also presents several risks, particularly for novice lifters. The potential for flexion-distraction injuries, increased biomechanical stress on joints, reduced muscle activation, and the presence of poor biomechanical regions all highlight the dangers of using the Smith machine for squats. Proper technique, adequate supervision, and possibly opting for free weight squats may mitigate some of these risks.
Sources and full results
Most relevant research papers on this topic