Confounding factors can cause some researchers to believe that there’s a direct cause-and-effect relationship in their studies. For example, if they were to examine whether taking a vitamin would increase an athlete’s stamina, there are likely other factors besides the vitamin that could influence their results. It could be sleep quality, caffeine intake, time of day, and many factors that are outside of the researchers’ control.
In a 2015 Australian review led by exercise physiologist Israel Halperin from Edith Cowan University, the researchers wrote, “By controlling for potentially confounding variables, the risk of an alternative (erroneous) explanation accounting for the treatment effects is reduced.”
They identified several confounding factors that exercise scientists tend to overlook or ignore when they conduct experiments, including the pitch and tone of the coach or researcher’s voice, what the test subjects focus on when they move, the number of men and women who are watching the subjects, mental fatigue, and the type of background music. All these factors have shown to affect performance outcome in exercise science.
“The main reason is that unless they pay close attention to these confounding effects, they won’t be able to trust their data,” Halperin told Massage & Fitness Journal. He gave an example of an eight-week strength and conditioning program for a group of female volleyball players who are tested for maximal strength, power, and cardiovascular endurance.
“[Let‘s say] due to logistical constrains, the first testing day was scheduled after a mentally fatiguing three-hour lecture concerning the upcoming financial year of the team,” he said. “The gym was relatively empty and the head coach could not make it because of an important meeting. And so, the assistant coach, who has a quiet voice, provided the instructions and encouragement instead. At the end of the eight-week program, the second testing day took place. This time, the gym was packed and the female volleyball squad performed their strength and conditioning session. Loud house music was playing in the background, and the head coach provided the instructions [with] strong verbal encouragement.”
He said that the vollyeball players showed significant improvement after the testing but questioned whether the positive outcome caused by the program or the inconsistent testing environment? he asked.
“Was it simply the loud music, female observers, set of instructions, verbal encouragement, and lack of mental fatigue in second [test day] that led to the positive improvements?“ Halperin said. “The truth is we don’t know, and that’s why it’s so incredibly important to control for these variables, especially given that the magnitude of their effects can be quite large.”
This is an example of the post-hoc fallacy, which is based on the Latin phrase “post hoc propter ergo hoc” which means “after this, therefore, because of this.” In a 2024 study published in JAMA Network, two researchers wrote that post-hoc fallacy “is similar to tunnel vision or status quo reasoning and can contribute to medical error.”
In a massage therapy example, your migraine headache that has been bothering you for a week is gone after you received a full-body massage. So did the massage actually alleviate the headache or did other factors also contribute to your improvement? Perhaps it was the massage room ambience and the smell of the massage lotion that helped calm you. Or the therapist’s warm personality? Maybe the headache would have gone away on its own with or without a massage?
Going back to Halperin’s review, sometimes the athletes’ performance may be affected by overlooked factors. For example, Halperin et al. reported that exercise test subjects who know the exercise endpoint in terms of distance, time, or number of repetitions often outperform those who have no idea what much more they have to do.
In a 2009 experiment, researchers from the University of Exeter compared cyclists who knew the distance (control) versus those who did not know the distance (experimental). The latter group was never given distance feedback during the exercise, and they were considerably slower than those who knew the distance they had covered.
Likewise, the number of female observers can affect how well heterosexual male test subjects perform. A 2012 British study found that recreational male runners tend to have lower rates of exertion when there are women watching them compared to an all-male observer group. Another study from the University of Virginia also found similar outcomes among male cyclists. However, when the roles are reversed, women performed almost the same regardless of who is watching.
Internal validity
In research, Halperin et al. wrote that internal validity as the extent to which changes in a dependent variable can be confidently attributed to changes in an independent variable. This allows for trustworthy conclusions about cause and effect between both variables. To achieve this, researchers must control for confounding variables that could otherwise explain the results.
“The effects of attentional focus, knowledge of exercise endpoint, verbal encouragement, positive and negative feedback, number and gender
of observers, music, and mental fatigue should also be considered given their meaningful effects on physical performance,” Halperin et al. concluded. “Scientific manuscripts could include, where appropriate, details of specific methodological approaches employed to quantify and/or reduce the risk of confounding factors.”
Updated: March 27, 2026. Originally published April 11, 2015.
Nick Ng, BA
Nick Ng is the editor of Massage & Fitness Jounal and the managing editor for My Neighborhood News Network.
An alumni from San Diego State University with a bachelor’s degree in graphic communications, Nick had completed his massage therapy training at International Professional School of Bodywork in San Diego in 2014. In 2021, he earned an associate’s degree in journalism at Palomar College.
When he gets a chance, he enjoys weightlifting at the gym, salsa dancing, and exploring new areas in the Puget Sound area in Washington state.
