High intensity training became popular in 2010s, and for good reason. Intense sessions take little time, make ya sweat (so you feel like you are doing some major work), and can bring about many benefits. But is HIT training helping or hurting your goals? I posted a bit about this earlier on in the week and readers went into a little frenzy. So let me shed some lighten the subject. Read on.
What is HIT?
High intensity interval training (HIIT or HIT) utilizes repeated high intensity bouts of exercise (i.e. 10 seconds to 5 minutes) completed at an intensity greater than the anaerobic threshold with brief recovery periods in between. The idea behind such training, is to place stress on the physiological systems that are used in endurance exercise in a repetitive fashion and more than what is actually required to complete the activity.
Consider the Athlete First.
First things first. When using HIIT for athletes, it’s important to consider the athlete’s training status (trained or untrained?), goal and overall demands of total programming. For example, strength and power athletes may want to limit high intensity aerobic training as concurrent use of heavy resistance and intense aerobic exercise can diminish the quality of signals needed for anabolism.
Let’s talk about this for a minute.
The high oxidative stress that comes with high intensity may hamper power development (Fleck & Kramer, 2014). Keep in mind that this is especially at high velocities of muscle actions and may occur after weeks of concurrent training. However, this will depend on the athlete’s training status (incompatibility is more prominent in untrained people), overall volume/frequency, and whether both types are performed on the same day. There are ways to reduce compatibility issues (see tips below) but most people do not appear to be able to adapt to both modes of training in high frequencies and intensities.
On a side note, strength training does not negatively affect endurance performance, including the development of peak oxygen consumption. In fact, resistance training programs may help endurance athletes by improving performance, preventing injuries and increasing lactic acid threshold.
HOWEVER, if you are gonna train both, it is highly recommended to:
- Reduce intensity and volume.
- Use non-running forms of aerobic conditioning when you can.
- Perform lower body resistance training on days that lower body aerobic endurance training is not being performed / upper body resistance training on days that lower body aerobic endurance training is being performed.
- Take 1-2 days off for complete rest and recovery.
OK, back to HIT training. When compared to continuous submaximal training alone, significant improvements in endurance performance are well known in sedentary and recreationally active individuals. In trained athletes, they will likely reach a trained state that plateaus in metabolic adaptations and further improvements in performance may only be achieved through HIT training. A good indicator of whether or not endurance training will not be improved by increasing submaximal training volume is once a person has reached VO2Max > 60ml/kg/min (Laursen and Jenkins, 2002).
Benefits of HIT
HIT can bring about several improvements in highly trained and it’s important to note that trained individuals will not have the same response as untrained athletes. So I’ve split them into two groups, noted below.
In Untrained Athletes.
If the athlete’s goal is to enhance speed or anaerobic endurance, HIT can improve endurance performance greater than continuous training alone (Laursen and Jenkins, 2002). This is related to up regulation of both oxidative and glycolytic energy systems, which means improved energy state in working muscles and greater preservation of high energy phosphates. Additionally, enhanced peak anaerobic power and output and VO2Max seem to be common responses to HIT in untrained individuals.
Another benefit of HIT training is that an athlete can have rapid improvements despite misconception that it takes years. For example: VO2Max increased after only 10 weeks of HIT alternating 40 min cycling intervals at VO2Max1 day and 40 min high intensity running the next. Even a single session had skeletal muscle adaptations occur.
In Trained Athletes.
Some benefits noted include improved heat tolerance (an enhanced sweat capacity and cutaneous blood flow), a greater use of fatty acids, enhanced oxidative enzyme activity, improved skeletal muscle buffering capacity (may contribute to improved glycolic ATP yield and higher exercise intensity), altered Na+-K+-ATPase and sarcoplasmic reticulum CA2+-ATPase to regulate activity pumps for maintaining muscle membrane potential, adaptation of the CNS and endocrine systems, increases in myoglobin, capillary density (may improve lactate removal), and fiber type characteristics.
Alright, let’s get into the nitty gritty. What are the guidelines for optimal HIT training?
- Each athlete should have regular assessments of training status to make improvements to the HIT program.
- Sufficient recovery is necessary to be able to detect benefits from HIT (fatigue and overtraining can play a role in decreased performance).
- Recovery intervals of 2:1, 1:1 and 1:2 are all commonly used.
- Heart rate can be used to monitor recovery (measure HR immediately following a HIT interval and then monitoring the time it takes for the HR to decrease).
- Although a shorter rest period may mean less work achieved, it has also been suggested that supramaximal HIT with short rest periods may maximally tax aerobic and anaerobic capacities.
- An active recovery may be justified to help facilitate lactate removal.
- A taper is essential following a phase of increased volume and intensity. Example: middle distance runners can reduce volume by at least 75% during a 6-day taper (there was no difference between 50-75% reduction) (Laursen and Jenkins, 2002).
- Higher and longer intensities of interval training should be periodized as they can interfere with strength, power and muscle size, especially in those untrained (Fleck & Kramer, p 167).
- It has been noted that several minutes above 90% of VO2max for an optimal stimulus (Thomas, 2019).
For Trained Athletes
For trained athletes, although little information is available, there are some recommendations on how best to use HIT when preparing trained athletes for competition. For optimal improvements in endurance performance:
- Data suggests Vmax has been successful to establish the intensity for runners, and that HIT should be performed between 50 – 60% of T max.
Note: A more demanding intensity is needed for elite athletes, so using critical velocity may not be as effective.
For Untrained Athletes
- Critical velocity/critical power (longer HIT performed at an intensity between Tlac and Vmax) is appropriate to increase VO2 to the level of VO2max in untrained individuals.
- For cyclists, a more conventional approach may be more reasonable and the author suggests that supramaximal sprinting may be more effective to improve endurance performance.
- Note: Increases have been shown in trained cyclists at 4 HIT sessions (20×60 seconds at P 120 sec recovery) over 2 weeks in off season (p<5) Laursen and Jenkins, 2002).
So there you have it. Have a question? Feel free to send me a message.
Happy training friends!!
Fleck, S. J., & Kraemer, W. J. (2014). Designing resistance training programs (4th ed.). Champaign, IL: Human Kinetics.
Laursen, PB, Jenkins, DG (2002). The scientific basis for high-intensity interval training: optimising training programmes and maximising performance in highly trained endurance athletes. Sports Med 32: 53–73.