Get aroused and be stronger.

From Schmidt et al.:

Effort magnitude is commonly thought to reflect motivation, but little is known about the influence of emotional factors. Here, we manipulated the emotional state of subjects, via the presentation of pictures, before they exerted physical effort (squeezing a hand grip) to win money. After highly arousing pictures, subjects produced more force and reported lower effort sensation, regardless of monetary incentives. Functional neuroimaging revealed that emotional arousal, as indexed by postscan ratings, specifically correlated with bilateral activity in the ventrolateral prefrontal cortex. We suggest that this region, by driving the motor cortex, constitutes a brain pathway that allows emotional arousal to facilitate physical effort.

Figure - The emotional incentive force task. Successive screens displayed in every trial are shown from left to right, with durations in milliseconds. Emotional pictures that could be neutral or arousing (with positive or negative valence) were shown before physical effort. Effort was triggered by simultaneously showing the amount of money at stake, materialized as coin images (1 cent, 10 cents, or 1 {euro}), and a thermometer in which fluid level represented the force exerted on the hand grip. Subjects knew that the top of the thermometer corresponded to the monetary incentive, such that the more they squeezed the hand grip, the more money they would win. The last screen informed subjects about the cumulative total of monetary earnings.