Post hoc ergo propter hoc—Latin for “after this, therefore because of this”—is a common logical fallacy in the fitness industry. You’ve likely seen workout programs promoted as the best for losing weight or building muscle. The problem with these claims isn’t always that the workouts are ineffective, unless they’re poorly designed, but that they often ignore the many factors that influence results beyond the training program itself.
Let’s focus on weight loss as an example, though this fallacy applies to nearly any fitness goal.
Many training programs that combine resistance training and cardiovascular exercise can contribute to weight loss. However, weight loss is influenced by a wide range of variables, both inside and outside the gym.
For instance, a workout that keeps your heart rate elevated will increase calorie burn, which adds to your total daily energy expenditure. Over time, this may result in weight loss. But many modern fitness programs also include nutritional guidance, introducing another significant variable which is arguably more important to this goal than the exercise alone. So, was it the training or the nutrition that caused the weight loss?
The answer is usually both but nutrition typically plays the bigger role. Reducing calorie intake by cutting back on sugary drinks or snacks often has a more significant impact on fat loss than trying to "burn it off" through exercise alone. That’s where the saying “You can’t out-train a bad diet” comes from. Even intense workouts burn relatively few calories compared to the number you can save through dietary changes. Think of it this way: If the calories aren't consumed to begin with then you don't need to 'work them off', and you don't want to get in the habit of bargaining with yourself like that anyway because that's a fast track to using exercise as a way to punish yourself for eating too much or using it as permission to eat junk food. Either way you approach that, punitive or permissive, it's no bueno.
While exercise alone isn't the most efficient way to drive fat loss, certain training strategies can help optimize it.
High-intensity training, for example, is associated with Excess Post-exercise Oxygen Consumption (EPOC). This is when your body continues burning calories after the workout to restore oxygen levels and recover. While this process does contribute to total energy expenditure, the effect is modest—not the massive “afterburn” it’s sometimes hyped to be.
Resistance training is another highly effective tool for optimizing fat loss especially in the long run. Building muscle increases your metabolic rate because muscle tissue requires more energy to maintain than fat generally speaking. More importantly, resistance training improves insulin sensitivity. This is crucial because insulin resistance which is a pre-cursor to type 2 diabetes makes it harder for the body to manage calories efficiently, increasing fat storage. Improving insulin sensitivity helps regulate energy use and makes weight maintenance easier in the long run.
To piggyback on that last idea, skeletal muscle is the primary site for glucose disposal. This is one reason that it's so important for blood glucose control in those looking to prevent type 2 diabetes. As your muscles and liver store glucose (sugar) as glycogen (stored sugar), they bind about 0.4 grams of water per gram of glycogen. When you deplete glycogen through intense training, you may lose water weight, which can be mistaken for fat loss. This is one of the reasons that you see very large individuals lose weight more rapidly at the start of their fitness in some cases, especially if they are restricting carbohydrates.
Even when someone sees results, the reasoning behind those results may be flawed. Fitness marketing, especially on social media, often cherry-picks cause and effect. “I did this workout and lost 10 pounds” may sound convincing, but it ignores the full context: changes in diet, stress, sleep, or just being in a calorie deficit for the first time in years.
When we attribute success to one variable and ignore others, we risk forming unrealistic expectations. If someone buys into a so-called “best” program and doesn’t get the promised results, they may become discouraged and give up altogether.
Understanding logical fallacies like post hoc ergo propter hoc helps you become a smarter consumer of health and fitness content. Specific claims surrounding workouts, diets, or supplements, should always be evaluated in the broader context of all the factors that influence success.
When you’re first starting out, you’ll often see big improvements with simple, sustainable habits. Focus on consistency before worrying about what’s "optimal". Save that conversation for later after you’ve mastered the basics and picked the low-hanging fruit for your health.
