Introduction
High-intensity interval training (HIIT) is widely praised for its ability to enhance endurance performance. However, a deeper look reveals that HIIT should not be viewed as isolated “epic” workouts. According to Stephen Seiler's 2024 paper “It’s about the Long Game, Not Epic Workouts: Unpacking HIIT for Endurance Athletes,” the most effective use of HIIT is part of a broader, long-term strategy that emphasises balance, consistency, and integration into an athlete's overall training load.
Seiler challenges the common tendency to treat HIIT as a magic bullet for maximising VO2 max or heart rate (HR) response. Instead, he advocates for seeing HIIT as part of a balanced training approach. This blog will break down the key findings of Seiler’s paper, providing practical tips, training ideas, and insights for serious athletes who are looking to leverage HIIT for long-term endurance success.
Understanding HIIT in the Context of Endurance Training
Many athletes approach HIIT as a way to push themselves to their limits, chasing maximal VO2 max or lactate threshold (LT2) improvements. However, Seiler’s research stresses that successful endurance athletes integrate HIIT into their training without over-emphasising its role. In fact, most of their training volume—about 80%—is performed at intensities below the first lactate turn point (LT1), with HIIT making up a smaller but strategically important portion of the total load.
Key points from Seiler’s paper:
HIIT is essential, but it’s not the main driver of long-term success.
A majority of successful endurance athletes' training is low intensity (<LT1).
There is no "optimal" HIIT prescription that works for everyone.
What Makes HIIT Effective?
The paper identifies three critical factors for designing effective HIIT sessions:
Work Bout Duration: How long you’re pushing in each interval.
Accumulated Work Duration (AWD): The total duration of high-intensity work in a session.
Recovery Duration: How long you rest between intervals.
Seiler points out that extending the duration of each work bout significantly alters an athlete’s physiological response. For example, in studies with well-trained cyclists, sessions with longer intervals (e.g., 4 x 16 minutes) produced lower peak exertion but sustained higher power outputs over time compared to shorter bouts like 4 x 4 minutes.
Practical Training Sessions Based on Seiler's Findings
Here are some actionable HIIT training sessions that align with the research findings:
1. Threshold Focused HIIT Session
Goal: Build endurance and increase time spent at or near the lactate threshold.
Workout: 4 x 8 minutes at 90% of VO2 max with 2 minutes of easy spinning or light jogging in between.
Why It Works: According to Seiler, such sessions balance intensity and accumulated work, allowing athletes to spend more time near their physiological limits without overloading their system.
2. Lactate Clearance Session
Goal: Improve the body’s ability to clear lactate efficiently.
Workout: 3 x 13 x 30 seconds hard, 15 seconds easy, with 3 minutes of rest between sets.
Why It Works: Short intervals like these maximise the central cardiovascular response while teaching the muscles to better handle lactate accumulation. This mirrors real-world race conditions.
3. Sustained VO2 Max Training
Goal: Increase VO2 max without maxing out perceived exertion.
Workout: 4 x 16 minutes at LT2 with 4-minute recovery between each interval.
Why It Works: Longer intervals allow athletes to achieve near-maximal heart rate without overwhelming perceived exertion, enabling consistent quality sessions.
HIIT Is an Optimisation, Not a Maximisation Problem
One of the standout concepts from Seiler’s work is the idea that endurance training should be viewed as an "optimisation" problem, not a maximisation one. This means that chasing the hardest, most intense session isn’t necessarily going to lead to the best long-term results.
Key Takeaways:
Balance: Successful athletes mix HIIT with substantial volumes of low-intensity training (LIT).
Recovery Matters: The body’s adaptation from HIIT happens over time. Athletes need to allow for adequate recovery to maximize performance improvements.
Avoid Burnout: Too much HIIT without enough LIT or recovery can lead to overtraining.
The Science Behind HIIT Adaptation
Seiler dives into the molecular responses triggered by HIIT sessions. Each bout of HIIT training activates different cellular pathways responsible for enhancing endurance. These include:
AMP-activated protein kinase (AMPK): Helps improve energy regulation.
Mitochondrial biogenesis: Increases the number and efficiency of mitochondria, which are key for long-term endurance performance.
Importantly, Seiler notes that the body adapts to HIIT over time, and that initial large responses to HIIT training can plateau. Therefore, continually increasing the intensity or volume of HIIT is not necessary. Instead, focusing on optimising the balance between high-intensity and low-intensity training is key for sustained endurance improvement.
Case Studies: How Elite Athletes Use HIIT
Seiler highlights real-world examples of elite athletes successfully integrating HIIT into their training:
Norwegian XC Skiers: Athletes performed approximately 100 “hard” sessions a year (including races, threshold, and HIIT) within a total of 500 sessions, showing that HIIT is just one part of a broader training spectrum.
Elite Cyclists: In studies of elite cyclists, those who spent more time on controlled, submaximal efforts interspersed with targeted HIIT saw greater long-term gains than those who consistently pushed for maximal sessions.
Conclusion: How to Make HIIT Work for You
The key takeaway from Seiler’s paper is that HIIT should not dominate your training but rather complement it. Incorporating well-structured HIIT sessions into an overall plan that emphasises low-intensity training (LIT) and smart recovery will yield the best results over time.
Actionable Tips:
Plan HIIT strategically: Aim for 1–2 sessions per week, focusing on quality, not just intensity.
Balance with low-intensity work: Remember, 80% of your training should be below LT1.
Monitor recovery: Give yourself time to recover fully from HIIT sessions to maximize the benefits.
HIIT isn’t about the hardest workout; it’s about the long-term strategy. Adopt this mindset and enjoy the sustained endurance success it brings.
By applying these principles from Seiler's research, athletes can effectively integrate HIIT into their routines, ensuring they optimise both performance and recovery, leading to better endurance outcomes over the long haul.
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