Hybrid Functional Electrical Stimulation Improves Anaerobic Threshold in First Three Years after Spinal Cord Injury

The purpose of the present investigation was to assess the effects of whole-body exercise on the anaerobic threshold in individuals with spinal cord injury (SCI). Maximal oxygen uptake (VO(2)max) and oxygen uptake at anaerobic threshold (AT) were measured before and after six months of hybrid functional electrical stimulation row training in 47 participants with SCI aged 19-63, neurological levels of injury C4-L1, American Spinal Injury Association Impairment Scale grades A-D, and time since injury at enrollment from three months to 40 years. Changes in VO(2)max differed with time since injury, with greater increases earlier post-injury. The early chronic group (n = 31) increased VO(2)max from 1.65 +/- 0.54 L/min at baseline to 1.83 +/- 0.66 L/min at six months (p < 0.05), while the late chronic group (>3 years since injury; n = 16) did not change (1.42 +/- 0.44 at baseline to 1.47 +/- 0.41 L/min at six months, p = 0.36). Consistent with VO(2)max changes, AT increased in the early chronic group (1.03 +/- 0.31 to 1.20 +/- 0.40 L/min, p < 0.05) and did not change in the late chronic group (0.99 +/- 0.31 to 0.99 +/- 0.26 L/min, p = 0.92). Cumulative duration of exercise training was positively correlated to change in VO(2)max (r = 0.475, p < 0.05) but not to change in AT. Hybrid functional electrical stimulation row training is effective for increasing aerobic capacity and anaerobic threshold in individuals with SCI; however, these fitness benefits are only significant in individuals initiating the exercise intervention within three years of injury.