V02 'overshoot' during moderate-intensity exercise in endurance-trained athletes: the influence of exercise modality.
ABSTRACT The purpose of this study was to investigate the influence of exercise modality on the 'overshoot' in V(O2) that has been reported following the onset of moderate-intensity (below the gas exchange threshold, GET) exercise in endurance athletes. Seven trained endurance cyclists and seven trained endurance runners completed six square-wave transitions to a work-rate or running speed requiring 80% of mode-specific GET during both cycle and treadmill running exercise. The kinetics of V(O2) was assessed using non-linear regression and any overshoot in V(O2) was quantified as the integrated volume (IV) of O(2) consumed above the steady-state requirement. During cycling, an overshoot in V(O2) was evident in all seven cyclists (IV = 136 +/- 41 ml) and in four runners (IV = 81 +/- 94 ml). During running, an overshoot in V(O2) was evident in four runners (IV = 72 +/- 61 ml) but no cyclists. These data challenge the notion that V(O2) always rises towards a steady-state with near-exponential kinetics in this exercise intensity domain. The greater incidence of the V(O2) overshoot during cycling (11/14 subjects) compared to running (4/14 subjects) indicates that the overshoot phenomenon is related to an interaction between high levels of aerobic fitness and exercise modality. We speculate that a transient loss in muscle efficiency as a consequence of a non-constant ATP requirement following the onset of constant-work-rate exercise or an initially excessive recruitment of motor units (relative to the work-rate) might contribute to the overshoot phenomenon.
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ABSTRACT: An incremental ramp exercise is a protocol that is frequently used in the domain of exercise testing to get an insight into the exercise tolerance of both healthy active populations (including athletes) and patients, due to the specific characteristics of the protocol. The continuous and linear increase in work rate is not only less strenuous for populations with a very low exercise capacity but it requires the aerobic metabolism to adapt to the continuously changing conditions. Therefore, this protocol can provide important information on the adaptive capacity of individuals to exercise in non-steady-state conditions. The ramp exercise has also been used in the past two decades to get an insight into the underlying mechanisms of the oxygen uptake (·VO₂) response (and kinetics) to exercise. Against the expectations, it has been shown that the parameters that quantify the ·VO₂ response to ramp exercise do not completely correspond to those obtained from constant work-rate transitions and incremental step exercise. For that reason, it could be concluded that the ·VO₂ response is specific to ramp exercise, and thus is determined by other mechanisms than those which determine other protocols. Although the ·VO₂ response to ramp exercise has a high level of reproducibility and a uniform pattern can be observed, especially for the ·VO₂ response below the gas exchange threshold (GET) [above the GET, the ·VO₂ response is less clear], some prudence is necessary when interpreting potential differences in the ·VO₂ response between populations. Several methodological issues (e.g. baseline work rate, ramp slope) exert an important impact on the ·VO₂ response to ramp exercise. The main purpose of this review is to provide an overview of the methodological and physiological factors that have an impact on the ·VO₂ response to ramp exercise. It is of importance that exercise physiologists take these factors into consideration, not only prior to the conductance of the ramp exercise in a variety of subjects, but also when interpreting the obtained results.Sports Medicine 05/2012; 42(6):511-26. · 5.24 Impact Factor
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ABSTRACT: The purpose of this study was to test whether the higher slope of the oxygen uptake/work rate relationship (DeltaVO2/DeltaW) in aerobically trained subjects compared with less trained counterparts during a ramp protocol is related to changes in muscle fiber activation. Ten cyclists and 10 physically active (PA) students performed two ramp exercises (ramp 25 protocol and relative ramp protocol, leading to exhaustion in 12 min) and a step protocol (20-60-100-140-180-220 W). Pulmonary gas exchange was measured, and muscle fiber activity was recorded with surface EMG of the musculus vastus lateralis. V O2 and integrated EMG (iEMG) were described as functions of work rate up to the gas exchange threshold, and linear regression analysis was used to determine the DeltaVO2/DeltaW and the slope of the iEMG/W relationship (DeltaiEMG/DeltaW). The statistical analysis revealed a higher DeltaVO2/DeltaW in cyclists compared with PA students in ramp exercises (ramp 25 = 9.98 +/- 0.51 vs 9.18 +/- 0.59 mL x min(-1) x W(-1); relative ramp = 9.87 +/- 0.30 vs 9.16 +/- 0.33 mL x min(-1) x W(-1) in the cyclists and PA students, respectively; P < 0.05) but not in step exercise (9.97 +/- 0.32 and 9.83 +/- 0.37 mL x min(-1) x W(-1) in cyclists and PA students, respectively; P > 0.05). In addition, cyclists demonstrated a higher DeltaiEMG/DeltaW in ramp exercises (0.96 +/- 0.14% x W(-1) and 0.98 +/- 0.14% x W(-1) in ramp 25 and relative ramp, respectively) compared with step exercise (0.75 +/- 0.12% x W(-1), P < 0.05), whereas in the PA students, DeltaiEMG/DeltaW did not differ between the ramp protocol (0.75 +/- 0.10% x W(-1) and 0.70 +/- 0.12% x W(-1) in ramp 25 and relative ramp, respectively) and the step protocol (0.77 +/- 0.17% x W(-1), P > 0.05). The present study reveals that trained cyclists demonstrate reduced mechanical efficiency in the ramp protocol and that this phenomenon is associated with an "overactivation" of muscle fibers.Medicine and science in sports and exercise 11/2009; 42(2):402-8. · 4.48 Impact Factor
- Medicine and science in sports and exercise 07/2010; 42(7):1427; author reply 1428. · 4.48 Impact Factor