By Carrie Aspin, Exercise Physiologist

In the world of fitness, it’s hard to know what’s what when you’re starting out.

There seems to be so many ways to skin a cat and many“truths” flying around on what’s the best way to get fit/maintain that fitness!

Society has trended towards a desk-based lifestyle which has been offset by the trend of hard and fast fitness.

In the world of science where physiology is black and white and marketing cannot paint it a shade of grey, a review of this behaviour and its effect on fitness, health and disease prevention are providing researchers with a shift in their former understanding of the topic.

It was previously thought that high intensity interval training (HIIT) was dangerous within the general population and should be reserved for top athletes only.

However, research is suggesting that there is definitely a time and place for HIIT, however this is typically after building an aerobic endurance base first.

Before we break this down let’s define the terms as simply as possible.

  • HEALTH: Nopresence of disease whichcan be any of the following:
    • Metabolic- diabetes, thyroid, lipid conditions
    • Cardiac- arrhythmias, hypertension, cardiovascular artery disease
    • Neurological- Stroke, MS, Depression/anxiety
    • Musculoskeletal- Arthritis, RA, OA
    • Respiratory- Asthma, COPD, bronchitis
  • FITNESS: The result of an accumulation of physical activity over time. The unit of measure to quantify fitness is %VO2. The higher the better! We need a VO2 of 20% just to sustain physiological function; untrained individuals may be as low as 50% high level perhaps 85%.This indicates that a sedentary lifestyle directly correlates to poor physiological functioning, a precursor to morbidities listed above. Fitness is comprised of aerobic and anaerobic energies.
  • AEROBIC: Through age we see a natural decline in aerobic capacity for movement longer than two minutes. Sustaining continuous movement requires:
    • Respiration: breathing deeply and faster to deliver oxygen to the muscles
    • Circulation: The greater the volume of blood inside each beat the more oxygen delivered to working muscles. The greater your stroke volume (amount of blood pumped by the heart with each beat) the lower your heart rate.
    • Metabolism: The utilization of those nutrients used for energy carried by oxygen.
  • ANAEROBIC THRESHOLD: As you work at a higher intensity, the energy delivery changes. The bi-product of that change is cellular waste known as lactic acid. The greater that threshold and tolerance of that production, within anaerobic capacity is deemed athletic fitness.
  • ANAEROBIC: The ‘Nos’ of our energy system. An energy that is supplied for moments of power and explosive delivery of strength for a duration 0-60secs. Commonly seen in sprinters and weightlifts for example where the oxygen delivery is low and recovery periods are high. NOT exclusive for sport performance. A low VO2 will see an anaerobic response to perform daily tasks in place of basic aerobic capacity in heart failure patients.

All types of fitness have a metabolic effect (how the training mode affects your insides). Current global recommendation for health and disease prevention is 150minutes of physical activityper week. So that’s 30mins x5 days at moderate intensity or 20mins 3-5 days vigorous intensity. That duration will keep you physiologically set at equal excluding the effects of nutrition. There is a solid inverse relationship between physical activity and chronic disease and previously, “moderate intensity continuous exercise” (MICE) was thought to be the way.

Let’s look at the metabolic effect of HIIT since this is the latest craze. It is not maximal training. It still uses the aerobic pathway but at the more anaerobic end of the spectrum due to intensity and shorter bouts compared to MICE. The physiological cost of exercising that way is such that you continue to burn calories at a faster rate hours after compared to MICE which does not stress the system the same way. A recent publication by ProfessorNeil Smart (2018) showed an in-depth investigation into the relevance for HIIT for chronic rehabilitation.

  • Healthy members- ↑VO2 35%, MICE 16%
  • Coronary artery disease- HIIT ↑VO2 10% more than MICE over 12 weeks
  • Heart failure has a typical VO2 of 13- HIIT ↑VO2 37%, MICE ↑VO2 5%
  • Metabolic syndrome- HIIT has been shown to fully resolve symptoms in this condition and reduce cardiovascular disease progression by 25%

Metabolic stress is good!!!!! BUT……….it must be attenuated with recovery!For example, 4x 4-minute bouts of exertion in one session with 3minute’s recovery between. So the idea of being involved in HIIT style programming is correct for pushing our capacity as a healthy or chronically classified person, but what we are seeing out there is that the prescription of it, is not.

HIIT is ideal for after you have built an aerobic ENDURANCE base first BEFORE tapping into the anaerobic threshold. It’s like learning to run before you can walk. Yes, yes it feels good (afterwards) and adherence trends are higher with shorter exercise sessions but it’s but safety first people!

My advice is to mix it up. Train HIIT, MICE, strength, don’t forget mobility every week at least once.

Just a foot note……….one 4-minute HIIT session at 90% intensity is equivalent to 15minutes MICE, so if you can’t get away from the office try this: 4 minutes of burpees and squats. Your circulation, respiration and metabolism will thank you for it.

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