The Science Behind the Float: How AlterG Changes Biomechanics, Muscle Activation, and Recovery

For runners and coaches who live by data, one thing is clear: not all miles are created equal. Training variables like surface, incline, footwear, and fatigue all affect running mechanics—but perhaps nothing changes the equation more than bodyweight support.

At Princeton Sports and Family Medicine, P.C. in Lawrenceville, New Jersey, we use the AlterG Anti-Gravity Treadmill not just for injury recovery, but to help runners optimize biomechanics, reduce load, and gain new insights into their movement. This blog explores the science behind how running at different bodyweight levels affects kinematics, kinetics, and muscle activation.

Biomechanics Under Reduced Load: What the Research Shows

1. Kinematics: Joint Angles and Stride Dynamics

Studies show that running at 60–80% bodyweight on the AlterG leads to:

• Increased cadence

• Shortened stride length

• Reduced vertical oscillation

• Earlier foot-off and decreased ground contact time

What this means: Offloading changes the shape of the gait cycle, often improving efficiency and helping runners rehearse shorter, faster strides—a key for reducing overstriding and braking forces.

▶️Practical tip for coaches: Use AlterG to help athletes develop midfoot strike patterns and improve cadence without increasing metabolic cost.

2. Kinetics: Ground Reaction Forces and Joint Loading

Perhaps the biggest benefit of the AlterG is the significant reduction in peak ground reaction forces (GRF). Research shows:

• 40–60% reduction in impact forces at 60% bodyweight

• Reduced loading rates at the hip, knee, and ankle

• Lower braking impulse, especially during early stance

This reduced mechanical stress allows for more frequent running and earlier return from injury—while also enabling high-mileage runners to manage cumulative load.

▶️ Useful for runners with stress injuries, tendinopathy, and early arthritis.

3. Muscle Activation: What Happens to the Workload?

EMG studies demonstrate that unweighted running shifts the burden away from certain muscle groups:

• Decreased activation of gluteus maximus, hamstrings, and calf muscles

• Slight reduction in quad activity

• Hip flexors and dorsiflexors often maintain or increase activity during swing phase

What this means: With less demand for propulsion and support, muscles work differently—allowing a neuromuscular reset and low-fatigue technique training. However, long-term use without strength training may lead to deconditioning if not balanced properly.

▶️ Ideal for re-patterning gait post-injury or offloading a specific muscle group in recovery.

Recovery and Training Implications

The AlterG isn’t just a rehab tool—it’s a training variable. By modulating bodyweight, athletes can:

• Reduce DOMS and muscle fatigue after races or hard blocks

• Preserve neuromuscular form during easy or recovery runs

• Log additional aerobic miles without exceeding safe weekly load

• Run with greater frequency while staying below the injury threshold

Summary: Key Metrics at a Glance

Who Should Use This?

• Data-driven runners managing high load

• Coaches guiding athletes through return-to-run

• Post-injury runners reconditioning movement

• Masters athletes dealing with wear and tear

• Triathletes looking for high-volume, low-impact mileage

Explore your biomechanics in a new way.
Contact Princeton Sports and Family Medicine, P.C. to schedule an AlterG gait analysis and performance session. Run smarter—at any bodyweight.

Author

Peter Wenger, MD Peter C. Wenger, MD, is an orthopedic and non-operative sports injury specialist at Princeton Sports and Family Medicine, P.C., in Lawrenceville, New Jersey. He is board certified in both family medicine and sports medicine. Dr. Wenger brings a unique approach to sports medicine care with his comprehensive understanding of family medicine, sports medicine, and surgery. As a multisport athlete himself, he understands a patient’s desire to safely return to their sport.