The Power of 30/30s, 30/15s & 40/20s: The VO₂max Interval Formats Every Cyclist Should Use
When it comes to improving VO₂max, few cycling workouts are as effective—or as misunderstood—as 30/30s, 30/15s, and 40/20s. These short, repeatable, high-oxygen-demand intervals have become staples for endurance cyclists, triathletes, and time-crunched riders who want maximum performance with minimal training time.
These formats work because they keep you near your VO₂max for longer, without the massive fatigue caused by long 3–5 minute efforts.
Below, we break down the differences, how to use each format, and how to fuel them for consistent performance.
Why Work-to-Rest Ratio Matters
30/30s (1:1 ratio)
Intensity: 130–140% FTP “on”, 50–60% FTP “off”
Set length: 8–10 minutes
RPE: 8–9/10
The classic format. Hard enough to elevate oxygen uptake, but forgiving enough to accumulate high-quality intervals without blowing up. Many cyclists find these deliver the highest total quality work across a training block.
30/15s (2:1 ratio)
A more advanced variation. Slightly more demanding than 30/30s but still highly repeatable. These are ideal for riders already comfortable at high intensity.
40/20s (2:1 ratio)
Intensity: 120–130% FTP “on”, 50–60% FTP “off”
Set length: 8–10 minutes
RPE: 8–9/10
40/20s often spike VO₂ faster because the “on” duration is longer. They’re a favourite among riders chasing peak aerobic power and punching power for climbs and surges.
What Delivers the Biggest Gains?
The truth is simple:
The best interval format is the one you can stick with week after week.
Consistency beats intensity every time.
If 30/30s feel smooth and repeatable, use them.
If you respond better to longer “on” periods, try 40/20s.
If you want a harder challenge, 30/15s provide a potent stimulus.
How to Fuel These VO₂max Sessions
High-intensity intervals depend on muscle glycogen, fast carbohydrate delivery, and stable electrolytes. Under-fuelled sessions lead to power drop-off and lower oxygen uptake.
Use these guidelines:
Before the session (15–20 min prior)
Take 20–30g fast carbohydrates.
Examples:
• Energy gel
• Energy chews
• Half a high-carb bar
• Sports drink with electrolytes and carbs
This raises blood glucose, improving oxygen utilisation and repeatability.
During the session
Sip carbohydrates + electrolytes between sets. Aim for:
• 20–40g carbs per hour for shorter sessions
• Electrolytes (200–500mg sodium) depending on sweat rate
Carbs maintain power output. Electrolytes support focus and neuromuscular control.
This is where products like high-carb drink mixes, energy gels, and hydration solutions are most effective—especially dual-source carbohydrate fuels.
Who Should Use VO₂max Intervals?
These sessions are ideal for:
• Cyclists building race-season fitness
• Triathletes wanting higher aerobic ceilings
• Time-crunched riders targeting maximum training impact
• Anyone wanting better performance on climbs, surges, and race moves
• Runners and multisport athletes looking to increase VO₂max safely
The Takeaway
VO₂max gains aren’t about suffering. They’re about repeated exposure to the right stimulus.
Choose the interval format that keeps your cadence smooth, your technique controlled, and your effort repeatable.
Pair that with smart endurance sports nutrition—carbohydrates, hydration, and electrolytes—and you’ll unlock breakthroughs in power, efficiency, and overall performance.