If you are a runner, a cyclist, or a regular at a CrossFit gym, you have probably heard the term “Active Recovery.” The phrase itself seems a bit oxymoronic, but the concept appears to have some basis in science (More on that later).
Active recovery is the use of low-intensity exercise to resupply nutrients to muscles and to speed up the removal of waste products produced during bouts of high-intensity training or competition. Think of activities like walking, hiking, light lifting, scrimmages, etc. This is contrasted with passive recovery where physical activity is restricted. The theory is that active recovery allows you to train or compete more quickly and more often.
In reviewing articles written on the topic, I found two primary uses of the term Active Recovery (AR). Nearly all scientific studies evaluating AR do so within the confines of a single workout. But when coaches and trainers speak or write about AR, they typically mean light exercise on an off-day following a heavy day of exercise. This inconsistent use of terminology may or may not be a problem, but let’s first see what we can learn from the studies.
What Does the Science Say?
Blood Lactate Levels:
Multiple studies have demonstrated that lower blood lactate levels can be achieved using AR versus passive recovery (PR) regardless of the type of exercise. Examples include:
- Researchers evaluating eleven swimmers each completing two 100 meter trials with a 15 minute found that “five minutes of active recovery during a 15-min interval period is adequate to facilitate blood lactate removal.” 
- Fourteen healthy subjects performing supra-maximal intermittent exercises showed “blood lactate disappearance was faster in trained than untrained subjects during combined active recovery. This result suggests that the level of physical fitness plays an important role mainly in the pattern of blood lactate decrease during combined active recovery.” 
- And a study involving eighteen male cyclists found that blood lactate removal with active recovery was significantly better than with passive. 
However, reducing blood lactate levels will not improve the perceived levels of muscle soreness: “The perceptions of pain and soreness that result from intense eccentric exercise are not related to lactate buildup at all…. blood and muscle lactate levels do rise considerably during intense eccentric and concentric exercise, however values for blood and muscle lactate return to normal within 30-60 minutes post exercise.” (reference)
Central Nervous System:
In a study evaluating the effects of cold water immersion (CWI) and AR, the researchers found that CWI showed “some improvement in post-exercise cardiac autonomic regulation compared to AR. Further, AR is not recommended if the aim is to accelerate the parasympathetic reactivation.” 
Based on this study, AR does not appear to accelerate recovery for the central nervous system.
Free Fatty Acids:
A study evaluating fourteen well trained males, found that in high intensity and moderate intensity exercise, “AR resulted in lower Free Fatty Acid [FFA] peaks and lower overall FFA concentrations while performing AR.” 
This is interesting, but not surprising, since fatty acids tend to be a primary fuel source during low-intensity exercise. The question, raised by the study, is if there are health benefits associated with AR in reducing the plasma levels of FFA.
Resynthesis of Muscle Glycogen:
“In a cross-over design, six college-aged males performed three, 1-min exercise bouts at approximately 130% VO2max with a 4-min rest period between each work bout. Data suggest that the use of passive recovery following intense exercise results in a greater amount of muscle glycogen resynthesis than active recovery over the same duration.” 
It is expected that muscle glycogen would not be replenished at the same level as compared to PR since plasma insulin levels are lower during AR.
White Blood Cell Count:
“It would appear that active recovery at low intensity after strenuous exercise can maintain sufficient adrenergic activation to counteract the post-exercise drop in WBCC.” 
- As intermittent exercise alternated with passive recovery is characterized by a slower decline in oxyhemoglobin than during intermittent exercise alternated with active recovery at 40% of VO2max, it may also allow a higher reoxygenation of myoglobin and a higher phosphorylcreatine resynthesis, and thus contribute to a longer time to exhaustion. 
- In a test with twelve male subjects involving an intermittent run to exhaustion with AR or PR, “results showed that intermittent runs to exhaustion with passive recovery allowed subjects to run for a significantly longer time than intermittent runs to exhaustion with active recovery. 
From a scientific point of view, looking only at single exercise sessions, the benefits of AR are mixed. Blood lactate and FFA levels are reduced and the typical post-exercise drop in white blood cells is mitigated. On the hand, AR doesn’t appear to help with CNS recovery, limits the rate in which muscle glycogen is replenished, and doesn’t improve the athletic performance of endurance related sports.
But science has yet to provide much insight in evaluating the benefits of off-day AR. For that we should listen to the wisdom of coaches, trainers, and ultimately to your own body. If you are the type of person that finds rest days to be mental torture, having an alternative like AR that allows you to be in the gym may be the perfect solution, a rest day that allows you to recover.
Credit to Truly Huge for a good background read on this topic: Effects of active recovery on various physiological systems.
Photo credit: pennstatelive
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