Wendy wants to know if a new sports drink improves physical performance. The number of push-ups each participant can complete in 1 minute is recorded first. The participants are then given 8 ounces of the sports drink, and the number of push-ups completed in 1 minute is recorded again. Wendy finds that the number of push-ups completed is less after consuming the new sports drink. This finding is likely the result of a ________ effect.