Optimizing VO₂max: Comparing the Effects of Different Exercise Modalities

In our companion article, Why Everyone Is Talking About VO₂max as the Ultimate Longevity Maker, we introduced VO₂ max as one of the most powerful predictors of longevity and healthspan available to us – and why knowing and improving it is a clinical priority, not just an athletic one. Here, we go deeper: breaking down the evidence on which exercise modalities most effectively raise VO₂ max, how training intensity and volume interact, and how to structure a practical, sustainable weekly program that works for where you are right now.

Different exercise modalities improve VO₂max to varying degrees, with intensity playing a key role. Among healthy young to middle-aged adults, aged 18-45 with a mean baseline VO2max of approximately 41 mL/kg/min, high-intensity interval training (HIIT) produces greater gains in VO₂max compared to moderate-intensity continuous training (MICT), though both elicit meaningful improvements compared to no exercise.¹ Among patients with established cardiovascular disease, (CVD) water-based exercise has also demonstrated meaningful improvements in peak VO₂. ²  

• HIIT: Improvement in VO₂max is +5.5 mL/kg/min vs. no-exercise control (healthy adults, ages 18–45; training duration ≥2 weeks)

• Robust gains are observed with programs lasting 6–13 weeks, ≥3 days/week, and ≥10 minutes of high-intensity work per session.³
• High volume (15 min or more), long intervals (≥2 min) HIIT performed for ≥4–12 weeks produce the largest VO₂max gains, outperforming both short intervals  (≤30 s) and low-volume (≤5 min) protocols when compared to both control groups and moderate-intensity continuous training (MICT).⁴
• Continuous endurance training: Improvement in VO₂max is +4.9 mL/kg/min vs. no-exercise control (healthy adults, ages 18–45; training duration ≥2 weeks.¹

• Typical protocols use intensities of 50–75% VO₂ reserve (approximately 60–75% HRmax – maximum heart rate), 30–60 minutes per session, 3–5 days/week.⁵
• There were possibly greater improvements at a younger age (additional increase of 2.4 mL/kg/min), longer intervention duration (additional 2.2 mL/kg/min), and lower baseline fitness (additional 1.4 mL/kg/min).¹
• Water-based exercise: +3.4 mL/kg/min vs. no-exercise control (CAD patients; systematic review and meta-analysis) ²
• Resistance training: +1.89 mL/kg/min (95% CI: 1.21–2.57) vs. no-exercise control (healthy adults >60 years; 2–3 sessions/week for 24 weeks) ⁶

While HIIT may provide a stronger stimulus, long-term adherence and cumulative training volume are equally important for sustained improvements. 

Key takeaways

• Higher intensity → greater VO₂max gains
• Moderate training → sustainable and effective
• Combination → optimal long-term approach

HIIT vs Zone 2 Training

There has been considerable interest in Zone 2 (moderate-intensity) training in recent years. The evidence, however, consistently shows that higher intensities produce larger VO₂max improvements when total work is equated.

A landmark 6-week randomized controlled trial (RCT) comparing matched exercise volumes found that near-maximal interval training (95% VO₂R; 5×5 min intervals, 3 days per week) increased VO₂max by 20.6%, vigorous intensity (75% VO₂R; 40-minute sessions, 4 days per week) by 14.3%, and moderate-intensity training (50% VO₂R; 60-minute sessions, 4 days per week) by 10.0%. ⁷

Notably, a volume-matched 8-week RCT in healthy moderately trained males found that neither long slow distance training (70% HRmax) nor lactate threshold training (85% HRmax) produced any significant improvement in VO₂max, while high-intensity interval groups training at 90-95% HRmax improved VO₂max by 5.5–7.2%.⁸

A 2024 randomized clinical trial found that HIIT produced the greatest change in  VO₂max, while moderate-intensity exercise (zone 2) produced a modest increase in VO₂max after 6 weeks of training. ⁹

Key takeaways

• Near-maximal intensity (HIIT): +20.6% VO₂max – 95% VO₂R; 5×5-min intervals with 5-min active recovery at 50% VO₂R; 3 sessions/week ⁷
• Vigorous intensity: +14.3% VO₂max – 75% VO₂R; continuous; 40 min/session; 4 sessions/week ⁷
• Moderate intensity (zone 2): +10.0% VO₂max – 50% VO₂R; continuous; 60 min/session; 4 sessions/week ⁷

Zone 2 Training: Effective for Most, but Not a Universal Prescription 

Zone 2 training– steady, sustainable aerobic exercise where you can still hold a conversation but feel like you are working – can meaningfully improve VO₂max, but its effectiveness depends significantly on baseline fitness and training volume. Your baseline fitness level sets the bar for how hard you need to work, because the minimum intensity required to drive VO2max adaptation rises as fitness improves. The fitter the individual, the greater the intensity needed to provoke adaptation. This means that Zone 2 is not a universal prescription – it is a moving target. For someone at the lower end of the fitness spectrum, Zone 2 effort may be appropriate or exceed for what is needed to drive adaptation, while for a well-trained individual, it may not be enough. Understanding where you fall on that spectrum starts with knowing your VO₂max and whether it is a true reflection of your aerobic ceiling, or a snapshot of a single effort under imperfect conditions. ¹⁰ 

How Fitness Level Changes What Zone 2 Can Do for You

If an individual’s VO₂max has been confirmed as a true maximal value and falls below 40 ml/kg/min, their cardiovascular system is at a stage where even light exercise constitutes a meaningful physiological challenge. Intensities as low as 30% VO₂ reserve – roughly the effort of a comfortable walk, a leisurely cycle, or easy swimming laps – can produce real and meaningful improvements in aerobic capacity. This sits at or below the lower boundary of what most people think of as Zone 2, yet at this fitness level it likely provides sufficient overload to drive genuine adaptation.

An important note: “comfortable walk” and “leisurely cycle” are relative descriptions. For someone who has been sedentary, this is an appropriate starting point. For someone who has been training consistently, these same activities may feel like no work at all and will carry no meaningful training stimulus. Use this as a starting point for a conversation with your healthcare provider, not as a self-directed protocol. ¹¹

If an individual’s VO₂max sits above 40 mL/kg/min, their body has adapted to effort and needs a bigger challenge to keep improving. A minimum of 45% VO₂ reserve is typically required to elicit further gains – an effort where you are breathing noticeably harder, able to speak in short sentences but not hold a comfortable conversation. ¹²  

Think: cycling at a pace that requires attention and consistent effort, running at a tempo where you can speak but only in clipped, deliberate phrases rather than full flowing sentences, rowing at a sustained moderate pace, swimming with focused effort, hiking uphill with a pack. True Zone 2 (roughly 60-70% HRmax or 40-60% VO₂R) generally meets this threshold, but only when sustained for adequate duration. Easy Zone 2 that felt challenging months ago may no longer be enough. ¹³ 

Volume matters just as much as intensity. Even at lower intensities, Zone 2 training can produce large improvements in VO₂max, but only if you do enough of it. Moderate intensity continuous training performed at approximately 60–70% of VO₂max has been shown to produce a net improvement of approximately 3.78 mL/kg/min – a 16% gain – in sedentary older adults across controlled trials, with greater improvements associated with programs lasting more than 20 weeks. ¹⁴

For sedentary individuals specifically, moderate-intensity training alone produces meaningful aerobic gains, confirming that you do not need high-intensity sessions to meaningfully develop your aerobic engine when you are starting from a lower fitness baseline. ¹⁵ 

The catch is that “sufficient volume” means considerably more than the 20-30 minute sessions most people associate with Zone 2 training. The studies supporting these large improvements typically involve 45-60 minutes per session, 3-5 days per week, sustained over at least 13-20 weeks – totaling 150-300+ minutes per week. 

Volume is the mechanism that compensates for lower intensity: if you are not pushing as hard, you need to accumulate more total time to deliver the same adaptive signal to your heart and lungs. ¹⁶ 

While Zone 2 training provides meaningful cardiovascular and metabolic benefits and can contribute to improvements in VO₂max – particularly in sedentary or less-trained individuals – it is not the most effective standalone strategy for maximizing VO₂max.

Evidence suggests that higher-intensity exercise, particularly interval training performed near an individual’s VO₂max, produces larger improvements in cardiorespiratory fitness by providing a stronger stimulus to both central adaptations (heart function and stroke volume) and peripheral adaptations (muscle oxygen utilization).

Zone 2 remains an important foundational component of an exercise program due to its accessibility, sustainability, and ability to build aerobic capacity, but relying on Zone 2 alone is unlikely to produce optimal VO₂max outcomes. A well-rounded program that incorporates both lower-intensity aerobic training and strategically prescribed higher-intensity intervals appears to be the most effective approach for maximizing cardiorespiratory fitness.¹⁷

The takeaway is straightforward: match your Zone 2 volume and intensity to where your fitness is right now – and be willing to adjust both as you improve, with the guidance of a skilled professional. If you are just starting out, moderate-intensity training at sufficient volume is highly effective. If you have been training consistently, you will need to either increase volume substantially, work closer to the upper boundary of Zone 2, or incorporate higher-intensity sessions to keep your VO₂max progressing. ¹⁸

Evidence-Based Weekly Training Structure for VO₂max Development

The most effective approach to improving VO₂max combines aerobic base work, high-intensity stimulus, and strength training in a structure that is sustainable over months and years. The following framework reflects the weight of current evidence for healthy adults and those in supervised clinical programs.

Zone 2 Aerobic Base: 3-4 Sessions per Week, 30-45 Minutes

The aerobic foundation of any VO₂max program is built through consistent moderate-intensity aerobic work. The recommended structure is 3-4 sessions per week of 30-45 minutes at Zone 2 intensity. Modality is secondary to consistency: walking, cycling, swimming, rowing, or any rhythmic aerobic activity achieves the same physiological stimulus when performed at the correct intensity.^{19  20} 

One practical note going further: training zone terminology is not standardized across the literature or among providers and label the “Zone 2” in particular is used inconsistently.  Some clinicians and coaches define Zone 2 as an effort easy enough to hold a relaxed conversation; others define it as hard enough that conversation becomes noticeably effortful.  Throughout this article, Zone 2 refers to the intensity described above – conversational but genuinely effortful, with audibly elevated breathing. We encourage you to clarify definitions with any provider or coach you are working with, since the same label can mean meaningfully different things depending on the source. ²¹

Zone 2 sessions are also the primary vehicle for training volume accumulation, which is independently associated with cardiovascular health outcomes. ²² 

VO₂max Intervals (HIIT): 1-2 Sessions per Week

The high-intensity stimulus for VO₂max development is provided by 1-2 dedicated interval sessions per week, structured as follows:

• Effort duration: 3-5 minutes per interval at near-maximal aerobic intensity (RPE 17-19, ≥85-90% HRmax, unable to speak more than 1-2 words).^{23  24}
• Number of intervals: 3-6 efforts per session, depending on fitness level and goals.
• Recovery: Full recovery between efforts, equal to or greater than work duration, performed as complete rest or very light activity.
• Frequency: 1 session per week for beginners; 2 sessions for trained individuals with strong recovery capacity.²⁵

This structure is designed to maximize total time spent near VO₂max, which is the primary driver of cardiorespiratory adaptation. More than 2 HIIT sessions per week in non-athlete populations is generally associated with diminishing returns and increased injury risk. 

Strength training: 2–3 sessions per week:

Resistance training is a critically underappreciated component of VO₂max development and longevity. While it produces modest direct VO₂max improvements, its effects are additive through distinct physiological pathways.

Preservation of skeletal muscle mass:

VO₂max declines with age in part due to the progressive loss of skeletal muscle (sarcopenia). Sarcopenia preferentially strips away metabolically active muscle tissue, reducing the body’s capacity to extract and utilize oxygen during exercise. Research confirms skeletal muscle capillarization – the ability to build new blood vessels – and VO2max are both significantly lower in sarcopenic, older adults compared to non-sarcopenic peers, underscoring the direct link between muscle mass preservation and aerobic capacity. ²⁶  Resistance training helps preserve and build muscle mass, creating a larger and more metabolically active tissue base for oxygen utilization. Regular resistance exercise is a well-established and potent countermeasure against sarcopenic muscle loss and its benefits on mitochondrial function in aging skeletal muscle are increasingly recognized. ²⁷  This enhances the body’s ability to extract and use oxygen during exercise, through mechanisms distinct from cardiac function, thereby complementing the adaptations achieved through aerobic training.

Together, aerobic and resistance training target both determinants of VO₂max:

• Aerobic training → central (cardiopulmonary fitness)
• Resistance training → peripheral (oxygen extraction and muscle preservation)

The combination of aerobic and resistance training is consistently supported in the literature as the most comprehensive approach to VO₂max development, improving both cardiorespiratory and muscular determinants of aerobic capacity simultaneously – benefits that neither modality achieves alone. ²⁸ 

Seeking Personalized Care

At our practice, we include VO2max as part of our assessment. We encourage all of our patients to inquire about their VO2max and cardiometabolic fitness – and to explore personalized ways to improve it. Our team is here to guide and support you every step of the way. We are committed to providing the individualized care you deserve, helping you move forward with confidence and strength. You have the power to take charge of your health. We are here to partner with you to achieve your goals. To learn more about our medical, nutrition, and health coaching services, contact us at 646.627.8000, fill out this form for a complimentary discovery call, or email Bridget@drbojana.com

For more on VO2max, please see our article on How You Can Improve Your VO₂max: A Starting Point for Beginners.

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