Fig 1.
Schematic representation of an experimental trial.
The combination of target level 2 and the easy mental task is illustrated. A trial lasts for 16 seconds, 7.5 seconds of which were used for instructions. The handgrip is measured for 4 seconds. During the subsequent 4.5 seconds, participants either perform the mental task (easy or difficult) or take a short break for the same duration (no mental task).
Fig 2.
Produced force relative to maximum voluntary contraction in each RPE target level.
The difference between each RPE-level represents a 20% increase in subjective effort. As the differences between the compared RPE-levels are equivalent, equivalence in translating subjective effort to objective performance would require a linear increase of produced force across RPE target-levels. However, the deviation between target levels 60% to 80% significantly differs from the other two deviates (20–40, 40–60), resulting in a nonlinear pattern. This indicates that equivalent differences in subjective efforts do not translate to equivalent differences in produced force across all effort levels. N = 43. Error bars represent the standard deviation.
Fig 3.
Force generation over time, separated by physical effort level and mental effort condition.
N = 43. Scaled submaximal voluntary force production under to-be-produced effort target RPE-levels (%MVC). Shaded areas represent 95% confidence intervals. The generated force differed significantly between the physical effort levels. A significant three-way interaction was revealed in physical effort levels 40%, 60%, and 80%. Between conditions, comparisons revealed steeper slopes in the low and high mental effort conditions compared to the no mental effort conditions at the beginning of physical effort levels 60% and 80%. Additional between-condition comparisons revealed steeper slopes in the low mental effort condition compared to no mental effort towards mid-experiment in levels 40%, 60%, and 80%.