Research Review By Dr. Demetry Assimakopoulos©

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Date Posted:

October 2012

Study Title:

Physiological adaptations to low-volume, high-intensity interval training in health and disease

Authors:

Gibala MJ, Little JP, MacDonald MJ et al.

Author's Affiliations:

Department of Kinesiology, McMaster University, Hamilton, ON; School of Arts and Sciences, University of British Columbia, Kelowna BC; Exercise Metabolism Group, RMIT University, Bundoora Victoria, Australia

Publication Information:

Journal of Physiology 2012; 590(5): 1077-1084.

Background Information:

High-intensity training (HIT) is a form of exercise characterized by short, intermittent bouts of vigorous activity, which are interspersed with longer periods of low-intensity exercise or (relative) ‘rest’. HIT has been shown to be an effective alternative to typical long distance endurance training. It has also been shown to provide similar, and sometimes superior, changes in a number of physiological, performance and health-related markers in both healthy and diseased populations.

Less research has been performed on a different kind of HIT called ‘low-volume HIT’. Growing evidence is suggesting that individuals perceive low- volume HIT as more enjoyable and tolerable compared to long, slow, distance exercise. It also allows for favorable physiological changes that are comparable to long term, continuous, moderate-intensity exercise, despite the shorter time commitment and lower total exercise volume (1). This evidence is potentially important from the perspective of public health, as a ‘lack of time’ is the most common barrier keeping individuals from performing regular exercise.

In this narrative review, the authors endeavor to review the mechanisms responsible for improved cardiovascular and skeletal muscle metabolic control that occur as a result of low-volume HIT. They also discuss why low-volume HIT may be a preferable adjunct to therapy for individuals suffering from chronic disease, and how it may be integrated into performance training.

HIT Methods:

The most common way to implement an HIT protocol is through the Wingate Test, which consists of 30 seconds of extremely vigorous cycling, utilizing a supra-maximal workload. The typical volume prescribed is 4-6 bouts, separated by approximately 4 minutes of recovery, for a total of 2-3 minutes of HIT, over the course of 20 minutes.

As few as six training sessions of HIT, totaling approximately 15 minutes of all out cycling, over the course of 2 weeks has the power to increase aerobic fitness levels. Other favourable adaptations include an increase in aerobic fitness, increased resting glycogen content, a decrease in the rate of glycogen utilization and blood lactate content, an increased capacity for lipid oxidation, superior peripheral vascular structure/function, improved time-to-exhaustion trials, and increased maximal oxygen uptake.

Additionally, HIT has an amazing ability to elicit an increase in the concentration of skeletal mitochondria. This is mediated by an increase in the activation of a protein called PGC 1-alpha. This co-activator is known to be the ‘master regulator’ of mitochondrial biogenesis. Exercise intensity is the main factor contributing to PGC-1 alpha activation. The signals which activate PGC-1 alpha, and thus mitrochondrial biogenesis in response to low-volume HIT are not totally understood. However, this mechanism is important to understand, as even a modest increase in PGC-1 alpha concentration in muscle leads to favourable outcomes in oxidative capacity, anti-oxidant concentration, glucose uptake, resistance to sarcopenia and inflammation.

While the impact of HIT on cardiovascular structure has been investigated, few of these studies have utilized a low-volume HIT protocol. As little as 2 weeks of HIT has been shown to increase VO2 max, while 6 weeks of HIT has shown to be an effective time frame to increase VO2 peak to the same extent as traditional long slow distance endurance training. Low-volume HIT has been proven to improve endothelial function and to increase the compliance of peripheral arteries in young healthy men and women. Yet, the mechanisms which regulate these cardiovascular adaptations have yet to be examined comprehensively.

Research Summary:

  • The authors believe that in healthy individuals, HIT training using a Wingate cycle ergometer (a stationary cycling machine which is designed to measure work-rate) may be neither completely safe, tolerable, nor available to some individuals. They suggest a more practical form of exercise called low-volume HIT that is both time efficient and tolerable enough to be applied to all individuals, including at-risk populations.
  • To perform a low-volume HIT protocol, it is necessary to decrease the absolute intensity of the work bouts, but increase their duration and shorten the rest intervals. They suggest performing 10x60 second bouts, at a constant intensity, eliciting a 90% maximal heart rate. Rest intervals should be approximately 60 seconds. The exercise session would result in10 minutes of HIT, over the course of a 20 minute exercise bout.
  • Higher-volume HIT has been shown to enhance cardiorespiratory fitness in a number of populations, including those with coronary artery disease, congestive heart failure, metabolic syndrome and obesity. In many studies, the gains in cardiorespiratory fitness after HIT were greater than the gains found subsequent to long term, continuous, moderate-intensity training.
  • Additional studies have found specific beneficial changes in resting blood pressure and left ventricular morphology.
  • Studies have shown that as few as 6 sessions of HIT over the course of 2 weeks can improve insulin sensitivity in sedentary, overweight individuals. This is mediated by an increase in muscle glucose uptake via an enhanced GLUT4 translocation. The translocation stimulated by HIT is 2x as great as the changes stimulated by high-volume endurance training. Because of this, low-volume HIT is well tolerated by those with type 2 diabetes.
  • Recent findings have shown that athletes from a variety of disciplines, including rowing, running, cycling and cross-country skiing, may benefit from polarized training (2). Seventy-five percent of their training is performed at low intensities, while the remaining 10-15% is performed at supra-maximal intensities. They surmise that this distribution is optimal for elite athletes who compete in endurance events.
  • To put this in context, a series of investigations examining the use of HIT in endurance athletes found that training sessions using a training volume of 8 x 4 minutes at 85% peak aerobic power output significantly enhanced performance. Interestingly, however, a separate group who performed short, supra-maximal bouts (12 x 30 sec at 175% peak power output) were just as effective at increasing performance.

Clinical Application & Conclusions:

Low-volume, high intensity training is a potent and time-efficient method for inducing favourable adaptations in the cardiovascular system and in skeletal muscle. This training method can lead to improved health and performance outcomes. Also, this system shows positive changes in individuals at risk for cardiometabolic disorders. However, the exact benefits of low-volume HIT in at-risk populations are unclear and require further study.

Practically, low-volume HIT can and should be applied to these populations. In athletes, 15-20% of their training should be low-volume HIT. An additional positive factor is the fact that a long distance athlete may become acclimatized to picking up the pace and fighting through the lactic acid build-up that comes with short bursts of high intensity exercise. Protocols can be performed on a treadmill, stationary cycle or rowing machine, using heart rate as an intensity measure. You can do this on a treadmill by manipulating either the grade or speed. A low-volume HIT protocol can also be performed outside by repeatedly running hills.

Exercise therapy targeted towards high-risk individuals should be performed under the supervision of qualified exercise professionals, a nurse or a physician. It is paramount that the exercise professional be well versed in first aid/CPR, physiology of disease, how the individual disease is affected by exercise and how their medication may change their body’s response to exercise (for example, beta-blockers used in individuals with heart conditions have will blunt the heart rate response. This makes it extremely difficult to use heart rate as a parameter to measure exercise intensity. Instead, practitioners could utilize the Borg Rating of Perceived Exertion Scale).

Additionally, in the case of training at-risk individuals, it is paramount to perform a fitness test prior to starting a training program. This is important because their tolerance to exercise may be much lower than an individual of the general population. Do not make assumptions about how fit a high-risk individual is – do a fitness test, and design your protocol around their tolerance to exercise.

For more information, go to the American College of Sports Medicine website (www.acsm.org) and read their various position statements on these topics. They also have a number of textbooks that provide more information on working with athletes and at-risk populations.

Study Strengths / Weaknesses:

Weaknesses:
  • Many of the studies in this field take place over the course of several weeks. Longer studies lasting months-to-years performed on various clinical cohorts are required.
Strengths:
  • The authors emphasize not only the physiological benefits of low-volume HIT (i.e. cardiometabolic and performance changes), but the fact that HIT is an extremely time efficient form of exercise, which will ultimately increase compliance.

Additional References:

  1. Gibala MJ & McGee SL. Metabolic adaptations to short-term high-intensity interval training: a little pain for a lot of gain? Exerc Sport Sci Rev . 2008; 36: 58–63.
  2. Guellich A, Seiler S, Emrich E. Training methods and intensity distribution of young world-class rowers. Int J Sports Physiol Perform. 2009; 4: 448–460.