Does a single bout maximal effort forearm exercise test for determining critical impulse result in maximal oxygen delivery and consumption in men? A randomized crossover trial.

In a single bout maximal effort isometric forearm handgrip exercise test (maximal effort exercise test, MXT), contraction impulse exhibits exponential decay to an asymptote equivalent to critical impulse (CI). It is unknown whether oxygen delivery (O_2del) and consumption ($\dot{\text{V}}{\text{O}}_2$) achieved at CI are maximal. Healthy men participated in a randomized crossover trial at Queen's University (Kingston, ON) between October 2017-May 2018. Participants completed an MXT and forearm incremental exercise test to limit of tolerance (IET-LOT) (7 completed MXT followed by IET-LOT vs. 4 completed IET-LOT followed by MXT) within a 2 week period. Data are presented as mean ± standard deviation. Maximal forearm blood flow (FBF) and O_2del were not different in 11 men (21 ± 2.5 years) between MXT and IET-LOT (FBF = 473.8 ± 132.2 mL/min vs. 502.3 ± 152.3 mL/min; P = 0.482, η_p² = 0.015; O_2del = 85.2 ± 23.5 mL/min vs. 92.2 ± 37.0 mL/min; P = 0.456, η_p² = 0.012). However, MXT resulted in greater maximal $\dot{\text{V}}{\text{O}}_2$ than IET-LOT (44.5 ± 15.2 mL/min > 36.8 ± 11.4 mL/min; P = 0.007, η_p² = 0.09), due to greater oxygen extraction (54.0 ± 10.0% > 44.4 ± 8.6%; P = 0.021, η_p² = 0.185). As CI was 88.6 ± 8.2% of IET-LOT contraction impulse, maximal O₂ cost of contractions in MXT was greater than IET-LOT (0.45 ± 0.14 mL/min/Ns > 0.33 ± 0.09 mL/min/Ns; P < 0.001, η_p² = 0.166). In healthy men, MXT identifying CI results in similar peak oxygen delivery but greater peak $\dot{\text{V}}{\text{O}}_2$ via increased extraction compared to an IET-LOT, indicating increased oxygen cost. MXT-CI may better estimate maximal $\dot{\text{V}}{\text{O}}_2$ than traditional IET-LOT for this exercise modality.