Anti-Gravity Treadmill Training for Prevention and Rehabilitation of Running Injuries

List of Abbreviations


Anterior cruciate ligament


AlterG® Anti-Gravity Treadmill™


Body weight




Kilometers per hour


Lower-body positive pressure




Meters per second


Miles per hour


Rating of perceived exertion

V ˙
O 2 Max

Maximum rate of oxygen consumption


Research has documented that a large number of adults run as their primary form of leisure-time physical activity and that a substantial proportion of runners at every level suffer from running injuries. Several systematic reviews have reported that the most common running-related injuries were found to be medial tibial stress syndrome, Achilles tendinopathy, plantar fasciitis, and patellofemoral pain syndrome.

Although findings have been inconsistent, risk factors for overuse injuries include prior injury, being a novice runner, , having a long stride length, being a rearfoot striker, and elements of training such as high mileage, rapid increases in training load, and doing speed training. Long-distance running by definition includes repeated impact on the lower limbs, and applying forces repeatedly can lead to positive remodeling of a structure. However, this only occurs if the forces do not exceed load capacity and if sufficient time is provided between force applications for recovery. If this is not the case, an overuse injury could be the result.

Given the high rate of overuse injuries in runners of all levels, and the modest effect of interventions to prevent running injuries, there is a need to find better ways to balance the appropriate stress levels needed for positive remodeling with sufficient rest to prevent running injuries. One modality that allows for running while systematically controlling impact forces is the use of a treadmill that uses air pressure to provide lower-body support, which we explore in this chapter.

The AlterG® Anti-Gravity Treadmill™ is the main type of lower-body positive pressure (LBPP) treadmill currently marketed. The AlterG® was originally developed by Dr. Robert Whalen, a NASA engineer tasked with finding a way to allow astronauts to exercise in a zero-gravity environment. He developed a lower-body negative air pressure bubble using differential air pressure (DAP) technology, enabling astronauts to run or walk on a treadmill in space, which could prevent, reduce, or attenuate muscle atrophy, maintain bone density, and prevent or slow declines in cardiorespiratory fitness. His son, Sean, subsequently reversed the treadmill and, instead of negative pressure, developed the LBPP treadmill for use on earth. The first prototype was developed in 2005, and the treadmill was dubbed the AlterG® Anti-Gravity Treadmill TM . The device is like an airbag on a treadmill (see Fig. 12.1 ) and allows users to run or walk while their body weight is partially supported to as little as 20% of their original body weight in 1% increments. The Food and Drug Administration (FDA) approved the AlterG® in 2008 for use in medical settings .

Fig. 12.1, The AlterG® anti-gravity treadmill™ PRO model.

Fig. 12.2, Lower-body positive pressure treadmill metabolic conversion table in miles per hour and minutes per mile.

Body weight–supported walking or running is not new. Harness systems and underwater treadmills are two such examples currently used in training and rehabilitation settings. A body of literature has examined the evidence for effectiveness of different modalities providing partial body weight support on clinical populations such as in stroke rehabilitation. However, the AlterG® treadmill is the only modality that does not require a pool, nor a harness system or other setup, and allows for systematic unloading in 1% increments. Since its first prototypes, the AlterG® has had a close connection with long-distance running. Some of the first users of the AlterG® were elite distance runners under coach Alberto Salazar, including Galen Rupp, two-time Olympic medalist (10,000 m in 2012 and Marathon in 2016) and former American Record holder in the 5,000 m, Dathan Ritzenhein. Famously, Ritzenhein used the AlterG® in 2007 after being diagnosed by MRI with a stress reaction of the third metatarsal and successfully returned to high-performance running within 8 weeks after diagnosis (see Box 12.1 ).

Box 12.1
Case Study of a World-class Runner Training on the AlterG® After a Stress Reaction of the third metatarsal

Case Study of a world-class runner

Dathan Ritzenhein, former US record holder in the 5,000 m, Olympian, and medalist in the World Half Marathon championships has a history of stress fractures in his feet and femur. He has previously stated that his career had been determined as much by injuries as by his fitness.

In February of 2008, he experienced pain in his left foot, and an MRI revealed a stress reaction in the third metatarsal. As mentioned in his case study : “When I got the diagnosis and MRI results that I had a stress reaction of the 3rd metatarsal in my left foot I caught a plane the next day to Oregon so I could train on Alberto's AlterG® treadmill which had been set up in a Colorado Altitude Training environmental room.”

Dathan Ritzenhein won the 2008 Healthy Kidney 10 km.He started running at 65% of his body weight, running twice daily for 60 min, progressing to 87% over a 3-week period. In week 4, he stayed at the same 87% body weight, and starting in week 5, he progressively added overground running.

He started adding in 10 min of overground running in the second of the daily sessions each day and, after a week, ran 60 min overground each second session. Over the next 4 weeks, he progressed to his regular schedule.

In total, only 8 weeks after initial diagnosis, Dathan Ritzenhein won the Healthy Kidney 10 km road race in 28:08, a time that still ranks as one of the top American road 10 kilometer performances in history.

This chapter focuses specifically on the use of the AlterG® treadmill for prevention and rehabilitation of running injuries. We first review the types of treadmills available and what is known about the accuracy of the machine. Second, we review research examining the impact of running on the treadmill on stride characteristics and impact forces, metabolic demand, and running performance. Next, we summarize the available evidence on use of the machine in prevention of running injuries. Finally, we provide practical recommendations for the clinician working with runners and identify areas for future research.

How Does the Machine Work?

A user zips into the specialized AlterG® shorts similar to a wetsuit or kayak shorts. The shorts have a zipper attached to it that zip onto a bag on the treadmill, creating a sealed environment optimal for air pressure support. After the user is zipped onto the airbag at hip height, a force plate under the treadmill measures the user's weight and calibrates the machine accordingly using positive air pressure. The home screen shows speed (in MPH, KM/HR, or M/S), incline, and proportion of full body weight ( not the amount of body weight support ; for example, 80% is indicative of 80% of full body weight, or 20% body weight support).

Types of AlterG® Treadmills

The AlterG® company currently markets several types of AlterG® treadmills (see Table 12.1 ). They all use the same air pressure technology to provide body weight support. The differences between the treadmills are in the type of treadmill, maximum speed forward and backward, maximum incline, and users' height and weight range. The top model has higher ranges and uses higher-end equipment like the Woodway treadmill.

Table 12.1
Types of AlterG® Anti-Gravity Treadmills TM and Their Specifications.
Photo credit AlterG® Marketing Resources:
Feature FIT 100 VIA 400/400M VIA 400X PRO P500
Type of Treadmill Generic Generic Generic Woodway
Unloading range (in 1% increments) 20%–100% body weight 20%–100% body weight 20%–100% body weight 20%–100% body weight
Minimum Speed 0.1 MPH 0.1 MPH 0.5 MPH 0.1 MPH
Maximum Speed 12.0 MPH 12.0 MPH 15.0 MPH 18.0 MPH
Maximum incline None 15% 15% 15%
Maximum Backwards Speed None −3.0 MPH −5.0 MPH −10.0 MPH
User weight range 85-350 lbs 85–400 lbs 85–400 lbs 85–400 lbs
Size range of neoprene shorts 3XS-4 XL (XS to 4XL, 3XS custom) 3XS-4 XL (XS to 4XL, 3XS custom) 3XS-4 XL (XS to 4XL, 3XS custom) 3XS-4 XL (XS to 4XL, 3XS custom)
User Height Range 4’ 8” – 6’ 4” 4’ 8” – 6’ 4” 4’ 8” – 6’ 4” Small: 5 ft- 6 ft 4 inch
Medium: 5”6- 6”10
Large: 6” to 7”4
Gait analytics (step length, Symmetry, Stance Time Symmetry, Cadence, Pain scale) Not Included Included Included Included
Video Monitoring Not Included Included Included Included
MPH , Miles Per Hour; lbs , pounds.

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