Zone 2 is all the rage at the moment but a recent research paper has called that into question.
“ Much Ado about Zone 2. : A Narrative Review Assessing the Efficacy of Zone 2 Training for Improving Mitochondrial Capacity and Cardiorespiratory Fitness in the General Population”. argued that zone 2 is not optimal for aerobic development and that higher intensities are better to maximise aerobic development.
T”hey concluded that “ current evidence does not support Zone 2 training as the optimal intensity for improving mitochondrial or fatty acid oxidative capacity,””
Keep in mind the review was discussing zone 2 in relation to non elite athletes and with a focus on improving cardiovascular health rather than improving performance of endurance athletes.
You may be thinking surely improving mitochondrial or fatty acid oxidative capacity will improve endurance performance and therefore we should ditch zone 2 and run more in zone 3 or above .
However we need to look at this in the context of our training as a whole.
The discussion on what is best should take into account how much training one can do in the different zones, how much time the athlete has to train and how much training one is doing at higher intensities.
The more time we spend in zone 3 or higher the more fatigue we create and the less overall training we can do.
Sure we might be able to spend 3 hours in zone 3 or above each week but is that as good as 6 hours with 5 hours of zone 2, and thther hour a mix of zone 3,4 and 5 ? Almost definitely not.
Given that many trail and ultra runners will train 8-10 hours or more, the only way we can maintain that is to make sure the majority is in zone 2.
When you balance the greater time you can spend in zone 2 each week and the fact zone 2 has less fatigue than zone 3 therefore does not affect higher intensity training sessions ( zone 4+ ) or longer sessions, zone 2 is a clear winner.
Zone 3 does have its place though – see the video on speed sessions – tempo running is typically mid zone 3 .
One key point to take from this study is it highlights that easy running alone will not fully trigger all the cardiovascular and structural adaptions that higher intensities will. Any good training program needs a mix of training intensities that is specific for the athlete and the race they are training