What’s the Best Interval Training for Endurance Athletes? A Scientific and Practical Guide
Introduction
Interval training is a foundational component of endurance performance development. It allows athletes to target specific physiological systems by manipulating work-to-rest ratios, intensity, and duration. Numerous studies have demonstrated its effectiveness across various sports, with different interval formats yielding distinct adaptations that depend on the athlete's demands and the specific sport (Laursen & Jenkins, 2002; Seiler & Tønnessen, 2009). This paper explores the scientific basis behind common interval prescriptions, categorises them by physiological target, and offers practical application strategies within an evidence-informed coaching framework.
Physiological Basis of Interval Training
Interval training enhances performance by applying repeated bouts of high-intensity effort interspersed with recovery periods. These sessions target adaptations in both central and peripheral systems, including cardiac output, mitochondrial biogenesis, lactate buffering, neuromuscular recruitment, and capillary density (Midgley, McNaughton & Wilkinson, 2006). The effectiveness of a given interval format depends on how well it matches the desired adaptation and the athlete’s current training phase.
VO₂ Max Intervals
Purpose and Mechanism
VO₂ max intervals aim to improve maximal oxygen uptake by maximising cardiovascular strain and oxygen delivery during work intervals. These efforts increase stroke volume and central cardiac efficiency (Midgley et al., 2006), often performed at 90–100% of VO₂ max intensity.
Recommended Formats
4 x 4 minutes at 95–100% VO₂ max, 2–3 minutes rest
5 x 5 minutes at 90–95% of max heart rate, 2 minutes rest
Practical Application
These intervals are most effective when athletes already possess a strong aerobic base and are targeting ceiling improvements. They are commonly applied during specific preparation phases in endurance sports, particularly in disciplines that require repeated high-intensity efforts, such as cross-country or Enduro mountain biking. Wisloff et al. (2007) demonstrated superior cardiovascular adaptations from 4 x 4-minute intervals compared to steady-state training of longer duration.
Lactate Threshold (LT2) Intervals
Purpose and Mechanism
Threshold intervals target the athlete’s ability to sustain high submaximal intensities, improving lactate clearance and buffering capacity (Coyle, 1995). These efforts sit just below or around the lactate turnpoint (LT2), typically at 85–95% of maximal heart rate or 90–100% of functional threshold power (FTP).
Recommended Formats
3 x 12–15 minutes at 90% FTP or 85–90% HRmax, 3 minutes rest
4 x 8 minutes at 100% FTP, 2–3 minutes rest
Practical Application
Threshold training is especially relevant for athletes competing in events that require prolonged efforts at or near their anaerobic threshold. For example, mountain bike Enduro athletes benefit from threshold intervals during climbing stages or longer descents, where pacing near LT2 is required repeatedly throughout competition days. These intervals are often used during general preparation and early competition phases.
Anaerobic and Neuromuscular Intervals
Purpose and Mechanism
Short-duration, high-intensity intervals target the phosphocreatine system and recruit fast-twitch muscle fibres. These intervals promote neuromuscular efficiency, rate of force development, and sprint capacity, which are essential in disciplines involving repeated maximal efforts or rapid changes in intensity (Laursen & Jenkins, 2002).
Recommended Formats
8 x 30 seconds at 150% FTP or maximal effort, 3 minutes rest
10 x 1 minute at 120–130% FTP, 1–2 minutes rest
Practical Application
These intervals are highly taxing and require full recovery between repetitions to maintain quality. They are best reserved for late pre-season or in-season phases when anaerobic capacity and neuromuscular sharpness are performance priorities. Overuse may lead to excessive fatigue or diminished return due to central nervous system stress (Zemková, 2014).
Muscular Endurance and Tempo Intervals
Purpose and Mechanism
Longer intervals at sub-threshold intensity build muscular endurance and fatigue resistance by improving aerobic metabolism and capillarisation (Saunders et al., 2004). These intervals are typically performed at 75–85% of FTP or 70–85% of maximum heart rate.
Recommended Formats
3 x 20 minutes at 80–85% FTP, 5 minutes rest
Continuous tempo effort: 45–60 minutes at 75–85% HRmax
Practical Application
Muscular endurance intervals are often used in early phases of training to increase aerobic volume efficiently. They support an athlete’s ability to maintain output during longer training days or stage racing formats. In mountain biking, these intervals are also used to simulate sustained climbing and the demands of multi-hour races.
Periodisation and Integration
Interval training must be aligned with the athlete’s periodisation model. For example, aerobic and tempo intervals are prioritised in the base phase to develop general capacity, while VO₂ max and threshold work are introduced progressively in the build phase. High-intensity anaerobic intervals are typically included closer to competition to peak neuromuscular performance.
A well-balanced training program includes variation in interval types, planned recovery weeks, and a progressive increase in load and intensity over time (Issurin, 2008). Frequency and volume should reflect the athlete’s training age, discipline, and proximity to key events.
Conclusion
Interval training is a highly effective method for improving performance in endurance sports. By tailoring intensity, duration, and recovery, coaches can target specific physiological systems and create meaningful adaptation. VO₂ max intervals raise the athlete’s aerobic ceiling, threshold intervals enhance sustainable power, and anaerobic intervals develop peak force and sprint capacity. When integrated thoughtfully into a periodised training model, these intervals form a cornerstone of athletic progression.
In summary, the best interval is the one that aligns with the athlete’s current needs, event demands, and training phase. The role of the coach is to understand these variables and apply interval prescriptions in a way that maximises adaptation while managing fatigue.
References
Coyle, E. F. (1995). Integration of the physiological factors determining endurance performance ability. Exercise and Sport Sciences Reviews, 23, 25–63.
Issurin, V. (2008). Block periodization versus traditional training theory: A review. Journal of Sports Medicine and Physical Fitness, 48(1), 65–75.
Laursen, P. B., & Jenkins, D. G. (2002). The scientific basis for high-intensity interval training: Optimising training programmes and maximising performance in highly trained endurance athletes. Sports Medicine, 32(1), 53–73.
Midgley, A. W., McNaughton, L. R., & Wilkinson, M. (2006). Is there an optimal training intensity for enhancing the maximal oxygen uptake of distance runners? Sports Medicine, 36(2), 117–132.
Saunders, P. U., Pyne, D. B., Telford, R. D., & Hawley, J. A. (2004). Factors affecting running economy in trained distance runners. Sports Medicine, 34(7), 465–485.
Seiler, S., & Tønnessen, E. (2009). Intervals, thresholds, and long slow distance: the role of intensity and duration in endurance training. Sports Science, 13, 32–53.
Wisloff, U., Ellingsen, Ø., & Kemi, O. J. (2009). High-intensity interval training to maximise cardiac benefits of exercise training? Exercise and Sport Sciences Reviews, 37(3), 139–146.
Zemková, E. (2014). Sport-specific assessment of the effectiveness of neuromuscular training in competitive athletes: A review. Sports Medicine, 44(7), 1025–1046.
