Characterization of Ventilatory Off-Kinetics Following Arm and Leg Cycling in Incomplete Spinal Cored Injured Men

Abstract

INTRODUCTION: The minute ventilation (VE) off-kinetics phase has been associated with greater muscle oxygen deficiency and slower muscle oxygen adjustments to exercise. Neural mechanisms are implicated in VE off-kinetics as recovery from exercise may be mediated by breathing frequency. Motor incomplete spinal cord injury (miSCI) is associated with significant cardiopulmonary impairment that may alter the off-kinetic response during arm and leg exercise. PURPOSE: The purpose of this study was to characterize the VE off-kinetics following both arm and leg exercises in adults with cervical miSCI compared to a group of age matched peers (CON). PARTICIPANTS: miSCI: Age: 31 (18.1) years, Height 185.7 (6.0) cm, Weight 75.9 (14.4) kg. CON: Age: 32 (4.6) years, Height: 178(3.6)cm, Weight 92.9(16.3) kg. METHODS: Both groups completed arm and leg cycle tests on separate days at an intensity that elicited a VE equal to 30% of measured maximum voluntary ventilation (MVV% L·min-1). VE off-kinetics was analyzed over the 5 minutes following the 30% MVV bout using a mono-exponential model. Amplitude (Amp), in liters (L), was defined as the change from exercise to steady state of asymptote approaching baseline and tau(τ)(seconds) as the time taken to reach 63% of the of the end-recovery amplitude. RESULTS: miSCI group: τ(s) and Amp(L) for arm and leg cycling were as follows: 67.9(9.8) and -20.5 (11.53), and 101.6 (19.5) and -23.4(14.5). The average arm τ was 33.7(29.27) faster than leg cycling with a 2.8(9.41) liter decrease in amplitude. CON group: τ(s) and Amp(L) for arm and leg cycling were as follows: 56.7(5.9) and -43.4(4.4) and 90.13 (17.83) and -49.2(4.9), respectively. On average, arm τ was 33.39(16.5) seconds faster than leg cycling while the Amp was 5.8(3.29) liters lower. On average, τ was 11.19 and 11.50 s slower for arm and leg cycling, respectively when compared to CON. Amplitude was also lower with 22.8 and 25.8 liter difference in arm and leg cycling, respectively. CONCLUSION: The miSCI group reported a longer τ following both arm and leg exercise than the CON group suggesting a prolonged recovery phase. A prolonged VE off-kinetic phase may, in part, contribute to reduced functional performance in adults with chronic miSCI. Character count w/o spaces: 1907/2000.