Active Recovery- Aren’t we just Building an Aerobic Base?

Active recovery is a term which is popular in the functional fitness space. When competitive athletes are asked how often they train, a common structure appears to be ‘five days a week, one day of complete rest and one day of active recovery’. But what does active recovery mean and what is its purpose? The generally held view seems to be that a day of low load, low heart rate, longer duration training helps to reduce DOMS, flushes lactate out of the muscles, keeps us moving so we don’t stiffen up and enhances recovery. 

Whilst active recovery has been shown to have some effect on reduction in muscle DOMS when performed immediately after a training session (ie. cooling down), I have not been able to find any evidence that active recovery undertaken the following day has any effect on muscle soreness, fatigue or mobility (although it may be that these studies simply haven’t been carried out yet). (1)

I would argue that these low heart rate, slow, longer duration training days are crucial, but for a completely different reason. In the world of endurance training, many athletes and coaches adopt what is known as the polarised training model. Research carried out on elite level (national and international medal-winning) rowers from the 1970s through to the 2000s tracked training volume and intensity over this period. What this research showed was that as time went on, the rower’s training volume increased, from around 19 to 24 hours a week, but the intensity distribution also changed. The percentage of work done at high intensity decreased, and the percentage of work done at low intensity, longer duration increased. Compared with the athletes winning medals in the 1970s, medal winners in the 1990s had about a 12% higher VO2 max, without an increase in body mass. Polarised training comprises roughly 80-90% of training volume at low intensity, with 10-20% at high intensity. (2)

A quick note about lactate zones before we continue.

A study in trained endurance cyclists compared polarised training (80% of training done in lactate zone 1, 20% in zone 3) to a threshold training model (57% zone 1, 43% zone 2) on the effectiveness of improving physiological adaptation and endurance performance. Results showeud that polarised training resulted in an increased peak power output and improved time to exhaustion at 95% of peak power output compared to threshold training. (3)

A study of forty eight runners, cyclists, triathletes and cross-country skiers compared high-volume training, high-intensity-interval training, threshold training and polarised training programs. Polarised training demonstrated the greatest increase in VO2 max, time to exhaustion, peak velocity/power and velocity/power at the lactate turnpoint (LT2). Interestingly HIIT was the only program that reduced body mass. (4)

Another study in cyclists- this time longitudinal- tracked training distribution and VO2 max through a competitive year. This showed that during off-season training, which was predominantly (80-90%) low intensity focused, VO2 max increased on average from around 430 to 460 watts. During competition season training, where the percentage of low-intensity training decreased significantly, and high-intensity training increased, VO2 max did not improve. Now, this isn’t to say cyclists should only train at low intensity all year round – during competition they also need strong anaerobic fitness to be able to climb hills and sprint to the finish line – but it demonstrates that the aerobic base fitness is built in the off-season. (5)

Training in zone 1 has been shown to stimulate several physiological adaptations:

1.     It increases the number of mitochondria within muscle cells, which are the microscopic engine room of aerobic metabolism

2.     It increases capillary density within muscles, blood volume and plasma volume, therefore increasing oxygen delivery

3.     It increases lipolysis (fat utilisation) which reduces blood lactate by decreasing carbohydrate metabolism and may result in an increase in lactate threshold 

4.     It causes minimal disturbance in hormonal or immune function, whereas excessive high-intensity training can cause impaired immune function

5.     Recovery of the autonomic nervous system (heart rate variability) is quicker than from zone 2 or 3 training where no difference was seen 

(3, 6, 7)

Points 4 and 5 mean that high volumes of zone 1 training can be carried out with low risk of overtraining, or in our case, zone 1 training can be carried out on a ‘recovery’ day with minimal negative impact on the rest of the training week. 

CrossFit is not an endurance sport, so I am not suggesting that we all start adopting a polarised training model, as all the improvements that have been demonstrated are related to endurance parameters. What I am suggesting is that the primary outcome of an ‘active recovery’ session may not be short term recovery; instead it is building an aerobic base. This building will lead to enhanced recovery in the long run due to improved aerobic efficiency, but will also have the multitude of other beneficial effects highlighted above. This also demonstrates the importance of making these sessions ‘easy’ and not going too hard (we’ve all seen some highly questionable instagram ‘recovery’ workouts)– the adaptations only occur in zone 1! 

So next time you look at your training week, rather than thinking about active recovery days, consider ‘five days a week, one day of complete rest and one day of aerobic base training’. 



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