Interval training, also known as high-intensity interval training or HIIT, is now a core part of training for endurance athletes, from short-distance competitors to long-distance athletes such as Ironman triathletes. Substantial evidence (Gibala, 2019) supports HIIT for maximizing improvements in performance markers including cardiac output, the heart's capacity to deliver blood to muscle; maximal oxygen uptake, or VO2max, the body's capacity to use oxygen; and maximal aerobic speed. It also requires less time and is therefore more efficient than continuous moderate-intensity training.
When planning interval sessions, however, athletes must decide between long intervals of more than 3 minutes and short, highly explosive efforts, also known as SIT, such as 30-60-second sprints. A study in the European Journal of Sport Science (Taylor, 2013) compared runners who trained 3 times per week for 6 weeks using long HIIT (4-6 sets of 4 minutes with 4 minutes of recovery), SIT (7-12 sets of 30 seconds with 2.5 minutes of recovery), or a control protocol (30 minutes of continuous running). All groups improved performance in a 3000-meter test, a 40-meter sprint and repeated-sprint capacity, but the SIT group achieved the greatest improvements.
Other researchers have compared short and long intervals. A recent study by Bent Ronnestad's group (Ronnestad, 2020) assigned elite cyclists to short intervals (3 blocks of 13 sets lasting 30 seconds, with 15 seconds between sets and 3 minutes between blocks) or long intervals (4 sets of 5 minutes, with 2.5 minutes between sets) for 3 weeks, with 3 sessions per week. Short intervals produced larger improvements in maximal aerobic power (3.7 vs -0.3%) and threshold power (2.0 vs -2.8%), as well as power during a 20-minute time trial (4.7 vs -1.4%). These findings confirm results previously reported by the same authors in cyclists (Ronnestad, 2015), when the same short-interval protocol produced greater improvements than long intervals in maximal oxygen uptake and performance tests lasting 30 seconds, 5 minutes and 40 minutes.
Short intervals of approximately 30 seconds can therefore improve endurance performance more than longer intervals of approximately 5 minutes in runners and cyclists. Another study (Zelt, 2014) compared different short intervals. For 4 weeks, 3 times per week, athletes performed intervals lasting 30 seconds or 15 seconds; both protocols used 4-6 sets with 4.5 minutes of recovery. Both groups achieved similar improvements in maximal oxygen uptake, power during a 30-second test and power at the anaerobic threshold.
In summary, very short intervals (<30 seconds) appear to benefit endurance athletes more than long intervals (>3 minutes). Reducing interval duration from 30 to 15 seconds may also preserve the improvements while maintaining the same recovery time, thereby reducing training stress. These findings could indicate that generating high power peaks—explosive actions that recruit fast-twitch fibers and improve the rate of force development—is what matters for these athletes. Nevertheless, the most appropriate strategy may be to alternate different stimuli across the season, combining short and long intervals with continuous sessions and increasing specificity as the main goal approaches.
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References
– Gibala MJ, Bostad W, McArthy DG. Physiological adaptations to interval training to promote endurance. 10: 180-184, 2019.
– Taylor P, Cicioni-kolsky D, Lorenzen C, Williams MD, Guy J. Endurance and sprint benefits of high-intensity and supramaximal interval training. Eur J Sport Sci 13: 304–311, 2013.
– Zelt, JGE, Hankinson, PB, Foster, WS, Williams, CB, Reynolds, J, Garneys, E, Tschakovsky, ME, and Gurd, BJ. Reducing the volume of sprint interval training does not diminish maximal and submaximal performance gains in healthy men. Eur J Appl Physiol 114: 2427–2436, 2014.
– Rønnestad BR, Hansen J, Nygaard H, Lundby C. Superior performance improvements in elite cyclists following short‐interval vs effort‐matched long‐interval training. Scand. J. Med. Sci. Sports, In press. 2020.
– Rønnestad BR, Hansen J, Vegge G, Tønnessen E, Slettaløkken G. Short intervals induce superior training adaptations compared with long intervals in cyclists – An effort-matched approach. Scand. J. Med. Sci. Sports, vol. 25, no. 2: 143–151, 2015.
AUTHOR
Pedro Valenzuela
Researcher in the Physiology Unit at the University of Alcalá and the Performance Monitoring Unit at the Sports Medicine Center (AEPSAD, Madrid High Performance Center).
Website: www.fissac.com
