Influence Of Priming Exercise On Muscle Deoxygenation Kinetics During Upright And Supine Cycle Exercise

Abstract

A bout of prior heavy “priming” exercise typically reduces the time constant of fundamental phase oxygen uptake (VO2) kinetics (τVO2) in the supine position, an effect that is generally absent during upright exercise. This priming-induced speeding of pulmonary VO2 kinetics has been attributed to increased muscle oxygenation at the onset of the second bout. However, the extent to which priming-induced improvements in muscle oxy/deoxygenation status differ across distinct muscle regions, as well as between deep vs. superficial muscle and with respect to body position, remains unknown. PURPOSE: To examine the impact of priming exercise on pulmonary VO2 and muscle deoxygenation kinetics at three muscle sites (superficial rectus femoris [RFs], deep [VLd] and superficial [VLs] vastus lateralis) using time-resolved near-infrared spectroscopy during upright (U) and supine (S) exercise. METHODS: 7 healthy men completed an incremental ramp test to determine VO2 max and the gas exchange threshold in S. 4 visits followed whereby participants performed two 6-min bouts of heavy exercise separated by 6-min unloaded pedalling in two conditions: 1) during constant power exercise at 40%Δ in S; and 2) during exercise at the same absolute work rate in U. Pulmonary VO2 and muscle deoxy[heme] kinetics were determined during each test. RESULTS: τVO2 was reduced in bout 2 in S (bout 1: 42 ± 12 vs. bout 2: 31 ± 7 s, P = 0.016) but not in U (bout 1: 32 ± 9 vs. bout 2: 28 ± 5 s, P = 0.32). The fundamental phase τdeoxy[heme] was greater in bout 2 for RFs in both postures (S, bout 1: 20 ± 7 vs. bout 2: 31 ± 18 s; U, 1: 11 ± 3 vs. bout 2: 23 ± 9 s, P = 0.021), whereas it was increased in bout 2 for VLs during U only (bout 1: 10 ± 3 vs. bout 2: 15 ± 4 s, P = 0.028). The fundamental phase muscle deoxy[heme] amplitude was greater in bout 2 for RFs (P = 0.001) and VLs (P = 0.024) in both U and S. Both the fundamental phase τdeoxy[heme] and amplitude did not differ between bouts 1 and 2 for VLd in either position (both P > 0.05). CONCLUSION: Prior heavy exercise reduced τVO2 in S but not U. This was accompanied by a greater amplitude and slower rate of muscle deoxygenation in superficial but not deep muscle. The contrasting responses of deep and superficial muscle to priming exercise in both U and S suggests that these muscles rely on fundamentally different O2 transport strategies.