Higher Heart Rates During Locomotor High-Intensity Interval Training Are Associated With Gait Asymmetry and Fatigue...

Individuals poststroke with severe hemiparesis and deconditioning may have physical difficulty walking fast and/or long enough to perform vigorous cardiovascular intensity during locomotor high-intensity interval training (HIIT). We hypothesized that baseline walking function would be associated with the average percent heart rate reserve (%HRR) performed during locomotor HIIT.

Baseline assessments included walking endurance (6-min walk test), comfortable and fast walking speed (10-m walk), step length and single-limb support symmetry (electronic walkway), and metabolic cost of fast walking (ml O₂/kg/m during a graded maximal exercise test). Covariates included peak heart rate (HRpeak) and respiratory exchange ratio (RER) achieved during the graded maximal exercise test and baseline self-reported fatigue (PROMIS fatigue scale). To reduce bias, %HRR was examined during treadmill HIIT, consisting of 20 minutes of repetitive 30 seconds of maximal walking speed separated by 30 to 60 seconds of standing passive recovery, performed 3×/week.

Twenty-seven individuals were allocated to HIIT (age 63 ± 10 years, 2.7 ± 1.4 years poststroke). Less baseline walking step length symmetry ( $\hat{\beta }=-0.28$ , P = .03) and less baseline fatigue poststroke ( $\hat{\beta }=-0.86$ , P = .02) were associated with a higher cardiovascular intensity achieved during the first week of locomotor HIIT. Across 12 weeks of HIT, baseline factors were no longer associated with %HRR.

Few baseline walking characteristics were associated with cardiovascular intensity during the initiation of locomotor HIIT, potentially because of large variability in the heart rate response. As individuals progressed over time and were able to reach higher cardiovascular intensity, the associations were abrogated.