Cycling through Covid: Do face masks affect exercise capacity?

In the first of a series of scientific review, courtesy of the IBFI's scientific sub-committee, Glasgow based fitter Nuno Gama summarises research looking at the cardiopulmonary impact of wearing surgical and N95 masks during exercise.

The use of face masks to limit or stop indirect pathogenic transmission of the coronavirus disease 2019(COVID-19) is perhaps one of the most controversial topics in the sports performance scene of current times. With most governments adopting compulsory mask usage policies, there is debate emerging whether respiratory capacity is diminished in healthy, athletic or populations with decreased lung function.

Fikenzer and colleagues (2020) looked at the differences in cardiopulmonary exercise capacity between three mask conditions: no mask, disposable surgical mask and disposable FFP2/N95 mask. The study involved 12 male volunteers (age 38.1; SD = 6.2 years) with a BMI of 24.5 (highest normal; SD of 2kg/m2), recruited from the medical staff at the Leipzig University Hospital. Cardiac output, stroke volume, heart rate, VO2max and spirometry data (see diagram, below) were collected continuously at rest, during the task and during recovery.

Participants completed three ramp tests to exhaustion (with 48h between tests, each one corresponding to a mask condition, randomised prior to testing) but were not blinded to the type of mask. The stepwise protocol consisted of a 50W increments with the duration of 3 minutes and an initial step of 50W until voluntary exhaustion. To understand the spirometry results, the diagram provides information on the parameters measured on a respiratory test.

Tidal volume - amount of air breathed during normal respiration

Inspiratory reserve volume - amount of air inhaled above tidal volume during a deep breath

Expiratory reserve volume - amount of air exhaled below tidal volume during forceful breath out

Residual volume - amount of air left in the lungs after max exhalation

Vital capacity - the most amount of air in a max exhalation after a max inhalation

Inspiratory capacity - total volume that can be inspired after the end of a normal breath cycle at rest

Functional residual capacity - volume of air left in the lungs at the end of a passive respiration at rest

RESULTS

At rest, results show that tidal volume did not differ across conditions, but that breathing frequency was reduced for the FFP2/N95 mask alone (from ~15 bpm to ~13 bpm). This could mean a higher pressure force is needed to overcome the higher airflow resistance offered by the FFP2/N95 mask. This in turn reduced the frequency of respiration to a slower, but more effective (since all haemodynamic parameters were also maintained) breathing. The forced vital capacity was significantly reduced by the masks (~8% reduction for surgical mask and ~12 for FFP2/ N95 mask). This is significant because it suggests both masks limit the amount of air passing through the mask at max inspiration and exhalation.

At maximal load, the results show reductions in tidal volume (from ~3 L with no mask, to ~2.7 L with the FFP2/N95 mask), breathing frequency (41 bpm no mask, 37 bpm FFP2/N95 mask) and ventilation (131 L/min no mask to 99L/min FFP2/ N95 mask). These reductions were for the FFP/ N95 mask alone and no differences were found between “no mask” and “surgical mask” in all physiological and cardiopulmonary parameters. Furthermore, maximal power and maximal oxygen uptake were reduced only by the use of the FFP2/N95 mask, and results for the surgical mask did not differ from the “no mask” condition. These results seem to suggest that the use of the more robust FFP2/N95 mask will decrease oxygen availability and as such, respiration becomes slower but more strenuous. It would be interesting to measure thorax expansion to understand if forced vital capacity correlates well with the “breathing harder” hypothesis.

ANALYSIS

Contrary to the authors’ conclusions, I did not see clear and sustained evidence from this study that a surgical mask is any different (in cardiopulmonary and metabolic measures) than not wearing a mask, during exercise.

If we consider that at rest there were significant reductions in function with a surgical mask and that these dissipate during exercise, then we can assume that any air resistance introduced by the surgical mask is overcome by breathing harder. The same is not true for the FFP2/N95 mask.

One limitation of this study is that the sample of participants can be considered untrained cyclists (2h of physical activity per week, not specified to be cycling). A plethora of research confirms that untrained cyclist show a greater acute metabolic response to exercise than trained cyclists, so it would be interesting to test if the respiratory and metabolic changes seen with mask usage by untrained riders are present in trained cyclists (or even intermediate riders or commuters). For example, if a cyclist rides to work every day, will they overcome the physiological deficits introduced by the mask, as we see in hypoxia training? It would be also valuable to determine the minimum amount of cycling (per week) needed to overcome the detrimental effects of mask usage. Furthermore, we know novice riders experience greater muscle coactivation when compared to trained cyclists (e.g. Chapman, Vicenzino, Blanch, and Hodges, 2008), despite similar timings in EMG peaks[MOU2] . This coactivation results in longer periods of muscle activation with a direct metabolic consequence. For this reason in future research it would be important to randomly include individuals with different training levels to understand if the results presented in this study are an effect of the mask usage, or the level of training of the participants.

Lastly, the increase in airway resistance introduced by the masks was identified by the authors as the main reason for the “negative impact on cardiopulmonary capacity” (Fikenzer et al., 2020), but, it is possible that the increased resistance to airflow introduced by the masks could be offset by the increase in air pressure as the cyclist travels through air (we know that the faster we ride, the more air pressure we build up in front of us). Could the positive air pressure that builds up in front of the rider be enough to off set the air flow resistance introduced by the mask? This study introduces an important concept in the “new normal” methodology of training and cycling against air resistance is an important research question that needs addressing.

Nuno Gama, PhD, is the founder of ORBIS LaB, a laboratory for advanced biomechanics and sports performance, based in Glasgow, UK.