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Interval training HIIT parade: 10-10s vs. 15-15s
SPB looks at brand new research comparing two simple 15-minute high-intensity interval training protocols, explains which works best and how athletes can apply it in training
The topic of interval training to develop higher levels of fitness has been extensively covered in many previous SPB articles – and for good reason; excellent empirical evidence from dozens of high-quality studies have demonstrated that a wide variety of interval training protocols (ie varying interval durations and intensities) are effective for enhancing the efficiency of both the aerobic and anaerobic energy producing systems in the muscles(1).
From long to short
Originally developed for endurance athletes and popularized in the 1950s by the Olympic champion, Emil Zatopek, interval sessions were typically modelled around intervals lasting from 2-10 minutes, which suited the aerobic energy demands of runner whose events spanned 10km to marathon distances. Over the years and decades however, evidence merged that intervals using much shorter efforts can deliver very significant benefits for not only endurance athletes competing over long distances, but also for a wide range of other athletes competing in different sports where shorter, more intense burst of activity are required.
The landmark study in this respect was carried out by a Japanese professor called Izumi Tabata of the National Institute of Fitness and Sports in Kanoya, Japan in 1997(2). Tabata designed a scientific study that compared the fitness outcomes of speed skaters who trained using one of two protocols:
· One hour of steady-state, moderate-intensity (70% of maximum oxygen uptake - VO2 max) endurance training on a stationary bicycle for five days each week.
· A 4-minute period of eight intervals with a 2:1 ratio between work and rest (ie 8 sets of 20 seconds of work followed by 10 seconds of rest). During the work phase, intensity was kept very high at 170% of VO2 max (ie at an intensity well in excess of what the athletes could have sustained over a longer period - with pedalling speeds at 90 rpm).
The results showed that (perhaps unsurprisingly), the Tabata intervals resulted in improvements to the athletes’ anaerobic capacity whereas the steady-state trained athletes made no such gains. However, the Tabata-trained athletes also made substantial gains in maximum oxygen uptake (VO2 max), indicating that the very short, high-intensity protocol had actually been able to boost aerobic endurance as well as anaerobic performance, equalling the gains achieved by the steady state group!
The benefits of going short
Following Tabata’s work, the interest in shorter-length intervals at high intensity (also known as high-intensity interval training or HIIT) mushroomed. Subsequent research established that the inclusion of high-intensity intervals in a training program has been unequivocally found to produce greater fitness gains than just adding in extra steady-state aerobic training(3). Indeed, numerous studies with athletes from a wide range of sports have revealed that high-intensity interval training (abbreviated as HIIT from this point onwards) can produce a range of significant physiological and performance improvements. These include(4,5):
· Lower submaximal heart rates for a given submaximal work rate.
· Higher maximum oxygen uptake capacity (VO2max).
· Better repeated sprint ability.
· Improved jumping performance.
HIIT in soccer
Like many team sports, soccer demands high levels of both aerobic and anaerobic fitness. In particular, anaerobic fitness is needed to sustain the ability to perform repeated high-speed sprints during a match, which research shows is a key determinant for success and what separates elite players from those who are merely good(6,7)! Unsurprisingly therefore, the use of HIIT as a training tool for soccer players has become very popular among soccer coaches.
Incorporating HIIT sessions in soccer players’ training programs is backed by robust and recent evidence since the use of various HIIT formats to improve aerobic and anaerobic fitness in soccer has been demonstrated to be a time-efficient method of improving endurance - importantly leaving more time for training the all-important sport-specific skills(8,9). But what kind of HIIT sessions might work best for soccer performance? From the evidence published to date, we can conclude that HIIT using effort lengths ranging from 10-60 seconds can improve both aerobic and anaerobic capacities in players(10,11). Moreover, these kinds of interval sessions have also been shown to enhance game performance, such as distance covered at high speed, number of sprints and ball involvements(12,13).
Balancing fatigue, time and benefits
Unlike sports such as distance running, cycling, and to a lesser extent swimming, team sportsmen and women such as soccer players have to spend a considerable proportion of their training time developing and practicing skills. Therefore, fitness training routines needs to be time efficient (ie deliver good gains per unit of time invested) and also not too fatiguing - since practicing skill acquisition in a fatigued state is known to be more challenging compared to a fresh and rested state(14). And as mentioned above, there’s also a need to develop anaerobic power and sprinting ability.
For this reason, many coaches opt to use sprint interval sessions up to 20 seconds’ duration, which because of their intensity, are efficient at developing speed and power in addition to aerobic benefits, and without excessive fatigue(15). But within this span of short durations, is there an optimal interval duration, and if so, what kind of rest length in between each effort is recommended? While there’s no one formula that will work for all, some new research on this topic provides a valuable insight.
New research
To try and clarify and provide more detail, a team of Greek scientists has just published new research on HIIT training for soccer players, which appears in the ‘Journal of Sports Science and Medicine’(16). In this study, the researchers compared the effects of a 6-week program of HIIT consisting of either 10-second linear sprint intervals or 15-second intervals, which also included some change of direction.
To do this, 26 young soccer players were recruited from two local teams and were divided into two groups – Group A and Group B. Following yo-yo shuttle run testing (see below) for aerobic capacity and jump height capacity (a measure of explosive power), the two groups were each split into two halves and performed the following over a 14-week period:
· Group A – six weeks of HIIT training twice per week with half of the group performing 10-second intervals with 10-second rests in between, and the other half performing 15-second intervals with changes of direction interspersed with 15 seconds of rest.
· Group B – six weeks of normal soccer training without HIIT.
After six weeks of training, both groups took a 2-week break over Christmas performing only low volume and low-intensity work. Then the groups were reversed as follows:
· Group A – six weeks of normal soccer training without HIIT.
· Group B – six weeks of HIIT training twice per week with half of the group performing 10-second intervals with 10-second rests in between, and the other half performing 15-second intervals with changes of direction interspersed with 15 seconds of rest.
The reason for this structure was to enable a ‘crossover’ design, where each group performs both the intervention and the control (a more scientifically rigorous design because each player effective serves as their own control – see figure 1).
Yo-yo shuttle run testing
Figure 1: Scheme of the HIIT vs. control interventions for Group A and B
In terms of the actual HIIT training involved, the intervals sessions were structured in the following way for both the 10-10 and 15-15 interval programs:
· HIIT was in addition to the normal soccer training (details below) and was performed twice per week, two and four days after the weekly soccer match.
· Each HIIT session started with a brief warm up then included two sets of 6 minutes, with the pace set at 100% vVO2max (the speed that produces maximal oxygen uptake – ie fast!), and with three minutes of recovery between sets.
· In the 10-10 intervals, players ran from the center line of field to approximately the goal line (a distance of around 45 metres depending on the player’s vVO2max) for 10 seconds with 10 seconds passive recovery (10s/10s), totalling 18 repetitions per set.
· In the 15-15 intervals, shuttle-runs were performed back and forth, starting from the center line of the field to markers placed 33-37 metres away (depending on the player’s vVO2max) and returning to the same line in 15 seconds, with 15 seconds passive recovery, totalling 12 repetitions per set.
The full soccer training program performed during the control periods by groups A and B is shown in detail in table 1 of the study. At the beginning and end of each 6-week intervention, all the players underwent yo-yo testing and countermovement jump height testing to determine changes in aerobic capacity and explosive power respectively. During the HIIT itself, the players were continually monitored for levels of perceived exertion.
The findings
As you might expect from the previous research, both of the 6-week HIIT interventions resulted in significantly improved high-intensity aerobic/anaerobic performance as measured in the yo-yo testing. However, what was really interesting is that the when the players performed the 10 seconds on/10 seconds off intervals, the gains were much greater; compared to the 15-15 intervals, the 10-10 protocol resulted in an 18.5% improvement in total distance covered in the yo-yo test compared to 9.0% improvement for the 15-15 protocol (see figure 2). VO2max improved by 5.6% with the 10-10 intervals but only 3.0% with the 15-15, and running speed at VO2max improved by 3.2% with the 10-10s vs. 1.8% with the 15-15 intervals.
When it came to the countermovement jump performance, this remained unchanged across both HIIT protocols, with no difference between protocols. However, another important finding, and one that is very relevant for athletes who need to perform skills training in addition to fitness training was at perceived exertions during the HIIT sessions was much higher in the 15-15 protocol compared to the 10-10 protocol. Using the 1-10 scale, interval sessions performing 10-10 intervals scored an average of 4.7, while those using the 15-15 protocol scored 6.4.
Figure 2: HIIT protocols and distance covered in the yo-yo test
Black bars = before HIIT protocol; grey bars = after protocol. The gains in distance covered in the yo-yo test following 10-10 interval training (left), were significantly greater than following the 15-15 protocol (second left). The right hand graph shows countermovement jump performance, which did not change significantly following either protocol.
Practical advice for athletes
These results are very encouraging for all athletes, but especially those who need to train for repeated high-intensity bursts of effort (which includes many team sport players) without expending too much time and effort – leaving plenty of time for skills and match training. While both HIIT protocols produced significant benefits, it was the 10-10 one that resulted in the best gains, and was the least tiring to execute in training. Moreover, the gains obtained were very significant in terms benefits on the pitch. For example, if we compared two equally fit players, a 3.2% gain in vVO2 in the player using the 10-10 HIIT protocol would mean that in a 30-metre dash for the ball, he/she would be a metre ahead of the opponent – enough to take control of the play. And over a busy period of play required repeated sprints, he/she could expect to cover nearly 25% more distance on the pitch!
How can athletes use this information in practice? Well, adding in 1-2 15-minute sessions of 10 on/10 off HIIT (as described above) per week seems to give great results. However, timing is important; if you’re training to be in peak condition for an event or matches later in the season, the use of this HIIT protocol is best performed in the 2-3 months beforehand (but stopping HIIT 1-2 weeks before event to make sure you’re fresh). Also, bear in mind that while this HIIT protocol was rated quite low in terms of perceived exertion, it’s still intense. This means you should ensure you have a good aerobic base in place before introducing a HIIT protocol like this. Where fitness sharpening is required, two sessions per week of this HIIT protocol is desirable; where fitness maintenance is needed (eg during the peak of the season), one session per week is likely to suffice.
In terms of establishing your training intensity of each effort, the researchers used 100% of vVO2max. Although this is accurately established in a lab, you can get a reasonable approximation by performing a graded exercise test, where you gradually increase your running/cycling/ swimming etc speed every 2-3 minutes. You heart rate will increase with effort but there will come a point where increasing your effort any more does not produce a rise in heart rate – that is approximately your vVO2max speed/power output. Another way of getting an approximation (although less accurate) is to establish your maximum sustainable speed/power output for four minutes, which will roughly correspond to vVO2max.
References
1. Sports Med. 2001;31(1):13-31
2. Med Sci Sports Exerc 1997; Volume 29(3), pp 390-395
3. Sport Med. 2015;45:1469–1481
4. Front. Physiol. 2018;9:1012
5. Limits Hum. Endur. 2013;76:51–60
6. PLoS One. 2017 Feb 15;12(2):e0171462
7. ’Managing high-speed running load in professional soccer players’ SPSR 2019 March (53) volume 1
8. Sports Medicine 2023. 53(3), 577-594
9. Sports 2024 (Basel) 12(1), 2
10. Journal of Sports Sciences 2013. 31(13), 1441-1450
11. Sports (Base) 2023 11(3), 59
12. Journal of Human Kinetics 2022. 8(83), 257-265
13. Med Sci Sports Exerc 2001. 33(11), 1925-1931
14. J Neurophysiol. 2020 Sep 1;124(3):844-855
15. Asian Journal of Sports Medicine 2015. 6(4), e25723
16. J Sports Sci Med. 2024 Dec 1;23(4):812–821
Andrew Hamilton
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