Locomotor training intensity after stroke: Effects of interval type and mode

Abstract

Background and Objectives: High-intensity interval training (HIIT) is a promising strategy for improving gait and fitness after stroke, but optimal parameters remain unknown. We tested the effects of short vs long interval type and over-ground vs treadmill mode on training intensity. Methods: Using a repeated measures design, 10 participants with chronic hemiparesis performed 12 HIIT sessions over 4 weeks, alternating between short and long-interval HIIT sessions. Both protocols included 10 minutes of over-ground HIIT, 20 minutes of treadmill HIIT and another 10 minutes over-ground. Short-interval HIIT involved 30 second bursts at maximum safe speed and 30-60 second rest periods. Long-interval HIIT involved 4-minute bursts at ~90% of peak heart rate (HR_peak) and 3-minute recovery periods at ~70% HR_peak. Results: Compared with long-interval HIIT, short-interval HIIT had significantly faster mean overground speeds (0.75 vs 0.67 m/s) and treadmill speeds (0.90 vs 0.51 m/s), with similar mean treadmill HR (82.9 vs 81.8%HR_peak) and session perceived exertion (16.3 vs 16.3), but lower overground HR (78.4 vs 81.1%HR_peak) and session step counts (1481 vs 1672). For short-interval HIIT, training speeds and HR were significantly higher on the treadmill vs. overground. For long-interval HIIT, the treadmill elicited HR similar to overground training at significantly slower speeds. Conclusions: Both short and long-interval HIIT elicit high intensities but emphasize different dosing parameters. From these preliminary findings and previous studies, we hypothesize that overground and treadmill short-interval HIIT could be optimal for improving gait speed and overground long-interval HIIT could be optimal for improving gait endurance.

Keywords: Aerobic exercise; high-intensity interval training; locomotion; overground; treadmill.

Figure 1.. Study design.

Each participant performed 12 sessions of high-intensity interval training (HIIT) over approximately 4 weeks, alternating between short-interval HIIT sessions (S) and long-interval HIIT sessions (L). The first session was randomized across participants.

Figure 2.. Session structure and training protocols.

Light gray boxes depict target heart rates (long-interval HIIT plus warm up and cool down for short-interval HIIT). Dark gray boxes depict target speeds (short-interval HIIT bursts were performed at maximum safe speed, which was continually progressed as able throughout the session). Black lines depict examples of actual heart rate responses. HR_peak, peak heart rate from symptom-limited exercise testing.

Figure 3.. Within-session training intensity changes by protocol.

Values are averaged across sessions within the statistical model. Error bars depict standard error. Dashed lines indicate the mean baseline comfortable and fastest gait speed from the 10m walk test. Treadmill speeds are consistent (not peak) training speeds. *Significant (p<0.05) between-protocol difference. ^†Significant within-protocol change.