If you’ve ever watched a pro cyclist attack on a climb, only to settle back and recover while still maintaining a brutal pace, you’ve witnessed the physiological adaptation that over/under intervals build. These workouts are the secret weapon for developing lactate tolerance and the ability to surge repeatedly without blowing up. Unlike straightforward threshold intervals that teach you to hold steady power, over/unders force your body to produce lactate during the “over” portions, then immediately process it during the “under” segments—all while continuing to work at a demanding intensity. The result? You train your body to function efficiently in that uncomfortable zone where lactate is accumulating but you need to keep pushing.
Whether you’re preparing for criteriums with repeated attacks, hilly road races, or simply want to build the fitness to respond to surges on group rides, mastering over/under intervals will transform your ability to hurt—and recover—again and again. In this blog post, we show you how.
Table of Contents
The Physiology of Lactate Shuttling
Lactate is not just a waste product – it’s an active metabolic intermediary and fuel source. During high-intensity efforts (the “overs”), lactate production exceeds clearance capacity, causing accumulation in working muscles. The key adaptation from over/under training occurs during the “under” portions, where you’re working at a pace that still requires significant oxygen but allows your body to clear and utilize accumulated lactate.
Lactate shuttling refers to the process by which the body converts lactate produced during high-intensity exercise into energy. This process occurs in the mitochondria of muscle cells and is an important adaptation for endurance athletes. During the recovery intervals, lactate produced in fast-twitch muscle fibers is transported to slow-twitch fibers, the heart, and liver where it’s converted back to pyruvate and used aerobically for energy. This process trains your body’s MCT (monocarboxylate transporter) proteins, which become more efficient at shuttling lactate. The result is improved lactate clearance capacity – you can tolerate higher lactate levels and clear them more quickly.
Using lactate as fuel
Lactate contains nearly the same energy as glucose, and can be used as a fuel source by the body during exercise, particularly during high-intensity efforts. Training can improve the body’s ability to utilize lactate, which can enhance performance. When you train your body to efficiently convert lactate back to pyruvate, you’re essentially creating an additional fuel source during sustained efforts. Elite athletes have higher concentrations of MCT1 and MCT4 transporters, allowing them to shuttle lactate more effectively.
During the “under” intervals, your oxidative muscle fibers consume lactate as fuel, sparing glycogen. This is crucial for endurance events where glycogen preservation matters. The mitochondria in these fibers take up lactate and oxidize it through the Krebs cycle. Regular over/under training increases mitochondrial density and the enzymes necessary for this process, making your body more “lactate-tolerant” and efficient at using it as fuel rather than letting it accumulate.
Structuring the Interval
Intervals are a common training technique that involve alternating periods of high-intensity effort with periods of recovery. A effective over/under intervals typically follow these principles:
- “Over” intensity: 105-110% of FTP (threshold power)
- “Under” intensity: 85-95% of FTP
- Duration ratio: Usually 1:1 or 2:1 (over:under)
- Total interval length: 8-20 minutes of continuous work
- Recovery between sets: 5-10 minutes easy spinning
The “over” shouldn’t be so hard that you blow up; it should be sustainable in short bursts. The “under” isn’t true recovery – you’re still at tempo or sweet spot intensity, which is the sweet spot for lactate processing. The continuous nature without complete rest is what makes these so effective.
Example: 2 min @ 105% FTP / 2 min @ 90% FTP
The 2 min interval is a classic structure. Here’s how it works in practice:
Sample workout: 3 x 12 minutes (three sets of three 2-min over/2-min under cycles)
During each 12-minute block:
- Minutes 0-2: 105% FTP (over) – lactate accumulates
- Minutes 2-4: 90% FTP (under) – partial clearance while still working
- Minutes 4-6: 105% FTP (over) – accumulation resumes on already-elevated levels
- Minutes 6-8: 90% FTP (under) – clearance while fatigued
- Minutes 8-10: 105% FTP (over) – the hardest surge
- Minutes 10-12: 90% FTP (under) – fighting to maintain form
The brilliance is that each successive “over” gets harder because you’re not fully clearing lactate during the “under” portions. By the third or fourth surge, you’re riding at 105% FTP with elevated lactate levels, training your body to function in this challenging physiological state.
Mental Toughness: The "Burning" Sensation
Over/unders are as much a mental workout as physical. The “”burning”” sensation during intense exercise is often a mental challenge for athletes. This comes from hydrogen ion accumulation and the metabolic stress of incomplete recovery. Unlike VO2 max intervals where you get full rest, over/unders teach you to embrace discomfort continuously.
Mental strategies:
- Focus on the under: Treat each “under” as active recovery, focusing on smooth pedaling and controlled breathing
- Break it into chunks: Count down individual intervals rather than the whole set
- Embrace the burn: Reframe the sensation as productive stress – you’re building lactate tolerance
- Cadence focus: Maintain steady cadence (typically 85-95 rpm) to create rhythm and distraction
- Acceptance: The third and fourth “overs” in a set will hurt – expect it and accept it
Developing mental toughness can help you push through this discomfort and maintain performance. This workout trains your brain to drill through those periods of high stress, crucial for breakaway efforts, hard climbs, or closing gaps in races. Techniques like visualization, positive self-talk, and mindfulness can be helpful.
Progressing Over/Unders Through a Season
Over/under intervals involve alternating between two different intensity levels (e.g., above and below lactate threshold). Some sample training below:
Base/Early Build (Weeks 1-4):
- 2-3 sets of 8 minutes (2 min over/2 min under x 2)
- Over: 103-105% FTP
- Focus on form and technique
Mid Build (Weeks 5-8):
- 3 sets of 12 minutes (2 min over/2 min under x 3)
- Over: 105-108% FTP
- Increase intensity slightly
Peak/Specialty (Weeks 9-12):
- 3-4 sets of 12-16 minutes
- Vary the structure: try 3 min over/1 min under or 1 min over/3 min under
- Over: 108-110% FTP
- Add race-specific variations (standing efforts, terrain simulation)
Maintenance/Race Phase:
- 2 sets of 10-12 minutes
- Maintain intensity but reduce volume
- Use as quality maintenance during event weeks
Progressing these intervals over the course of a season can help build fitness and prepare for specific race demands.
Indoor Trainer vs. Outdoor Execution
Indoor trainers and outdoor riding both have their advantages. Indoor training allows for controlled conditions and precise monitoring of effort, while outdoor riding offers variety and real-world conditions. A balanced approach that incorporates both can be beneficial for cyclists.
Indoor Advantages:
- Perfect power control – hit exact targets every interval
- No traffic, stoplights, or terrain interruptions
- Controlled environment for consistent pacing
- Easier to focus on internal sensations and form
- Data collection is cleaner for tracking progress
Indoor Challenges:
- Monotonous and mentally draining
- Heat accumulation (use fans!)
- No momentum or coasting – continuous resistance
- Can feel harder than equivalent outdoor effort
Outdoor Advantages:
- More engaging and mentally sustainable
- Natural cooling from airflow
- Momentum helps through intervals
- More race-specific neuromuscular patterns
- Better for practicing position changes and standing efforts
Outdoor Challenges:
- Finding appropriate terrain (steady climbs or flat roads)
- Traffic and interruptions
- Wind and gradient affect power consistency
- Harder to nail exact intervals
Recommendations:
- Start indoors to learn the feel and dial in pacing
- Progress to outdoor execution on steady climbs or quiet roads
- Use indoor for precise build phase work
- Use outdoor 4-6 weeks before goal events for specificity
- If outdoor, find a 3-5% climb or long flat section with minimal interruptions
Embracing the Burn for Real-World Performance
Over/under intervals aren’t just another workout to check off your training plan—they’re a direct simulation of the physiological demands you’ll face in competitive cycling and hard group rides. The beauty of these intervals lies in their specificity: racing rarely involves steady efforts at threshold. Instead, it’s a constant dance of surges above threshold followed by incomplete recovery, exactly what over/unders train you to handle. Yes, they’re uncomfortable. Yes, the third and fourth “over” segments will test your resolve. But that discomfort is precisely what builds the lactate clearance capacity, mental fortitude, and muscular endurance that separate riders who can only hold steady power from those who can attack, respond, and attack again.
Start conservatively, progress intelligently through the season, and don’t be afraid to experiment with different interval structures as you dial in what works for your physiology. When race day arrives and you need to close a gap after a hard climb or respond to a late-race attack, your body will thank you for all those minutes spent dancing between suffering and survival.
Related Cycling and Training Content
For further cycling and training tips, you can also listen to the Ask The Pedalist podcast, where we discuss common cycling topics.
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