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

Abstract

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 (VO₂max) 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 VO₂max differed with time since injury, with greater increases earlier post-injury. The early chronic group (<3 years since injury; n = 31) increased VO₂max 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 VO₂max 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 VO₂max (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.

Keywords: exercise test; exercise therapy; neurological rehabilitation; sports for persons with disabilities.

FIG. 1.

Example of V slope plot during graded exercise test. Individual data points represent 10-sec averages in gas exchange. At the anaerobic threshold, increases in carbon dioxide production (VCO₂ in L/min) exceed increases in oxygen uptake (VO₂ in L/min).

FIG. 2.

Relationship between time since injury (months) and change in maximal oxygen uptake. (A) Early chronic spinal cord injury (<3 years). (B) Late chronic spinal cord injury (>3 years). VO₂max, maximal oxygen uptake.