Cardiorespiratory fitness is among the most powerful predictors of long-term health available in medicine today, and VO2 max is how we measure it. This post focuses on what most people want to know after learning that: how do you improve it?
VO2 max is highly trainable, more trainable in many ways than people over 40 expect. The declines that come with age are real, but they are not fixed. With a structured, evidence-based training approach, meaningful improvements in VO2 max are achievable at any age, and the health return on those improvements is well-documented.
This post lays out the protocol we built for Aeternitas members: the physiology behind it, the training zones, the weekly structure, and the specific considerations that make the over-40 context distinct.
Why VO2 Max Declines After 40, and Why It Does Not Have to Decline as Fast
VO2 max decline is not a flat, uniform process. Large longitudinal studies show the rate accelerates with age: roughly 3–5% per decade in the 30s and 40s, steepening to 15–20% per decade after age 60–70 in sedentary adults. By age 50, a sedentary individual who had a VO2 max of 45 mL/kg/min at age 25 might be at 35 or below. By 65, they may be approaching the threshold where independent living and basic physical function become compromised.
The mechanisms behind this decline are well understood:
- Reduced maximum heart rate: Maximum heart rate declines roughly 1 beat per year after age 20. Lower max heart rate means lower maximum cardiac output at peak exercise.
- Decreased stroke volume: The heart’s ability to fill completely and eject maximally at peak effort diminishes with age in the absence of training.
- Reduced skeletal muscle mitochondrial density: Mitochondria, the cellular engines that extract oxygen and produce ATP, decline in density and efficiency in sedentary muscle over time.
- Loss of lean muscle mass (sarcopenia): Metabolically active muscle is the primary site of oxygen utilization. Less muscle means lower oxygen extraction capacity.
- Reduced blood volume: Plasma volume, which carries oxygen to working muscles, decreases with deconditioning.
Every one of these mechanisms is trainable. Physically active adults show an attenuated rate of decline compared to sedentary adults, and this difference is more pronounced with higher-intensity activity. In individuals who take a structured, progressive approach to training, the decline can be slowed further, and meaningful absolute improvements can be achieved well into the 60s and 70s.
The Two Training Modalities That Drive VO2 Max
The research on VO2 max improvement converges on a clear answer: the most effective program combines Zone 2 aerobic training as the foundation with high-intensity interval training (HIIT) as the accelerator. Each addresses a distinct physiological mechanism, and each is necessary.
Zone 2 Training: Building the Aerobic Engine
Zone 2 refers to sustained exercise at a moderate intensity, specifically at or below the first lactate threshold. In practical terms, this is the intensity at which you can hold a conversation but are clearly working: easy cycling, brisk walking, light jogging, or elliptical at a steady pace.
Zone 2 training contributes to mitochondrial biogenesis and fat oxidation adaptations, particularly when performed at higher volumes. Mitochondria are a central limiting factor for oxygen extraction in most non-elite adults. Building mitochondrial density is how you raise the ceiling on how much oxygen your muscles can use at any given intensity. It is worth noting that higher-intensity exercise also potently stimulates mitochondrial biogenesis; the optimal training intensity distribution depends on the individual’s volume, baseline, and goals.
Zone 2 training also supports fat oxidation capacity, the ability to efficiently burn fat as fuel at moderate intensities, which preserves glycogen for higher-intensity efforts and supports metabolic health.
For identifying Zone 2 without laboratory testing:
- Talk test: you can speak in complete sentences but would not want to sing
- Heart rate: roughly 60–70% of maximum heart rate (use 220 minus your age as a rough estimate of max heart rate)
- Perceived exertion: 4–6 on a 10-point scale, working but sustainable indefinitely
- Nasal breathing: if you are predominantly mouth breathing, you have likely exceeded Zone 2
Weekly Zone 2 target: 3–4 hours, accumulated in sessions of 45–90 minutes. Shorter sessions can be accumulated across the week. Consistency over weeks and months matters more than any single session duration.
High-Intensity Interval Training: Raising the Ceiling
While Zone 2 builds the mitochondrial infrastructure, high-intensity intervals (specifically VO2 max intervals, work performed at or above your second ventilatory threshold) are the stimulus that directly drives VO2 max upward.
At very high intensities, the oxygen delivery system faces maximum demand: the heart pumps as much blood as possible, the lungs oxygenate as rapidly as possible, and the muscles extract and use oxygen at maximal rate. This stimulus, applied repeatedly in interval format, drives cardiovascular adaptation.
The most evidence-supported HIIT protocol for VO2 max in adults:
- Interval duration: 3–8 minutes at approximately 90–95% of maximum heart rate
- Recovery: equal or slightly longer active recovery between intervals
- Volume: 4–6 intervals per session
- Frequency: 1–2 sessions per week; more is not better, as recovery is where adaptation occurs
- Classic protocol: 4 x 4-minute intervals at 90–95% max HR, 3-minute active recovery between intervals (the “Norwegian 4×4,” from Helgerud et al. 2007)
HIIT carries higher injury risk than Zone 2 training, particularly in individuals with cardiovascular risk factors or musculoskeletal vulnerabilities. A physician evaluation and a baseline VO2 max assessment are appropriate first steps before introducing high-intensity work. At Aeternitas, HIIT protocols are prescribed by your exercise physiologist after your baseline evaluation, not guessed at from an online template.
Strength Training: The Essential Complement
Resistance training does not directly raise VO2 max in the same way as aerobic training, but it creates the physiological substrate on which VO2 max improvements are built. Specifically, it:
- Preserves and builds lean muscle mass, the primary site of oxygen extraction
- Improves insulin sensitivity, metabolic health, and body composition, all of which support aerobic adaptation
- Reduces injury risk during high-intensity aerobic work: stronger muscles, tendons, and joints tolerate interval training better
- Independently predicts longevity: grip strength and leg strength are among the strongest functional predictors of all-cause mortality
Minimum effective dose for strength: 2–3 sessions per week, targeting all major muscle groups, with progressive overload over time. For adults over 40, protein intake in the range of 1.6–2.0 grams per kilogram of body weight per day supports muscle protein synthesis; most adults significantly undereat protein for muscle maintenance.
A 12-Week VO2 Max Improvement Protocol for Adults Over 40
The following is a representative training structure. Individual prescriptions at Aeternitas are calibrated to your baseline VO2 max, cardiovascular risk profile, musculoskeletal status, and available time. Do not begin a HIIT protocol without a physician evaluation first.
| Phase / Weeks | Training Structure |
|---|---|
| Weeks 1–4: Foundation | Zone 2 only. 3–4 sessions per week, 45 minutes each. Build the aerobic base and establish training tolerance before introducing intensity. No HIIT in this phase. |
| Weeks 5–8: Introduction | Zone 2 (3 sessions per week, 45–60 min) plus HIIT x1 per week (4 x 4-minute intervals, 3-minute recovery). Strength training x2 per week throughout. |
| Weeks 9–12: Consolidation | Zone 2 (3 sessions per week, 60 min) plus HIIT x2 per week (4–6 x 4-minute intervals). Strength training x2–3 per week. Begin tracking perceived effort at Zone 2 pace; improvement shows as reduced effort for the same pace. |
| Month 4 onward: Progression | Re-test VO2 max at 3 months. Adjust protocol based on results and physician review. Progressive overload principle applied, gradually increasing volume and intensity as fitness improves. |
| Key metric: VO2 max re-test at 12 weeks | Expected improvement: approximately 10–15% in previously sedentary individuals; 5–10% in moderately active individuals. Results vary. The trend matters more than any single test. |
Recovery: The Missing Variable
For adults over 40, recovery is not a passive variable; it is an active training input. The adaptations that improve VO2 max occur during recovery, not during the session itself. Insufficient recovery is the primary reason most training programs fail to produce expected improvements.
Sleep: 7–9 hours per night. Growth hormone, released primarily during slow-wave sleep, supports cardiovascular and muscular adaptation. Poor sleep blunts training adaptations directly.
Protein and carbohydrate timing: Consuming protein within 2 hours of resistance training supports muscle protein synthesis. Carbohydrate replenishment after high-intensity sessions supports glycogen restoration and reduces cortisol elevation.
Heart rate variability (HRV): HRV monitoring, available through consumer wearables, provides a signal of recovery status. Low HRV on a training morning suggests the body is not recovered; a light Zone 2 session or rest is more appropriate than a planned HIIT session.
Training load management: More is not better for VO2 max. Over-training drives cortisol elevation, impairs adaptation, and in adults over 40 significantly elevates injury risk. Two HIIT sessions per week is the ceiling for most non-athletes.
Tracking Progress
The only reliable way to know whether your training is improving your VO2 max is to measure it before and after. Consumer fitness trackers offer estimates, but their error margins are clinically significant.
At Aeternitas, VO2 max is measured directly at baseline and re-tested annually (or more frequently when a specific training intervention is in progress). Between formal tests, the following training metrics serve as useful proxies for improvement:
- Reduced perceived effort at a fixed Zone 2 pace: the same speed or resistance feels easier over time
- Lower heart rate at the same absolute workload: a direct reflection of improved cardiac efficiency
- Improved recovery rate post-interval: heart rate drops more rapidly in the first 60–90 seconds after a hard effort
- Increased time-to-fatigue at a fixed intensity: you can sustain Zone 2 effort longer before it begins to feel like Zone 3
Frequently Asked Questions
Can you improve VO2 max after 40?
Adults in their 50s and 60s have demonstrated meaningful improvements in VO2 max following structured training programs. The rate of improvement may be somewhat slower than in younger adults, but the capacity for adaptation remains real at any age. The key is a structured approach, consistent execution, and adequate recovery.
How long does it take to improve VO2 max?
Measurable improvements are typically seen within 6–8 weeks of consistent training. Meaningful improvements, moving up a fitness category, generally occur within 12–16 weeks with a structured protocol. Significant gains take 6–18 months of sustained effort.
Is HIIT safe for adults over 40?
HIIT is safe for most adults over 40 with a physician evaluation first, an adequate aerobic base, and appropriate progressive introduction. The primary risks are cardiovascular events during exercise (rare but higher in high-intensity work without prior screening) and musculoskeletal injury. A baseline VO2 max test, a cardiovascular risk assessment, and an exercise physiologist-designed protocol reduce both risks substantially.
Should I do Zone 2 or HIIT to improve VO2 max?
Both, in the appropriate ratio. Zone 2 builds the mitochondrial foundation; HIIT applies the direct VO2 max stimulus. An effective approach for adults over 40 is to perform the majority of training volume in Zone 2 (roughly 80%) with high-intensity work making up the remainder. Neither in isolation is as effective as the combination, though the evidence for specific ratios is strongest in well-trained endurance athletes; for recreational adults, the exact distribution matters less than consistency and progressive overload.
How do I get a proper VO2 max test in Charlotte, NC?
Aeternitas Health offers clinically supervised VO2 max testing by a clinical exercise physiologist as part of the evaluation day in Charlotte, NC. Exercise prescriptions are built from your measured VO2 max, cardiovascular risk profile, and individual goals.
Dr. Corey Helton, MD is the founder of Aeternitas Health, a physician-led longevity and precision medicine practice in Charlotte, NC. He founded Aeternitas to practice anticipatory, data-driven medicine aimed at long-term outcomes rather than present symptoms alone. Aeternitas is a direct-pay practice with a deliberately limited panel.
References
- Letnes JM, Dalen H, Aspenes ST, et al. Age-Related Change in Peak Oxygen Uptake and Change of Cardiovascular Risk Factors. The HUNT Study. Prog Cardiovasc Dis. 2020;63(6):730–737. doi:10.1016/j.pcad.2020.09.002
- Ara I, Gómez-Cabrera MC, Garatachea N. Exercise as a Therapy for Successful Aging. Scand J Med Sci Sports. 2025;35(9):e70133. doi:10.1111/sms.70133
- Bahls M, Ittermann T, Ewert R, et al. Physical Activity and Cardiorespiratory Fitness — A Ten-Year Follow-Up. Scand J Med Sci Sports. 2021;31(3):742–751. doi:10.1111/sms.13882
- Storoschuk KL, Moran-MacDonald A, Gibala MJ, Gurd BJ. Much Ado About Zone 2: A Narrative Review Assessing the Efficacy of Zone 2 Training for Improving Mitochondrial Capacity and Cardiorespiratory Fitness in the General Population. Sports Med. 2025. doi:10.1007/s40279-025-02261-y
- MacInnis MJ, Gibala MJ. Physiological Adaptations to Interval Training and the Role of Exercise Intensity. J Physiol. 2017;595(9):2915–2930. doi:10.1113/JP273196
- Fiorenza M, Gunnarsson TP, Hostrup M, et al. Metabolic Stress-Dependent Regulation of the Mitochondrial Biogenic Molecular Response to High-Intensity Exercise in Human Skeletal Muscle. J Physiol. 2018;596(14):2823–2840. doi:10.1113/JP275972
- Helgerud J, Høydal K, Wang E, et al. Aerobic High-Intensity Intervals Improve VO2max More Than Moderate Training. Med Sci Sports Exerc. 2007;39(4):665–671. doi:10.1249/mss.0b013e3180304570
- Bækkerud FH, Solberg F, Leinan IM, et al. Comparison of Three Popular Exercise Modalities on V̇O2max in Overweight and Obese. Med Sci Sports Exerc. 2016;48(3):491–498. doi:10.1249/MSS.0000000000000777
- Stöggl T, Sperlich B. Polarized Training Has Greater Impact on Key Endurance Variables Than Threshold, High Intensity, or High Volume Training. Front Physiol. 2014;5:33. doi:10.3389/fphys.2014.00033
- Silva Oliveira P, Boppre G, Fonseca H. Comparison of Polarized Versus Other Types of Endurance Training Intensity Distribution on Athletes’ Endurance Performance: A Systematic Review With Meta-Analysis. Sports Med. 2024;54(8):2071–2095. doi:10.1007/s40279-024-02034-z
- Rivera-Köfler T, Varela-Sanz A, Padrón-Cabo A, Giráldez-García MA, Muñoz-Pérez I. Effects of Polarized Training vs. Other Training Intensity Distribution Models on Physiological Variables and Endurance Performance in Different-Level Endurance Athletes: A Scoping Review. J Strength Cond Res. 2025;39(3):373–385. doi:10.1519/JSC.0000000000005033
- Chodzko-Zajko WJ, Proctor DN, Fiatarone Singh MA, et al. American College of Sports Medicine Position Stand: Exercise and Physical Activity for Older Adults. Med Sci Sports Exerc. 2009;41(7):1510–1530. doi:10.1249/MSS.0b013e3181a0c95c
- Amaro-Gahete FJ, De-la-O A, Jurado-Fasoli L, et al. Changes in Physical Fitness After 12 Weeks of Structured Concurrent Exercise Training, High Intensity Interval Training, or Whole-Body Electromyostimulation Training in Sedentary Middle-Aged Adults: A Randomized Controlled Trial. Front Physiol. 2019;10:451. doi:10.3389/fphys.2019.00451
- Milanović Z, Sporiš G, Weston M. Effectiveness of High-Intensity Interval Training (HIT) and Continuous Endurance Training for VO2max Improvements: A Systematic Review and Meta-Analysis of Controlled Trials. Sports Med. 2015;45(10):1469–1481. doi:10.1007/s40279-015-0365-0
- Morton RW, Murphy KT, McKellar SR, et al. A Systematic Review, Meta-Analysis and Meta-Regression of the Effect of Protein Supplementation on Resistance Training-Induced Gains in Muscle Mass and Strength in Healthy Adults. Br J Sports Med. 2018;52(6):376–384. doi:10.1136/bjsports-2017-097608
- Jäger R, Kerksick CM, Campbell BI, et al. International Society of Sports Nutrition Position Stand: Protein and Exercise. J Int Soc Sports Nutr. 2017;14:20. doi:10.1186/s12970-017-0177-8
- Nunes EA, Colenso-Semple L, McKellar SR, et al. Systematic Review and Meta-Analysis of Protein Intake to Support Muscle Mass and Function in Healthy Adults. J Cachexia Sarcopenia Muscle. 2022;13(2):795–810. doi:10.1002/jcsm.12922
- LaMonte MJ, Hyde ET, Nguyen S, et al. Muscular Strength and Mortality in Women Aged 63 to 99 Years. JAMA Netw Open. 2026;9(2):e2559367. doi:10.1001/jamanetworkopen.2025.59367
Medically reviewed by Dr. Corey Helton, MD. Review date: June 2026.
This article is for general educational purposes only. It is not medical advice and is not a substitute for diagnosis or treatment by a qualified physician. Reading it does not create a physician-patient relationship with Aeternitas. Talk with your own physician before making changes to your health, medications, supplements, or care.
