Interval Training

A recent study was published that is now making its way around the news lately, and I thought I would touch on that. Here’s what you need to know:

  • The study had 4 groups:
    • Vigorous Resistance Training (RT) only
    • High Intensity Interval Training only (HIIT)
    • Combined light RT and moderate cardio
    • Control group (that did nothing)
  • The population was sedentary adults 30 or younger or older than 64
  • The study was done for 12 weeks
  • Variables that were measured at baseline and after 12 weeks:
    • Insulin sensitivity
    • Aerobic fitness
    • Mitochondrial respiration
    • Lean mass

So here’s what happened:

  • The group that did vigorous RT had more lean mass gains (duh)
  • The group that did HIIT improved their aerobic fitness the most (also duh)
  • The group that did both had modest gains in aerobic fitness and lean mass
  • Everyone experience better blood sugar levels (insulin sensitivity)

These were observed in both age groups

What was surprising:

  • In the HIIT group, the older group saw changes in over 400 genes, while the younger group saw 274 genes change. Most of this was due to changes in the number and health of their mitochondria (the powerhouse of the cell). Aerobic fitness is heavily dependent on enzyme activity in the mitochondria, so many genes are involved. HIIT by far influenced the most genes compared to the other groups, see table below if you’re interested:

 

# Genes Δ HIIT RT Combo
Young 274 74 170
Old 400+ 33 19

 

So what is High Intensity Interval Training exactly? We hear that term thrown around a lot. Interval training is just alternating periods of work and rest. High intensity is a relative term. How intense the work is relative for the individual. What might take a 25 year old athlete to get to 90% of their max heart rate will be way more work than a sedentary 65 year old. The general recommendations are to start with a 1:3 work to rest ratio, and as you progress, work to 1:2 and 1:1 ratios if using time based intervals. So let’s say you sprint on the treadmill for 30 seconds, then hop off onto the sides and rest for 90 seconds, repeating for a set number of repetitions. Another method is to sprint as fast as possible for a given distance, time, or reaching a target heart rate, then resting until you reach 60% of your predicted maximum heart rate (or true max if you have had it measured), then repeating once we know from a heart rate monitor that you are recovered to go again. That is the basics of what it is.

Interval training does not have to be done with sprinting. You can also use an exercise bike, such as an airdyne or a spin bike, you can use the stairmill, rowing machine, swimming, etc. In fact, for most beginner clients with no real exercise history, I would not start them with sprinting. Same for people with orthopedic issues, I would use the rower or bike instead and even start with low intensity intervals. Interval training does not have to be done with just a traditional cardio method either. It can be done using other methods, or even combined. For example, you can use battle ropes, push-ups, kettlebell swings, burpees, etc., all combined in timed circuit.

So, we know that interval training influences a lot of genes with sedentary people, young and old, but why else do it? HIIT is far superior to steady state cardio when it comes to fat loss. HIIT is also very effective at improving aerobic fitness capacity. So if your goals include becoming more fit and losing fat, HIIT would be a great part of a well rounded workout program.

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