High-Low training is safe and effective in improving outcomes in a rodent model of chronic cervical spinal cord injury

Repeated exposure to hypoxia (oxygen levels below sea-level atmospheric conditions, ∼21%) alternated with regular voluntary exercise, known colloquially as ‘Living High, Training Low’, or simply ‘High-Low’, is used by elite athletes to boost exercise benefits and athletic performance. While paradigms of High-Low training have been utilized by Olympic athletes for decades, the therapeutic potential of a High-Low regimen in the context of neurotrauma has yet to be investigated. This long-term experiment evaluated the independent and combined effects of repeated hypoxic exposure and voluntary exercise on functional outcomes within the context of preclinical spinal cord injury (SCI). We hypothesized that combinatorial High-Low training enhances functional recovery, beyond either exercise or repeated exposures to hypoxia alone, to improve outcomes after SCI. Adult female rats (n=62) underwent a high-cervical hemisection (LC2H) to model spinal cord injury. At 6 weeks post-SCI, treatment (access to exercise wheel, repeated exposure to normobaric hypoxia at rest, or alternation of both) began in the surviving subjects (n=49). Despite initiation of treatment beyond the acute post-injury phase, High-Low therapy significantly improved respiratory function and prevented the development of SCI-associated anxiety-like behaviors. Notably, repeated in vivo exposure to normobaric hypoxia induced a shift in peripheral T cell profiles, characterized by increased CD4 ⁺ and reduced CD8 ⁺ expression. These findings indicate that combining repeated exposure to hypoxia with voluntary exercise as a therapy could promote recovery in the existing spinal cord-injured population. Collectively, this work provides a foundational first step for further investigation of High-Low training as a rehabilitation therapy for individuals living with SCI.