A longitudinal study on the interchangeable use of whole-body and local exercise thresholds in cycling

PURPOSE: This study longitudinally examined the interchangeable use of critical power (CP), the maximal lactate steady state (MLSS) and the respiratory compensation point (RCP) (i.e., whole-body thresholds), and breakpoints in muscle deoxygenation (m[HHb](BP)) and muscle activity (iEMG(BP)) (i.e., local thresholds). METHODS: Twenty-one participants were tested on two timepoints (T1 and T2) with a 4-week period (study 1: 10 women, age = 27 ± 3 years, [Formula: see text] = 43.2 ± 7.3 mL min(−1)kg(−1)) or a 12-week period (study 2: 11 men, age = 25 ± 4 years, [Formula: see text] = 47.7 ± 5.9 mL min(−1) kg(−1)) in between. The test battery included one ramp incremental test (to determine RCP, m[HHb](BP) and iEMG(BP)) and a series of (sub)maximal constant load tests (to determine CP and MLSS). All thresholds were expressed as oxygen uptake ([Formula: see text] ) and equivalent power output (PO) for comparison. RESULTS: None of the thresholds were significantly different in study 1 ([Formula: see text] : P = 0.143, PO: P = 0.281), but differences between whole-body and local thresholds were observed in study 2 ([Formula: see text] : P < 0.001, PO: P = 0.024). Whole-body thresholds showed better 4-week test–retest reliability (TEM = 88–125 mL min(−1) or 6–10 W, ICC = 0.94–0.98) compared to local thresholds (TEM = 189–195 mL min(−1) or 15–18 W, ICC = 0.58–0.89). All five thresholds were strongly associated at T1 and T2 (r = 0.75–0.99), but their changes from T1 to T2 were mostly uncorrelated (r = − 0.41–0.83). CONCLUSION: Whole-body thresholds (CP/MLSS/RCP) showed a close and consistent coherence taking into account a 3–6%-bandwidth of typical variation. In contrast, local thresholds (m[HHb](BP)/iEMG(BP)) were characterized by higher variability and did not consistently coincide with the whole-body thresholds. In addition, we found that most thresholds evolved independently of each other over time. Together, these results do not justify the interchangeable use of whole-body and local exercise thresholds in practice.