Functional Threshold Power Field Test Exceeds Laboratory Performance in Junior Road Cyclists

Abstract

Vinetti, G, Rossi, H, Bruseghini, P, Corti, M, Ferretti, G, Piva, S, Taboni, A, and Fagoni, N. The functional threshold power field test exceeds laboratory performance in junior road cyclists. J Strength Cond Res 37(9): 1815–1820, 2023—The functional threshold power (FTP) field test is appealing for junior cyclists, but it was never investigated in this age category, and even in adults, there are few data on FTP collected in field conditions. Nine male junior road cyclists (16.9 ± 0.8 years) performed laboratory determination of maximal aerobic power (MAP), 4-mM lactate threshold (P_4mM), critical power (CP), and the curvature constant (W′), plus a field determination of FTP as 95% of the average power output during a 20-minute time trial in an uphill road. The level of significance was set at p < 0.05. Outdoor FTP (269 ± 34 W) was significantly higher than CP (236 ± 24 W) and P_4mM (233 ± 23 W). The $\dot{V}{\mathrm{O}}_{2\text{peak}}$ of the field FTP test (66.9 ± 4.4 ml·kg⁻¹·min⁻¹) was significantly higher than the $\dot{V}{\mathrm{O}}_{2\text{peak}}$ assessed in the laboratory (62.7 ± 3.7 ml·kg⁻¹·min⁻¹). Functional threshold power was correlated, in descending order, with MAP (r = 0.95), P_4mM (r = 0.94), outdoor and indoor $\dot{V}{\mathrm{O}}_{2\text{peak}}$ (r = 0.93 and 0.93, respectively), CP (r = 0.84), and W′ (r = 0.66). It follows that in junior road cyclists, the FTP field test was feasible and related primarily to aerobic endurance parameters and secondarily, but notably, to W′. However, the FTP field test significantly exceeded all laboratory performance tests. When translating laboratory results to outdoor uphill conditions, coaches and sport scientists should consider this discrepancy, which may be particularly enhanced in this cycling age category.

Figure 1.

Altimetric profile of the ascent. Labels refer to average grade of each kilometer.

Figure 2.

Average power–duration data from the laboratory constant-power trials (open dots) and the field 20-minute time trial (filled dot) and derived parameters: CP (continuous line), FTP (dotted line), P_4mM (dashed line). Error bars show standard deviation. CP = critical power; FTP = functional threshold power; P_4mM = PO at the 4-mM blood lactate concentration; PO = power output; T_lim = duration.

Figure 3.

Comparison of selected laboratory parameters with the FTP. FTP = functional threshold power; CP = critical power; P_4mM = power output at the 4-mM blood lactate concentration; MAP = maximal aerobic power of the incremental test; $\dot{V}{\mathrm{O}}_{2\text{peak}}$ = peak oxygen consumption of the incremental test; W′ = curvature constant of the CP model.