Intervals, Thresholds, and Long Slow Distance: the Role of Intensity and Duration in Endurance Training

TLDR

Endurance training manipulates intensity, duration, and frequency, and while high‑intensity interval training has become popular, the relative benefits of short, intense bouts versus longer, slower sessions remain debated among athletes, coaches, and scientists. The study aims to evaluate whether interval and continuous training both contribute to effective endurance training in untrained to moderately trained subjects, challenging the prevailing interval‑training craze. Elite athletes train mostly below lactate threshold and use high‑intensity intervals sparingly; evidence indicates that a best‑practice approach combines large volumes of low‑intensity training with judicious high‑intensity intervals across the training cycle.

Abstract

Endurance training involves manipulation of intensity, duration, and frequency of training sessions. The relative impact of short, high-intensity training versus longer, slower distance training has been studied and debated for decades among athletes, coaches, and scientists. Currently, the popularity pendulum has swollen towards high-intensity interval training. Many fitness experts, as well as some scientists, now argue that brief, high-intensity interval work is the only form of training necessary for performance optimization. Research on the impact of interval and continuous training with untrained to moderately trained subjects does not support the current interval craze, but the evidence does suggest that short intense training bouts and longer continuous exercise sessions should both be a part of effective endurance training. Elite endurance athletes perform 80 % or more of their training at intensities clearly below their lactate threshold and use high-intensity training surprisingly sparingly. Studies involving intensification of training in already well-trained athletes have shown equivocal results at best. The available evidence suggests that combining large volumes of low-intensity training with careful use of high-intensity interval training throughout the annual training cycle is the best-practice