Differences in VO2max Measurements Between Breath-by-Breath and Mixing-Chamber Mode in the COSMED K5.

Winkert K; Kirsten J; Kamnig R; Steinacker JM; Treff G

International journal of sports physiology & performance.
16(9):1335-1340, 2021 Mar 26.

PURPOSE: Automated metabolic analyzers are frequently utilized to measure
maximal oxygen consumption (VO2max). However, in portable devices, the
results may be influenced by the analyzer’s technological approach, being
either breath-by-breath (BBB) or dynamic micro mixing chamber mode (DMC).
The portable metabolic analyzer K5 (COSMED, Rome, Italy) provides both
technologies within one device, and the authors aimed to evaluate
differences in VO2max between modes in endurance athletes.

METHODS: Sixteen trained male participants performed an incremental test
to voluntary exhaustion on a cycle ergometer, while ventilation and gas
exchange were measured by 2 structurally identical COSMED K5 metabolic
analyzers synchronously, one operating in BBB and the other in DMC mode.
Except for the flow signal, which was measured by 1 sensor and transmitted
to both devices, the devices operated independently. VO2max was defined as
the highest 30-second average.

RESULTS: VO2max and VCO2@VO2max were significantly lower in BBB compared
with DMC mode (-4.44% and -2.71%), with effect sizes being large to
moderate (ES, Cohen d = 0.82 and 1.87). Small differences were obtained
for respiratory frequency (0.94%, ES = 0.36), minute ventilation (0.29%,
ES = 0.20), and respiratory exchange ratio (1.74%, ES = 0.57).

CONCLUSION: VO2max was substantially lower in BBB than in DMC mode.
Considering previous studies that also indicated lower VO2 values in BBB
at high intensities and a superior validity of the K5 in DMC mode, the
authors conclude that the DMC mode should be selected to measure VO2max in