For bosses and managers around the country, here's a tip: Maybe you should cool it with all that positive reinforcement.

In a recent study covered in the Harvard Business Review, behavioral scientist Brandon Irwin used "planks" — the immeasurably sucky gym exercise in which you sustain a push-up position for as long as possible — to study how encouragement affects motivation.

The subjects in the experiment did two sets of planks. Some did both sets by themselves, while others did one set alone, and the second with a virtual plank expert (yup, a plank expert) projected onto a screen. Half the experts were saying things like "come on," "you can do it," and "you got this," while the other half just existed on the screen, silently emanating their superior planking abilities.

The results: In all cases, the subject with the virtual partner sustained the plank longer. But subjects with silent experts planked for 33 percent longer, while those with "encouraging" experts planked only 22 percent longer.

The lesson? When it comes to motivating people, silent superiority may help more than supportive cheers.

Irwin gave one possible explanation for the counterintuitive finding: Apparently, the subjects being coddled started considering themselves planking-equals to the experts, "despite a lot of evidence to the contrary."

"A big reason why superior partners are motivating is that people want to compare favorably with others," Irwin told the Harvard Business Review. "But if anything undermines your belief that a partner is better, you feel you don’t have to put in as much effort to achieve a favorable comparison."

Knowing that the presence of others helps motivate, Irwin and his team followed up with another study examining how being part of a group that's striving for the same goal can affect motivation. For this study, the subjects rode exercise bikes over five sessions.

"We used a similar setup: some with virtual partners, some without. In this study, though, all the partners were silent. This time the results we got were even more pronounced. Subjects with partners doubled their time on the bikes.

However, the study added another element: One group was told they were on a team and contributing to a team score over the five sessions. Subjects with partners in that group tripled their time on the bikes." [HBR]

The conclusion here: That sharing a goal with others makes people work harder — "especially when you know you’re the weaker link in the team."