Exercise Science and Neurophysiology of Post-Workout Intersession Active Recovery
With a focus on road cycling
I n this article, the focus is on post-workout and intersession active recovery, with perhaps a future separate article on intra-workout active recovery. E.g. the following would be more of an example for such a separate article:
Active recovery between intervals might be better due to keeping the aerobic system more active and making it contribute more in further intervals.
Source: Sprinting, Excessive Sugar, Active Recovery, and More — Ask a Cycling Coach 370 — YouTube, TrainerRoad
The addition of “intersession” is meant to signify how active recovery could also enhance future-session performance (e.g. carbohydrate replenishment).
The term “post-workout” is meant to signal a relationship between active recovery and a previous strenuous exercise session.
Content
- Definitions of Active Recovery in Cycling
- Physiology
- How Does Active Recovery Not Hinder (Future-Session) Performance?
- Effect of Active Recovery on MEV/MAV/MRV
- Bimodal BFR-Enhanced Active Recovery?
- Lactate Clearance and Effect on Subsequent Adaptations and Performance
□ Maximal Lactate Steady State - Biochemistry
- Type 1 Slow-Twitch Oxidative Muscle Fibers
- Nutrition - Neurophysiology
- Autonomic Nervous System
□ Audio-Assisted Active Recovery? - ChatGPT-4 (Summary)
Definitions of Active Recovery in Cycling
When following Dr. Andrew Coggan’s 7 power zones, active recovery tends to fall within <55% Functional Threshold Power (FTP) or <0.75 Intensity Factor (IF), with the former being used/preferred outdoors (e.g. due to higher Normalized Power (NP) and its respective effects on fitness) and the latter indoors (e.g. an ergometer isopower workout), see: https://www.trainerroad.com/forum/t/endurance-rides-feel-absolutely-useless/89127/235?u=lorenz_duremdes, Dr. Andrew Coggan.
The following table showcases the different power zones and will keep using this for the remainder of this article for simplicity purposes (the source of the table also contains heart rate based training zones).
Which has the following weighted physiological adaptations per zone:
Another option is to model it similarly as in resistance training, namely the “stimulating repetitions model based on reps in reserve” (with reps in reserve being dependent on task failure), as seen in the image below:
(For those wanting some more nuance or food for thought: The Evidence is Lacking for “Effective Reps” (strongerbyscience.com))
Physiology
How Does Active Recovery Not Hinder (Future-Session) Performance?
Active recovery mostly makes use of slow-twitch muscle fibers as seen in this image below:
55% FTP ≈ 44% of VO2 max:
In trained runners, one might expect FTP to lie at about 85 to 87 percent of their power at VO2max, and closer to 90 percent (or higher) of power at VO2max in elite runners. In contrast, FTP in trained cyclists might lie at 80 to 82 percent of their power at VO2max.Source: https://www.trainingpeaks.com/blog/the-differences-between-running-and-cycling-power/
The aforementioned can be combined with (or used to understand) the following chart, which depicts exercise intensity multiplied by duration resulting in fatigue (arbitrary units):
One can see how increasing exercise intensity as a percentage of FTP results in exponentially greater fatigue. This is due to e.g. greater skeletal muscle fiber recruitment i.e. Henneman’s size principle:
Motor neurons with large cell bodies tend to innervate fast-twitch, high-force, less fatigue-resistant muscle fibers, whereas motor neurons with small cell bodies tend to innervate slow-twitch, low-force, fatigue-resistant muscle fibers. In order to contract a particular muscle, motor neurons with small cell bodies are recruited (i.e. begin to fire action potentials) before motor neurons with large cell bodies.
Source: Henneman’s size principle — Wikipedia
I.e. starting from type 1 slow-twitch oxidative fibers > type 2a fast-twitch oxidative > type 2x fast-twitch glycolytic.
See the heading “Biochemistry > Type 1 Slow-Twitch Oxidative Muscle Fibers” and “Neurophysiology > Autonomic Nervous System” below for more information on how active recovery doesn’t hinder performance.
Effect of Active Recovery on MEV/MAV/MRV
Definition of MRV
The highest volume of training an athlete can do in a particular microcycle (or any chosen timescale e.g. session) and still recover to present a full overload in the next microcycle.
Source: How Much Should I Train?: An Introduction to the Volume Landmarks (Renaissance Periodization) by Dr. Mike Israetel and Dr. James Hoffmann, p. 9
Volume-driven adaptations like endurance and hypertrophy benefit from all methods that raise Maximum Recoverable Volume (MRV) and lower Minimum Effective Volume (MEV) without impeding adaptation capacity.
Source: How Much Should I Train?: An Introduction to the Volume Landmarks (Renaissance Periodization) by Dr. Mike Israetel and Dr. James Hoffmann, p. 53
As we can now interpolate, the effect of active recovery (when done properly) would elevate both MAV and MRV without impeding adaptation capacity.
MRV is increased due to active recovery reducing peripheral fatigue.
MAV is increased due to being able to train more (which brings with it fatigue, but as fatigue is now lower through active recovery, more fatigue can be accumulated as well as its concomitant fitness adaptations, see: Dr. Banister’s impulse-response model).
Furthermore, the following study shows that 1 hour of single-leg cycling at a corresponding 65–70% VO2 max (~52–56% FTP i.e. zone 1 of Coggan’s 7 power zones), progressively increases i.a. muscle protein synthesis 3 hours post-workout (see: https://www.facebook.com/StrengthandConditioningResearch/photos/a.314294568681572/3029846213793047/, for an infographic by Chris Beardsley):
Reasoning what it would do with MEV is a more tricky one. One could extrapolate using the study mentioned above (Intensity- and Duration-Based Options to Regulate Endurance Training — PMC (nih.gov)), that active recovery might actually increase MEV (which is more often than not, non-beneficial) due to being further away from task failure (see also: Fatigue Dependent Training Plan Design — FasCat Coaching).
However, if the reduction in fatigue due to active recovery outweigh its respective increase in MEV due to e.g. increasing the next-session(s) Training Stress Score (and its respective comparatively higher fitness improvements i.e. Acute Training Load and more importantly Chronic Training Load), then one could argue from a physiological standpoint that it’s still comparatively more advantageous to engage in active recovery, at least in this ‘in vitro’ example.
Another speculation could be that if active recovery reduces stress hormones (e.g. cortisol) while stimulating e.g. endorphin (a ‘mood elevator’), then it could decrease MEV through such mechanisms (cortisol is considered a catabolic hormone).
Note: I haven’t been able to find explicit research/data indicating precise values or a range of values in terms of aerobic exercise intensity (e.g. based on heart rate/FTP or VO2 max) that would reduce e.g. cortisol and/or increase e.g. endorphin. The following study, however, does show explicit data on this matter although not specifically in the active recovery zone (see e.g. TABLE 2, Overview of the pilot data investigating the intensity of the aerobic exercise (Ex1) and (Ex2).):
Although the aforementioned (Note) might appear Talmudic (e.g. you can perhaps simply base it off whether active recovery makes you ‘feel less stressed’ or not), I personally still think it’s an interesting question.
Bimodal BFR-Enhanced Active Recovery?
A better K+ regulation after blood flow restriction (BFR)-training is associated with an elevated blood flow to exercising muscles and altered muscle antioxidant function, as indicated by a higher reduced to oxidised glutathione (GSH:GSSG) ratio, compared to control, and an increased thigh net K+ release during intense exercise with concomitant antioxidant
infusion.Extrapolation: BFR combined with active recovery might enhance recovery even further. There also might be an optimization/trade-off between the BFR-enhanced active recovery session length (e.g. the longer the session, the longer BFR diminishes blood flow) vs. its potential benefits post-BFR active recovery session.
Therefore, another radical option might be more hybrid (i.e. bimodal BFR-enhanced active recovery):
- Active Recovery with BFR: Initially, you would engage in active recovery while using BFR.
- Optimizing Duration of BFR: The key challenge here is determining the optimal duration for which BFR should be applied during active recovery. This duration should be long enough to induce the desired physiological responses (e.g. hyperaemia) but not so long as to cause excessive discomfort or risk of adverse effects.
- Transitioning to BFR-Free Active Recovery: After the optimal duration of BFR, you would then continue the active recovery session without BFR. This phase would allow enhanced blood flow (reactive hyperaemia) to return to the muscles, potentially aiding in the flushing out of metabolic waste products and facilitating nutrient delivery.
- Potential Benefits of the Hybrid Approach: This approach might offer a balance between the enhanced metabolic and hypoxic stress of BFR and the traditional benefits of active recovery. It could potentially lead to improved recovery, enhanced muscle adaptation, and possibly greater gains in muscle strength and endurance, compared to doing either active recovery or BFR in isolation.
Lactate Clearance and Effect on Subsequent Adaptations and Performance
While lactate itself doesn’t directly cause fatigue, its accumulation can contribute to the buildup of hydrogen ions and the associated decrease in muscle pH, which might contribute to muscle fatigue and shut down muscle contraction[The Hybrid Athlete by Alex Viada, p. 47].
Lactate is also shown to be a potent metabolic stimulus, which is important for adaptation (as cited below), while active recovery improves lactate clearance. Therefore this could raise questions whether this concomitant lactate removal attenuates subsequent adaptations (and performance) or not.
The following study is done primarily through running:
High-intensity interval training (HIIT) can be extremely demanding and can consequently produce high blood lactate levels. Previous studies have shown that lactate is a potent metabolic stimulus, which is important for adaptation. Active recovery (ACT) after intensive exercise, however, enhances blood lactate removal in comparison with passive recovery (PAS) and, consequently, may attenuate endurance performance improvements. Therefore, the aim of this study was to examine the influence of regular ACT on training adaptations during a HIIT mesocycle.
Conclusion: Regular use of individualized ACT did not attenuate training adaptations during a HIIT mesocycle compared to PAS. Interestingly, we found that the ACT group obtained a significantly higher anaerobic lactate threshold (AT) following the training program compared to the PAS group. This could be because ACT allows a continuation of the training at a low intensity and may activate specific adaptive mechanisms that are not triggered during PAS.
Wingate Anaerobic Test
During active recovery, the subject pedaled the cycle ergometer at 80 revolutions per minute at an intensity equal to 40% VO2peak.
After supramaximal leg exercise, active recovery produced significant decreases in both absolute and relative measures of blood lactate concentration when compared with the sports massage and rest conditions.
Maximal Lactate Steady State (MLSS)
FTP is a surrogate of MLSS (Dr. Andrew Coggan) and the latter could therefore be an important metric to measure (and estimate) athletic performance (although the latter furthermore requires e.g. Power Duration Model or Maximal Power Available (Xert), in terms of external validity).
…the anaerobic threshold (AnT) is important in evaluation of endurance exercise performance (10, 17). When performing tests to detect the AnT, the purpose is to identify the highest exercise intensity one can maintain over time without blood lactate accumulation, often referred to as the Maximal Lactate Steady State (MLSS) (4). The MLSS is defined as the highest workload or velocity (MLSSv) or blood lactate concentration (BLC) (MLSSc) that can be maintained without continual lactate accumulation over time and is considered the gold standard measurement of individual anaerobic threshold (IAnT) (5, 6, 17)
Interpolation: As cited by the first study (i.e. “…we found that the ACT group obtained a significantly higher anaerobic lactate threshold (AT) following the training program compared to the PAS group”), intersession active recovery could on its own (i.e. not accounting for e.g. indirectly increasing CTL) increase subsequent performance through e.g. increasing MLSS.
Biochemistry
Type 1 Slow-Twitch Oxidative Muscle Fibers
Slow-twitch muscle fibers are also a lot more fatigue-resistant and recover faster.
Slow-twitch muscle fibers have high concentrations of mitochondria and myoglobin. Although they are smaller than the fast-twitch fibers, they are surrounded by more capillaries (1,2) (source: Fast-Twitch Vs. Slow-Twitch Muscle Fiber Types + Training Tips | NASM) i.e. they can make more use of fat oxidation and aerobic glycolysis.
As active recovery is a relatively low % of VO2 max, it mostly utilizes stored fat to supply ATP demands (fatty acid catabolism), which means glycogen is being spared.
Slow-twitch muscle fibers also possess a higher defense against reactive oxygen species (ROS) due to e.g. containing higher glutathione but also (synergystically) having a higher antioxidant enzyme activity such as superoxide dismutase.
Source: Redox Profile of Skeletal Muscles: Implications for Research Design and Interpretation — PubMed (nih.gov)).A greater ROS scavenging capacity might be due to more antioxidant enzyme expression in oxidative muscle, mostly resulting from higher content mitochondria.
Source: Mitochondrial Properties in Skeletal Muscle Fiber — PMC (nih.gov))High levels of reactive oxygen species result in contractile dysfunction and fatigue.
Source: REACTIVE OXYGEN SPECIES: IMPACT ON SKELETAL MUSCLE — PMC (nih.gov)Extrapolation: By engaging in active recovery (as well as a <30 minute cooling down in other strenuous sessions), slow-twitch fibers, with their elevated antioxidant capacity, might help in scavenging these harmful ROS (resulting/accumulating from previous workout(s)), aiding muscle repair and minimizing oxidative stress.
Further references/reading on muscle fiber types and their different properties:
Comprehensive article on reactive oxygen species and their impact on skeletal muscle:
Caveat
Because ROS/reactive nitrogen species (RNS) are mediators in skeletal muscle adaptations to exercise, the chronic supplementation of antioxidants might prevent the beneficial effects of exercise, including mitochondrial biogenesis and hypertrophy.
Nutrition
The following article gives an in-depth overview on how to adjust your nutrition according to calories/carbohydrates burned through exercise:
During active recovery, almost all of the calories burned are coming from stored fat (fatty acid catabolism), so there’s no critical need to consume extra carbohydrates in terms of recovering from this session (as opposed to e.g. doing a workout at FatMax (approximately upper zone 2) with the same duration, as 50% of the calories used would be coming from carbohydrates).
However, when having a more macroscopic perspective (anything longer than 1 session e.g. a microcycle), it could be beneficial to replace most of the calories burned from active recovery with carbohydrates, to replenish glycogen stores.
The calculation is simple: carbohydrates (g) = calories burned / 4
>1 gram of carbohydrate = 4 caloriesSo if you have an FTP of 277 W and do an active recovery session (55% FTP) for 30 minutes, you would burn:
(277 W · 0.55) · (30m · 60s) / 0.24 / 4.18 / 1E3 = 249 calories
Meaning that you could replenish your glycogen stores with 249/4=62 g of carbohydrates without gaining fat.
See the following for a more detailed explanation of the formula and its units:
Other possible advantages in relation to nutrition with active recovery are:
- More easily meeting one’s required micronutrients (e.g. vitamins) when replenishing calories burned from active recovery.
- When choosing to refuel calories burned from active recovery with carbohydrates, one can apply nutrient timing (e.g. 15m before the workout) to e.g.:
- Enhance absorption (through e.g. elevated insulin sensitivity or assisting the passage of food through the intestines[Horner et al. (2015), ‘Acute exercise and gastric emptying: a metaanalysis and implications for appetite control’, Sports Medicine, 45(5), 659–78; Keeling et al. (1990), ‘Orocecal transit during mild exercise in women’, Journal of Applied Physiology, 68(4), 1350–3.][In Praise of Walking — The New Science of How We Walk and Why It’s Good for Us (by Shane OMara), p. 14])
- Attenuate reactive hypoglycemia (especially when consuming sugars with a high glycemic index).
Neurophysiology
Autonomic Nervous System
When talking about the neurophysiology (in this case the autonomic nervous system balance i.e. (para)sympathetic nervous system balance), exercise for ≤120 minutes below the first ventilatory threshold causes minimal disturbance in autonomic nervous system balance (source: How to Get in the Best Shape You’ve Ever Been In: Block Periodization — YouTube, Dylan Johnson). Besides, active recovery is usually done shorter than 2 hours (e.g. 30 minutes).
One’s ventilatory threshold is said to reflect levels of anaerobiosis and lactate accumulation.
…
For most people this threshold lies at exercise intensities between 50% and 75% of VO2 max.
Extra: Comparison studies of more athletic people have shown that your ventilatory threshold occurs at a higher intensity if you are more active or have been training for that exercise (i.e. principle of specificity).
The aforementioned could also be another reason why active recovery doesn’t hinder (next-session) performance.
Audio-Assisted Active Recovery?
Music may be an effective approach for improving post-exercise parasympathetic reactivation, resulting in a faster recovery and a reduction in cardiac stress after exercise.Source: Music Attenuated a Decrease in Parasympathetic Nervous System Activity after Exercise | PLOS ONE
Extrapolation: The study mentioned uses a somewhat RPE-based method equal to “somewhat hard” to adjust the resistance during cycling on an ergometer (i.e. 60 W for males and 40 W for females), so we can’t say for certain what power/heart zone this would recide in (a guesstimate could be approximately zone 2).
Besides, this study is being done without (or at least not deliberately) involvement of e.g. previous-session peripheral/central fatigue (e.g. 24 hours beforehand), with all its forthcoming effects such as increased (nor)epinephrine (which might even be larger in trained endurance athletes, see: sports adrenal medulla).
So a careful extrapolation must be made that listening to one’s preferred music during active recovery might enhance the recuperation effects of the latter (from a physiological and empirical standpoint, unless there are studies out there mentioning this explicitly that I haven’t been able to find yet, otherwise my advise would be to just do whatever you feel best with or motivates you the most, etc).
ChatGPT-4 (Summary)
This comprehensive article delves into the exercise science and neurophysiology of post-workout intersession active recovery, with a specific focus on road cycling. It explores various aspects of active recovery, including its physiological, biochemical, and neurophysiological dimensions, and how they contribute to enhancing future-session performance in endurance athletes, particularly cyclists.
Key Highlights
Definitions of Active Recovery in Cycling
- Active recovery is typically performed at less than 55% of Functional Threshold Power (FTP) or less than 0.75 Intensity Factor (IF).
- Different power zones are identified, each with its specific physiological adaptations.
Physiology of Active Recovery
- Non-Hindrance to Future-Session Performance: Active recovery primarily uses slow-twitch muscle fibers and is performed at an intensity that does not significantly add to fatigue, thus not hindering future performance.
- Effect on Training Volume and Intensity: Active recovery can influence Maximum Effective Volume (MEV), Maximum Adaptive Volume (MAV), and Maximum Recoverable Volume (MRV), potentially increasing the capacity for training volume and intensity without impeding adaptation.
- Lactate Clearance: Engaging in active recovery improves lactate clearance and might positively affect subsequent adaptations and performance.
Biochemistry
- Muscle Fiber Utilization: Type 1 slow-twitch oxidative fibers are predominantly used during active recovery. These fibers are more fatigue-resistant and recover quicker.
- Nutritional Aspects: During active recovery, energy primarily comes from fat oxidation, sparing glycogen stores. Nutritional strategies should consider this aspect for optimal recovery and performance.
Neurophysiology
- Autonomic Nervous System: Active recovery is believed to cause minimal disturbance in the autonomic nervous system balance, aiding in quicker recovery.
- Audio-Assisted Recovery: Incorporating music into active recovery sessions might enhance parasympathetic reactivation and improve recovery rates.
Bimodal BFR-Enhanced Active Recovery
- This novel approach combines blood flow restriction (BFR) with active recovery to potentially enhance recovery further. It involves initial active recovery with BFR followed by a BFR-free phase, aiming to balance metabolic stress and traditional recovery benefits.
Practical Implications and Training Adjustments
- Nutrition and Recovery: It emphasizes the importance of appropriate nutritional strategies in conjunction with active recovery, such as carbohydrate replenishment to optimize glycogen stores.
Caveats and Considerations
- The article cautions against the overuse of antioxidants, as they might interfere with exercise-induced adaptations.
