Comparison of Slow Component Phase of O2 Kinetics and Oxygen Saturation During Running and Cycling

Abstract

0101 The slow component phase (SC) of oxygen uptake kinetics arises when individuals exercise at workloads greater than their lactate threshold (>LT) and can be seen in both running and cycling exercises. However, it has been reported that the SC in cycling is significantly greater than the SC in running when exercising at the same absolute workload. It is unclear at this point what the physiological reasons are for this difference, but it has been hypothesized that more type II fibers are being recruited during cycling. Purposes: To determine if there was a difference in the slow component phase of oxygen uptake during running and cycling when athletes exercised at the same absolute workload and to establish whether the difference was related to a decrease in percent muscle oxygen saturation (StO2) of the working muscle (vastus lateralis in cycling and gastrocnemius in running). Methods: Nine male triathletes underwent two incremental exercise tests (5–6 minute stages per workload), to near maximal effort, and two maximal exercise tests, running and cycling. The test was randomized and separated by ≈1 week. During the tests, StO2, blood lactate (HLa), and oxygen uptake (VO2) were obtained during each workload. HLa was drawn one minute before the end of each stage and was graphed to determine lactate threshold (LT). StO2 and VO2 data points were graphed for two workloads (LT and 50%Δ LT and VO2 max). The SC was determined by a best fit line analysis. Results: (Mean ± SD) ΔVO2 during the SC (50%Δ) of the running test (1.01 ± 0.48 ml/min/kg) was significantly less than that during the cycling test (1.94 ± 0.66 ml/min/kg, p<0.05). The average StO2 during the SC (LT) of the two tests were similar (running = 58.54% ± 13.00% and cycling = 62.33% ± 12.14%). However, the StO2 during the SC (50%Δ) of the running test was significantly greater than during the cycling test (run = 54.48% ± 14.30% and cycling = 39.95% ± 11.19%, p<0.05). Conclusion: The difference between the running and cycling ΔVO2 during the slow component phase of oxygen uptake is related to significantly lower StO2 values during cycling. As a result, low muscle StO2 values may contribute to the slow component phase of O2 uptake kinetics.