VO2max can be achieved on an LBPPT at 100% BW with an incline-running protocol. The LBPPT is a suitable training device for athletes and allows training at high running speeds and high aerobic stimuli with the benefit of low vGRF and a near-normal movement pattern, although manipulation of gravitational weight causes some adaptations in locomotion.

Running on a lower-body positive-pressure (LBPP) treadmill allows effects of weight support on leg muscle activation to be assessed systematically, and has the potential to facilitate rehabilitation and prevent overloading. The aim was to study the effect of running with weight support on leg muscle activation and to estimate relative knee and ankle joint forces. Runners performed 6-min running sessions at 2.22 m/s and 3.33 m/s, at 100%, 80%, 60%, 40%, and 20% body weight (BW). Surface electromyography, ground reaction force, and running characteristics were measured. Relative knee and ankle joint forces were estimated. Leg muscles responded differently to unweighting during running, reflecting different relative contribution to propulsion and antigravity forces. At 20% BW, knee extensor EMG peak decreased to 22% at 2.22 m/s and 28% at 3.33 m/s of 100% BW values. Plantar flexors decreased to 52% and 58% at 20% BW, while activity of biceps femoris muscle remained unchanged. Unweighting with LBPP reduced estimated joint force significantly although less than proportional to the degree of weight support (ankle). It was concluded that leg muscle activation adapted to the new biomechanical environment, and the effect of unweighting on estimated knee force was more pronounced than on ankle force. Keywords: rehabilitation, body weight support, EMG, estimated joint load, runningEarly mobilization after injury and surgery on the lower extremities is essential to reduce adverse effects of immobilization and to facilitate rehabilitation. Walking or running with weight support on a lower-body positive-pressure (LBPP) treadmill is a new training and rehabilitation modality. 1,2 A recent study indicated strong correlation between tibiofemoral force and treadmill ground reaction force in a small group of elderly patients during slow walking. 3 Another study showed that runners can reduce peak vertical ground reaction forces while maintaining the aerobic stimulus when running on a LBPP treadmill. 4 Even training at high speeds and high aerobic stimuli with the benefit of low vertical ground reaction force and near-normal movement pattern can be performed on the LBPP treadmill. 5 Furthermore, no adverse impact on systemic and head cardiovascular parameters has been found. 6 However, the effect of different levels of LBPP weight support during running on neuromuscular adaptations and their possible associations to joint forces have not been studied systematically.During level running, leg muscles support body weight (BW) against gravity and accelerate/decelerate the body mass in a forward direction. BW, as measured in Newton, is directly related to gravity, while body mass (kg) is independent of gravity. Therefore, by unweighting in a LBPP chamber, it is possible to create a new biomechanical environment where the vertical forces are reduced while forces associated with horizontal acceleration/deceleration of the body remain unchanged. This allows systematic study of individual leg muscle contribution to body support against grav...