Comparison Of Different Methods Used To Prescribe Exercise Intensities From Ramp-incremental Exercise

The oxygen uptake (V̇O2) vs power output (PO) relationship from ramp exercise (RAMP) is used to prescribe aerobic exercise. During a RAMP, as PO increases, there is a delay in breath-by-breath V̇O2 that contributes to a misalignment of V̇O2 from PO. This lag is known as the mean response time (MRT). If the MRT is not considered in exercise prescription, RAMP-identified POs will elicit V̇O2 values that are higher than intended. Three methods are used to quantify MRT including linear modeling (MRTLin), exponential modeling (τ’), and the steady-state method (MRTSS). PURPOSE: To compare the time delays between MRTLin, τ’, and the MRTSS at 75%, 85%, and 15% of the difference between estimated lactate threshold (θL)and V̇O2peak (Δ15%). METHODS: 10 males (24.6 ± 7.7 yr, V̇O2max 3.69 ± 0.72 L.min-1, Peak PO V̇O2max 352 ± 57 W, θL PO 180 ± 58 W, θL V̇O2 2.22 ± 0.69 L.min-1) performed a 30W/min RAMP on a cycle ergometer (CYCLE). τ’ and the MRTLin were calculated from the RAMP and converted to a coincident PO. Three 30 min CYCLE trials were performed on separate days, at τ’ left-shifted 75% and 85% of θL, and Δ15%. The RAMP PO corresponding to the steady-state V̇O2 from the 75% θL trial PO was determined. The difference between that PO and the 75% θL trial PO was the MRTSS. Pre-and post-blood lactates were recorded from all trials. RESULTS: τ’ and MRTLin were different (22 ± 13 W, 17 ± 9 W, P=0.04). MRTSS was similar to τ’ and MRTLin (22 ± 11 W, (P=1.000, P= 0.07). The τ’ and MRTLin-corrected POs corresponding to the V̇O2 over the last 5 min of the 75% of θL trial (114 ± 53 P=0.573 and 121 ± 49 P=0.372, respectively) were similar to the actual PO performed (116 ± 52). τ’ and MRTLin-corrected POs corresponding to the V̇O2 last 5 min at 85% of θL (142 ± 70, 149 ± 66, P=0.087 respectively) were similar to the actual PO performed(140 ± 65). The τ’-corrected PO corresponding to the V̇O2 last 5 min at Δ15% (P=0.088) was similar to the actual PO performed. The MRTLin-corrected PO corresponding to the V̇O2 last 5 min at Δ15% (P= 0.025) was different from the actual PO. CONCLUSION: Left-shifting the RAMP PO by τ’ or MRTLin results in a similar corresponding V̇O2 at 75% or 85% of θL. At Δ15% only left-shifting by τ’ results in the same PO as is performed. Using τ’ or MRTLin can be used with confidence when prescribing exercise below θL. At intensities slightly above θL only left-shifting by τ’ is reliable.

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