Spring is here and the great melt has begun! While I could be talking about the pristine white, and sometimes roadside-black, snow what I’m really referring to is that time of year when we start to worry about how we’ll look in the revealing clothing that comes with warmer weather. We worry about how we’ll lose the few extra pounds we have added during the hibernation of winter (AKA sitting on the couch and watching too much TV).
So if trimming up is your goal and you frequently go for jogs you need to know that there is a better way! Interval training!
Before embarking on a high-intensity interval training (HIIT) program you need to have an aerobic base. So if you’re not able to do a minimum of 20 minutes of steady-state cardio exercise (continuous training at the same relative intensity e.g. jogging) you are not ready for HIIT.
Before I continue let me say that regardless of your exercise approach, if your diet is not a healthy one then you will find it very hard to reach your fitness goals. So, assuming you’ve put down the burger and fries for lean-protein options with lots of healthy vegetables here is the best approach to losing those stubborn last few pounds.
Why it works
High-intensity Interval training (HIIT) is more effective than the traditional jog or steady-state cardio exercise for a few reasons but they all add up to one thing. You will be able to do more “work” during your session by
- increasing the intensity of your work and/or
- increasing the length of your workout. Interval training allows you to do this by incorporating periods of “rest” (usually active rest by lowering the intensity of the activity – e.g. slow jog).
Doing more work burns more calories, plain and simple.
So the reasons to implement interval training are:
- More can be accomplished in a given time frame
- Acute Effect - fatigue is delayed with the same amount of work in the same amount of time: allowing the subject to continue working longer and accomplishing more work and therefore more beneficial effect.
- Chronic Effect – physiological developments allows for those mechanisms that cause fatigue to be even further delayed allowing the subject to continue working and burning more calories.
How to Apply
While determining the optimal work-to-rest ratio is not easy it is also not as important for the average person (vs elite athletes). The concept is solid. Go hard for a period of time and rest accordingly (not too long – but long enough that you can go hard again.) Again, to truly benefit from interval training a minimum level of cardio fitness must be achieved first. I would recommend the following steps
- Begin with continuous exercise of low-moderate intensity for 20-30 minutes. Once you can do that go to step 2
- Interval train with 2 minutes moderate intensity with 3-6 minutes of rest (work-to-rest ratio of 1:1.5 to 1:3)
- Increase to moderate-to-high intensity intervals of 30-60 seconds with 2-3 minutes rest (work-to-rest ratio of 1:2 to 1:6)
- Lastly, if desired but reserved for advanced subjects, high intensity intervals of ~30 seconds with 4+ minutes rest (work-to-rest ratio of 1:8+)
Except for the most intense intervals (not recommended for the average person) the “rest” should be active “rest”, such as a slow jog.
The greater the intensity the shorter the work period and the longer the rest period should be. Have you ever seen sprinters train? They’ll often incorporate a work-to-rest ratio of 1-10 or more. They’ll sprint all out for 30 seconds then rest for 5 minutes as at that intensity they’ve exhausted their creatine phosphate (CP) stores that drive power exercise. These CP stores can take upwards of 8 minutes to fully replenish. I don’t recommend this kind of work-to-rest ratio for beginners, however.
Base the work intensity on your heart rate. Here is a very basic guideline for work (your
trainer should be able to give you more specific goals based on your particulars):
The science bit, for those who want proof, or the fitness nerds like me!
MORE WORK IS ACCOMPLISHED (more work means more calories expended!)
“..properly spaced work-to-rest intervals allow more work to be accomplished at higher exercise intensities with the same or less fatigue than during continuous training at the same relative intensity”[i]
Studies have shown that at a given intensity of exertion more work is accomplished before exhaustion is reached when the session includes properly spaced rest periods as opposed to steady state exercise.
This means that if you have a limited amount of time to get your workout in (and really, who doesn’t?) you can achieve greater intensity and, therefore, greater effect with interval training. So if you only have 30 minutes on your lunch break and you want to get a workout in you can actually run further with interval training than steady-state training, as the rest periods allow for increased intensity. One early study showed that at a given intensity 5 minutes of steady-state cardio (running) vs. 5 minutes of running with rest periods included (work-to-rest ratios of 2:1, 1:1, & 1:2) showed significantly more work was accomplished with the interval training. “Therefore much more training can be accomplished at higher intensities with interval training: this concept has been established for over 45 years”[ii]
Even when less work is accomplished there is a greater result in fat loss with high-intensity interval training!![iii]
ACUTE EFFECT - DELAYED EXHAUSTION MEANS MORE WORK ACCOMPLISHED (more work means more calories expended! Seeing a pattern here?!)
Less fatigue is experienced in a given time frame with the same amount of work (with HIIT you can therefore extend the length of your workout session)
Short intervals of work and rest showed much less blood lactate accumulation and much less depletion of muscle glycogen – both mechanisms for fatigue – in a given time when compared to long work intervals and rest.
The chart above shows how much less fatigued a subject would be with the shorter intervals while achieving the same level of work (600 seconds work total for all subjects) at a given intensity. Those who did the 60 seconds work with 120 seconds rest had accumulated more blood lactate and exhausted more muscle glycogen – these subjects would likely be close to exhaustion while the other two groups are more likely to be very capable of continuing the session beyond the 30 minutes and therefore accomplishing more work. While this particular study does not include steady state exercise it’s reasonable to assume that it would be more exhausting (and has shown to be so in other studies) than any of these interval examples. In all likelihood, the steady-state cardio subject would not be able to last for 30 minutes at the assigned intensity.
Another example: A runner scampering along without stopping at his/her current best 10k velocity might be able to sustain the pace for only 25 minutes or so during a workout; by breaking the effort down into 8-minute intervals, however, the same runner could often work at 10k velocity for a total of 32 minutes (four 8-minute intervals), thus boosting the 'quality' of the session by 28% [v]
CHRONIC EFFECT - PHYSIOLOGICAL BENEFITS There is a greater physiological effect causing an extended benefit (creating more efficient and therefore more effective workouts going forward.)
Studies have also shown the athletes who incorporate HIIT have long lasting physiological developments that further increase fat-burning potential.
- VO2 max increases (maximum oxygen uptake – a measure of aerobic performance) - HIIT more efficiently improves VO2 max than stead state training [vi]
- Fat oxidation increases – you more readily burn fat as a fuel when you’ve trained with high-intensity intervals. Not only does this help you lose the fat you are targeting but it has the added benefit of preserving muscle glycogen thereby delaying the onset of fatigue[vii]
- Blood lactate accumulation is delayed due to more efficient buffering/clearance mechanisms[viii]
A team from Japan’s National Institute of Fitness and Sport found that a high-intensity intermittent training program achieved bigger gains in VO2max than a program of steady cycling (Tabata et al., 1997).
Effectiveness of SST vs HIIT - Active male subjects were assigned to one of two groups, each training 5 days per week for 6 weeks. One group followed a training program involving 60 min of moderate intensity exercise (70% VO2max), for a total of 5 hours per week. The VO2max in this group improved by an average of 9%. Training sessions of the other group consisted of eight all-out work bouts, each lasting 20 s, with 10 s of rest. This group cycled for a total of only 20 min per week, yet their VO2max improved by 15%!!
A 40-km time trial depends almost entirely on energy provided by the aerobic system. Work bouts lasting 30 seconds depend primarily on anaerobic energy, and were not expected to enhance performance but did. This paradox may be resolved by the findings of Rodas et al. (2000), who reported that a high-intensity intermittent training program increases oxidative enzyme activity in muscle.[ix]
Granted these studies were conducted with athletes – however, the science is sound and applicable at an appropriate level for the common person.
Interval training can be fun, effective and a time saver! Use it wisely and combined with a healthy diet you’ll see the results.
[i] Essentials of Strength Training and Conditioning - Page 36
[ii] Paper by Christensen et al 1960. Source: Essentials of Strength Training and Conditioning - Page 36
[iii] In a study by Tremblay et al. a group of endurance trained individuals were compared to a group of high-intensity interval trained individuals and even though there was a significant difference in the energy expenditure with the endurance group expending more calories, the interval group had a much greater reduction in skinfold measurements at the end of the study - https://www.nsca.com/Education/Articles/Change-Up-the-Pace-Interval-Training/
[iv] Astrand & Rodahl, 1977 – source http://coachsci.sdsu.edu/swim/bullets/55%20ITHIITUSRPT.pdf
[vi] A team from Japan’s National Institute of Fitness and Sport found that a high-intensity intermittent training program achieved bigger gains in VO2max than a program of steady cycling (Tabata et al., 1997). Source: http://www.sportsci.org/jour/0101/cf.htm
[viii] Burgomaster, KA et al 2005-2006. Source: Essentials of Strength Training and Conditioning - Page 37