# The time course of physiological adaptations to high-intensity interval training in older adults PMID: 33392430 Journal: Aging medicine (Milton (N.S.W)) Published: 2020-09-17 Authors: Herrod PJJ, Blackwell JEM, Boereboom CL, Atherton PJ, Williams JP, Lund JN, Phillips BE ## Question What is the time course of cardiorespiratory and physiological adaptations to the same reduced-exertion HIIT protocol in healthy older adults? ## Summary This study tested how quickly healthy older adults adapt to a supervised cycling HIIT program. Adults aged 65-85 completed the same 16.5-minute HIIT session three times per week for either 2, 4, or 6 weeks, while a control group did no intervention. Exercise tolerance improved after only 2 weeks, anaerobic threshold improved after 4 and 6 weeks, and VO2peak improved clearly after 6 weeks. Resting systolic blood pressure improved after 4 and 6 weeks, while body composition did not change. The protocol was fully supervised with continuous ECG monitoring, making it useful for dose-timing insight but not a direct unsupervised consumer template. ## Population - Healthy community-dwelling older adults aged 65-85. - Sample size: 40 - Age: 65-85 years - Sex: Not extracted - Fitness level: Recreationally active but not doing regular formal exercise - Health status: Healthy and medically screened ## Methodology - Non-randomized group comparison of 2-, 4-, and 6-week HIIT durations plus no-intervention control. - 2, 4, or 6 weeks of HIIT; control period 6 weeks. - Fully supervised exercise laboratory with cycle ergometer and continuous 12-lead ECG monitoring. - Controlled study design. ## Protocol - Reduced-exertion HIIT. - Modality: Cycle ergometer. - Work intervals: 1 min. - Recovery: 90 sec active recovery. - Sets or repetitions: 5 intervals. - Intensity: 90-110% of CPET peak power output. - Session duration: 16.5 min. - Frequency: 3 sessions/week. - Program length: 2, 4, or 6 weeks. - Progression: No progression extracted; protocol duration varied by group. - No-intervention control. - Program length: 6 weeks. ## Outcomes ### Exercise tolerance Status: improved Peak power improved after 2, 4, and 6 weeks of HIIT, with no change in controls. 2 weeks +15 W, 4 weeks +17 W, 6 weeks +16 W; all P<0.001. ### Anaerobic threshold Status: improved Anaerobic threshold improved after 4 and 6 weeks but not 2 weeks. 4 and 6 weeks both +1.9 mL/kg/min; both P<0.001. ### VO2peak Status: improved VO2peak improved only after 6 weeks. 6 weeks 23.8 to 26.8 mL/kg/min; P=0.046. ### Resting systolic blood pressure Status: improved Resting systolic blood pressure decreased after 4 and 6 weeks, not after 2 weeks or control. 4 weeks 140 to 132 mmHg, P=0.047; 6 weeks 143 to 134 mmHg, P=0.02. ### Body composition Status: no clear change No significant changes in lean mass, body fat percentage, or lean leg mass. No significant main time effect or group*time interaction. ## Practical Insights - For older adults, exercise tolerance can improve before VO2peak does. - A 5 x 1-min protocol three times weekly may need about 4 weeks for anaerobic-threshold changes and 6 weeks for VO2peak changes. - Short HIIT blocks should not be positioned as body-composition interventions based on this study. ## Limitations - Small groups. - Healthy older volunteers only. - Laboratory supervision and ECG monitoring limit consumer translation. - Adherence and adverse-event details were not clearly extracted. - Randomization status unclear from extracted text. ## Safety And Adherence - Sessions were fully supervised with continuous 12-lead ECG monitoring. - No adverse events were extracted from the full text. ## Original Sources - [PubMed](https://pubmed.ncbi.nlm.nih.gov/33392430/) (pubmed) - [DOI](https://doi.org/10.1002/agm2.12127) (doi) - [PMC full text](https://www.ncbi.nlm.nih.gov/pmc/articles/PMC7771560/) (full text) ## Agent Guidance Preserve the paper-level scope of this note. Do not generalize beyond the population, protocol, measured outcomes, and limitations above.