A "Step-Ramp-Step" Protocol to Identify the Maximal Metabolic Steady State

Relationship between functional threshold power, ventilatory threshold and respiratory compensation point in road cycling

BACKGROUND

The purpose of this study was to assess the relationship between power output and relative power output at the functional threshold power, ventilatory threshold and respiratory compensation point in road cyclists.

METHODS

Forty-six road cyclists (age 38 ± 9 years; height 177 ± 9 cm; body mass 71.4 ± 8.6 kg; body mass index 22.7 ± 2.2 kg·m-1; fat mass 7.8 ± 4%, VO2max 61.1 ± 9.1 ml·min-1·kg-1) performed a graded exercise test in which power output and relative power output at the ventilatory landmarks were identified. Functional threshold power was established as 95% of the power output during a 20-minute test.

RESULTS

Power output and relative power output at the functional threshold power were higher than at the ventilatory threshold (p < 0.001). There were very large to near perfect correlations for power output (95% CI for r from 0.71 to 0.9) and relative power output (95% CI for r from 0.79 to 0.93) at the functional threshold power and respiratory compensation point. Mean bias in power ouput and relative power output measured at RCP compared with FTP was not significant (mean bias 95% CI from -7 to 10 W and - 0.1 to 0.1 W/kg, respectively).

CONCLUSIONS

Power output and relative power output at the functional threshold power are higher than at the ventilatory threshold. Power output and relative power output at the functional threshold power and respiratory compensation point are strongly related, but caution is required when using both concepts indistinctly.

Ramp vs. step tests: valid alternatives to determine the maximal lactate steady-state intensity?

PURPOSE

The aims of this study were (1) to investigate if the respiratory compensation point (RCP) as derived from ramp incremental (RI) exercise could accurately predict the power output (PO) at the maximal lactate steady state (MLSS), and (2) to compare its accuracy with the second lactate threshold (LT₂) obtained from step incremental (SI) exercise.

METHODS

Nineteen participants performed a RI test (30 W·min^-1) to determine RCP, a SI test (30 or 40 W·3 min^-1) to determine LT₂, and two or more constant work rate (CWR) tests to determine MLSS. For each participant, the [Formula: see text]O₂/PO relationship for RI and CWR exercise was established. The ramp-identified PO at RCP was corrected by accounting for the gap between these relationships using the individually determined [Formula: see text] O₂/PO regression above GET (RCP_corr-1) or using a fixed regression slope (RCP_corr-2). LT₂ was determined using four methods: D_max, modified D_max (ModD_max), 4-mM threshold (LT_4mM) and an expert-determined LT₂ (LT_2-expert).

RESULTS

RCP_corr-1 (235 ± 69 W), RCP_corr-2 (228 ± 58 W) and LT_2-expert (227 ± 61 W) were not different from MLSS (225 ± 60 W). D_max (203 ± 53 W) underestimated MLSS, while RCP (280 ± 60 W), ModD_max (235 ± 67 W) and LT_4mM (234 ± 68 W) overestimated MLSS. The [Formula: see text]O₂ at RCP (3.13 ± 0.79L·min^-1) and LT_2-expert (2.99 ± 0.19L·min^-1) did not differ from MLSS (3.05 ± 0.72 L·min^-1).

CONCLUSION

This study demonstrated that RCP as derived from RI exercise and LT₂ as derived from SI exercise can be equally accurate to determine the PO associated with MLSS. Although these results confirmed the suitability of RI and SI tests for this purpose, they also highlighted the importance of an appropriate threshold method selection and the eye of the expert.

Prior exercise impairs subsequent performance in an intensity- and duration-dependent manner

Prior constant-load exercise performed for 30-min at or above maximal lactate steady state (MLSS_p) significantly impairs subsequent time-to-task failure (TTF) compared with TTF performed without prior exercise. We tested the hypothesis that TTF would decrease in relation to the intensity and the duration of prior exercise compared with a baseline TTF trial. Eleven individuals (6 males, 5 females, aged 28 ± 8 yrs) completed the following tests on a cycle ergometer (randomly assigned after MLSS_p was determined): (i) a ramp-incremental test; (ii) a baseline TTF trial performed at 80% of peak power (TTF_b); (iii) five 30-min constant-PO rides at 5% below lactate threshold (LT_-5%), halfway between LT and MLSS_p (Delta₅₀), 5% below MLSS_p (MLSS_-5%), MLSS_p, and 5% above MLSS_p (MLSS_+5%); and (iv) 15- and 45-min rides at MLSS_p (MLSS₁₅ and MLSS₄₅, respectively). Each condition was immediately followed by a TTF trial at 80% of peak power. Compared with TTF_b (330 ± 52 s), there was 8.0 ± 24.1, 23.6 ± 20.2, 41.0 ± 14.8, 52.2 ± 18.9, and 75.4 ± 7.4% reduction in TTF following LT_-5%, Delta₅₀, MLSS_-5%, MLSS_p, and MLSS_+5%, respectively. Following MLSS₁₅ and MLSS₄₅ there were 29.0 ± 20.1 and 69.4 ± 19.6% reductions in TTF, respectively (P < 0.05). It is concluded that TTF is reduced following prior exercise of varying duration at MLSS_p and at submaximal intensities below MLSS. Novelty: Prior constant-PO exercise, performed at intensities below MLSS_p, reduces subsequent TTF performance. Subsequent TTF performance is reduced in a linear fashion following an increase in the duration of constant-PO exercise at MLSS_p.

Impact of supine versus upright exercise on muscle deoxygenation heterogeneity during ramp incremental cycling is site specific

PURPOSE

We tested the hypothesis that incremental ramp cycling exercise performed in the supine position (S) would be associated with an increased reliance on muscle deoxygenation (deoxy[heme]) in the deep and superficial vastus lateralis (VLd and VLs, respectively) and the superficial rectus femoris (RFs) when compared to the upright position (U).

METHODS

11 healthy men completed ramp incremental exercise tests in S and U. Pulmonary [Formula: see text]O₂ was measured breath-by-breath; deoxy[heme] was determined via time-resolved near-infrared spectroscopy in the VLd, VLs and RFs.

RESULTS

Supine exercise increased the overall change in deoxy[heme] from baseline to maximal exercise in the VLs (S: 38 ± 23 vs. U: 26 ± 15 μM, P < 0.001) and RFs (S: 36 ± 21 vs. U: 25 ± 15 μM, P < 0.001), but not in the VLd (S: 32 ± 23 vs. U: 29 ± 26 μM, P > 0.05).

CONCLUSIONS

The present study supports that the impaired balance between O₂ delivery and O₂ utilization observed during supine exercise is a regional phenomenon within superficial muscles. Thus, deep muscle defended its O₂ delivery/utilization balance against the supine-induced reductions in perfusion pressure. The differential responses of these muscle regions may be explained by a regional heterogeneity of vascular and metabolic control properties, perhaps related to fiber type composition.