Measures and Metrics: Take Another Breath
Breathing Frequency: Mania or Madness?
I hope you have caught your breath after reading the riveting review of respiratory anatomy and physiology. It was a necessary precursor to a meaningful discussion on the application of breathing frequency as a metric for exercise intensity.
Thus far in our exploration of measures and metrics, we have reviewed RPE and HR as markers of internal stress in response to load. What does breathing frequency add to monitor load except for another metric to keep track of? Hold your breath…. it is exciting.
There is some subjectivity that can’t be escaped using RPE, and it does rely on effectiveness of self-assessment which is particularly challenging for beginners, or cyclists in the thick of competition. There is good data to confirm that breathing frequency is tightly coupled to RPE. In addition to being a more objective measure, breathing frequency can change more rapidly in response to stochastic efforts, like big climbs or sprints during an otherwise steady effort. A rider may have difficulty describing RPE as the difference between 9 and 10 cresting a hill, while breathing frequency responds instantaneously and can be measured in smaller units than the Borg scale.
Does breathing frequency offer any more insight into response to load than heart rate? Maybe not more insight, but clearer insight. Breathing frequency is not confounded by sleep, hydration, and heat, making it a “purer” measure of stress in response to the watts being generated.
From a practicality standpoint, breathing can be used to help athletes monitor exercise targets or zones more readily as it does not have a lag like heart rate response. Ventilatory thresholds (VT) are described by changes in minute ventilation (tidal volume x breathing frequency) during exercise intensity (see graph). If an athlete can carry on a conversation while cycling, they are below the VT1 turn point (talk test). These workouts would be valuable for active recovery and endurance type work (Zones 1 and 2). An athlete who is unable to speak in continuous sentences, stringing together single words strung together by forceful exhalations, would be at or near VT2. Just below this, an athlete would be working in sweet spot or at threshold. Above that, whereby words were replaced by gasps, the athlete is likely doing VO2 efforts in Zone 5.
Ventilatory thresholds VT1 and VT2 have practical application for athletes to identify work rates. Zones are depicted by shaded yellow columns.
Wait… these thresholds look familiar. VT1 and VT2 have a very special relationship with lactate thresholds (LT). The graph above and below should look very similar with exercise intensity on the X axis. The dependent variable on the Y axis has changed from minute ventilation to blood lactate.
Lactate thresholds LT1 and LT2 require blood analysis.
The third graph includes both variables as they increase with work rate. Note the two “turn points”, ventilatory threshold 1 (VT1) and VT2 and lactate threshold 1 (LT1) and LT2, occur nearly at the same exercise intensity. Measuring blood lactate is tricky, uncomfortable, invasive and certainly inconvenient if not done in a lab. The metabolic events that increase blood lactate also increase hydrogen ions (H+), which is a driver for ventilation, making breathing frequency an easier metric to record (if you have a sensor) or be aware of.
VT1= ventilatory threshold, VT2= respiratory compensation, LT1= lactate threshold, LT2= onset blood lactate accumulation (OBLA)
Perhaps the most exciting potential for breathing frequency is prediction of failure, allowing an athlete to ride close to the sun without getting burned. This is something HR cannot predict.
Most athletes are familiar the idea of calculating heart rate reserve (HRR) to describe zones of training. HRR is found by subtracting resting HR from HRmax, and then using a percentage of HRR to provide training targets. HRmax is not affected by training, and decreases with age. Resting HR decreases in response to training. Therefore, HRR accounts for individual differences in RHR. For example, if JoeCyclist has a HRmax of 190bpm and RHR of 70bpm, RHR= 120bpm. After training adaptations, his RHR is 60bpm, RHR= 130bpm. If JoeCylist continues to train at a target of 70% HRmax (133bpm), he will be working relatively less hard.
Breathing frequency reserve can be calculated in the same way. It is the difference between maximal breathing frequency and resting breathing frequency. The breathing reserve is larger compared to the HRR. During exercise, a lower percentage of breathing frequency is utilized. As the ratio of breathing reserve approximates HRR, reaching physiological limits is imminent. This is a powerful monitor of fatigue and tool for predicting failure to hold pace (Listen to the Fast Talk Labs podcast episode #363 with Dr. Stephen Seiler).
Cool. Can this be measured outside of the lab? Yes, breathing frequency reserve can be measured with a sensor and compared to % HRR to predict failure. Tymeware is one of several companies to keep your eye on. Visma-Lease A Bike used Tymeware technology during the Tour de France.
For non-Tour de France athletes, one more sensor equals one more investment in hardware, and one more set of metrics to keep track of. You will have to decide is a sensor is worth the investment. Don’t fall prey to marketing. Do your research. There will likely be wearables in addition to chest straps with differing comfort and reliability. Breathing frequency is fairly straightforward, but there will likely be claims to also measure tidal volume in order to get minute ventilation. Integrating these metrics into a platform, understanding norms and ranges and response patterns will all take a toll. Measures and metrics: mania or madness? Keep it simple. Just breathe.
What if we just simplify things and be aware of our breathing? Simple, and for most athletes, sufficient. As an exercise physiologist and coach, I cannot over emphasize the power of this very simple tool. It is bullet proof. Unlike HR, it is not subject to the influences of sleep, hydration and heat. Nor does it have a delay, such that when you are trying to achieve a max sprint for 20 seconds on: 10 seconds off, breathlessness is nearly instantaneous while HRmax is never achieved due to the lag and recovery time. It is driven by the centers in the brain very similar to RPE, but removes the subjective component.
Having athletes be aware of changes in ventilation to stay within their desired zone and monitor recovery from an interval is a powerful tool. And free. Nobody can “fake” breathing. If you are gassed, you need to suck air. And if you aren’t gassed and feign fatigue in hopes to lure another rider into doing the work, you’ll likely hyperventilate, blow off too much CO2 and quickly restore normal ventilation. The BS meter on breathing is tightly regulated.
Breathe responsibly.
