AlterG Anti-Gravity Treadmill: How Unweighted Training Works
By Thom Salo, COL USA (Ret), NASM CPT, 5x Ironman, Longevity Director Updated May 11, 2026
Sisu offers AlterG anti-gravity treadmill access as part of the studio’s recovery and movement infrastructure. It is one of the most underrated tools available for adults who want to keep moving through injury, surgery, weight loss, or the slow accumulation of joint wear that comes with age. The technology was developed by NASA. It is widely used in professional sports medicine, orthopedic rehabilitation, and military trauma recovery. It is rare in the wellness market, and rarer still as a standalone, drop-in service available to the public outside of physical therapy clinics.
What is the AlterG Anti-Gravity Treadmill?
The AlterG is a treadmill enclosed in a pressurized chamber from the waist down. The user steps in, zips into a pair of compression shorts that seal to the chamber, and the chamber inflates with air to a pressure that gently lifts the body upward. The result is a controlled reduction in body weight while walking or running, ranging from full weight (100 percent) down to as little as 20 percent of body weight in 1 percent increments.
The technology is called Lower Body Positive Pressure, or LBPP. It was originally developed at the NASA Ames Research Center in the 1990s as a way to study locomotion in fractional-gravity environments and as a possible exercise countermeasure for astronauts on long-duration missions. The commercial spinout that became AlterG took the technology out of the laboratory and into orthopedic medicine, where the use case turned out to be more immediately practical: using unweighting to allow injured or recovering patients to walk and run with reduced ground reaction forces.
The biomechanics behind it are straightforward. Ground reaction force is the force the body absorbs each time the foot strikes the ground. At full body weight, this force runs roughly 1.5 to 2.5 times body weight during walking and 2.5 to 3 times body weight during running. Reducing body weight on the treadmill reduces the impact forces the joints, bones, and soft tissues have to absorb in proportion. A 200-pound runner unweighted to 70 percent of body weight is functionally a 140-pound runner. The cardiovascular system, the gait pattern, and the coordination remain intact. The mechanical load is dialed down.
This unlocks training and rehabilitation that would otherwise be impossible.
The Science: What Unweighting Does
Three lines of research support the use of LBPP in rehabilitation and training.
Reduced joint loading. Patil and colleagues at Scripps Clinic published a 2013 study in the Journal of Orthopaedic Research using instrumented knee implants to directly measure the forces inside the knee during LBPP walking and jogging. Reductions in body weight produced predictable, strongly correlated reductions in knee force across the unweighting range, with peak knee force scaling from roughly five times body weight at full load and 4.5 mph down to under one times body weight at 25 percent body weight at 1.5 mph (Patil et al., 2013). This is the foundational evidence that unweighting reduces joint stress in a quantifiable way. For a patient recovering from a total knee replacement or with degenerative joint disease, the difference between exercising and not exercising often comes down to whether the load can be lowered enough to make movement tolerable.
Preserved cardiovascular response, reduced impact loading. Hoffman and Donaghe’s 2011 study in Archives of Physical Medicine and Rehabilitation tested the physiologic responses to LBPP treadmill exercise in healthy adults at multiple unweighting levels. The heart-rate to oxygen-consumption relationship held constant across the unweighting range, meaning standard cardiovascular training zones translate cleanly to the AlterG, while ground reaction forces decreased in proportion to the body-weight reduction (Hoffman & Donaghe, 2011). Earlier work by Cutuk and colleagues at UCSD established that LBPP ambulation has no adverse cardiovascular impact and produces only minimal alterations in gait kinematics, supporting the basic safety profile of the technology (Cutuk et al., 2006). What this means in practice: an injured runner using the AlterG at 60 to 80 percent body weight can still produce a real aerobic training response while protecting the injured tissue.
Safe, tolerated rehabilitation in postoperative care. Bugbee and colleagues at Scripps Clinic published a 2016 pilot randomized trial in the American Journal of Orthopedics comparing antigravity-treadmill rehabilitation to standard land-based gait training in patients recovering from total knee arthroplasty. The trial established that AlterG-augmented rehabilitation was safe and well-tolerated in the early postoperative period, with both arms reaching equivalent functional outcomes at four weeks and treating therapists rating the AlterG protocol highly (Bugbee et al., 2016). The paper supports the AlterG as a safe modality for post-TKA recovery, not as a tool that demonstrably accelerates functional recovery beyond standard PT. Tenforde and colleagues published a 2012 case study in PM&R documenting an elite runner with a pelvic stress injury who used an antigravity treadmill to maintain conditioning and return to competition on what the authors described as an accelerated timeline (Tenforde et al., 2012). Together, these papers illustrate the AlterG’s clinical role: most useful when applied in the gap between injury or surgery and full-load return to activity.
A 2022 narrative review in Arthroscopy, Sports Medicine, and Rehabilitation extended the application across running medicine: bone stress injuries, ACL reconstruction, partial-weight-bearing orthopedic protocols (Achilles, ankle, and tibial fracture rehabilitation), and structured return-to-run programs in athletes (Vincent, Madsen, & Vincent, 2022).
Sisu’s Role: A Wellness Facility, Not a Medical Provider
The use cases described in the rest of this guide overlap with medical territory: post-surgical rehabilitation, injury recovery, chronic joint conditions. A clear boundary statement is in order before going further.
Sisu Longevity Studio is a wellness facility. We are not a medical facility. We do not employ physicians or licensed physical therapists in a clinical capacity, we do not diagnose or treat medical conditions, and we do not provide rehabilitation services as a clinical offering. The AlterG and the rest of the modalities at Sisu are wellness tools, not medical treatments.
For members in active medical care or formal rehabilitation, Sisu plays a supporting role. We work with care providers. We partner with physical therapy practices, surgeons, and physicians who want to coordinate AlterG access for their patients. And we welcome members who wish to perform recovery protocols prescribed by their own care providers, using the AlterG and other Sisu modalities as the venue for that prescribed work.
What we will not do is inject ourselves into the patient-provider relationship. Decisions about diagnosis, treatment progression, modification of a rehabilitation plan, or clinical care belong to the member and their care team. Sisu provides the tool and the space. The clinical judgment stays where it belongs.
A Note for Physical Therapy Practices
Many physical therapy clinics in the Colorado Springs region treat patients who would benefit from access to an AlterG but who do not have one in clinic. The capital cost is significant, the floor space is significant, and not every practice can justify the investment.
Sisu Longevity Studio is open to partnerships with PT practices that need AlterG access for their patients. The AlterG at Sisu is professional-grade with the Stride Smart NEO+ gait analytics package, and the studio can accommodate referred patients on a session-by-session basis. PT practices interested in this arrangement can contact the studio directly.
What Makes Sisu’s AlterG Different
The AlterG installed at Sisu is the AlterG NEO+ with the Stride Smart gait analytics package. The Stride Smart system uses an in-chamber camera array to capture stride length, step rate, gait symmetry, and ground contact time during the session. The analytics produce a session-by-session report showing how gait quality changes across a rehabilitation arc or training cycle.
For the post-surgical patient, the symmetry data shows objectively whether the surgical leg is bearing equivalent load or compensating. For the runner returning from a stress injury, the cadence and stride-length data document the gradual rebuild of running mechanics. For the older adult, the gait quality metrics document the impact of training over time.
The other point of differentiation is access. AlterG units are uncommon outside of physical therapy clinics in most metropolitan areas, and Colorado Springs is no exception. Sisu Longevity Studio is the only public-access AlterG facility in the region outside of clinical PT practice. Members can use the AlterG as part of a Sisu Premium membership tier, on a per-session basis, or as part of a referred PT relationship.
What a Session Looks Like at Sisu
A typical AlterG session at Sisu runs 20 to 45 minutes, depending on the use case.
The user changes into the AlterG compression shorts (provided), steps into the chamber, and zips the shorts to the chamber seal. The system calibrates the user’s body weight automatically. The unweighting target is set, the treadmill belt starts, and the session begins.
During the session, the user can walk or run, adjust the unweighting setting, change speed and incline, and watch the Stride Smart real-time gait feedback on the in-chamber screen. Most users find the experience itself unremarkable: it feels like walking or running with significantly less impact, and the adaptation is immediate.
The Stride Smart analytics generate a session report at the end, capturing pace, distance, average unweighting, and gait quality metrics. For members in a structured rehabilitation or training arc, these reports become a session-over-session record of progress.
For new members, a Sisu coach or technician walks through the first session to familiarize the user with the controls, the unweighting calibration, and the protocol appropriate to the user’s goal. After the first session, most members run their own sessions independently.
Experience AlterG at Sisu
Three ways to begin:
- Schedule a free tour: see the studio, meet the team, no commitment.
- Explore membership tiers: pricing, packs, and how the AlterG fits into the Sisu approach.
- Book a single session: drop in and try it.
References
- Bugbee, W. D., Pulido, P. A., Goldberg, T., & D’Lima, D. D. (2016). Use of an anti-gravity treadmill for early postoperative rehabilitation after total knee replacement: A pilot study to determine safety and feasibility. American Journal of Orthopedics, 45(4), E167-E173. PMID: 27327921
- Cutuk, A., Groppo, E. R., Quigley, E. J., White, K. W., Pedowitz, R. A., & Hargens, A. R. (2006). Ambulation in simulated fractional gravity using lower body positive pressure: cardiovascular safety and gait analyses. Journal of Applied Physiology, 101(3), 771-777. DOI: 10.1152/japplphysiol.00644.2005
- Hoffman, M. D., & Donaghe, H. E. (2011). Physiological responses to body weight-supported treadmill exercise in healthy adults. Archives of Physical Medicine and Rehabilitation, 92(6), 960-966. DOI: 10.1016/j.apmr.2010.12.035
- Patil, S., Steklov, N., Bugbee, W. D., Goldberg, T., Colwell, C. W. Jr., & D’Lima, D. D. (2013). Anti-gravity treadmills are effective in reducing knee forces. Journal of Orthopaedic Research, 31(5), 672-679. DOI: 10.1002/jor.22272
- Tenforde, A. S., Watanabe, L. M., Moreno, T. J., & Fredericson, M. (2012). Use of an antigravity treadmill for rehabilitation of a pelvic stress injury. PM&R, 4(8), 629-631. DOI: 10.1016/j.pmrj.2012.02.003
- Vincent, H. K., Madsen, A., & Vincent, K. R. (2022). Role of antigravity training in rehabilitation and return to sport after running injuries. Arthroscopy, Sports Medicine, and Rehabilitation, 4(1), e141-e149. DOI: 10.1016/j.asmr.2021.09.031
Sisu Longevity Studio | 10855 Hidden Pool Heights, Suite 140 | Colorado Springs, CO 80908
