# High-Intensity Interval Training Improves Cognitive Flexibility in Older Adults PMID: 33137993 Journal: Brain Sciences Published: 2020-10-29 Authors: Mekari S, Neyedli HF, Fraser S, O'Brien MW, Martins R, Evans K, Earle M, Aucoin R, Chiekwe J, Hollohan Q, Kimmerly DS, Dupuy O ## Question Does six weeks of high-intensity interval training improve executive-function components in healthy older adults compared with moderate-intensity continuous training or resistance training? ## Summary A 6-week supervised cycling HIIT program improved aerobic fitness and produced a selective improvement in cognitive flexibility in healthy older adults. Moderate continuous cycling and resistance training also improved aerobic fitness, but only HIIT improved the Stroop task switching condition. ## Population - Healthy, cognitively intact older adults recruited from Acadia Active Aging. - Sample size: 69 - Age: Mean age 68 +/- 7 years. - Sex: 46 females and 23 males. - Fitness level: Already physically active about three times per week through an active-aging program. - Health status: Healthy older adults without major cognitive, neurological, psychiatric, cardiovascular, pulmonary, metabolic, orthopedic, or musculoskeletal contraindications. ## Methodology - Randomized controlled trial with three parallel supervised exercise groups: HIIT, moderate-intensity continuous training, and resistance training. - 6 weeks - Supervised exercise sessions in an academic/community active-aging setting. - Randomized and controlled study design. ## Protocol - Cycling HIIT. - Modality: Cycle ergometer. - Work intervals: 15 seconds at 100% peak power output. - Recovery: 15 seconds passive recovery at 0% peak power output, with 5 minutes passive recovery between the two sets. - Sets or repetitions: Two sets of repeated 15-second work/rest intervals; initial total interval time 40 minutes, increased to 45 minutes for most sessions. - Intensity: 100% peak power output during work intervals, with a 15 W increase in the final 2 weeks. - Session duration: 5-minute warm-up at 25% peak power output plus 40-45 minutes of intervals and recovery; final two sessions tapered to 35 minutes. - Frequency: 3 sessions per week. - Program length: 6 weeks; 18 planned sessions with at least 80% attendance required for post-testing. - Progression: Interval time increased after the first 2 weeks, intensity increased by 15 W in the final 2 weeks, and the final two sessions were shortened as a taper. - MICT and resistance training. - Modality: Cycle ergometer for MICT; machine, cable, and core exercises for resistance training. - Work intervals: MICT used continuous cycling; resistance training used sets of strength exercises. - Recovery: MICT had no intervals; resistance training used 30-60 seconds rest between sets. - Sets or repetitions: MICT was one continuous bout. Resistance training used eight exercises, initially 2 sets of 10 repetitions, progressing to 12 repetitions before load increases. - Intensity: MICT at 60% peak power output. Resistance training began at about 70% perceived 1-repetition maximum. - Session duration: MICT was 34 minutes initially, then 39 minutes for most sessions, with final taper sessions of 30 minutes. Resistance-training session duration was not clearly reported. - Frequency: 3 sessions per week. - Program length: 6 weeks. - Progression: MICT received the same late 15 W increase and taper concept as HIIT. Resistance training progressed repetitions before increasing load. ## Outcomes ### VO2max Status: improved All groups improved aerobic fitness, with the largest within-group effect in HIIT. Group-by-time interaction p = 0.001; HIIT t(23) = 9.10, p < 0.001, d = 1.86. ### Stroop switching response time Status: improved Only HIIT significantly improved the switching condition, interpreted as improved cognitive flexibility. Group-by-time interaction F(2,65) = 11.0, p < 0.001, partial eta squared = 0.25; HIIT t(23) = 6.89, p < 0.001, d = 1.06. ### Stroop naming and interference Status: mixed Naming and interference showed time effects but no clear group-specific advantage, and accuracy analyses did not suggest a speed-accuracy tradeoff. Speed-accuracy tradeoff checks p > 0.30. ## Practical Insights - Short-interval cycling HIIT can be delivered to screened older adults under supervision using peak-power-output targets. - For cognitive-flexibility goals, the article supports repeated brief work/rest cycling intervals rather than assuming all exercise modes have equivalent executive-function effects. - The protocol is equipment-based and relatively long for HIIT, so a bodyweight game adaptation would need lower-impact movements, conservative progression, and careful monitoring. ## Limitations - Participants were healthy, cognitively intact, and already physically active, limiting generalization to sedentary or frail older adults. - The intervention lasted only 6 weeks. - Executive function was assessed with selected Stroop task components rather than a broad cognitive battery. - The study did not include mechanistic measures explaining the cognitive effect. - Resistance-training exposure may have been too short to produce cognitive changes. ## Safety And Adherence - Participants were screened for cardiovascular, neurological, cognitive, and musculoskeletal risks. - Maximal exercise tests were ECG monitored. - No adverse-event outcomes were reported in the extracted article text. ## Original Sources - [PubMed](https://pubmed.ncbi.nlm.nih.gov/33137993/) (pubmed) - [DOI](https://doi.org/10.3390/brainsci10110796) (doi) - [PMC full text](https://www.ncbi.nlm.nih.gov/pmc/articles/PMC7693870/) (full text) ## Agent Guidance Preserve the paper-level scope of this note. Do not generalize beyond the population, protocol, measured outcomes, and limitations above.