Recovery: A Multitude of Murky Metrics
Managing your energy is an essential skill for high performance, both in and out of the gym. In order to grow in all domains of life—mentally, emotionally, physically—the key is to create stresses that force you to gradually adapt and improve. Physical training—throwing an additional 10 lbs. onto the bar to build strength or sprinting uphill to boost aerobic capacity—is a tangible application of this so-called “adaptive stress.” But we must be careful not to subject ourselves to unabated stress, lest we slip from functional overreaching into the chronic fatigue and decreased performance that signals overtraining.
The only way to reap the rewards and come back sharper, stronger, and better than before is to recover fully, allowing those gains seep in and manifest. But a fast-paced, hyper-productive, and digitally distracted world leaves little room for intentional respite and recovery. Hence the recent rise of tech, tools, and supplements that claim to enhance recovery. The fitness industry is capitalizing on this trend. And consumers are shelling out some serious cash to accelerate their recovery from a hard charging lifestyle.
Despite the hype around new and innovative recovery tools, we are still flying blind most of the time. What is the best strategy to enhance your recovery? What tools do you need? How do you know if these techniques are actually working? The issue is that we still do not have a standard metric or battery of tests to accurately assess recovery. Most people are not clued in to accurately gauge their own recovery. And as the adage goes, “you cannot manage what you cannot measure.”
Recovery status is function of multiple inputs, influenced by both your physiology and your psychology. Let’s consider the mountain of metrics that could be potential inputs in a recovery assessment.
First are day to day objective metrics, which include:
Heart rate metrics: Monitoring heart rate is a good way to see how recovery progresses because your heart rate is a function the interplay between the sympathetic (“flight or fight”) and parasympathetic (“rest and digest”) branches of our autonomic nervous systems. During exercise our sympathetic nervous system dominates. Our ability to recover afterwards is a function of our parasympathetic or vagal tone.
Resting Heart Rate (RHR): A measure of your heartbeat when you are at complete rest, ideally monitored while sleeping or first thing in the morning before getting out of bed. A lower resting heart rate usually indicated improved fitness and recovery. The average person’s resting heart rate is somewhere between 60 and 90 beats per minute, but can be as low as 40 beats per minute for highly trained athletes. Once you know your average resting heart rate, any increase by 5-7 beats per minute or 10% is a good indication that the body is not fully recovered. The resting heart rate is also an important health indicator. A 2013 study in the journal Heart tracked the cardiovascular health of about 3,000 men for 16 years and found that a high resting heart rate was linked with lower physical fitness and higher blood pressure, body weight, and levels of circulating blood fats. The researchers also discovered that the higher a person’s resting heart rate, the greater the risk of premature death.
Heart Rate Recovery (HRR): A measure of the rate of decline in heart rate after the cessation of exercise. Essentially, you measure your heart rate immediately after a bout of intense exercise and again each minute afterwards and subtract one from the other. The faster your heart rate recovers, the higher your level of fitness. A heart rate recovery of 15-20 beats per minute after one minute of rest is considered about average for heart health and anything faster than that reflects good heart health. A 1999 study published in the New England Journal of Medicine found that abnormally low HRR was associated with double the risk of dying over 6 years. In a follow-up study, the same researchers found that HRR less than 13 beats/min doubled the 5-year risk of death. The strong relationship between heart rate recovery and cardiovascular health suggests that we should be looking at this metric when assessing risk of heart disease.
Heart Rate Variability (HRV): A measure of the difference in the amount of time between successive heart beats. HRV gives a real time measurement of the dynamic interplay between our sympathetic and parasympathetic drives. If a person’s system is in more of a fight-or-flight mode, the variation between subsequent heartbeats is low. If one is in a more relaxed state, the variation between beats is high. The faster you are able to switch between these inputs, the healthier your autonomic nervous system and the more efficiently you recover. Over the past few decades, research has shown a relationship between low HRV and worsening depression or anxiety. A low HRV is even associated with an increased risk of death and cardiovascular disease. In contrast, a high HRV may indicate higher cardiovascular fitness and resilience to stress. The real time feedback of HRV shows how more mindfulness, sleep, and physical activity affects your nervous system and recovery.
Sleep quality and sleep duration: Sleep is the ultimate recovery aid. You can spend your whole day in a cryotherapy chamber or on a foam roller, but if you are not getting adequate sleep, your recovery will be subpar. Sleep repairs the tissue damage from hard training, boosts immunity, and reduces inflammation, all of which contribute to proper recovery. And this is not only a function of how much time you spend in bed each night, but more importantly, the depth and quality of your sleep. Growth hormone, which stimulates muscle growth and repair, bone building and fat burning is released during deep sleep. In contrast, sleep deprivation wreaks havoc on physical performance with effects including slower muscle recovery, changes in mood, increased levels of cortisol, decreased glycogen synthesis, and increased ratings of perceived exertion. Patients who are experiencing the stress of critical illness in an ICU often suffer from sleep deprivation due to frequent treatments, alarms and lights, and loss of circadian rhythm. Much like an athlete experiencing the recurrent stress of physical training, these patients will not recover as quickly without deep, uninterrupted sleep. When it comes to recovery, sleep is king.
Hydration status: An acute change in body mass of 2% or greater, which is generally a function of hydration status, can impair recovery. Our hydration status impacts everything from our immune status to body temperature to cardiac output. Our muscles are actually 75% water. Adequate hydration after physical training enables protein synthesis and muscle repair, digestion to replenish glycogen stores, and reduced fatigue, and higher heart rate variability. A good rule of thumb for proper hydration status is to make sure urine is pale to slightly yellow in color.
Second are the day to day subjective (including psychological) metrics
Appetite: Appetite loss is a well-known symptom of overtraining. Depending on the severity, a loss of appetite may interfere with adequate energy and nutrient intake, and result in inadequate recovery.
Soreness: Soreness is a normal response to intense training. The microtrauma to your muscles is the stimulus for growth. The growth will not happen without adequate time for repair, however. And the soreness from inadequate repair also increases your chances of injury.
Energy level: Some days you simply won’t have the juice. And that is ok. The old adage to “listen to your body” is extremely valuable. However, the pertinent word here is “body.” The key is to distinguish low energy from under recovery from low motivation, feeling lazy, or mental stress.
Mood: Your mind and body are connected. In fact, they are one in the same. And so it should come as no surprise that your mental state impacts your recovery. And vice versa—your recovery status can impact your mood. If you are feeling apathetic, grouchy, or even depressed or anxious, this can be a reflection of physical fatigue from subpar recovery.
Health: if you are flirting with that line towards overtraining, your immune system cannot perform optimally, and you will be more susceptible to illness. When you feel a scratchy throat or runny nose coming on, this is a good indication to take it easy and rest up.
Yesterday’s performance: perhaps the best indicator of your recovery status is how you have performed over the past few days. A downward trend in performance is a good signal that it is time to take your foot off the gas.
Third are field based tests, which measure levels fitness and therefore provide a useful barometer. Any decrement in fitness may be and early warning sign of suboptimal recovery or even overtraining. Examples of common and validated tests include (but are by no means limited to):
Maximal 3-km run time trial.
Submaximal heart rate: Heart rate throughout various intensities between resting and maximal heart rate. Moderate submaximal intensity ranges from 50-75% of maximum heart rate, whereas vigorous submaximal intensity ranges from 75-99% of maximum heart rate. You would use a heart rate monitor to measure how your heart rate responds to various workloads (i.e. speed, resistance, incline, etc.) and what workloads are necessary to take you from moderate (50-75% MHR) to vigorous intensity (75%+ MHR) range.
Changes in physiological markers such as VO2 max, running economy, and lactate threshold all might also be useful.
And finally, there are laboratory-based physiological measures and blood biomarkers that might also indicate recovery status. These include:
Markers of Inflammation and Muscle Breakdown
CRP: high CRP indicates stress and inflammation within the body often resulting from the breakdown of tissues. Generally, exercise interventions reduce CRP levels, at least in patients with higher baseline CRP and high lipid profiles, such as those with heart disease. High-intensity training increases inflammation and temporarily results in increased CRP. If you do not get sufficient recovery, CRP levels will remain elevated.
Circulating free plasma DNA: after chronic excessive resistance exercise, plasma DNA concentrations increase in proportion to training load, suggesting that plasma DNA may be a sensitive marker for overtraining-induced inflammation.
Cytokines like IL-6: Adaptation through tissue healing and strengthening occurs via activation of a local inflammatory response and recruitment of cytokines like IL-6. With continued intense training and absence of adequate rest, this inflammatory response can become amplified, chronic, and pathologic. Evidence indicated that increased production of and/or intolerance to interleukin (IL)-6 during exercise may be a marker of overtraining/under recovery.
Creatine Phosphokinase (CPK) and Lactate Dehydrogenase (LDH) are enzymes found to be raised in the blood after exercise. While this has been reported from intense training, it is not necessarily a marker for overtraining. However, very high levels of CPK in the blood do indicate that overtraining may be imminent. Raised CPK occurs as a direct consequence of damage to muscle cells and often runs in parallel with post-exercise muscle soreness.
Plasma urea: concentration of nitrogenous wastes in the blood plasma (e.g. urea, 3-methyl histidine and uric acid) may provide a measure of muscle protein breakdown and hence may be markers of overtraining
Plasma glutamine: The concentration of plasma glutamine has been suggested as a possible indicator of excessive training stress with abnormally low levels of plasma glutamine are commonly reported in overtrained athletes
Markers of Impaired Immunity: The immune system is extremely sensitive to stress - both physiological and psychological - and thus, potentially, immune variables could be used as an index of stress in relation to exercise training. Possible variables might include:
Leukocyte counts
T-lymphocytes
Salivary IgA
Hormones: the data here seems to be quite murky, but you may see changes in levels of:
TSH
GH/IGF-1
Testosterone/Cortisol ratio
Micronutrient composition: Various micronutrients (vitamins A, C, D, E, B2, B6, and B12, folic acid, iron, selenium, and zinc) are essential for immune function. Immune function may be improved by restoring deficient micronutrients to recommended levels, thereby supporting faster recovery.
This list of recovery metrics is long and overwhelming. The idea of keeping track of these metrics feels impossibly cumbersome. Let me reassure you that not only would tracking all of this be incompatible with a normal life, it is not at all useful. Most of these metrics are dynamic and influenced by a multitude of stimuli that may or may not relate to your body’s recovery status.
Until we have the proper testing to determine one’s recovery status, most of the new tools and techniques cannot be scientifically validated. This is not to say that they do not work and do not make you feel better for one reason or another. Placebo is powerful. But it will difficult to substantiate their impact on recovery since we lack standardized metrics. And it will be difficult to set metrics since we cannot completely remove the placebo effect when evaluating different recovery modalities.
Coming next in this three-part series on Recovery, I will put posit a strategy on how best to integrate some of the above metrics into a comprehensive, yet manageable recovery assessment and then share the essential tools to get you started.