Abstract TP342: Blood lactate thresholds of stroke survivors are modified in response to a 12-week high-intensity interval training intervention

Introduction: Survivors of chronic subcortical strokes often face lower limb disabilities, leading to a sedentary lifestyle and slower walking speeds than other older adults. Increasing physical activity is vital for regaining independence, enhancing quality of life, and reducing mortality rates. Research indicates that high-intensity interval training (HIIT) can improve walking speed and functional capabilities in these patients. However, there is still uncertainty about how HIIT achieves these improvements. We hypothesize that lactate, produced during intense exercise, plays a key role in enhancing motor skills. Methods: We evaluated the walking speed of four veterans with lower limb disabilities resulting from chronic subcortical strokes in response to a 36-session (12-week) HIIT intervention using stationary recumbent bikes. After the intervention, participants who improved their walking speed by at least 0.10 m/s were classified as responders, while those who did not improve were classified as resistors. We assessed walking speed, mobility, and gait characteristics at baseline and after the 12-week HIIT program. Additionally, we measured the participants’ exercise-induced blood lactate levels during the 2nd, 4th, 7th, 10th, and 28th HIIT sessions. A lactate level of 4.0 mmol/L or higher indicated that the participant entered anaerobic respiration. Results: Preliminary analysis indicates functional improvements in response to HIIT include a more efficient gait, increased stability, reduced risk of falls, and corresponding increases in walking speed and mobility (Table 1). Out of the four participants, one did not improve their walking speed and was classified as a resistor. The other three participants showed improvements in walking speeds ranging from 0.16 to 0.34 m/s (Figure 1). The three responders achieved blood lactate levels above 6 mmol/L by the 10th session and improved their fitness levels to the point that anaerobic glycolysis was no longer achieved by the 28th session. The resistor did not show any improvements in fitness levels or modifications to their blood lactate threshold (Figure 2). Conclusion: In conclusion, our findings suggest that cycling interventions post-stroke can lead to significant improvements in gait, mobility, and walking speed. Furthermore, we propose that blood lactate may serve as a mechanistic factor in determining which participants respond to and which resist the intervention.