Experiences of physical exertion guide our assessments of effort. While these assessments critically influence our decisions to engage in daily activities, little is known about how they are generated. We had female and male human participants exert grip force and assess how effortful these exertions felt; and used magnetic resonance spectroscopy to measure their brain GABA concentration. We found that variability in exertion (i.e., the coefficient of variation in their force exertion profile) was associated with increases in assessments of effort, making participants judge efforts as more costly. GABA levels in the sensorimotor cortex (SM1) moderated the influence of exertion variability on overassessments of effort. In individuals with higher sensorimotor GABA, exertion variability had a diminished influence on overassessments of effort. Essentially, sensorimotor GABA had a protective effect on the influence of exertion variability on inflations of effort assessment. Our findings provide a neurobiological account of how the brain's GABAergic system integrates features of physical exertion into judgments of effort, and how basic sensorimotor properties may influence higher-order judgments of effort.

SIGNIFICANCE STATEMENT Feelings of effort critically shape our decisions to partake in activities of daily living. It remains unclear how the brain translates physical activity into judgments about effort (i.e., "How effortful did that activity feel?"). Using modeling of behavior and neuroimaging, we show how the nervous system uses information about physical exertion to generate assessments of effort. We found that higher variability in exertion was associated with increases in assessments of effort, making participants judge efforts as more costly. GABA, the brain's main inhibitory neurotransmitter, moderated the influence of exertion variability on overassessments of effort. These findings illustrate how low-level features of motor performance and sensorimotor neurochemistry influence higher-order cognitive processes related to feelings of effort.

体力消耗的经历指导我们对努力的评估。虽然这些评估严重影响我们参与日常活动的决定，但人们对它们是如何产生的知之甚少。我们让女性和男性参与者施加握力，并评估这些努力的费力程度；并使用磁共振波谱法测量了他们大脑中的 GABA 浓度。我们发现，用力的变异性（即用力曲线的变异系数）与努力评估的增加有关，使参与者认为努力的成本更高。感觉运动皮层 (SM1) 中的 GABA 水平调节了运动变异性对努力过度评估的影响。在感觉运动 GABA 较高的个体中，运动变异性对努力过度评估的影响较小。本质上，感觉运动 GABA 对运动变异性对努力评估膨胀的影响具有保护作用。我们的研究结果为大脑的 GABA 能系统如何将体力消耗特征整合到努力判断中，以及基本感觉运动特性如何影响更高阶的努力判断提供了神经生物学解释。

意义声明努力的感觉对我们参与日常生活活动的决定至关重要。目前尚不清楚大脑如何将身体活动转化为对努力程度的判断（即“该活动感觉有多努力？”）。通过行为建模和神经影像学，我们展示了神经系统如何利用有关体力消耗的信息来生成努力评估。我们发现，运动量的较高变异性与努力评估的增加有关，使参与者认为努力的成本更高。 GABA 是大脑的主要抑制性神经递质，可以调节运动变化对努力过度评估的影响。这些发现说明了运动表现和感觉运动神经化学的低水平特征如何影响与努力感相关的高阶认知过程。