A treadmill control protocol combining nonlinear, equally smooth increases in speed and gradient: Exercise testing for subjects with gait and exercise limitations

Abstract 

Incremental exercise testing with a linear increase in work rate is the recommended method for clinical exercise testing. A recent protocol (A), incorporating a linear increase in speed and a nonlinear increase in gradient, has been developed which addresses some limitations of traditional testing methods. It does not account for those with an impaired gait pattern. We propose and assess a novel protocol (B) incorporating nonlinear increases in both speed and gradient.

We theoretically develop a new treadmill control protocol (B), determine oxygen uptake response linearity, initial metabolic rate and cardiopulmonary response parameters (peak oxygen uptake, lactate threshold, dynamic O₂ cost) and compare the outcome measures with two previously verified IET protocols (A and C (constant speed with linear increase in gradient)). Feasibility and outcomes were explored with a subject with incomplete spinal cord injury.

The average initial metabolic rate () was substantially lower during protocol A (0.49 () lmin⁻¹) and protocol B (0.52 () lmin⁻¹) than during protocol C (1.35 () lmin⁻¹). The average linearity of the response during protocols A and B (correlation co-efficients 0.97 () and 0.95 (), and co-efficients of determination 0.94 () and 0.91 (), respectively) were higher than during protocol C (correlation co-efficient 0.91 () and co-efficient of determination 0.84 ()). The average dynamic O₂ cost for protocol C (6.53 () mlmin⁻¹W⁻¹) was lower than that of protocol A (10.02 () mlmin⁻¹W⁻¹) and protocol B (10.03 () mlmin⁻¹W⁻¹). No differences were found in these parameters between protocols A and B.

The new protocol B performs better than protocol C and is comparable with protocol A. When testing subjects with an impaired gait pattern, it may be advantageous to use the new protocol B due to the gradual increases in both speed and gradient throughout the test.

Keywords: Exercise physiology, Treadmill exercise, Incremental exercise testing, Gait impairment, Spinal cord injury