Save Your Breath
Our last two newsletters have brought us up to speed on respiratory anatomy and physiology, and using ventilatory thresholds (V1 and V2) to monitor training intensity. What if we could use breath to train AND train to have more breath?
Most cyclists are familiar with training skeletal muscles to improve pedaling performance. Squats and deadlifts may give us more power through the pedal. Could adding resistance training for our diaphragm and other inspiratory muscles provide a performance benefit? And what about those Breathe Right nasal strips worn by Team Visma | Lease a Bike in the Tour de France?
The answer to these questions is best answered by asking a different question: what is the limiting factor in maximal oxygen consumption (VO2max) and performance? If the answer is ventilation, then perhaps there is merit to exploring inspiratory muscle training (IMT) or nasal strips to improve VO2max and performance.
Before we look at the research on IMT and nasal strips, a short physiology review on ventilation as it relates to VO2max.
VO2 can be described by the Fick equation for oxygen supply and demand.
VO2= cardiac output x arterial-venous O2 difference.
This equation represents the interplay between oxygen supplied by the heart (cardiac output = heart rate x stroke volume), delivery (oxygen rich arterial blood) and utilization (tissues demand oxygen- the rest is returned to the heart in oxygen poor venous blood). During exercise, oxygenated blood to organs like the gut is shunted away and redistributed to working skeletal muscles. This redistribution is very effective in using most of the oxygen available. Very little returns in the heart in the venous blood.
In order for oxygen to be consumed by working muscles, it must pass through four stages of gas exchange. A limitation in any of these steps could impact maximal oxygen consumption.
Ventilation (airflow in/out of lungs)
Gas exchange (oxygen diffusion from lungs to blood)
Cardiac output (pumping capacity in L/min) and oxygen transport
Muscle oxygen utilization
There is little debate that the supply chain (3, cardiac output & oxygen transport) is the primary limiting factor in VO2max. Muscles demand more than what the cardiovascular system can supply, due in part to training adaptations, such as increased mitochondrial density, mitochondrial enzyme activity and capillarization (4, muscle oxygen utilization).
So that’s it, right? If cardiac output is the limiting factor, only performance enhancing strategies aimed at increasing supply, like blood doping, would be effective. Why even open up a discussion about breath training?
We noted in the anatomy and physiology newsletter that the lung is “over built” with respect to capacity. Ignoring disease states such as asthma or COPD, structural airway issues like a deviated septum, ventilation (1) is not a limiting factor.
Or is it? Here is the argument for nasal strips: breathing through the nose vs the mouth offers the benefit of air purification and humidification. At high volumes and velocities, the nasal passage is often limiting, forcing cyclists (and other athletes) to mouth breathe. If we clarify that ventilation isn’t a limiting factor, but rather ventilation through the nasal passages is limiting, then perhaps the nasal strips have merit.
Nasal strips may increase nasal cavity cross-sectional area, stabilize the nasal vestibule and increase airflow, which gives the perception of reduced dyspnea (shortness of breath). We know that the perception becomes reality, so it may very well be that these athletes feel as though can perform better. The data does not support that theory.
A 1999 cycling ergometer trial found no difference in cardiorespiratory function, work output, and perceived exertion using nasal strips vs placebo. More recently, a 2021 systematic review and meta-analysis of over 600 studies found the external nasal dilator strip showed no improvement in VO2max., HR and RPE outcomes in healthy individuals during exercise. But they sure look like fun.
Team Visma | Lease a Bike Jonas Vingegaard
There is surprising and revolutionizing data out of Jerome Dempsey’s lab at UW- Madison to suggest that in highly trained endurance athletes, gas exchange (2) may impact performance (review). Recall that the alveoli of the lung do not adapt to training, while capillarization and perfusion of the alveoli adapt well to training. This creates a mismatch between ventilation and perfusion (V:Q ratio we talked about in the anatomy and physiology newsletter). Paradoxically, the more fit and adapted an athlete becomes, the more likely gas exchange inefficiencies are to occur. This mismatch doesn’t have a solution, certainly not nasal strips.
There is another shortcoming within the respiratory system, however, that may be improved by inspiratory muscle training (IMT). Most cyclists are familiar with the benefits of doing squats and deadlifts to strengthen quadriceps and hamstrings. Respiratory muscles are also skeletal muscles that can adapt to training. The lung itself is overbuilt with respect to capacity and does not adapt to training, but the skeletal muscles used to inflate the lung are not overbuilt and can adapt to training.
A 2006 study revealed that work output by respiratory muscles during sustained heavy exercise may limit performance in elite cyclists. Dempsey et al. “unloaded” the work of breathing using mechanical ventilation, and observed cyclists had improved endurance and sustained higher power outputs, but did not improve VO2max. This study suggests that respiratory fatigue of the diaphragm or supporting inspiratory muscles may impair ventilation by reducing effective gas exchange (2), or by “stealing” blood flow from working leg muscles (4).
IMT may play a small but important role in improving gas exchange by improving the fatiguability of respiratory muscles. In a 2002 study, highly trained cyclists performed 6 weeks of IMT (30 breaths, 2 x day) and showed ~5% improvements in simulated time trial performance and reported decreased perceived breathing effort. A 2012 meta-analysis reports IMT consistently improved performance in recreationally trained athletes, ~2–5% in time trial performance, increased time to exhaustion, and reduced breathing effort. However, the effect is smaller and less consistent in highly trained athletes. A 2018 systematic review concluded benefits of IMT are most notable when ventilatory loads are high (altitude, heat, sustained near VO2max efforts).
Power Breathe
IMT is not a large investment in time or equipment, and it certainly won’t hurt. Dr. Dempsey summarizes this well in this quote from Is the Healthy Respiratory System (Always) Built for Exercise?
“Accordingly, under special circumstances, functions of the lung (in the highly trained) and/or the respiratory muscles (in trained and untrained) will impede performance. However, the major, universal contributors to exercise performance limitation in health reside primarily in the relatively ‘weak links’ to O2 transport and utilization provided by limitations to skeletal muscle blood flow and O2 utilization by skeletal muscle.”
Bottom line: keep pushing the pedals. The cardiovascular training adaptations are where the big gains lie.
