HIIT Workouts: The importance of keeping training progressive

Anyone who trains seriously, knows that to achieve consistent improvements, training must be progressive.

One of the easiest ways to do this is to work to a specific exercise intensity. For instance, if you lift weights you might focus on completing a set number of repetitions. And as this becomes easier you increase the resistance by lifting heavier. When it comes to endurance training, we do this by training to a percentage of maximum effort – normally with the use of a heart rate monitor or perceived effort. So, how effective is this and is it really important?

The importance of interval training progression

The importance of keeping training progressive was highlighted by research, looking at the effects of short term (10 days) high intensity interval training (HIIT) on fitness and markers of fitness in untrained, but healthy individuals.

The 10 days of intensified training involved a combination of HIIT sessions (four sessions of 6x5mins@90-100%VO2max) and moderate intensity training sessions (six sessions of 45-90mins @ 75%VO2max).

What did the researchers find? Firstly, short-term intensified training increased protein abundance and mitochondrial gene expression. Highlighting, just how quickly you can adapt to interval training. Secondly, after just 10 days of intensified training, the relative workload was now significantly lower. And even though the workrate was the same, the subjects were now cycling at a much lower % of VO2max – 64% vs 72% of VO2 max.

This highlights how important it is to increase workrate as our fitness improves. In fact, after just 10 days of intense training the subjects would have to increase their training workload by ~15% to get the same fitness benefit. This is further reinforced by the researchers findings, that mitochondrial gene expression – an indication of training adaptation – was decreased after training, when workload wasn’t adjusted to account for training adaptations.

Summary of the HIIT research

  • Short term HIIT sessions and moderate intensity training led to significant increases in protein abundance and mitochondrial gene expression
  • Exercise intensity decreased at the same workload (post-training) from 72 to 64% VO2max
  • Mitochondrial gene expression – and therefore the level of training adaptation – was lower at the same workload following training.
  • Subjects would need to increase workload by 15% to maintain the same relative exercise intensity after the training adaptation.

Practical Implications of the research

In order to achieve a continuous training adaptation you should monitor fitness and adjust your workload as your conditioning improves. An effective way to do this, is to train at the same relative exercise intensity (% of maximum heart rate). This is more effective for sub-maximal training intensities – easy, moderate, tempo, lactate threshold training – than interval training where perceived effort may be more effective.

If using a power meter to control training intensity, then look to routinely assess your performance level using lactate threshold, or FTP Cycling tests. This will help to ensure you’re training at the same relative exercise intensity. For best results combine using a power meter with a heart rate monitor. This is the most effective way to control workrate, whilst also allowing you to monitor relative training intensity.

Reference:

Stepto NK, Benziane B, Wadley GD, Chibalin AV, Canny BJ, et al. (2012) Short-Term Intensified Cycle Training Alters Acute and Chronic Responses of PGC1α and Cytochrome C Oxidase IV to Exercise in Human Skeletal Muscle. PLoS ONE 7(12): e53080. doi:10.1371/journal.pone.0053080

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