The importance of maintaining relative exercise intensity

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Anyone who trains seriously knows that as your fitness improves you must increase your exercise workload in order to continue to see improvements. One of the easiest ways to do this is to maintain the same relative exercise intensity during your workout by training to a percentage of maximum effort – normally with the use of a heart rate monitor or perceived effort.

The importance of maintaining the same relative exercise intensity 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). The researchers observed that short-term intensified training led to increased protein abundance and mitochondrial gene expression, highlighting just how quickly you can adapt to intensified training. However, the researchers also noted that after just 10 days of HIIT training the % of VO2max required to exercise at the same pre-training workload had reduced from 72% to 64% of VO2max. Whilst this is good in terms of fitness it highlights how the subjects would have to increase their training workload significantly (by ~15% from 164w to 189w), after just 10 days of intensified training, in order to get the same fitness benefit. This is backed up by the researchers findings which observed that mitochondrial gene expression – an indication of training adaptation – was decreased after training at the same workload (but lower relative intensity).

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 after training
  • Subjects would need to increase the workload by 15% to maintain the same relative exercise intensity after the training period

Practical Implications of the research

In order to achieve a continuous training adaptation you should ensure you monitor fitness and adjust your workload so you train at the same relative exercise intensity (e.g. %HRmax). This is more related to sub-maximal training intensities (e.g. Easy, moderate, lactate threshold training) than interval training where you train around VO2max. The best way to achieve this is through working at a percentage of maximum heart rate which will help to ensure that your relative training intensity is maintained as your fitness level increases. If using power meters during sub-maximal training then you should regularly assess your fitness level in order to ensure that you are training at the same relative exercise intensity, and ideally use the power meter in combination with a heart rate monitor.

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